spring boot 源码解析13-@ConfigurationProperties是如何生效的

 2019-10-17 22:07  阅读(2715)
文章分类:Spring boot

前言

新的一年到了,在这里先祝大家新年快乐.我们在上一篇spring boot 源码解析12-servlet容器的建立 中 分析 ServerProperties时,发现其类上有@ConfigurationProperties 注解,加上该注解后,就会注入在application.properties中server开头的属性,那么它是怎么生效的呢?我们这篇文章就来分析一下.这篇文章内容比较长,大家慢慢看…

@ConfigurationProperties 使用方式

  1. 我们首先声明实体类,用于属性的注入.代码如下:

    public class People {
    
            private String name;
    
            private Integer age;
    
            private List address;
    
            private Phone phone;
    
            // get set 忽略,自己加上即可..
        }
    
        public class Phone {
    
            private String number;
    
            // get set 忽略,自己加上即可.. 
    
        }
    
  2. 在application.properties 中加入如下配置:

    com.example.demo.name=${aaa:hi}
        com.example.demo.age=11
        com.example.demo.address[0]=北京
        com.example.demo.address[1]=上海
        com.example.demo.address[2]=广州
        com.example.demo.phone.number=1111111
    
  3. @ConfigurationProperties 注解支持两种方式.

    1. 加在类上,需要和@Component注解,结合使用.代码如下:

      @Component
          @ConfigurationProperties(prefix = "com.example.demo")
          public class People {
      
              private String name;
      
              private Integer age;
      
              private List address;
      
              private Phone phone;
          }
      
    2. 通过@Bean的方式进行声明,这里我们加在启动类即可,代码如下:

      @SpringBootApplication
          public class DemoApplication {
      
              @Bean
              @ConfigurationProperties(prefix = "com.example.demo")
              public People people() {
      
                  return new People();
              }
      
              public static void main(String[] args) {
                  SpringApplication.run(DemoApplication.class, args);
              }
      
          }
      

    这里我们使用第2种,原因是这样好debug,看源码…

  4. 我们再写一个Controller进行测试一下吧.代码如下:

    @RestController
        public class TestController {
    
            @Autowired
            private People people;
    
            @RequestMapping("/get_name")
            public String getName() {
    
                return people.getName();
            }
    
            @RequestMapping("/get_address")
            public List getAddress() {
    
                return people.getAddress();
            }
    
            @RequestMapping("/get_phone_numer")
            public String getNumber() {
    
                return people.getPhone().getNumber();
            }
        }
    

    访问 /get_name,其返回值如下:

    hi

    访问 /get_address,其返回值如下:

    [“北京”,”上海”,”广州”]

    访问 get_phone_numer,其返回值如下:

    1111111

    使用方式就介绍完了,接下来,我们就来看看spring 是如何处理的吧.

解析

我们应该知道了@ConfigurationProperties 和 @Bean 或者 @Component 等只要能生成spring bean 的注解 结合起来使用,这样的话,当其他类注入该类时,就会触发该类的加载过程,那么在加载过程中,会调用AbstractAutowireCapableBeanFactory#applyBeanPostProcessorsBeforeInitialization.因此会触发ConfigurationPropertiesBindingPostProcessor#postProcessBeforeInitialization的调用,这里就是我们的起点.

  1. ConfigurationPropertiesBindingPostProcessor#postProcessBeforeInitialization 代码如下:

    public Object postProcessBeforeInitialization(Object bean, String beanName)
                throws BeansException {
            // 1. 获得类上的@ConfigurationProperties注解,如果注解存在,则调用postProcessBeforeInitialization 进行处理
            ConfigurationProperties annotation = AnnotationUtils
                    .findAnnotation(bean.getClass(), ConfigurationProperties.class);
            if (annotation != null) {
                postProcessBeforeInitialization(bean, beanName, annotation);
            }
            // 2. 寻找工厂方法上是否有@ConfigurationProperties 注解,如果存在的话,则调用postProcessBeforeInitialization进行处理
            annotation = this.beans.findFactoryAnnotation(beanName,
                    ConfigurationProperties.class);
            if (annotation != null) {
                postProcessBeforeInitialization(bean, beanName, annotation);
            }
            return bean;
        }
    

    2件事:

    1. 获得类上的@ConfigurationProperties注解,如果注解存在,则调用postProcessBeforeInitialization 进行处理
    2. 寻找工厂方法上是否有@ConfigurationProperties 注解,如果存在的话,则调用postProcessBeforeInitialization进行处理.对应的是@Bean的方式.
  2. 不管怎么样,最终都会调用ConfigurationPropertiesBindingPostProcessor#postProcessBeforeInitialization.代码如下:

    private void postProcessBeforeInitialization(Object bean, String beanName,
                ConfigurationProperties annotation) {
            Object target = bean;
            // 1. 实例化PropertiesConfigurationFactory,该类实现了FactoryBean, MessageSourceAware, InitializingBean 接口,并进行一些属性的设置
            PropertiesConfigurationFactory factory = new PropertiesConfigurationFactory(
                    target);
            factory.setPropertySources(this.propertySources);
            factory.setValidator(determineValidator(bean));
            // If no explicit conversion service is provided we add one so that (at least)
            // comma-separated arrays of convertibles can be bound automatically
            // 由于conversionService 一直为 null,因此会调用getDefaultConversionService
            factory.setConversionService(this.conversionService == null
                    ? getDefaultConversionService() : this.conversionService);
            if (annotation != null) {
                // 2. 如果注解存在,这是肯定的,不然也不会执行该方法,则根据@ConfigurationProperties的值进行配置
                factory.setIgnoreInvalidFields(annotation.ignoreInvalidFields());
                factory.setIgnoreUnknownFields(annotation.ignoreUnknownFields());
                factory.setExceptionIfInvalid(annotation.exceptionIfInvalid());
                factory.setIgnoreNestedProperties(annotation.ignoreNestedProperties());
                if (StringUtils.hasLength(annotation.prefix())) {
                    // 2.1 如果配置了prefix,或者value 值,则设置TargetName
                    factory.setTargetName(annotation.prefix());
                }
            }
            try {
                // 3. 进行绑定
                factory.bindPropertiesToTarget();
            }
            catch (Exception ex) {
                String targetClass = ClassUtils.getShortName(target.getClass());
                throw new BeanCreationException(beanName, "Could not bind properties to "
                        + targetClass + " (" + getAnnotationDetails(annotation) + ")", ex);
            }
        }
     3件事:
     实例化PropertiesConfigurationFactory,该类实现了FactoryBean, MessageSourceAware, InitializingBean 接口,并进行一些属性的设置. 将ConfigurationPropertiesBindingPostProcessor中的propertySources赋值给PropertiesConfigurationFactory 通过调用determineValidator方法,生成Validator,并进行赋值.代码如下:     private Validator determineValidator(Object bean) {
        // 1. 获得validator
        Validator validator = getValidator();
        // 2. 如果validator不等于null并且该Validator 支持该bean的话
        boolean supportsBean = (validator != null && validator.supports(bean.getClass()));
        if (ClassUtils.isAssignable(Validator.class, bean.getClass())) {// 3 如果当前类为Validator的子类
            // 3.1 如果supportsBean,则实例化ChainingValidator
            if (supportsBean) {
                return new ChainingValidator(validator, (Validator) bean);
            }
            // 3.2 否则强转为Validator
            return (Validator) bean;
        }
        // 4. 最后,如果supportsBean 则 返回Validator 否则 返回null
        return (supportsBean ? validator : null);
        } 4件事: 调用getValidator方法获得Validator.代码如下:     private Validator getValidator() {
        // 1. 由之前可知,该validator 一直都是null.
        if (this.validator != null) {
        return this.validator;
        }
        // 2. 如果localValidator 等于null并且是jsr303环境的话,则实例化ValidatedLocalValidatorFactoryBean,并赋值给localValidator,lazy-init
        // ValidatedLocalValidatorFactoryBean 实现了ValidatorFactory, ApplicationContextAware, InitializingBean, DisposableBean,SmartValidator, javax.validation.Validator
        if (this.localValidator == null && isJsr303Present()) {
        this.localValidator = new ValidatedLocalValidatorFactoryBean(
                this.applicationContext);
        }
        return this.localValidator;
        } 如果validator 不等于null,则直接返回.可是该validator是一直等于null.原因如下: ConfigurationPropertiesBindingPostProcessor 实现了InitializingBean接口,因此为调用其afterPropertiesSet方法,在该方法,有如下片段:     if (this.validator == null) {
        // 2. 尝试获得id 为 configurationPropertiesValidator,type为Validator 的bean,此时是没有获取到
        this.validator = getOptionalBean(VALIDATOR_BEAN_NAME, Validator.class);
        } 会尝试从beanFactory中获得id 为 configurationPropertiesValidator,type 为 Validator的bean,可是默认情况下,是不存在的. 如果localValidator 等于null并且是jsr303环境的话,则实例化ValidatedLocalValidatorFactoryBean,并赋值给localValidator,这是一个lazy-init,ValidatedLocalValidatorFactoryBean 实现了ValidatorFactory, ApplicationContextAware, InitializingBean, DisposableBean,SmartValidator, javax.validation.Validator接口. 如果不等于null,则直接返回 如果validator不等于null并且该Validator 支持该bean的话,则supportsBean等于true,否则为false. 如果当前类为Validator的子类 如果supportsBean为true,则实例化ChainingValidator,则初始化ChainingValidator.进行返回 否则强转为Validator,进行返回 最后,如果supportsBean 则 返回Validator 否则 返回null 如果ConfigurationPropertiesBindingPostProcessor#conversionService 等于null,则调用getDefaultConversionService获得默认的ConversionService.否则,直接将本类的conversionService 赋值给PropertiesConfigurationFactory 的ConversionService.还是由于conversionService一直为 null,因此会调用getDefaultConversionService.代码如下:         private ConversionService getDefaultConversionService() {
        // 又是lazy-init 风格
        // 1. 如果defaultConversionService 等于null,则意味着是第一次调用
        if (this.defaultConversionService == null) {
            // 1.1 实例化DefaultConversionService
            DefaultConversionService conversionService = new DefaultConversionService();
            // 1.2 调用autowireBean进行注入依赖,此时会注入converters,genericConverters
            this.applicationContext.getAutowireCapableBeanFactory().autowireBean(this);
            // 1.3 遍历converters,genericConverters 依次加入到conversionService的converters中
            for (Converter converter : this.converters) {
                conversionService.addConverter(converter);
            }
            for (GenericConverter genericConverter : this.genericConverters) {
                conversionService.addConverter(genericConverter);
            }
            // 1.4 赋值给defaultConversionService
            this.defaultConversionService = conversionService;
        }
        // 2. 如果不等于null,则直接返回
        return this.defaultConversionService;
        } 2件事: 如果defaultConversionService 等于null,则意味着是第一次调用,又是lazy-init 风格. 实例化DefaultConversionService 调用autowireBean进行注入依赖,此时会注入converters,genericConverters 遍历converters,genericConverters 依次加入到conversionService的converters中 赋值给defaultConversionService 如果不等于null,则直接返回 如果注解存在,这是肯定的,不然也不会执行该方法,则根据@ConfigurationProperties的值进行配置 如果配置了prefix,或者value 值,则设置TargetName.这个后面解析的时候会用到该值. 调用PropertiesConfigurationFactory#bindPropertiesToTarget,进行绑定 
    
