java连接mysql(二)

模拟转账成功时的业务场景

 import java.sql.*;

 public class TransactionDemo1 {

     public static void main(String[] args) throws SQLException, ClassNotFoundException {
         String url = "jdbc:mysql://localhost/xh";
         String username = "xiaohengdada";
         String password = "123456";

         Class.forName("org.gjt.mm.mysql.Driver");
         Connection conn = null;
         PreparedStatement st = null;
         ResultSet rs = null;

         try {
             conn = DriverManager.getConnection(url, username, password);
             conn.setAutoCommit(false);// 通知数据库开启事务(start transaction)
             String sql1 = "update account set money=money+100 where name='A'";
             st = conn.prepareStatement(sql1);
             int num1 = st.executeUpdate();
             if (num1 > 0) {
                 System.out.println("succeed to update A ");
             }
             String sql2 = "update account set money=money-100 where name='B'";
             st = conn.prepareStatement(sql2);
             int num2 = st.executeUpdate();
             if (num2 > 0) {
                 System.out.println("succeed to update B ");
             }
             conn.commit();// 上面的两条SQL执行Update语句成功之后就通知数据库提交事务(commit)
             System.out.println("成功！！！"); // log4j
         } catch (Exception e) {
             e.printStackTrace();
         } finally {
             // rs.close();
             st.close();
             conn.close();
         }
     }
 }

 import java.sql.*;

 public class TransactionDemo1 {
     public static void main(String[] args) throws SQLException, ClassNotFoundException {
         String url = "jdbc:mysql://localhost/xh";
         String username = "xiaohengdada";
         String password = "123456";

         Class.forName("org.gjt.mm.mysql.Driver");
         Connection conn = null;
         PreparedStatement st = null;
         ResultSet rs = null;

         try {
             conn = DriverManager.getConnection(url, username, password);
             conn.setAutoCommit(false);// 通知数据库开启事务(start transaction)
             String sql1 = "update account set money=money-100 where name='A'";
             st = conn.prepareStatement(sql1);
             st.executeUpdate();
             // 用这句代码模拟执行完SQL1之后程序出现了异常而导致后面的SQL无法正常执行，事务也无法正常提交，此时数据库会自动执行回滚操作
             int x = 1 / 0;
             String sql2 = "update account set money=money+100 where name='B'";
             st = conn.prepareStatement(sql2);
             st.executeUpdate();
             conn.commit();// 上面的两条SQL执行Update语句成功之后就通知数据库提交事务(commit)
             System.out.println("成功！！！");
         } catch (Exception e) {
             e.printStackTrace();
         } finally {
             st.close();
             conn.close();
         }
     }
 }

 import java.sql.*;

 public class TransactionDemo1 {
     public static void main(String[] args) throws SQLException, ClassNotFoundException {
         String url = "jdbc:mysql://localhost/xh";
         String username = "xiaohengdada";
         String password = "123456";

         Class.forName("org.gjt.mm.mysql.Driver");
         Connection conn = null;
         PreparedStatement st = null;
         ResultSet rs = null;

           try{
                 conn = DriverManager.getConnection(url,username,password);
                 conn.setAutoCommit(false);//通知数据库开启事务(start transaction)
                 String sql1 = "update account set money=money-100 where name='A'";
                 st = conn.prepareStatement(sql1);
                 st.executeUpdate();
                 //用这句代码模拟执行完SQL1之后程序出现了异常而导致后面的SQL无法正常执行，事务也无法正常提交
                 int x = 1/0;
                 String sql2 = "update account set money=money+100 where name='B'";
                 st = conn.prepareStatement(sql2);
                 st.executeUpdate();
                 conn.commit();//上面的两条SQL执行Update语句成功之后就通知数据库提交事务(commit)
                 System.out.println("成功！！！");
             }catch (Exception e) {
                 try {
                     //捕获到异常之后手动通知数据库执行回滚事务的操作
                     conn.rollback();
                 } catch (SQLException e1) {
                     e1.printStackTrace();
                 }
                 e.printStackTrace();
             }finally{

             }
     }
 }

设置回滚点：

 import java.sql.*;

 public class TransactionDemo1 {
     public static void main(String[] args) throws SQLException, ClassNotFoundException {
         String url = "jdbc:mysql://localhost/xh";
         String username = "xiaohengdada";
         String password = "123456";

         Class.forName("org.gjt.mm.mysql.Driver");
         Connection conn = null;
         PreparedStatement st = null;
         ResultSet rs = null;
         Savepoint sp = null;

         try {
             conn = DriverManager.getConnection(url, username, password);
             conn.setAutoCommit(false);// 通知数据库开启事务(start transaction)

             String sql1 = "update account set money=money-100 where name='A'";
             st = conn.prepareStatement(sql1);
             st.executeUpdate();

             // 设置事务回滚点
             // sp = conn.setSavepoint();

             String sql2 = "update account set money=money+100 where name='B'";
             st = conn.prepareStatement(sql2);
             st.executeUpdate();

             sp = conn.setSavepoint();
             // 程序执行到这里出现异常，后面的sql3语句执行将会中断
             int x = 1 / 0;

             String sql3 = "update account set money=money+100 where name='C'";
             st = conn.prepareStatement(sql3);
             st.executeUpdate();

             conn.commit();

         } catch (Exception e) {
             try {
                 /**
                  * 我们在上面向数据库发送了3条update语句， sql3语句由于程序出现异常导致无法正常执行，数据库事务而已无法正常提交，
                  * 由于设置的事务回滚点是在sql1语句正常执行完成之后，sql2语句正常执行之前,
                  * 那么通知数据库回滚事务时，不会回滚sql1执行的update操作
                  * 只会回滚到sql2执行的update操作，也就是说，上面的三条update语句中，sql1这条语句的修改操作起作用了
                  * sql2的修改操作由于事务回滚没有起作用，sql3由于程序异常没有机会执行
                  */
                 conn.rollback(sp);// 回滚到设置的事务回滚点
                 // 回滚了要记得通知数据库提交事务
                 conn.commit();
             } catch (SQLException e1) {
                 e1.printStackTrace();
             }
             e.printStackTrace();
         } finally {
         }
     }
 }