DBC中悲观锁介绍附案例详解

了解下DBC中悲观锁：

代码如下：

BDUtils 工具类：

package JDBC;

import java.sql.*;

public class BDUtils {

private BDUtils() {

}

static {

try {

Class.forName("com.mysql.jdbc.Driver");

} catch (ClassNotFoundException e) {

e.printStackTrace();

}

}

public static Connection connecTion() throws SQLException {

return DriverManager.getConnection("jdbc:mysql://localhost:3306/center", "root", "123456");

}

public static void close(Connection conn, Statement ps, ResultSet rt) throws SQLException {

if (conn != null) conn.close();

if (ps != null) ps.close();

if (rt != null) rt.close();

}

}

实现类一：

package JDBC;

import java.sql.Connection;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

public class JDBCDButils {

public static void main(String[] args) {

Connection conn = null;

PreparedStatement ps = null;

ResultSet rt = null;

try {

//获取资源

conn = BDUtils.connecTion();

//手动开启事务

conn.setAutoCommit(false);

String sql = "select * from center_user where center_name like ? for UPDATE";

ps =conn.prepareStatement(sql);

ps.setString(1, "王%");

rt = ps.executeQuery();

while (rt.next()){

System.out.println(rt.getString("center_name"));

}

//提交事务

conn.commit();

} catch (SQLException throwables) {

//回滚事务

if (conn != null){

try {

conn.rollback();

} catch (SQLException e) {

e.printStackTrace();

}

}

throwables.printStackTrace();

}finally {

try {

BDUtils.close(conn, ps, rt);

} catch (SQLException throwables) {

throwables.printStackTrace();

}

}

}

}

实现类二：

package JDBC;

import java.sql.Connection;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

public class JDBCDButilsT {

public static void main(String[] args) {

Connection conn = null;

PreparedStatement ps = null;

ResultSet rt = null;

try {

//获取资源

conn = BDUtils.connecTion();

String sql = "UPDATE center_user SET CENTER_AGE = ? where center_name = ? ";

ps = conn.prepareStatement(sql);

ps.setInt(1, 38);

ps.setString(2, "王涛");

int count = ps.executeUpdate();

System.out.println("共影响：" + count + "行");

} catch (SQLException e) {

e.printStackTrace();

} finally {

try {

BDUtils.close(conn, ps, rt);

} catch (SQLException e) {

e.printStackTrace();

}

}

}

}

输出结果：

Lock wait timeout exceeded; try restarting transaction

当实现类一的事务没有提交时， for update 查询语句进行了锁定，可以理解为行级锁锁定，其他任何程序或者线程在事务没有提交时，都不能对包含的数据进行DML操作