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：

1. 为了提高性能
2. 为了保持业务流程的完整性
3. 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!