     PropertiesConfigurationFactory#bindPropertiesToTarget 代码如下:     public void bindPropertiesToTarget() throws BindException {
            // 1.首先判断propertySources是否为null,如果为null的话,抛出异常.一般不会为null的
            Assert.state(this.propertySources != null, "PropertySources should not be null");
            try {
                if (logger.isTraceEnabled()) {
                    logger.trace("Property Sources: " + this.propertySources);
    
                }
                // 2. 将hasBeenBound 设为true
                this.hasBeenBound = true;
                // 3. 调用doBindPropertiesToTarget
                doBindPropertiesToTarget();
            }
            catch (BindException ex) {
                if (this.exceptionIfInvalid) {
                    throw ex;
                }
                PropertiesConfigurationFactory.logger
                        .error("Failed to load Properties validation bean. "
                                + "Your Properties may be invalid.", ex);
            }
        } 3件事: 首先判断propertySources是否为null,如果为null的话,抛出异常.一般不会为null的.因为该类在实例化的时候,已经对其进行赋值了 将hasBeenBound 设为true 调用doBindPropertiesToTarget.代码如下:         private void doBindPropertiesToTarget() throws BindException {
        // 1. 初始化RelaxedDataBinder 并进行设置一下属性. // target = SpringApplication.这样RelaxedDataBinder也就持有了SpringApplication
        RelaxedDataBinder dataBinder = (this.targetName != null
                ? new RelaxedDataBinder(this.target, this.targetName)
                : new RelaxedDataBinder(this.target));
        // 对于当前场景来说validator还是为null的,在 ConfigurationPropertiesBindingPostProcessor#postProcessBeforeInitialization 中,该validator为ValidatedLocalValidatorFactoryBean
        if (this.validator != null
                && this.validator.supports(dataBinder.getTarget().getClass())) {
            dataBinder.setValidator(this.validator);
        }
        if (this.conversionService != null) {
            // 持有了一系列的转换器
            dataBinder.setConversionService(this.conversionService);
        }
        dataBinder.setAutoGrowCollectionLimit(Integer.MAX_VALUE);
        dataBinder.setIgnoreNestedProperties(this.ignoreNestedProperties);
        dataBinder.setIgnoreInvalidFields(this.ignoreInvalidFields);
        dataBinder.setIgnoreUnknownFields(this.ignoreUnknownFields);
        // 2. 扩展点,空实现
        customizeBinder(dataBinder);
        // 3. 获得relaxedTargetNames,对于当前来说,其值为-->spring.main,也就是获得@ConfigurationProperties中配置的prefix
        Iterable relaxedTargetNames = getRelaxedTargetNames();
        // 4. 通过遍历target的属性,这里的target为SpringApplication.然后将SpringApplication的属性按照单词划分的规则,与relaxedTargetNames进行拼接
        // 举例说明:SpringApplication中有一个logStartupInfo属性,则拆分为log-startup-info,然后与spring.main拼接为
        // spring.main.log-startup-info 和 spring.main_log-startup-info
        // 通过拼接生成key
        Set names = getNames(relaxedTargetNames);
        // 5. 生成PropertyValues,此时就已经将配置文件中的占位符解析完了
        PropertyValues propertyValues = getPropertySourcesPropertyValues(names,
                relaxedTargetNames);
        // 6. 调用bind,进行绑定
        dataBinder.bind(propertyValues);
        if (this.validator != null) {
            dataBinder.validate();
        }
        // 7. 检查在绑定过程中是否出现异常,如果有的话,抛出BindException
        checkForBindingErrors(dataBinder);
        } 7件事: 初始化RelaxedDataBinder 并进行设置一下属性,target = People.这样RelaxedDataBinder也就持有了People. 如果validator不等于null,并且validator支持该类型的话,则设置RelaxedDataBinder的Validator,对于当前场景来说,是validator. 如果conversionService 不等于null,则设置ConversionService,这样RelaxedDataBinder就持有了一系列的转换器 设置AutoGrowCollectionLimit 为Integer.MAX_VALUE,该属性在处理集合属性注入时会用到 设置是否忽略嵌套属性,默认是false. 设置是否忽略不正确的属性,默认是false 设置是否忽略未知的子弹,默认是true 调用customizeBinder,这个扩展点,默认是空实现 调用getRelaxedTargetNames,对于当前来说,其值为–>com.example.demo,也就是获得@ConfigurationProperties中配置的prefix 通过遍历target的属性,这里的target为People.然后将People的属性按照单词划分的规则,与relaxedTargetNames进行拼接.举例说明: People中有一个name属性,则拆分后为name,然后与com.example.demo拼接为com.example.demo.name 调用getPropertySourcesPropertyValues,生成PropertyValues,在这步完成了占位符解析.这个步骤很关键,我们在第4点中进行分析. 调用bind,进行绑定 检查在绑定过程中是否出现异常,如果有的话,抛出BindException 
     getPropertySourcesPropertyValues.代码如下:         private PropertyValues getPropertySourcesPropertyValues(Set names,
                Iterable relaxedTargetNames) {
            // 1. 根据names和relaxedTargetNames 生成PropertyNamePatternsMatcher
            PropertyNamePatternsMatcher includes = getPropertyNamePatternsMatcher(names,
                    relaxedTargetNames);
            // 2. 返回PropertySourcesPropertyValues
            return new PropertySourcesPropertyValues(this.propertySources, names, includes,
                    this.resolvePlaceholders);
        } 根据names和relaxedTargetNames 生成PropertyNamePatternsMatcher.代码如下:     private PropertyNamePatternsMatcher getPropertyNamePatternsMatcher(Set names,
            Iterable relaxedTargetNames) {
        // 1. 如果ignoreUnknownFields 并且 target 不是map的子类,则返回DefaultPropertyNamePatternsMatcher,在@ConfigurationProperties中,ignoreUnknownFields默认是true
        if (this.ignoreUnknownFields && !isMapTarget()) {
            // Since unknown fields are ignored we can filter them out early to save
            // unnecessary calls to the PropertySource.
            return new DefaultPropertyNamePatternsMatcher(EXACT_DELIMITERS, true, names);
        }
        // 2. 如果relaxedTargetNames 不等于null,则通过对relaxedTargetNames去重后,返回DefaultPropertyNamePatternsMatcher
        if (relaxedTargetNames != null) {
            // We can filter properties to those starting with the target name, but
            // we can't do a complete filter since we need to trigger the
            // unknown fields check
            Set relaxedNames = new HashSet();
            for (String relaxedTargetName : relaxedTargetNames) {
                relaxedNames.add(relaxedTargetName);
            }
            return new DefaultPropertyNamePatternsMatcher(TARGET_NAME_DELIMITERS, true,
                    relaxedNames);
        }
        // Not ideal, we basically can't filter anything
        // 3. 返回默认的
        return PropertyNamePatternsMatcher.ALL;
        }
     3件事: 如果ignoreUnknownFields 并且 target 不是map的子类,则返回DefaultPropertyNamePatternsMatcher,在@ConfigurationProperties中,ignoreUnknownFields默认是true.在此时,由于target 为People,因此返回DefaultPropertyNamePatternsMatcher. 如果relaxedTargetNames 不等于null,则通过对relaxedTargetNames去重后,返回DefaultPropertyNamePatternsMatcher 返回默认的 返回PropertySourcesPropertyValues.其类图如下: 其构造器如下:     PropertySourcesPropertyValues(PropertySources propertySources,
            Collection nonEnumerableFallbackNames,
            PropertyNamePatternsMatcher includes, boolean resolvePlaceholders) {
        Assert.notNull(propertySources, "PropertySources must not be null");
        Assert.notNull(includes, "Includes must not be null");
        this.propertySources = propertySources;
        this.nonEnumerableFallbackNames = nonEnumerableFallbackNames;
        this.includes = includes;
        this.resolvePlaceholders = resolvePlaceholders;
        PropertySourcesPropertyResolver resolver = new PropertySourcesPropertyResolver(
                propertySources);
        for (PropertySource source : propertySources) {
            processPropertySource(source, resolver);
        }
        } 3件事: 属性赋值. 实例化PropertySourcesPropertyResolver 遍历propertySources,依次调用processPropertySource.代码如下:         private void processPropertySource(PropertySource source,
