Spring ContextLoaderListener源码分析 .

 2019-11-02 21:25  阅读(1177)
文章分类:Spring boot

http://blog.csdn.net/hz_blog/article/details/7688921

当我们要自动装配ApplicationContext配置信息时候,首先在web.xml配置ContextLoaderListener,下面是部分源代码:

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  1. publicclass ContextLoaderListener implements ServletContextListener {

  2. private ContextLoader contextLoader;

  3. /**

  4. * Initialize the root web application context.

  5. */

  6. publicvoid contextInitialized(ServletContextEvent event) {

  7. this.contextLoader = createContextLoader();

  8. this.contextLoader.initWebApplicationContext(event.getServletContext());//注意此处

  9. }

  10. protected ContextLoader createContextLoader() {

  11. returnnew ContextLoader();

  12. }

  13. public ContextLoader getContextLoader() {

  14. returnthis.contextLoader;

  15. }

  16. publicvoid contextDestroyed(ServletContextEvent event) {

  17. if (this.contextLoader != null) {

  18. this.contextLoader.closeWebApplicationContext(event.getServletContext());

  19. }

  20. }

  21. }

    public class ContextLoaderListener implements ServletContextListener { private ContextLoader contextLoader; /** * Initialize the root web application context. */ public void contextInitialized(ServletContextEvent event) { this.contextLoader = createContextLoader(); this.contextLoader.initWebApplicationContext(event.getServletContext());//注意此处 } protected ContextLoader createContextLoader() { return new ContextLoader(); } public ContextLoader getContextLoader() { return this.contextLoader; } public void contextDestroyed(ServletContextEvent event) { if (this.contextLoader != null) { this.contextLoader.closeWebApplicationContext(event.getServletContext()); } } }

我们主要了解下WebApplicationContext是怎么初始化出来的,首先contextInitialized(ServletContextEvent event)方法的this.contextLoader.initWebApplicationContext(event.getServletContext());进去之后我们看到

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  1. public WebApplicationContext initWebApplicationContext(ServletContext servletContext)

  2. throws IllegalStateException, BeansException {

  3. if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {

  4. thrownew IllegalStateException(

  5. “Cannot initialize context because there is already a root application context present – “ +

  6. “check whether you have multiple ContextLoader* definitions in your web.xml!”);

  7. }

  8. servletContext.log(“Initializing Spring root WebApplicationContext”);

  9. if (logger.isInfoEnabled()) {

  10. logger.info(“Root WebApplicationContext: initialization started”);

  11. }

  12. long startTime = System.currentTimeMillis();

  13. try {

  14. // Determine parent for root web application context, if any.

  15. ApplicationContext parent = loadParentContext(servletContext);

  16. // Store context in local instance variable, to guarantee that

  17. // it is available on ServletContext shutdown.

  18. this.context = createWebApplicationContext(servletContext, parent);

  19. servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);//注意此处

  20. currentContextPerThread.put(Thread.currentThread().getContextClassLoader(), this.context);

  21. if (logger.isDebugEnabled()) {

  22. logger.debug(“Published root WebApplicationContext as ServletContext attribute with name [“ +

  23. WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + “]”);

  24. }

  25. if (logger.isInfoEnabled()) {

  26. long elapsedTime = System.currentTimeMillis() – startTime;

  27. logger.info(“Root WebApplicationContext: initialization completed in “ + elapsedTime + ” ms”);

  28. }

  29. returnthis.context;

  30. }

  31. catch (RuntimeException ex) {

  32. logger.error(“Context initialization failed”, ex);

  33. servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);

  34. throw ex;

  35. }

  36. catch (Error err) {

  37. logger.error(“Context initialization failed”, err);

  38. servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err);

  39. throw err;

  40. }

  41. }

    public WebApplicationContext initWebApplicationContext(ServletContext servletContext) throws IllegalStateException, BeansException { if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) { throw new IllegalStateException( "Cannot initialize context because there is already a root application context present - " + "check whether you have multiple ContextLoader* definitions in your web.xml!"); } servletContext.log("Initializing Spring root WebApplicationContext"); if (logger.isInfoEnabled()) { logger.info("Root WebApplicationContext: initialization started"); } long startTime = System.currentTimeMillis(); try { // Determine parent for root web application context, if any. ApplicationContext parent = loadParentContext(servletContext); // Store context in local instance variable, to guarantee that // it is available on ServletContext shutdown. this.context = createWebApplicationContext(servletContext, parent); servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);//注意此处 currentContextPerThread.put(Thread.currentThread().getContextClassLoader(), this.context); if (logger.isDebugEnabled()) { logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" + WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]"); } if (logger.isInfoEnabled()) { long elapsedTime = System.currentTimeMillis() - startTime; logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms"); } return this.context; } catch (RuntimeException ex) { logger.error("Context initialization failed", ex); servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex); throw ex; } catch (Error err) { logger.error("Context initialization failed", err); servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err); throw err; } }

注意此处部分,说明当我们要得到一个WebApplicationContext只需要在ServletContext中获取属性名为WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE的常量值就可以得到一个ApplicationContext,最终可以获取spring配置文件中任意一个Bean对象

eg:

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  1. public String execute() throws Exception {

  2. // TODO Auto-generated method stub

  3. ApplicationContext conn=(ApplicationContext)ServletActionContext.getServletContext().getAttribute(WebApplicationContext.class.getName() + “.ROOT”);

  4. System.out.println(conn.getBean(“biz”));

  5. return SUCCESS;

  6. }

    public String execute() throws Exception { // TODO Auto-generated method stub ApplicationContext conn=(ApplicationContext)ServletActionContext.getServletContext().getAttribute(WebApplicationContext.class.getName() + ".ROOT"); System.out.println(conn.getBean("biz")); return SUCCESS; }

或者直接使用org.springframework.web.context.support.WebApplicationContextUtils这个抽象的工具类来获得WebApplicationContext,该类的方法

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  1. publicstatic WebApplicationContext getWebApplicationContext(ServletContext sc) {
  2. return getWebApplicationContext(sc, WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
  3. }

来源:http://ddrv.cn

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