JDBC事务处理空指针异常

[apkxzliuli]

package day01;

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



/**
* JDBC事务处理
* @author Administrator
*在Oracle数据库中，创建表account并插入测试数据
*
*/
public class Trans {
/**
* 该方法表示从账户from转账给账户to 转账金额为amount
*/
public void transfer(String from,String to,double amount){
Connection con=null;
Statement stmt=null;

try {

con=ConnectionSource.getConnection();
stmt=con.createStatement();

//更新数据的SQL语句
String sql1="update account1 set amount =amount- "+amount+"where id='"+from+"'";
String sql2="update account1 set amount =amount+"+amount+"where id='"+to+"'";
//关闭自动提交
System.out.println(sql1);
System.out.println(sql2);
con.setAutoCommit(false);
//执行SQL语句
stmt.executeUpdate(sql1);
stmt.executeUpdate(sql2);
//提交
con.commit();
} catch (SQLException e) {
try {
con.rollback();
} catch (SQLException e1) {
System.out.println("回滚事务异常！");
throw new RuntimeException(e1);
}
System.out.println("数据库访问异常！");
throw new RuntimeException(e);
}finally{
try {
if(stmt!=null){
stmt.close();
}
if(con!=null){
con.close();
}
} catch (SQLException e) {
System.out.println("释放资源时发生异常！");
}
}

}
public static void main(String[] args) {
Trans trans=new Trans();
trans.transfer("A", "B", 500);
}

}

[KeepSayingNo]

这个有什么问题呢？

[apkxzliuli]

运行出现空指针异常.....不知道如何处理