        PropertySourcesPropertyResolver resolver) {
        if (source instanceof CompositePropertySource) {
        processCompositePropertySource((CompositePropertySource) source, resolver);
        }
        else if (source instanceof EnumerablePropertySource) {
        processEnumerablePropertySource((EnumerablePropertySource) source,
                resolver, this.includes);
        }
        else {
        processNonEnumerablePropertySource(source, resolver);
        }
        } 如果PropertySource是CompositePropertySource的子类,则调用processCompositePropertySource方法,而该方法最终还是调用了processPropertySource,做递归处理. 如果PropertySource是EnumerablePropertySource的子类,则调用processEnumerablePropertySource.这里需要说明一下,我们是配置在application.properties中,那么其PropertySource 为 PropertiesPropertySource,是EnumerablePropertySource的子类,其继承结构如下: 因此,关于配置文件属性的注入,最终会在这里执行. 否则,调用processNonEnumerablePropertySource. 我们重点来看processEnumerablePropertySource,代码如下:     private void processEnumerablePropertySource(EnumerablePropertySource source,
        PropertySourcesPropertyResolver resolver,
        PropertyNamePatternsMatcher includes) {
        if (source.getPropertyNames().length > 0) {
        for (String propertyName : source.getPropertyNames()) {
            if (includes.matches(propertyName)) {// 如果存在的话,则加入到propertyValues中
                Object value = getEnumerableProperty(source, resolver, propertyName);
                putIfAbsent(propertyName, value, source);
            }
        }
        }
        } 思路很简单, 首先判断source中是否有属性的配置,如果有的话,则依次遍历之 在遍历过程中,会调用PropertyNamePatternsMatcher#matches 判断是否匹配.这里说明一下,这里使用的是DefaultPropertyNamePatternsMatcher,其matches 会依次遍历其内部的names 看是否与传入的propertyName 匹配,这里的names 就是在实例化时传入的com.example.demo.name等之类的东西. 如果匹配的话,则调用getEnumerableProperty 获得值.代码如下:     private Object getEnumerableProperty(EnumerablePropertySource source,
        PropertySourcesPropertyResolver resolver, String propertyName) {
        try {
        if (this.resolvePlaceholders) {
            return resolver.getProperty(propertyName, Object.class);
        }
        }
        catch (RuntimeException ex) {
        // Probably could not resolve placeholders, ignore it here
        }
        return source.getProperty(propertyName);
        } 如果resolvePlaceholders 为true,则调用PropertySourcesPropertyResolver#getProperty 处理,由于resolvePlaceholders 默认为true,因此一般都会执行这里. 否则,直接从EnumerablePropertySource 获取值即可. 调用putIfAbsent 将值,属性名,保存到propertyValues 中. 其中2.1 会调用如下代码:     public  T getProperty(String key, Class targetValueType) {
        return getProperty(key, targetValueType, true);
                } 最终调用如下代码:     protected  T getProperty(String key, Class targetValueType, boolean resolveNestedPlaceholders) {
        if (this.propertySources != null) {
        for (PropertySource propertySource : this.propertySources) {
        if (logger.isTraceEnabled()) {
        logger.trace("Searching for key '" + key + "' in PropertySource '" +
                propertySource.getName() + "'");
        }
        Object value = propertySource.getProperty(key);
        if (value != null) {
        if (resolveNestedPlaceholders && value instanceof String) {
            value = resolveNestedPlaceholders((String) value);
        }
        logKeyFound(key, propertySource, value);
        return convertValueIfNecessary(value, targetValueType);
        }
        }
        }
        if (logger.isDebugEnabled()) {
        logger.debug("Could not find key '" + key + "' in any property source");
        }
        return null;
        }
     3件事 如果propertySources 不等于null,则依次遍历propertySources,进行处理 通过调用PropertySource#getProperty进行获取 如果获取到值的话, 如果resolveNestedPlaceholders(这个一般都是true) 并且value 为String,则调用resolveNestedPlaceholders处理占位符–>${},一般这个步骤都会执行的. 打印日志 尝试对其进行转换. 如果经过第1步处理,还是没找到的话,则直接返回null 1.1.1.1 最终会调用如下方法.代码如下:         public String resolvePlaceholders(String text) {
        if (this.nonStrictHelper == null) {
        this.nonStrictHelper = createPlaceholderHelper(true);
        }
        return doResolvePlaceholders(text, this.nonStrictHelper);
        } 如果nonStrictHelper等于null,则调用createPlaceholderHelper进行实例化.lazy-init 风格. 调用AbstractPropertyResolver#doResolvePlaceholders.代码如下:     private String doResolvePlaceholders(String text, PropertyPlaceholderHelper helper) {
        return helper.replacePlaceholders(text, new PropertyPlaceholderHelper.PlaceholderResolver() {
        @Override
        public String resolvePlaceholder(String placeholderName) {
        return getPropertyAsRawString(placeholderName);
        }
        });
        } 这里直接调用了第一步实例化的PropertyPlaceholderHelper的replacePlaceholders进行处理,同时实例化了一个PlaceholderResolver,该类在获取值的时候会用到,这个后面会有介绍.PropertyPlaceholderHelper#replacePlaceholders 代码如下:     public String replacePlaceholders(String value, PlaceholderResolver placeholderResolver) {
        Assert.notNull(value, "'value' must not be null");
        return parseStringValue(value, placeholderResolver, new HashSet());
        } 最终调用如下代码:     protected String parseStringValue(
        String value, PlaceholderResolver placeholderResolver, Set visitedPlaceholders) {
        StringBuilder result = new StringBuilder(value);
        // 1. 通过String#indexOf 获取前缀(一般都是${)的下标
        int startIndex = value.indexOf(this.placeholderPrefix);
        // 2 如果存在
        while (startIndex != -1) {
        // 2.1 获得后缀,此时获得是最小的后缀,嵌套处理
        int endIndex = findPlaceholderEndIndex(result, startIndex);
        if (endIndex != -1) {// 3 如果endIndex 存在,
        // 3.1 通过字符串的截取获得占位符,如${placeholder},那么此时获得的是placeholder
        String placeholder = result.substring(startIndex + this.placeholderPrefix.length(), endIndex);
        String originalPlaceholder = placeholder;
        // 3.2 进行循环引用的检查,如果存在,则抛出IllegalArgumentException
        if (!visitedPlaceholders.add(originalPlaceholder)) {
        throw new IllegalArgumentException(
                "Circular placeholder reference '" + originalPlaceholder + "' in property definitions");
        }
        // Recursive invocation, parsing placeholders contained in the placeholder key.
        // 3.3 递归处理
        placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders);
        // Now obtain the value for the fully resolved key...
        // 3.4 进行解析占位符
        String propVal = placeholderResolver.resolvePlaceholder(placeholder);
        // 3.5 如果propVal 不等于null并且 valueSeparator(默认为 :)不等于null,则此时意味有默认值,
        // 那么此时调用placeholderResolver#resolvePlaceholder 进行解析,如果解析失败的话,则返回默认值
        if (propVal == null && this.valueSeparator != null) {
        int separatorIndex = placeholder.indexOf(this.valueSeparator);
        if (separatorIndex != -1) {
            String actualPlaceholder = placeholder.substring(0, separatorIndex);
            String defaultValue = placeholder.substring(separatorIndex + this.valueSeparator.length());
            propVal = placeholderResolver.resolvePlaceholder(actualPlaceholder);
            if (propVal == null) {
                propVal = defaultValue;
            }
        }
        }
        // 3.6
        if (propVal != null) {
        // Recursive invocation, parsing placeholders contained in the
        // previously resolved placeholder value.
        // 3.6.1 如果propVal 不等于null,则意味着解析成功,则继续递归处理,处理完后,进行替换,
    
