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：
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：
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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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