java中事务回滚吗_详解Java的JDBC API中事务的提交和回滚

如果JDBC连接是在自动提交模式下,它在默认情况下,那么每个SQL语句都是在其完成时提交到数据库。

这可能是对简单的应用程序,但有三个原因,你可能想关闭自动提交和管理自己的事务:

为了提高性能

为了保持业务流程的完整性

使用分布式事务

若要控制事务,以及何时更改应用到数据库。它把单个SQL语句或一组SQL语句作为一个逻辑单元,而且如果任何语句失败,整个事务失败。

若要启用,而不是JDBC驱动程序默认使用auto-commit模式手动事务支持,使用Connection对象的的setAutoCommit()方法。如果传递一个布尔值false到setAutoCommit(),关闭自动提交。可以传递一个布尔值true将其重新打开。

例如,如果有一个名为conn Connection对象,以下代码来关闭自动提交:

conn.setAutoCommit(false);

提交和回滚

一旦已经完成了变化,要提交更改,然后调用commit(在连接对象)方法,如下所示:

conn.commit( );

否则回滚更新对数据库所做的使用命名连接conn,使用下面的代码:

conn.rollback( );

下面的例子演示了如何使用一个提交和回滚对象:

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();

}

在这种情况下没有上述INSERT语句会成功,一切都将被回滚。

事务提交和回滚示例

以下是使用事务提交和回滚描述的例子。

基于对环境和数据库安装在前面的章节中做此示例代码已学习过。

复制过去下面的例子中JDBCExample.java,编译并运行,如下所示:

//STEP 1. Import required packages

import java.sql.*;

public class JDBCExample {

// 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 = "username";

static final String PASS = "password";

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 create statment with

// required arguments for RS example.

System.out.println("Creating statement...");

stmt = conn.createStatement(

ResultSet.TYPE_SCROLL_INSENSITIVE,

ResultSet.CONCUR_UPDATABLE);

//STEP 6: INSERT a row into Employees table

System.out.println("Inserting one row....");

String SQL = "INSERT INTO Employees " +

"VALUES (106, 20, 'Rita', 'Tez')";

stmt.executeUpdate(SQL);

//STEP 7: INSERT one more row into Employees table

SQL = "INSERT INTO Employees " +

"VALUES (107, 22, 'Sita', 'Singh')";

stmt.executeUpdate(SQL);

//STEP 8: Commit data here.

System.out.println("Commiting data here....");

conn.commit();

//STEP 9: 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 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

现在让我们来编译上面的例子如下:

C:>javac JDBCExample.java

当运行JDBCExample,它会产生以下结果:

C:>java JDBCExample

Connecting to database...

Creating statement...

Inserting one row....

Commiting data here....

List result set for reference....

ID: 100, Age: 18, First: Zara, Last: Ali

ID: 101, Age: 25, First: Mahnaz, Last: Fatma

ID: 102, Age: 30, First: Zaid, Last: Khan

ID: 103, Age: 28, First: Sumit, Last: Mittal

ID: 106, Age: 20, First: Rita, Last: Tez

ID: 107, Age: 22, First: Sita, Last: Singh

Goodbye!

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