        propVal = parseStringValue(propVal, placeholderResolver, visitedPlaceholders);
        // 进行替换
        result.replace(startIndex, endIndex + this.placeholderSuffix.length(), propVal);
        if (logger.isTraceEnabled()) {
            logger.trace("Resolved placeholder '" + placeholder + "'");
        }
        // 重新计算startIndex
        startIndex = result.indexOf(this.placeholderPrefix, startIndex + propVal.length());
        }
        else if (this.ignoreUnresolvablePlaceholders) {
        // Proceed with unprocessed value.
        // 3.6.2 如果没有解析成功并且ignoreUnresolvablePlaceholders,则重新计算startIndex
        startIndex = result.indexOf(this.placeholderPrefix, endIndex + this.placeholderSuffix.length());
        }
        else {
        // 3.6.3 抛出IllegalArgumentException
        throw new IllegalArgumentException("Could not resolve placeholder '" +
                placeholder + "'" + " in value \"" + value + "\"");
        }
        // 3.7 从visitedPlaceholders 删除.该算法有点类似dfs.
        visitedPlaceholders.remove(originalPlaceholder);
        }
        else {
        // 2.2 将startIndex 设为-1,则意味着已经处理完了
        startIndex = -1;
        }
        }
        return result.toString();
        } 3件事: 通过String#indexOf 获取前缀(一般都是${)的下标 如果存在 获得后缀,此时获得是最小的后缀,嵌套处理 如果endIndex 存在, 通过字符串的截取获得占位符,如${placeholder},那么此时获得的是placeholder 进行循环引用的检查,如果存在,则抛出IllegalArgumentException 调用parseStringValue,进行递归处理. 调用PlaceholderResolver#resolvePlaceholder进行解析占位符 如果propVal 不等于null并且 valueSeparator(默认为 :)不等于null,则此时意味有默认值,那么此时调用placeholderResolver#resolvePlaceholder 进行解析,如果解析失败的话,则返回默认值 如果propVal 不等于null,则意味着解析成功,则继续递归处理,处理完后,进行替换,重新计算startIndex 如果没有解析成功并且ignoreUnresolvablePlaceholders,则重新计算startIndex 其他情况下,则抛出异常 从visitedPlaceholders 删除.该算法有点类似dfs. 如果不存在,则将startIndex 设为-1,则意味着已经处理完了. 关于占位符的处理,集合,对象导航,属性转换的处理,我们这里先不解析,我们先解析最简单的情况,为People注入name 属性.并且配置文件中的配置如下: com.example.demo.name=hi 
     视线回到PropertiesConfigurationFactory#doBindPropertiesToTarget中来,此时执行完了getPropertySourcesPropertyValues,接下来就该执行第6步,调用DataBinder#bind进行绑定.这里还是假设我们只配置了com.example.demo.name=hi. 代码如下:     public void bind(PropertyValues pvs) {
            MutablePropertyValues mpvs = (pvs instanceof MutablePropertyValues) ?
                    (MutablePropertyValues) pvs : new MutablePropertyValues(pvs);
            doBind(mpvs);
        } 调用DataBinder#doBind,代码如下:     protected void doBind(MutablePropertyValues mpvs) {
            // 1. 检查是否存在不允许的字段存在,如果存在则删除
            checkAllowedFields(mpvs);
            // 2.检查是否存在Required 字段缺失的情况
            checkRequiredFields(mpvs);
            // 3. 进行注入
            applyPropertyValues(mpvs);
        } 3件事: 检查是否存在不允许的字段存在,如果存在则删除 检查是否存在Required 字段缺失的情况,如果存在,则抛出异常 调用applyPropertyValues进行注入.代码如下:     protected void applyPropertyValues(MutablePropertyValues mpvs) {
        try {
            // Bind request parameters onto target object.
            // 1. 进行注入
            getPropertyAccessor().setPropertyValues(mpvs, isIgnoreUnknownFields(), isIgnoreInvalidFields());
        }
        catch (PropertyBatchUpdateException ex) {
            // Use bind error processor to create FieldErrors.
            // 2. 如果抛出异常,则记录异常
            for (PropertyAccessException pae : ex.getPropertyAccessExceptions()) {
                getBindingErrorProcessor().processPropertyAccessException(pae, getInternalBindingResult());
            }
        }
        } 2件事: 进行注入. 调用getPropertyAccessor 获得ConfigurablePropertyAccessor.代码如下:     protected ConfigurablePropertyAccessor getPropertyAccessor() {
            return getInternalBindingResult().getPropertyAccessor();
        } 调用getInternalBindingResult,获得AbstractPropertyBindingResult.代码如下:     protected AbstractPropertyBindingResult getInternalBindingResult() {
        // 1. 同样是lazy-init,当第一次调用时 ,调用initBeanPropertyAccess 进行初始化
        if (this.bindingResult == null) {
        initBeanPropertyAccess();
        }
        return this.bindingResult;
        } 同样是lazy-init,当第一次调用时 ,调用initBeanPropertyAccess 进行初始化. initBeanPropertyAccess 代码如下:     public void initBeanPropertyAccess() {
        Assert.state(this.bindingResult == null,
        "DataBinder is already initialized - call initBeanPropertyAccess before other configuration methods");
        this.bindingResult = createBeanPropertyBindingResult();
        } 调用     protected AbstractPropertyBindingResult createBeanPropertyBindingResult() {
        // 1. 实例化BeanPropertyBindingResult
        BeanPropertyBindingResult result = new BeanPropertyBindingResult(getTarget(),
        getObjectName(), isAutoGrowNestedPaths(), getAutoGrowCollectionLimit());
        if (this.conversionService != null) {
        // 2. 这个步骤是一定会执行的, 进行初始化
        result.initConversion(this.conversionService);
        }
        if (this.messageCodesResolver != null) {
        // 3. 设置messageCodesResolver
        result.setMessageCodesResolver(this.messageCodesResolver);
        }
        return result;
        } 3件事: 实例化BeanPropertyBindingResult 这个步骤是一定会执行的, 进行初始化conversionService 设置messageCodesResolver 调用BeanPropertyBindingResult#getPropertyAccessor.     public final ConfigurablePropertyAccessor getPropertyAccessor() {
        // 1. lazy-inits
        if (this.beanWrapper == null) {
        // 1.1 最终调用PropertyAccessorFactory#forBeanPropertyAccess,直接实例化了BeanWrapperImpl
        this.beanWrapper = createBeanWrapper();
        this.beanWrapper.setExtractOldValueForEditor(true);
        this.beanWrapper.setAutoGrowNestedPaths(this.autoGrowNestedPaths);
        this.beanWrapper.setAutoGrowCollectionLimit(this.autoGrowCollectionLimit);
        }
        return this.beanWrapper;
        } 还是同样的味道,lazy-init,最终调用PropertyAccessorFactory#forBeanPropertyAccess,直接实例化了BeanWrapperImpl. 调用BeanPropertyBindingResult#setPropertyValues 进行注入. 如果在注入过程出现异常,则记录异常. 其中 1.3 BeanPropertyBindingResult#setPropertyValues ,代码如下:     public void setPropertyValues(PropertyValues pvs, boolean ignoreUnknown, boolean ignoreInvalid)
            throws BeansException {
    
        List propertyAccessExceptions = null;
        // 1. 获得propertyValues,一般情况下,此时传入的是MutablePropertyValues,因此直接通过MutablePropertyValues#getPropertyValueList 获取即可
        List propertyValues = (pvs instanceof MutablePropertyValues ?
                ((MutablePropertyValues) pvs).getPropertyValueList() : Arrays.asList(pvs.getPropertyValues()));
        // 2. 遍历propertyValues,依次调用setPropertyValue 进行处理
        for (PropertyValue pv : propertyValues) {
    
                // 删除一些无用的try-cath,减少篇幅...
                setPropertyValue(pv);
    
        }
    
        if (propertyAccessExceptions != null) {
            PropertyAccessException[] paeArray =
                    propertyAccessExceptions.toArray(new PropertyAccessException[propertyAccessExceptions.size()]);
            throw new PropertyBatchUpdateException(paeArray);
        }
        } 3件事: 获得propertyValues,一般情况下,此时传入的是MutablePropertyValues,因此直接通过MutablePropertyValues#getPropertyValueList 获取即可 遍历propertyValues,依次调用setPropertyValue 进行处理 如果propertyAccessExceptions != null,则意味在第2步处理中,出现了问题,则抛出PropertyBatchUpdateException. 其中第2步,最终调用的是AbstractNestablePropertyAccessor#setPropertyValue,代码如下:     public void setPropertyValue(PropertyValue pv) throws BeansException {
        PropertyTokenHolder tokens = (PropertyTokenHolder) pv.resolvedTokens;
        if (tokens == null) {
            String propertyName = pv.getName();
            AbstractNestablePropertyAccessor nestedPa;
            try {
                nestedPa = getPropertyAccessorForPropertyPath(propertyName);
            }
            catch (NotReadablePropertyException ex) {
                throw new NotWritablePropertyException(getRootClass(), this.nestedPath + propertyName,
                        "Nested property in path '" + propertyName + "' does not exist", ex);
            }
            tokens = getPropertyNameTokens(getFinalPath(nestedPa, propertyName));
            if (nestedPa == this) {
                pv.getOriginalPropertyValue().resolvedTokens = tokens;
            }
            nestedPa.setPropertyValue(tokens, pv);
        }
        else {
            setPropertyValue(tokens, pv);
        }
        } 调用getPropertyAccessorForPropertyPath,处理对象导航,还是由于此处分析的最简单的场景,因此这里返回的就是当前类. 调用getPropertyNameTokens,这里处理的是集合的情况.同样,这里先不进行分析 调用AbstractNestablePropertyAccessor#setPropertyValue,进行赋值.代码如下:     protected void setPropertyValue(PropertyTokenHolder tokens, PropertyValue pv) throws BeansException {
        if (tokens.keys != null) {
            processKeyedProperty(tokens, pv);
        }
        else {
            processLocalProperty(tokens, pv);
        }
        }
     2件事: 如果 PropertyTokenHolder 中的keys 不等于null,则意味着是要对集合进行赋值,为什么?这个我们后面有解释. 否则调用 processLocalProperty进行处理.因为我们这里分析的是最简单的情况,因此会在这里进行处理.代码如下:     private void processLocalProperty(PropertyTokenHolder tokens, PropertyValue pv) {
        // 1. 获得PropertyHandler
        PropertyHandler ph = getLocalPropertyHandler(tokens.actualName);
        // 2. 如果ph 等于null,或者 PropertyHandler 没有set方法
        if (ph == null || !ph.isWritable()) {
        // 2.1 如果该属性是可选的,则打印日志,否则抛出异常
        if (pv.isOptional()) {
    
            return;
        }
        else {
            throw createNotWritablePropertyException(tokens.canonicalName);
        }
        }
        // 3. 进行转换处理
        Object oldValue = null;
        Object originalValue = pv.getValue();
        Object valueToApply = originalValue;
        if (!Boolean.FALSE.equals(pv.conversionNecessary)) {
            if (pv.isConverted()) {
                valueToApply = pv.getConvertedValue();
            }
            else {
                if (isExtractOldValueForEditor() && ph.isReadable()) {
    
                        oldValue = ph.getValue();
    
