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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