2021-04-20 08:26  阅读(77)
文章分类:Java JDBC 教程 文章标签:JavaJDBC
©  原文作者:易百教程 原文地址:https://www.yiibai.com/jdbc

以下是使用事务教程中描述的setSavepoint和回滚的代码示例。

此示例代码是基于前面章节中完成的环境和数据库设置编写的。

复制并将以下示例代码保存到:JDBCSavepoint.java 中,编译并运行如下 -

    //STEP 1. Import required packages
    // See more detail at http://www.yiibai.com/jdbc/
    
    import java.sql.*;
    
    public class JDBCSavepoint {
       // JDBC driver name and database URL
       static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
       static final String DB_URL = "jdbc:mysql://localhost/EMP";
    
       //  Database credentials
       static final String USER = "root";
       static final String PASS = "123456";
    
    public static void main(String[] args) {
       Connection conn = null;
       Statement stmt = null;
       try{
          //STEP 2: Register JDBC driver
          Class.forName("com.mysql.jdbc.Driver");
    
          //STEP 3: Open a connection
          System.out.println("Connecting to database...");
          conn = DriverManager.getConnection(DB_URL,USER,PASS);
    
          //STEP 4: Set auto commit as false.
          conn.setAutoCommit(false);
    
          //STEP 5: Execute a query to delete statment with
          // required arguments for RS example.
          System.out.println("Creating statement...");
          stmt = conn.createStatement();
    
          //STEP 6: Now list all the available records.
          String sql = "SELECT id, first, last, age FROM Employees";
          ResultSet rs = stmt.executeQuery(sql);
          System.out.println("List result set for reference....");
          printRs(rs);
    
          // STEP 7: delete rows having ID grater than 104
          // But save point before doing so.
          Savepoint savepoint1 = conn.setSavepoint("ROWS_DELETED_1");
          System.out.println("Deleting row....");
          String SQL = "DELETE FROM Employees " +
                       "WHERE ID = 106";
          stmt.executeUpdate(SQL);  
          // oops... we deleted too wrong employees!
          //STEP 8: Rollback the changes afetr save point 2.
          conn.rollback(savepoint1);
    
        // STEP 9: delete rows having ID grater than 104
          // But save point before doing so.
          Savepoint savepoint2 = conn.setSavepoint("ROWS_DELETED_2");
          System.out.println("Deleting row....");
          SQL = "DELETE FROM Employees " +
                       "WHERE ID = 107";
          stmt.executeUpdate(SQL);  
    
          //STEP 10: Now list all the available records.
          sql = "SELECT id, first, last, age FROM Employees";
          rs = stmt.executeQuery(sql);
          System.out.println("List result set for reference....");
          printRs(rs);
    
          //STEP 10: Clean-up environment
          rs.close();
          stmt.close();
          conn.close();
       }catch(SQLException se){
          //Handle errors for JDBC
          se.printStackTrace();
          // If there is an error then rollback the changes.
          System.out.println("Rolling back data here....");
          try{
             if(conn!=null)
                conn.rollback();
          }catch(SQLException se2){
             se2.printStackTrace();
          }//end try
    
       }catch(Exception e){
          //Handle errors for Class.forName
          e.printStackTrace();
       }finally{
          //finally block used to close resources
          try{
             if(stmt!=null)
                stmt.close();
          }catch(SQLException se2){
          }// nothing we can do
          try{
             if(conn!=null)
                conn.close();
          }catch(SQLException se){
             se.printStackTrace();
          }//end finally try
       }//end try
       System.out.println("Goodbye!");
    }//end main
    
       public static void printRs(ResultSet rs) throws SQLException{
          //Ensure we start with first row
          rs.beforeFirst();
          while(rs.next()){
             //Retrieve by column name
             int id  = rs.getInt("id");
             int age = rs.getInt("age");
             String first = rs.getString("first");
             String last = rs.getString("last");
    
             //Display values
             System.out.print("ID: " + id);
             System.out.print(", Age: " + age);
             System.out.print(", First: " + first);
             System.out.println(", Last: " + last);
         }
         System.out.println();
       }//end printRs()
    }//end JDBCExample
    

编译并运行结果如下 -

    F:\worksp\jdbc>javac -Djava.ext.dirs=F:\worksp\jdbc\libs JDBCSavepoint.java
    
    F:\worksp\jdbc>java -Djava.ext.dirs=F:\worksp\jdbc\libs JDBCSavepoint
    Connecting to database...
    Thu Jun 01 02:35:49 CST 2017 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
    Creating statement...
    List result set for reference....
    ID: 100, Age: 28, First: Max, Last: Su
    ID: 101, Age: 25, First: Wei, Last: Wang
    ID: 102, Age: 35, First: Xueyou, Last: Zhang
    ID: 103, Age: 30, First: Jack, Last: Ma
    ID: 106, Age: 28, First: Curry, Last: Stephen
    ID: 107, Age: 32, First: Kobe, Last: Bryant
    
    Deleting row....
    Deleting row....
    List result set for reference....
    ID: 100, Age: 28, First: Max, Last: Su
    ID: 101, Age: 25, First: Wei, Last: Wang
    ID: 102, Age: 35, First: Xueyou, Last: Zhang
    ID: 103, Age: 30, First: Jack, Last: Ma
    ID: 106, Age: 28, First: Curry, Last: Stephen
    
    Goodbye!
    
    F:\worksp\jdbc>
    

可以看到,上面代码中只回滚到保存点(ROWS_DELETED_1),所以ID为106的这一行记录没有被删除,而ID为107的记录因为没有设置回滚点,直接提交删除了。

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