                }
                valueToApply = convertForProperty(
                        tokens.canonicalName, oldValue, originalValue, ph.toTypeDescriptor());
            }
            pv.getOriginalPropertyValue().conversionNecessary = (valueToApply != originalValue);
        }
        // 4. 进行赋值
        ph.setValue(this.wrappedObject, valueToApply);
        }       
        } 4件事 获得PropertyHandler,注意,这里调用的是BeanWrapperImpl.getLocalPropertyHandler代码如下:         protected BeanPropertyHandler getLocalPropertyHandler(String propertyName) {
        PropertyDescriptor pd = getCachedIntrospectionResults().getPropertyDescriptor(propertyName);
        if (pd != null) {
        return new BeanPropertyHandler(pd);
        }
        return null;
        } 调用getCachedIntrospectionResults 获得CachedIntrospectionResults.代码如下:         private CachedIntrospectionResults getCachedIntrospectionResults() {
        Assert.state(getWrappedInstance() != null, "BeanWrapper does not hold a bean instance");
        if (this.cachedIntrospectionResults == null) {
        // lazy-init,第一次调用时初始化
        this.cachedIntrospectionResults = CachedIntrospectionResults.forClass(getWrappedClass());
        }
        return this.cachedIntrospectionResults;
        } 同样的调调,lazy-init,调用CachedIntrospectionResults#forClass获得CachedIntrospectionResults. 注意,这里传入的是target,也就是 People.class.代码如下: static CachedIntrospectionResults forClass(Class<?> beanClass) throws BeansException { // 1. 尝试从strongClassCache,softClassCache中获取,如果不为空,则直接返回. CachedIntrospectionResults results = strongClassCache.get(beanClass); if (results != null) { return results; } results = softClassCache.get(beanClass); if (results != null) { return results; } // 2. 初始化 results = new CachedIntrospectionResults(beanClass); ConcurrentMap<Class<?>, CachedIntrospectionResults> classCacheToUse; // 3. 如果当前给定的类是否是给定的ClassLoader 或者是其父ClassLoader 加载的 或者 判断给定的classLoader 是否是acceptedClassLoaders的子classLoader // 一般都是这个了,那么就使用strongClassCache,否则使用softClassCache if (ClassUtils.isCacheSafe(beanClass, CachedIntrospectionResults.class.getClassLoader()) || isClassLoaderAccepted(beanClass.getClassLoader())) { classCacheToUse = strongClassCache; } else { if (logger.isDebugEnabled()) { logger.debug("Not strongly caching class [" + beanClass.getName() + "] because it is not cache-safe"); } classCacheToUse = softClassCache; } // 4. 加入缓存中 CachedIntrospectionResults existing = classCacheToUse.putIfAbsent(beanClass, results); return (existing != null ? existing : results); } 4件事: 尝试从strongClassCache,softClassCache中获取,如果不为空,则直接返回. 否则,进行初始化.CachedIntrospectionResults.其中,有如下代码:         beanInfo = (shouldIntrospectorIgnoreBeaninfoClasses ?
        Introspector.getBeanInfo(beanClass, Introspector.IGNORE_ALL_BEANINFO) :
        Introspector.getBeanInfo(beanClass)); 这里调用了java.beans.Introspector 获取BeanInfo,而CachedIntrospectionResults只是对BeanInfo包装而已,关于CachedIntrospectionResults的初始化,这里就不继续深入了,也没有必要. 如果当前给定的类是否是给定的ClassLoader 或者是其父ClassLoader 加载的 或者 判断给定的classLoader 是否是acceptedClassLoaders的子classLoader,那么就使用strongClassCache,否则使用softClassCache.一般就是strongClassCache 加入缓存中 调用CachedIntrospectionResults#getPropertyDescriptor 获得PropertyDescriptor.注意,这里返回的是java.beans.PropertyDescriptor.是关于java反射的.不懂的可以百度一下. 如果PropertyDescriptor 不等于null,就意味着在target 也就是 People 中找到了对应的属性.因此,直接返回BeanPropertyHandler. 否则,返回null. 如果ph 等于null,或者 PropertyHandler set方法不存在或者不是public的,如果该属性是可选的,则打印日志,否则抛出异常. 调用convertForProperty,进行属性的转换,这里就是真正属性转换的地方,同样,后面有解释 调用BeanPropertyHandler#setValue进行赋值.代码如下:     public void setValue(final Object object, Object valueToApply) throws Exception {
        // 1. 获得该属性对应的set方法
        final Method writeMethod = (this.pd instanceof GenericTypeAwarePropertyDescriptor ?
            ((GenericTypeAwarePropertyDescriptor) this.pd).getWriteMethodForActualAccess() :
            this.pd.getWriteMethod());
        // 2. 如果该方法为私有的,则通过反射的方式,设置为可访问的
        if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers()) && !writeMethod.isAccessible()) {
        if (System.getSecurityManager() != null) {
            AccessController.doPrivileged(new PrivilegedAction() {
                @Override
                public Object run() {
                    writeMethod.setAccessible(true);
                    return null;
                }
            });
        }
        else {
            writeMethod.setAccessible(true);
        }
        }
        // 3. 进行赋值
        final Object value = valueToApply;
        if (System.getSecurityManager() != null) {
        try {
            AccessController.doPrivileged(new PrivilegedExceptionAction() {
                @Override
                public Object run() throws Exception {
                    writeMethod.invoke(object, value);
                    return null;
                }
            }, acc);
        }
        catch (PrivilegedActionException ex) {
            throw ex.getException();
        }
        }
        else {
        writeMethod.invoke(getWrappedInstance(), value);
        }
        }
        }
     3件事:
     获得该属性对应的set方法 如果该方法为私有的,则通过反射的方式,设置为可访问的 通过writeMethod#invoke的方式调用set 方法 进行赋值. 
    
    
    
    
     至此,关于简单属性的注入(String类型)就分析完了,接下来就占位符,集合,对象导航,属性转换来分别做处理.
    
    
    
    
     占位符处理
     在之前的分析过程中,我们跳过了占位符处理工程的分析,这里我们将配置文件改为如下:
         com.example.demo.name=${aaa:hi}
     还是分析对People name 属性的注入. 之前的步骤同之前的分析的一样.只不过在PropertyPlaceholderHelper# parseStringValue处开始了对占位符的处理.代码如下:
         protected String parseStringValue(
                    String value, PlaceholderResolver placeholderResolver, Set<String> visitedPlaceholders) {
    
                StringBuilder result = new StringBuilder(value);
    
                // 1. 通过String#indexOf 获取前缀(一般都是${)的下标
                int startIndex = value.indexOf(this.placeholderPrefix);
                // 2 如果存在
                while (startIndex != -1) {
                    // 2.1 获得后缀,此时获得是最小的后缀,嵌套处理
                    int endIndex = findPlaceholderEndIndex(result, startIndex);
                    if (endIndex != -1) {// 3 如果endIndex 存在,
                        // 3.1 通过字符串的截取获得占位符,如${placeholder},那么此时获得的是placeholder
                        String placeholder = result.substring(startIndex + this.placeholderPrefix.length(), endIndex);
                        String originalPlaceholder = placeholder;
                        // 3.2 进行循环引用的检查,如果存在,则抛出IllegalArgumentException
                        if (!visitedPlaceholders.add(originalPlaceholder)) {
                            throw new IllegalArgumentException(
                                    "Circular placeholder reference '" + originalPlaceholder + "' in property definitions");
                        }
                        // Recursive invocation, parsing placeholders contained in the placeholder key.
                        // 3.3 递归处理
                        placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders);
                        // Now obtain the value for the fully resolved key...
                        // 3.4 进行解析占位符
                        String propVal = placeholderResolver.resolvePlaceholder(placeholder);
                        // 3.5 如果propVal 不等于null并且 valueSeparator(默认为 :)不等于null,则此时意味有默认值,
                        // 那么此时调用placeholderResolver#resolvePlaceholder 进行解析,如果解析失败的话,则返回默认值
                        if (propVal == null && this.valueSeparator != null) {
                            int separatorIndex = placeholder.indexOf(this.valueSeparator);
                            if (separatorIndex != -1) {
                                String actualPlaceholder = placeholder.substring(0, separatorIndex);
                                String defaultValue = placeholder.substring(separatorIndex + this.valueSeparator.length());
                                propVal = placeholderResolver.resolvePlaceholder(actualPlaceholder);
                                if (propVal == null) {
                                    propVal = defaultValue;
                                }
                            }
                        }
    
                        // 3.6
                        if (propVal != null) {
                            // Recursive invocation, parsing placeholders contained in the
                            // previously resolved placeholder value.
                            // 3.6.1 如果propVal 不等于null,则意味着解析成功,则继续递归处理,处理完后,进行替换,
    
