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 {
        }
    }
}