Java Mysql 简明教程

Java & MySQL - Commit & Rollback

一旦完成更改，并且你希望提交更改，请按照如下方式调用连接对象的 commit() 方法：

Once you are done with your changes and you want to commit the changes then call commit() method on connection object as follows −

conn.commit( );

否则，若要回滚对使用 conn 命名的 Connection 对数据库作出的更新，则使用以下代码：

Otherwise, to roll back updates to the database made using the Connection named conn, use the following code −

conn.rollback( );

以下示例说明了如何使用提交和回滚对象 -

The following example illustrates the use of a commit and rollback object −

try{
   //Assume a valid connection object conn
   conn.setAutoCommit(false);
   Statement stmt = conn.createStatement();

   String SQL = "INSERT INTO Employees  " +
                "VALUES (106, 20, 'Rita', 'Tez')";
   stmt.executeUpdate(SQL);
   //Submit a malformed SQL statement that breaks
   String SQL = "INSERTED IN Employees  " +
                "VALUES (107, 22, 'Sita', 'Singh')";
   stmt.executeUpdate(SQL);
   // If there is no error.
   conn.commit();
}catch(SQLException se){
   // If there is any error.
   conn.rollback();
}

在这种情况下，上述 INSERT 语句都不会成功，并且所有内容都将被回滚。

In this case, none of the above INSERT statement would success and everything would be rolled back.

以下是利用上述 commit 和 rollback 的示例。

Following is the example, which makes use of commit and rollback described.

此示例代码基于先前章节中完成的环境和数据库设置编写。

This sample code has been written based on the environment and database setup done in the previous chapters.

将以下示例复制并粘贴到 TestApplication.java 中，如下进行编译和运行：

Copy and paste the following example in TestApplication.java, compile and run as follows −

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class TestApplication {
   static final String DB_URL = "jdbc:mysql://localhost/TUTORIALSPOINT";
   static final String USER = "guest";
   static final String PASS = "guest123";
   static final String QUERY = "SELECT id, first, last, age FROM Employees";
   static final String INSERT_QUERY = "INSERT INTO Employees (first, last, age) values('Rita', 'Tez', 20)";
   static final String INSERT_QUERY_2 = "INSERT INTO Employees (first, last, age) values('Sita', 'Singh', 20)";

   public static void printResultSet(ResultSet rs) throws SQLException{
      // Ensure we start with first row
      rs.beforeFirst();
      while(rs.next()){
         // Display values
         System.out.print("ID: " + rs.getInt("id"));
         System.out.print(", Age: " + rs.getInt("age"));
         System.out.print(", First: " + rs.getString("first"));
         System.out.println(", Last: " + rs.getString("last"));
      }
      System.out.println();
   }

   public static void main(String[] args) {

      Connection conn = null;
      Statement stmt = null;
      try{
         // Open a connection
         System.out.println("Connecting to database...");
         conn = DriverManager.getConnection(DB_URL,USER,PASS);

         // Set auto commit as false.
         conn.setAutoCommit(false);

         // Execute a query to create statment with
         // required arguments for RS example.
         System.out.println("Creating statement...");
         stmt = conn.createStatement(
            ResultSet.TYPE_SCROLL_INSENSITIVE,
            ResultSet.CONCUR_UPDATABLE);

         // INSERT a row into Employees table
         System.out.println("Inserting one row....");
         stmt.executeUpdate(INSERT_QUERY);

         // INSERT one more row into Employees table
         stmt.executeUpdate(INSERT_QUERY_2);

         // Commit data here.
         System.out.println("Commiting data here....");
         conn.commit();

         // 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....");
         printResultSet(rs);

         // Clean-up environment
         rs.close();
         stmt.close();
         conn.close();
      }catch(SQLException se){
         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();
            }
         }catch(Exception e){
            e.printStackTrace();
         }finally{
            // finally block used to close resources
         try{
            if(stmt!=null)
               stmt.close();
         }catch(SQLException se2){
            se2.printStackTrace();
         }
            try{
               if(conn!=null)
                  conn.close();
            }catch(SQLException se){
               se.printStackTrace();
         }
      }
   }
}

现在让我们如下编译上述示例：

Now let us compile the above example as follows −

C:\>javac TestApplication.java
C:\>

运行 TestApplication 时，它会生成以下结果：

When you run TestApplication, it produces the following result −

C:\>java TestApplication
Connecting to database...
Creating statement...
Inserting one row....
Commiting data here....
List result set for reference....
ID: 1, Age: 23, First: Zara, Last: Ali
ID: 2, Age: 30, First: Mahnaz, Last: Fatma
ID: 3, Age: 35, First: Zaid, Last: Khan
ID: 4, Age: 33, First: Sumit, Last: Mittal
ID: 5, Age: 40, First: John, Last: Paul
ID: 6, Age: 20, First: Rita, Last: Tez
ID: 7, Age: 20, First: Sita, Last: Singh
C:\>