                            propVal = parseStringValue(propVal, placeholderResolver, visitedPlaceholders);
                            // 进行替换
                            result.replace(startIndex, endIndex + this.placeholderSuffix.length(), propVal);
                            if (logger.isTraceEnabled()) {
                                logger.trace("Resolved placeholder '" + placeholder + "'");
                            }
                            // 重新计算startIndex
                            startIndex = result.indexOf(this.placeholderPrefix, startIndex + propVal.length());
                        }
                        else if (this.ignoreUnresolvablePlaceholders) {
                            // Proceed with unprocessed value.
                            // 3.6.2 如果没有解析成功并且ignoreUnresolvablePlaceholders,则重新计算startIndex
                            startIndex = result.indexOf(this.placeholderPrefix, endIndex + this.placeholderSuffix.length());
                        }
                        else {
                            // 3.6.3 抛出IllegalArgumentException
                            throw new IllegalArgumentException("Could not resolve placeholder '" +
                                    placeholder + "'" + " in value \"" + value + "\"");
                        }
                        // 3.7 从visitedPlaceholders 删除.该算法有点类似dfs.
                        visitedPlaceholders.remove(originalPlaceholder);
                    }
                    else {
                        // 2.2 将startIndex 设为-1,则意味着已经处理完了
                        startIndex = -1;
                    }
                }
                return result.toString();
            }
     首先通过String#indexOf 获得 { 的下标,这里是存在的,因此继续处理。此时调用的是PropertyPlaceholderHelper#findPlaceholderEndIndex 获的后缀.比方说如果我们配置的是 ${aa} 那么此时返回的就是}的下标,如果配置的是{aa}${bb}我们返回的就是,a后面的}的下标.代码如下:
         private int findPlaceholderEndIndex(CharSequence buf, int startIndex) {
            int index = startIndex + this.placeholderPrefix.length();
            int withinNestedPlaceholder = 0;
            while (index < buf.length()) {
                if (StringUtils.substringMatch(buf, index, this.placeholderSuffix)) {
                    if (withinNestedPlaceholder > 0) {
                        withinNestedPlaceholder--;
                        index = index + this.placeholderSuffix.length();
                    }
                    else {
                        return index;
                    }
                }
                else if (StringUtils.substringMatch(buf, index, this.simplePrefix)) {
                    withinNestedPlaceholder++;
                    index = index + this.simplePrefix.length();
                }
                else {
                    index++;
                }
            }
            return -1;
        }
    
     接下来,进行字符截取,此时我们配置的是com.example.demo.name=${aaa:hi},截取后获得的是aaa:hi,
     第三步,将aaa:hi 作为参数,递归调用parseStringValue,由于此时aaa:hi 不存在${,因此直接返回的还是aaa:hi.
     接下来,判断是否存在:,对于当前,是存在的,因此对其进行截取分别获得actualPlaceholder,defaultValue.对于当前, actualPlaceholder = aaa, defaultValue = hi, 然后调用PlaceholderResolver#resolvePlaceholder获得值,如果actualPlaceholder 解析失败,则将propVal 设为默认值.关于这部分对于的源码如下:
         if (propVal == null && this.valueSeparator != null) {
                            int separatorIndex = placeholder.indexOf(this.valueSeparator);
                            if (separatorIndex != -1) {
                                String actualPlaceholder = placeholder.substring(0, separatorIndex);
                                String defaultValue = placeholder.substring(separatorIndex + this.valueSeparator.length());
                                propVal = placeholderResolver.resolvePlaceholder(actualPlaceholder);
                                if (propVal == null) {
                                    propVal = defaultValue;
                                }
                            }
                        }
     此刻,调用PlaceholderResolver#resolvePlaceholder,实际上调用的是在AbstractPropertyResolver#doResolvePlaceholders中实例化的PlaceholderResolver的实现.代码如下:
         private String doResolvePlaceholders(String text, PropertyPlaceholderHelper helper) {
                return helper.replacePlaceholders(text, new PropertyPlaceholderHelper.PlaceholderResolver() {
                    @Override
                    public String resolvePlaceholder(String placeholderName) {
                        return getPropertyAsRawString(placeholderName);
                    }
                });
            }
     因此这里最终调用PropertySourcesPropertyResolver#getPropertyAsRawString,代码如下:
             protected String getPropertyAsRawString(String key) {
                return getProperty(key, String.class, false);
            }
     调用了 org.springframework.core.env.PropertySourcesPropertyResolver.getProperty(String, Class, boolean)方法,接下来的故事,就很之前一样了,这里就不在赘述了.
     集合处理
     接下来我们将application.properties 改为
         com.example.demo.address[0]=北京
        com.example.demo.address[1]=上海
        com.example.demo.address[2]=广州
     这里分析对People 中 address 属性的注入. 同样,前面的准备工作都一样,在对属性进行注入时,会调用AbstractNestablePropertyAccessor#setPropertyValue,代码如下:
         public void setPropertyValue(String propertyName, Object value) throws BeansException {
                AbstractNestablePropertyAccessor nestedPa;
                try {
                    // 1. 生成AbstractNestablePropertyAccessor
                    nestedPa = getPropertyAccessorForPropertyPath(propertyName);
                }
                catch (NotReadablePropertyException ex) {
                    throw new NotWritablePropertyException(getRootClass(), this.nestedPath + propertyName,
                            "Nested property in path '" + propertyName + "' does not exist", ex);
                }
                // 2. 获得PropertyTokenHolder, getFinalPath 获得最终的PropertyName
                PropertyTokenHolder tokens = getPropertyNameTokens(getFinalPath(nestedPa, propertyName));
                // 3. 进行赋值
                nestedPa.setPropertyValue(tokens, new PropertyValue(propertyName, value));
            }
     这里调用了AbstractNestablePropertyAccessor#getPropertyNameTokens,代码如下:
         private PropertyTokenHolder getPropertyNameTokens(String propertyName) {
                PropertyTokenHolder tokens = new PropertyTokenHolder();
                String actualName = null;
                List<String> keys = new ArrayList<String>(2);
                int searchIndex = 0;
                while (searchIndex != -1) {
                    // 1. 获得 [ 的下标
                    int keyStart = propertyName.indexOf(PROPERTY_KEY_PREFIX, searchIndex);
                    searchIndex = -1;
                    if (keyStart != -1) {
                        // 2 如果存在的话,则截取获得]的下标
                        int keyEnd = propertyName.indexOf(PROPERTY_KEY_SUFFIX, keyStart + PROPERTY_KEY_PREFIX.length());
                        if (keyEnd != -1) {
                            // 3. 如果存在的话,则截取出actualName,例如[map],那么此时就是""
                            if (actualName == null) {
                                actualName = propertyName.substring(0, keyStart);
                            }
                            // 4. 截取出key 此时就是map
                            String key = propertyName.substring(keyStart + PROPERTY_KEY_PREFIX.length(), keyEnd);
                            if (key.length() > 1 && (key.startsWith("'") && key.endsWith("'")) ||
                                    (key.startsWith("\"") && key.endsWith("\""))) {
                                key = key.substring(1, key.length() - 1);
                            }
                            keys.add(key);
                            searchIndex = keyEnd + PROPERTY_KEY_SUFFIX.length();
                        }
                    }
                }
                tokens.actualName = (actualName != null ? actualName : propertyName);
                tokens.canonicalName = tokens.actualName;
                if (!keys.isEmpty()) {
                    // [ + StringUtils#collectionToDelimitedString(keys,][)+]
                    tokens.canonicalName += PROPERTY_KEY_PREFIX +
                            StringUtils.collectionToDelimitedString(keys, PROPERTY_KEY_SUFFIX + PROPERTY_KEY_PREFIX) +
                            PROPERTY_KEY_SUFFIX;
                    tokens.keys = StringUtils.toStringArray(keys);
                }
                return tokens;
            }
     步骤如下:
     首先获得[ 的下标 如果存在的话,则尝试获取]的下标. 如果存在的]下标的话, 则截取出属性值,对应于当前的情况,就是address.然后加入keys中. 如果不存在,则意味着不存在集合的情况.接下来的处理就很之前一样. 
     注意在这里, keys 只加入了一个, 如:0,为什么呢?
     因为我们是循环处理的,这点很重要.后面的步骤都是在此基础上进行的,在处理完com.example.demo.address[0]=北京 后,再处理 com.example.demo.address[1]=上海 .为啥呢? 因为在AbstractPropertyAccessor#setPropertyValues中我们是通过遍历的方式处理的,代码如下:
             for (PropertyValue pv : propertyValues) {
    
                        setPropertyValue(pv);
    
            }       
     接下来, 在AbstractNestablePropertyAccessor#setPropertyValue,由于此刻keys 不等于null,因此会执行processKeyedProperty.代码如下:
         protected void setPropertyValue(PropertyTokenHolder tokens, PropertyValue pv) throws BeansException {
                if (tokens.keys != null) {
                    processKeyedProperty(tokens, pv);
                }
                else {
                    processLocalProperty(tokens, pv);
                }
            }
     processKeyedProperty 代码如下:
         private void processKeyedProperty(PropertyTokenHolder tokens, PropertyValue pv) {
                // 1. 获得
                Object propValue = getPropertyHoldingValue(tokens);
                String lastKey = tokens.keys[tokens.keys.length - 1];
    
                if (propValue.getClass().isArray()) {
                    // 省略....
                }
    
                else if (propValue instanceof List) {
                    PropertyHandler ph = getPropertyHandler(tokens.actualName);
                    Class<?> requiredType = ph.getCollectionType(tokens.keys.length);
                    List<Object> list = (List<Object>) propValue;
                    int index = Integer.parseInt(lastKey);
                    Object oldValue = null;
                    if (isExtractOldValueForEditor() && index < list.size()) {
                        oldValue = list.get(index);
                    }
                    Object convertedValue = convertIfNecessary(tokens.canonicalName, oldValue, pv.getValue(),
                            requiredType, ph.nested(tokens.keys.length));
                    int size = list.size();
                    if (index >= size && index < this.autoGrowCollectionLimit) {
                        for (int i = size; i < index; i++) {
                            try {
                                list.add(null);
                            }
                            catch (NullPointerException ex) {
                                throw new InvalidPropertyException(getRootClass(), this.nestedPath + tokens.canonicalName,
                                        "Cannot set element with index " + index + " in List of size " +
                                        size + ", accessed using property path '" + tokens.canonicalName +
                                        "': List does not support filling up gaps with null elements");
                            }
                        }
                        list.add(convertedValue);
                    }
                    else {
                        try {
                            list.set(index, convertedValue);
                        }
                        catch (IndexOutOfBoundsException ex) {
                            throw new InvalidPropertyException(getRootClass(), this.nestedPath + tokens.canonicalName,
                                    "Invalid list index in property path '" + tokens.canonicalName + "'", ex);
                        }
                    }
                }
    
                else if (propValue instanceof Map) {
                    // 省略....
                }
    
                else {
                    throw new InvalidPropertyException(getRootClass(), this.nestedPath + tokens.canonicalName,
                            "Property referenced in indexed property path '" + tokens.canonicalName +
                            "' is neither an array nor a List nor a Map; returned value was [" + propValue + "]");
                }
            }
     2件事:
     调用getPropertyHoldingValue 获得 属性对应的对象. 对于当前,就是获得People 中address 所对应的对象实例.代码如下:     private Object getPropertyHoldingValue(PropertyTokenHolder tokens) {
            // Apply indexes and map keys: fetch value for all keys but the last one.
            // 1. 实例化PropertyTokenHolder
            PropertyTokenHolder getterTokens = new PropertyTokenHolder();
            getterTokens.canonicalName = tokens.canonicalName;
            getterTokens.actualName = tokens.actualName;
            getterTokens.keys = new String[tokens.keys.length - 1];
            System.arraycopy(tokens.keys, 0, getterTokens.keys, 0, tokens.keys.length - 1);
    
