mybatis简单入门实例

╰半橙微兮° 2022-03-01 12:46 291阅读 0赞

mybatis是一个数据持久层框架，他与hibernate相比，也有自己的优点，当我们进行多表关联查询的时候，很容易实现，因为他天生就是用来写sql实现功能的，而hibernate需要实现这个多表关联，也不是没有办法，就是稍微麻烦一些，hibernate是orm框架，对于简单的实体和表的映射非常的方便，但是一般的项目中，很多都是两个，甚至三个表，甚至更多表联合查询，hibernate就显得有些笨拙。mybatis的优势就体现出来了。

mybatis既有原生jdbc写sql的部分，但是他不是jdbc的加强版，而是jdbc的简洁版，不像jdbc那么复杂，需要处理connection,statement,resultset等，只需要根据相应的方法处理resultset，而不用关心其他。

这里介绍mybatis简单入门。

eclipse里面为了构建mybatis配置文件方便，可以将mybatis-mapper-3.0.dtd和mybatis-config-3.0.dtd配置到xml catalog里面。

首先构建maven工程。添加mybatis和mysql的依赖。

<dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
      <scope>test</scope>
    </dependency>
    <dependency>
    	<groupId>org.mybatis</groupId>
    	<artifactId>mybatis</artifactId>
    	<version>3.4.6</version>
    </dependency>
    <dependency>
    	<groupId>mysql</groupId>
    	<artifactId>mysql-connector-java</artifactId>
    	<version>5.1.46</version>
    </dependency>
    </dependencies>

准备实体类：User.java

package com.xxx.mybatis.domain;
    
    public class User {
    	private Integer id;
    	private String username;
    	private String password;
    	public Integer getId() {
    		return id;
    	}
    	public void setId(Integer 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;
    	}
    	@Override
    	public String toString() {
    		return "User [id=" + id + ", username=" + username + ", password=" + password + "]";
    	}
    	
    }

在实体类文件夹下构建mybatis映射文件：

UserMapper.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="com.xxx.mybatis.domain.UserMapper">
        <select id="find-by-id" resultType="com.xxx.mybatis.domain.User">
           select * from xx_user where id = #{id}
        </select>
        <insert id="insert-user">
        	insert into xx_user values(#{id},#{username},#{password})
        </insert>
        <update id="update-user">
        	update xx_user set 
        	username=#{username},
        	password = #{password}
        	where id = #{id}
        </update>
        <delete id="delete-by-id">
        	delete from xx_user where id = #{id}
        </delete>
        <select id="find-all" resultType="com.xxx.mybatis.domain.User">
        	select * from xx_user
        </select>
    </mapper>

配置文件：jdbc.properties，数据库配置信息

jdbc.driver=com.mysql.jdbc.Driver
    jdbc.url=jdbc:mysql://localhost:3306/mybatis?useUnicode=true&useSSL=false&characterEncoding=UTF-8
    jdbc.username=hadoop
    jdbc.password=hadoop

mybatis配置文件：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>
        <properties resource="jdbc.properties" />
        <environments default="development">
        	<environment id="development">
        	     <transactionManager type="JDBC" />
        	     <dataSource type="POOLED">
        	     	<property name="driver" value="${jdbc.driver}"/>
        	     	<property name="url" value="${jdbc.url}"/>
        	     	<property name="username" value="${jdbc.username}"/>
        	     	<property name="password" value="${jdbc.password}"/>
        	     </dataSource>
        	</environment>
        </environments>
        <mappers>
        	<mapper resource="com/xxx/mybatis/domain/UserMapper.xml"/>
        </mappers>
    </configuration>

单元测试类：

package com.xxx.mybatis;
    import java.io.InputStream;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    import org.apache.ibatis.io.Resources;
    import org.apache.ibatis.session.SqlSession;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.apache.ibatis.session.SqlSessionFactoryBuilder;
    import org.junit.Test;
    import com.xxx.mybatis.domain.User;
    public class MyBatisTest {
    	private static SqlSessionFactory sessionFactory;
    	
    	static {
    		try {
    			InputStream resource = Resources.getResourceAsStream("mybatis-config.xml");
    			sessionFactory = new SqlSessionFactoryBuilder().build(resource);
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    	
    	public static SqlSession getSession() {
    		return sessionFactory.openSession();
    	}
    	
    	@Test
    	public void insert() {
    		Map<String, Object> params = new HashMap<>();
    		params.put("id", 3);
    		params.put("username", "zhangsan");
    		params.put("password", "123456");
    		SqlSession session = getSession();
    		int res = session.insert("com.xxx.mybatis.domain.UserMapper.insert-user", params);
    		System.out.println("insert ok :"+(res==1));
    		session.commit();
    		session.close();
    	}
    	
    	@Test
    	public void update() {
    		Map<String, Object> params = new HashMap<>();
    		params.put("id", 1);
    		params.put("username", "superadmin");
    		params.put("password", "admin");
    		SqlSession session = getSession();
    		int res = session.insert("com.xxx.mybatis.domain.UserMapper.update-user", params);
    		System.out.println("update ok :"+(res==1));
    		session.commit();
    		session.close();
    	}
    	
    	@Test
    	public void query() {
    		SqlSession session = getSession();
    		User user = session.selectOne("com.xxx.mybatis.domain.UserMapper.find-by-id", 1);
    		System.out.println(user);
    	}
    	
    	@Test
    	public void delete() {
    		SqlSession session = getSession();
    		//Map<String, Object> params = new HashMap<>();
    		int res = session.delete("com.xxx.mybatis.domain.UserMapper.delete-by-id", 1);
    		System.out.println(res);
    		session.commit();
    		session.close();
    	}
    	
    	@Test
    	public void findAll() {
    		SqlSession session = getSession();
    		List<User> list = session.selectList("com.xxx.mybatis.domain.UserMapper.find-all");
    		System.out.println(list.size());
    		for(User user:list) {
    			System.out.println(user);
    		}
    	}
    }

mybatis不像hibernate有了实体，启动项目可以直接创建表，运行单元测试的方法前，我们需要在数据库中创建实体对应的表。

![20190322163945990.png][]

和hibernate类似，mybatis操作数据库，需要一个SqlSessionFactory，通过他来创建我们需要的会话SqlSession，有了会话，就可以操作数据库了，会话提供了select,insert,update,delete等相关操作，这些操作需要传入映射文件里面对应的id名称，对应了，就可以执行正确的方法，返回相应的结果。mybatis每一个增删改查方法的执行都有返回值，这一点比hibernate要好一些，hibernate的save,update,delete操作均是void返回类型，所以成功失败无法通过返回结果来知晓。

[20190322163945990.png]: /images/20220301/9407a041f33d4ec29748008e5cbd7cff.png