持久层框架：Mybatis快速入门

Mybatis/Hibernate/JPA作为持久层使用广泛的框架，在实际的项目中有很多的追随者。这篇文章将会通过简单的实例让完全不知道Mybatis为何物的入门者迅速Catchup，对于有一些Java基础的入门者应该能够很快学会如何使用Mybatis进行CRUD（增查改删）操作。

Mybatis的前世今生

时间	详细
2002	iBATIS一词来源于“internet”+“abatis”，是由Clinton Begin在2002年发起的开放源代码项目。是Apache旗下的项目
2010	由ASF（Apache Software Foundation） 迁到了Google Code，并改名为MyBatis
2013	迁到Github（https://github.com/mybatis/mybatis-3）。目前最新版本为3.4.1

目标

通过阅读和练习，预定达到以下目标

项番	详细内容
No.1	Mybatis项目环境搭建
No.2	使用Mybatis进行CRUD操作

预估练习时长：15分钟以内

事前准备

下载Mybatis

项目	详细信息
类型	Mybatis的JAR文件
版本	3.4.1
URL	https://github.com/mybatis/mybatis-3/releases

下载JDBC驱动

项目	详细信息
类型	MySQL的JDBC驱动
版本	5.1.40
URL	http://dev.mysql.com/downloads/connector/j/

DB设定

DB使用MySQL5.7，详细安装以及创建DB和Table请参看同样是持久层框架的Hibernate的如下入门内容。

项番	内容	URL
No.1	概要及准备	http://blog.csdn.net/liumiaocn/article/details/53555787
No.2	JDBC方式访问数据库	http://blog.csdn.net/liumiaocn/article/details/53559810

创建项目

创建项目，将上面下载的JAR文件加入到Dependencies中即可。

mybatis设定文件

在src根目录创建mybatis-config.xm设定文件，具体内容如下：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<environments default="DEV">
<environment id="DEV">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/hbtestdb?useSSL=false"/>
<property name="username" value="hbtestuser01"/>
<property name="password" value="hbtestuser01"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper class="com.liumiao.entity.UserMapper"/>
</mappers>
</configuration>

mapper也可以使用resouce的方式，使用xml进行mapping，本文将使用注解方式。

创建User类和UserMapper接口

User类

package com.liumiao.entity;

public class User {
private int userid;
private String username;
private String country;

public User() {
}

public User(int userid, String username, String country) {
this.userid = userid;
this.username = username;
this.country = country;
}

public int getUserid() {
return userid;
}

public void setUserid(int userid) {
this.userid = userid;
}

public String getUsername() {
return username;
}

public void setUsername(String username) {
this.username = username;
}

public String getCountry() {
return country;
}

public void setCountry(String country) {
this.country = country;
}

@Override
public String toString(){
return "User Information: "+userid+":"+username+":"+country;
}
}

UserMapper接口

package com.liumiao.entity;

import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;

public interface UserMapper {
@Insert("insert into hbtableuser (userid, username, country) values(#{userid},#{username}, #{country})")
public int insertUser(User user);

@Delete("delete from hbtableuser where userid = #{userid}")
public  int deleteUser(int userid);

@Delete("delete from hbtableuser")
public int deleteAllUser();

@Update("update hbtableuser set username=#{username}, country=#{country} where userid=#{userid}")
public  int updateUser(User user);

@Select("select userid, username, country from hbtableuser where userid=#{userid}")
public User retrieveUserByUserid(int userid);
}

Demo演示代码

import com.liumiao.entity.UserMapper;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import com.liumiao.entity.User;

public class Main {

public static void main(String[] args) {
try {
//Get SessionFactory & Session
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis-config.xml"));
SqlSession sqlSession = sqlSessionFactory.openSession();
System.out.println("Successfully got sqlSession from session factory.");

//Get UserMapper
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

//CRUD: Delete All Users
userMapper.deleteAllUser();
sqlSession.commit();

//CRUD: Create: Add user : 1001 liumiaocn
System.out.println("CRUD: Create: add 1001 ");
User user = new User(1001,"liumiaocn","China");
System.out.println("Now Begin to add user 1001: "+ user);
userMapper.insertUser(user);
sqlSession.commit();

System.out.println("CRUD: Create: add 1002 ");
user = new User(1002,"Michael","PRC");
System.out.println("Now Begin to add user 1002: "+ user);
userMapper.insertUser(user);
sqlSession.commit();
System.out.println();

//CRUD: Retrieve:  user : 1001
System.out.println("CRUD: Retrieve:  1001 ");
user = userMapper.retrieveUserByUserid(1001);
sqlSession.commit();
System.out.println("Retrieved user data: "+user);

//CRUD: Retrieve:  user : 1002
System.out.println("CRUD: Retrieve:  1002 ");
user = userMapper.retrieveUserByUserid(1002);
sqlSession.commit();
System.out.println("Retrieved user data: "+user);
System.out.println();

//CRUD: Update:  user : 1001
System.out.println("CRUD: Update:  1001 ");
User tmpUser = new User(1001,"MichaelLiu","PRC");
userMapper.updateUser(tmpUser);
sqlSession.commit();
System.out.println("Retrieved user data: "+user);

//CRUD: Retrieve:  user : 1001
System.out.println("CRUD: Retrieve:  1001 ");
user = userMapper.retrieveUserByUserid(1001);
sqlSession.commit();
System.out.println("Retrieved user data after Update : "+user);
System.out.println();

//CRUD: Delete
System.out.println("CRUD: Delete:  1002 ");
userMapper.deleteUser(1002);
sqlSession.commit();

sqlSession.close();
}
catch(Exception e){
System.out.println("Exception happened...");
e.printStackTrace();
}
}
}

实施结果确认

Successfully got sqlSession from session factory.
CRUD: Create: add 1001
Now Begin to add user 1001: User Information: 1001:liumiaocn:China
CRUD: Create: add 1002
Now Begin to add user 1002: User Information: 1002:Michael:PRC

CRUD: Retrieve:  1001
Retrieved user data: User Information: 1001:liumiaocn:China
CRUD: Retrieve:  1002
Retrieved user data: User Information: 1002:Michael:PRC

CRUD: Update:  1001
Retrieved user data: User Information: 1002:Michael:PRC
CRUD: Retrieve:  1001
Retrieved user data after Update : User Information: 1001:MichaelLiu:PRC

CRUD: Delete:  1002