            Object propValue;
            try {
                // 2. 获得值
                propValue = getPropertyValue(getterTokens);
            }
            catch (NotReadablePropertyException ex) {
                throw new NotWritablePropertyException(getRootClass(), this.nestedPath + tokens.canonicalName,
                        "Cannot access indexed value in property referenced " +
                        "in indexed property path '" + tokens.canonicalName + "'", ex);
            }
    
            if (propValue == null) {
                // null map value case
                if (isAutoGrowNestedPaths()) {
                    int lastKeyIndex = tokens.canonicalName.lastIndexOf('[');
                    getterTokens.canonicalName = tokens.canonicalName.substring(0, lastKeyIndex);
                    propValue = setDefaultValue(getterTokens);
                }
                else {
                    throw new NullValueInNestedPathException(getRootClass(), this.nestedPath + tokens.canonicalName,
                            "Cannot access indexed value in property referenced " +
                            "in indexed property path '" + tokens.canonicalName + "': returned null");
                }
            }
            return propValue;
        } 实例化PropertyTokenHolder 调用getPropertyValue,获得该属性所对应的对象–> propValue.代码如下:     protected Object getPropertyValue(PropertyTokenHolder tokens) throws BeansException {
        String propertyName = tokens.canonicalName;
        String actualName = tokens.actualName;
        // 1. 根据属性值获得PropertyHandler
        PropertyHandler ph = getLocalPropertyHandler(actualName);
        // 2. 如果PropertyHandler等于null或者没有get方法,抛出异常
        if (ph == null || !ph.isReadable()) {
            throw new NotReadablePropertyException(getRootClass(), this.nestedPath + propertyName);
        }
            // 3. 获得对应的属性值.
            Object value = ph.getValue();
            if (tokens.keys != null) {
                // 4. 如果tokens.keys 不等于null,这里是不会执行的
                if (value == null) {
                    // 4.1 如果autoGrowNestedPaths 值为true,则生成默认值,一般都会生成默认值的
                    if (isAutoGrowNestedPaths()) {
                        value = setDefaultValue(tokens.actualName);
                    }
                    else {
                        // 4.2 抛出异常
                        throw new NullValueInNestedPathException(getRootClass(), this.nestedPath + propertyName,
                                "Cannot access indexed value of property referenced in indexed " +
                                        "property path '" + propertyName + "': returned null");
                    }
                }
                String indexedPropertyName = tokens.actualName;
                // apply indexes and map keys
                // 5. 依次进行遍历
                for (int i = 0; i < tokens.keys.length; i++) {
                    String key = tokens.keys[i];
                    // 5.1 如果value等于null,则抛出异常
                    if (value == null) {
                        throw new NullValueInNestedPathException(getRootClass(), this.nestedPath + propertyName,
                                "Cannot access indexed value of property referenced in indexed " +
                                        "property path '" + propertyName + "': returned null");
                    }
                    else if (value.getClass().isArray()) {
                        // 省略...
                    }
                    else if (value instanceof List) {
                        int index = Integer.parseInt(key);
                        List list = (List) value;
                        growCollectionIfNecessary(list, index, indexedPropertyName, ph, i + 1);
                        value = list.get(index);
                    }
                    else if (value instanceof Set) {
                        // 省略...
                    }
                    else if (value instanceof Map) {
                        // 省略...
                    }
                    else {
                        throw new InvalidPropertyException(getRootClass(), this.nestedPath + propertyName,
                                "Property referenced in indexed property path '" + propertyName +
                                        "' is neither an array nor a List nor a Set nor a Map; returned value was [" + value + "]");
                    }
                    indexedPropertyName += PROPERTY_KEY_PREFIX + key + PROPERTY_KEY_SUFFIX;
                }
            }
            return value;
        }
     获得调用getLocalPropertyHandler获得PropertyHandler,这个我们前面已经分析过了. 如果PropertyHandler等于null或者没有get方法,抛出NotReadablePropertyException 获得对应的属性对象,也就是People 中的address. 如果tokens.keys 不等于null,对于当前来说,keys 不等于null,因此是会执行的. 如果autoGrowNestedPaths 值为true,则生成默认值,一般都会生成默认值的,否则抛出NullValueInNestedPathException. 依次进行遍历keys,针对value的不同类型做不同的处理,这里我们只看List,处理如下: 将key 转为index,注意这里传入的是0. 通过list.get(index)的方式获得下标所对应的对象. 
    
     如果propValue 等于null,如果autoGrowNestedPaths 属性值为true,则调用setDefaultValue 进行实例化,否则抛出NullValueInNestedPathException异常,一般情况下, autoGrowNestedPaths为true.同样,该方法一般情况下都会执行的.代码如下:     private PropertyValue createDefaultPropertyValue(PropertyTokenHolder tokens) {
        TypeDescriptor desc = getPropertyTypeDescriptor(tokens.canonicalName);
        Class type = desc.getType();
        if (type == null) {
            throw new NullValueInNestedPathException(getRootClass(), this.nestedPath + tokens.canonicalName,
                    "Could not determine property type for auto-growing a default value");
        }
        Object defaultValue = newValue(type, desc, tokens.canonicalName);
        return new PropertyValue(tokens.canonicalName, defaultValue);
        } 这样就实例化了,具体是怎么实例化的,这里就不展开了. 
    
    
     针对propValue的类型做不同的处理,如果该类型不是数字,List,Map,则抛出InvalidPropertyException.这里我们只分析list的情况,其他类似. 获得属性对应的对象 获得集合的泛型 获得下标 进行转换 如果下标大于集合的size,则将index – size 这段范围内,插入null值,最后在插入对应的值.否则,直接插入即可. 
    
     至此,集合的注入就分析完了.
     对象导航处理
     我们将配置文件改为如下:
         com.example.demo.phone.number=1111111
     这里分析对People 中 phone 的number 属性的注入. 还是同样的套路,前面的准备工作都一样,最终在进行属性注入时,调用了AbstractNestablePropertyAccessor#setPropertyValue.在该方法中调用了getPropertyAccessorForPropertyPath 用于处理嵌套属性.代码如下:
         protected AbstractNestablePropertyAccessor getPropertyAccessorForPropertyPath(String propertyPath) {
                // 1. 通过PropertyAccessorUtils#getFirstNestedPropertySeparatorIndex 获得下标
                int pos = PropertyAccessorUtils.getFirstNestedPropertySeparatorIndex(propertyPath);
                // Handle nested properties recursively.
                if (pos > -1) {
                    // 如果存在的话,则意味着有嵌套存在,则递归处理,例如 map[my.key],
                    String nestedProperty = propertyPath.substring(0, pos);// nestedProperty = map[my
                    String nestedPath = propertyPath.substring(pos + 1); // nestedPath = key
                    // 3. 获得嵌套对象
                    AbstractNestablePropertyAccessor nestedPa = getNestedPropertyAccessor(nestedProperty);
                    // 4. 获取AbstractNestablePropertyAccessor,递归调用
                    return nestedPa.getPropertyAccessorForPropertyPath(nestedPath);
                }
                else {
                    // 如果不存在,则返回this
                    return this;
                }
            }
     2件事:
     通过PropertyAccessorUtils#getFirstNestedPropertySeparatorIndex 获得下标.该方法最终调用了PropertyAccessorUtils#getNestedPropertySeparatorIndex,该方法处理的逻辑很简单,看是否存在.,代码如下:     private static int getNestedPropertySeparatorIndex(String propertyPath, boolean last) {
            boolean inKey = false;
            int length = propertyPath.length();
            int i = (last ? length - 1 : 0);// 起始下标
            while (last ? i >= 0 : i < length) {
                switch (propertyPath.charAt(i)) {
                    case PropertyAccessor.PROPERTY_KEY_PREFIX_CHAR: // [
                    case PropertyAccessor.PROPERTY_KEY_SUFFIX_CHAR:// ]
                        inKey = !inKey;
                        break;
                    case PropertyAccessor.NESTED_PROPERTY_SEPARATOR_CHAR: // .
                        if (!inKey) {
                            return i;
                        }
                }
                if (last) {
                    i--;
                }
                else {
                    i++;
                }
            }
            return -1;
        }
     如果存在嵌套属性,则递归处理 通过字符串截取,获得nestedProperty,nestedPath .对于当前来说, nestedProperty = phone, nestedPath = number 调用getNestedPropertyAccessor 获得AbstractNestablePropertyAccessor.代码如下:     private AbstractNestablePropertyAccessor getNestedPropertyAccessor(String nestedProperty) {
        // 1. 如果nestedPropertyAccessors 等于null,则实例化
        if (this.nestedPropertyAccessors == null) {
            this.nestedPropertyAccessors = new HashMap();
        }
        // Get value of bean property.
        // 2. 获取属性名
        PropertyTokenHolder tokens = getPropertyNameTokens(nestedProperty);
        String canonicalName = tokens.canonicalName;
        // 3. 获得对应的值
        Object value = getPropertyValue(tokens);
        if (value == null || (value.getClass() == javaUtilOptionalClass && OptionalUnwrapper.isEmpty(value))) {
            if (isAutoGrowNestedPaths()) {
                value = setDefaultValue(tokens);
            }
            else {
                throw new NullValueInNestedPathException(getRootClass(), this.nestedPath + canonicalName);
            }
        }
    
