JavaWeb开发：mybatis入门

【声明：】本文是作者（蘑菇v5）原创，版权归作者 蘑菇v5所有，侵权必究。本文首发在简书。如若转发，请注明作者和来源地址！未经授权，严禁私自转载！

mybatis官网

简介：

MyBatis 是一款优秀的持久层框架，它支持定制化SQL、存储过程以及高级映射。MyBatis避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。MyBatis 可以使用简单的 XML 或注解来配置和映射原生类型、接口和 Java的 POJO（Plain Old Java Objects，普通老式Java 对象）为数据库中的记录

安装和使用

要使用 MyBatis， 只需将 mybatis-x.x.x.jar 文件置于classpath 中即可。

如果使用 Maven来构建项目，则需将下面的 dependency 代码置于pom.xml文件中：

<dependency>
  <groupId>org.mybatis</groupId>
  <artifactId>mybatis</artifactId>
  <version>x.x.x</version>
</dependency>

操作步骤

1、创建配置文件

创建jdbc_config.properties和mybatis-config.xml文件，完成和数据库的连接设置操作

jdbc_config.properties：

username=ceshi
password=123
url=jdbc:mysql://localhost:3306/mybatis
driver=com.mysql.jdbc.Driver

mybatis-config.xml：

<?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>
<!--引入properties文件， -->
<properties resource="jdbc_config.properties">
<typeAliases>
        <package name="org.mybatis.example.model"/>
    </typeAliases>
  <environments default="development">
    <environment id="development">
      <transactionManager type="JDBC"/>
<!--读取properties文件里的数据-->
      <dataSource type="POOLED">
        <property name="driver" value="${driver}"/>
        <property name="url" value="${url}"/>
        <property name="username" value="${username}"/>
        <property name="password" value="${password}"/>
      </dataSource>
    </environment>
  </environments>
  <mappers>
    <mapper resource="org/mybatis/example/model/User.xml"/>
  </mappers>
</configuration>

2、根据数据表创建相应的实体类

public class User {
    private int id;
    private String username;
    private String password;
    private String nickname;
    private int type;
    private List<Address> addresses;
    
    public List<Address> getAddresses() {
        return addresses;
    }
    public void setAddresses(List<Address> addresses) {
        this.addresses = addresses;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public String getNickname() {
        return nickname;
    }
    public void setNickname(String nickname) {
        this.nickname = nickname;
    }
    public int getType() {
        return type;
    }
    public void setType(int type) {
        this.type = type;
    }
}

3、创建mapper.xml文件

创建mapper文件完成对实体类的映射

User.xml：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="org.mybatis.example.model.User">
    <insert id="add" parameterType="User">
        insert into t_user (username,password,nickname,type)
            value(#{username},#{password},#{nickname},#{type})
    </insert>
    
    <update id="update" parameterType="User">
        update t_user set password=#{password},nickname=#{nickname},
type=#{type} where id=#{id}
    </update>
    
    <delete id="delete" parameterType="int">
        delete from t_user where id=#{id}
    </delete>
    
    <select id="load" parameterType="int" resultType="User">
        select * from t_user where id=#{id}
    </select>
    
    <select id="list" resultType="User">
        select * from t_user
    </select>
</mapper>

4、创建SqlSessionFactory获取session执行相应的操作

创建SQlSession，并且通过SqlSession完成对数据库的操作

TestMyBatis：

public class TestMyBatis {

    @Test
    public void testDelete() {
    SqlSession session = null;
        try {
            session = MyBatisUtil.createSession();
            session.delete(User.class.getName()+".delete",10);
            session.commit();
        }  catch (Exception e) {
            e.printStackTrace();
            session.rollback();
        } finally {
            MyBatisUtil.closeSession(session);
        }
    }
    
    @Test
    public void testAdd() {
        SqlSession session = null;
        try {
            session = MyBatisUtil.createSession();
            User u = new User();
            u.setNickname("刘德华");
            u.setPassword("10086");
            u.setType(0);
            u.setUsername("ldh");
            session.insert(User.class.getName()+".add", u);
            session.commit();
        } catch (Exception e) {
            e.printStackTrace();
            session.rollback();
        } finally {
            MyBatisUtil.closeSession(session);
        }
    }
    
    @Test
    public void testLoad() {
        SqlSession session = null;
        try{
            session = MyBatisUtil.createSession();
            User u = (User)session.selectOne(User.class.getName()+".load", 1);
            System.out.println(u.getNickname());
        } finally {
            MyBatisUtil.closeSession(session);
        }
    }
    
    @Test
    public void testList() {
        SqlSession session = null;
        try{
            session = MyBatisUtil.createSession();
            List<User> us = session.selectList(
              User.class.getName()+".list", null);
            System.out.println(us.size());
        } finally {
            MyBatisUtil.closeSession(session);
        }
    }   
}

MyBatisUtil：

public class MyBatisUtil {
    private static SqlSessionFactory factory;
    static {
        try {
            InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
            factory = new SqlSessionFactoryBuilder().build(is);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    
    public static SqlSession createSession() {
        return factory.openSession();
    }
    
    public static void closeSession(SqlSession session) {
        if(session!=null) session.close();
    }
}