        // Lookup cached sub-PropertyAccessor, create new one if not found.
        // 4. 获得访问嵌套对象
        AbstractNestablePropertyAccessor nestedPa = this.nestedPropertyAccessors.get(canonicalName);
        if (nestedPa == null || nestedPa.getWrappedInstance() !=
                (value.getClass() == javaUtilOptionalClass ? OptionalUnwrapper.unwrap(value) : value)) {
            if (logger.isTraceEnabled()) {
                logger.trace("Creating new nested " + getClass().getSimpleName() + " for property '" + canonicalName + "'");
            }
            // 5. 如果不存在则创建一个,实例化的是BeanWrapperImpl
            nestedPa = newNestedPropertyAccessor(value, this.nestedPath + canonicalName + NESTED_PROPERTY_SEPARATOR);
            // Inherit all type-specific PropertyEditors.
            copyDefaultEditorsTo(nestedPa);
            copyCustomEditorsTo(nestedPa, canonicalName);
            // 6. 存入缓存
            this.nestedPropertyAccessors.put(canonicalName, nestedPa);
        }
        else {
            if (logger.isTraceEnabled()) {
                logger.trace("Using cached nested property accessor for property '" + canonicalName + "'");
            }
        }
        return nestedPa;
        } 6件事: 如果nestedPropertyAccessors 等于null,则实例化. lazy-init 调用getPropertyNameTokens 获得PropertyTokenHolder,对于当前,获得的是phone所对应的PropertyTokenHolder.这个方法,我们之前已经分析过了。 调用getPropertyValue , 获得phone所对应的对象。关于这个方法,我们也已经分析过了,此时会将people中的phone 实例化. 尝试从nestedPropertyAccessors缓存中获得AbstractNestablePropertyAccessor. 如果没有获得,则实例化一个BeanPropertyHandler.然后进行初始化后放入nestedPropertyAccessors. 递归调用getPropertyAccessorForPropertyPath. 那我们的例子来说,第一次传入的参数是phone.number,有嵌套属性,因此会在实例化phone所对应后的AbstractNestablePropertyAccessor后,会递归调用getPropertyAccessorForPropertyPath,此时由于传入的参数是number,因此方法退出,因此该递归最终返回的是 phone所对应后的AbstractNestablePropertyAccessor. 接着,AbstractNestablePropertyAccessor#getFinalPath,获得最终的路径,代码如下:      protected String getFinalPath(AbstractNestablePropertyAccessor pa, String nestedPath) {
            if (pa == this) {
                return nestedPath;
            }
            return nestedPath.substring(PropertyAccessorUtils.getLastNestedPropertySeparatorIndex(nestedPath) + 1);
        }   由于pa 不等于this,因此会调用PropertyAccessorUtils#getLastNestedPropertySeparatorIndex 方法获得最后一个. 所对应的下标,通过字符串截取后,获得属性名,此时,会获得number。 2个问题: 为什么pa 不等于 this? 还是拿例子来说话,this, 指的是people 所对应的AbstractNestablePropertyAccessor,pa 在当前来说,是phone所对应的AbstractNestablePropertyAccessor.明显不相等的. 为什么只需返回最后一个属性,就行了? 也就是 假如我们新增如下一个类型:     public class Operator {// 运营商
    
        private String name;
    
        // get set 忽略,自己加上即可..
        } 然后将Phone 改为如下:     public class Phone {
    
        private String number;
        private Operator operator;
    
        // get set 忽略,自己加上即可.. 
        } 将配置文件加入如下配置:     com.example.demo.phone.operator.name=移动 为什么此时返回是name? 理由很简单,因为在调用AbstractNestablePropertyAccessor#getPropertyAccessorForPropertyPath时是递归处理的,该方法会首先实例化People 中的phone,接着实例化Phone 中operator所对应的Operator对象.后续的故事,就是直接赋值了,我们已经分析过了. 
     属性转换处理
     这里,我们来看最后一个–>属性转换,将配置文件该为如下:
         com.example.demo.age=11
     之前的准备工作,就不在赘述了,在最终进行赋值时,会调用 AbstractNestablePropertyAccessor#processLocalProperty,而在该方法中的第三步,会调用AbstractNestablePropertyAccessor#convertForProperty进行转换处理,代码如下:
         protected Object convertForProperty(String propertyName, Object oldValue, Object newValue, TypeDescriptor td)
                    throws TypeMismatchException {
    
                return convertIfNecessary(propertyName, oldValue, newValue, td.getType(), td);
            }
    
     最终调用TypeConverterDelegate#convertIfNecessary,代码如下:
    
     获得自定义的PropertyEditor 从propertyEditorRegistry 获得自定义的ConversionService,这里使用的是org.springframework.boot.bind.RelaxedConversionService 如果PropertyEditor 等于null && conversionService 不等于null,&& newValue 不等于null,&& typeDescriptor 不等于null,则调用ConversionService#convert. … 
     这里由于不存在自定义的PropertyEditor,同时第2步获得的propertyEditorRegistry不等于null,因此最终会调用RelaxedConversionService#convert 进行转换,代码如下:
         public Object convert(Object source, TypeDescriptor sourceType,
                    TypeDescriptor targetType) {
                if (this.conversionService != null) {
                    try {
                        return this.conversionService.convert(source, sourceType, targetType);
                    }
                    catch (ConversionFailedException ex) {
                        // Ignore and try the additional converters
                    }
                }
                return this.additionalConverters.convert(source, sourceType, targetType);
            }
     2件事:
     如果conversionService 不等于null,则调用conversionService#convert 进行转换.对于当前,会执行这里, conversionService为GenericConversionService,代码如下:     public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
            Assert.notNull(targetType, "Target type to convert to cannot be null");
            // 1. 如果sourceType 等于null,则抛出ConversionFailedException
            if (sourceType == null) {
                Assert.isTrue(source == null, "Source must be [null] if source type == [null]");
                return handleResult(null, targetType, convertNullSource(null, targetType));
            }
            // 2. 如果source不等于null,并且sourceType 不是source 的类型,则抛出IllegalArgumentException
            if (source != null && !sourceType.getObjectType().isInstance(source)) {
                throw new IllegalArgumentException("Source to convert from must be an instance of [" +
                        sourceType + "]; instead it was a [" + source.getClass().getName() + "]");
            }
            // 3. 获得GenericConverter
            GenericConverter converter = getConverter(sourceType, targetType);
            if (converter != null) {
                // 3.1 如果Converter,则通过ConversionUtils#invokeConverter 进行转换
                Object result = ConversionUtils.invokeConverter(converter, source, sourceType, targetType);
                return handleResult(sourceType, targetType, result);
            }
            // 4. 当Converter 没有找到时 ,进行处理
            return handleConverterNotFound(source, sourceType, targetType);
        } 4件事: 如果sourceType 等于null,则抛出ConversionFailedException 如果source不等于null,并且sourceType 不是source 的类型,则抛出IllegalArgumentException 获得GenericConverter,如果Converter 不等于null,则通过ConversionUtils#invokeConverter 进行转换.代码如下:     protected GenericConverter getConverter(TypeDescriptor sourceType, TypeDescriptor targetType) {
        // 1. 实例化ConverterCacheKey
        ConverterCacheKey key = new ConverterCacheKey(sourceType, targetType);
        // 2. 尝试从converterCache 获取
        GenericConverter converter = this.converterCache.get(key);
        if (converter != null) {
            return (converter != NO_MATCH ? converter : null);
        }
    
        // 3. 从converters 获取
        converter = this.converters.find(sourceType, targetType);
        if (converter == null) {
            // 4. 如果还没有得到,则返回默认的Converter
            converter = getDefaultConverter(sourceType, targetType);
        }
    
        if (converter != null) {
            // 5. 如果不等于null,则放入缓存中
            this.converterCache.put(key, converter);
            return converter;
        }
    
        // 6. 如果converter 等于null,则在converterCache中放入NO_MATCH
        this.converterCache.put(key, NO_MATCH);
        return null;
        }
     6件事: 实例化ConverterCacheKey 尝试从converterCache 获取 从converters 获取 如果还没有得到,则返回默认的Converter 如果不等于null,则放入缓存中 如果converter 等于null,则在converterCache中放入NO_MATCH 对于当前,获得的是ConverterFactoryAdapter,其convert方法如下:         public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
            if (source == null) {
                return convertNullSource(sourceType, targetType);
            }
            return this.converterFactory.getConverter(targetType.getObjectType()).convert(source);
        } 最终调用的是StringToNumber#convert 方法,代码如下:     public T convert(String source) {
            if (source.isEmpty()) {
                return null;
            }
            return NumberUtils.parseNumber(source, this.targetType);
        } 至此,就将com.example.demo.age = 11 ,由原先的字符串,转换为了Integer.后面只需赋值即可了,关于这个,我们已经分析过了. 当Converter 没有找到时 ,进行处理 否则调用additionalConverters#convert 进行转换。 
    
     来源:[]()
    
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