java MyBatis

什么是MyBatis

1. MyBatis 持久层：简化工作量、灵活
2. Spring 粘合剂：整合框架、AOP、IOC、DI
3. SpringMVC 表現层：方便前后端数据的传输

MyBatis 是对 jdbc 的封装，将 SQL 语句放在映射文件中（XML），可以自动将输入参数映射到 SQL 语句的动态参数上，自动将 SQL 语句映射成 Java 对象。

入门示例

步骤：

1. 创建项目(meaven项目)

2. 导入响应的 jar 包,pom.xml 文件中的依赖为：

   <!-- 让IDEA不要忽略src目录下的xml文件 -->
   <build>
       <resources>
           <resource>
               <directory>src/main/java</directory>
               <includes>
                   <include>**/*.xml</include>
               </includes>
           </resource>
       </resources>
   </build>
   
   <dependencies>
       <dependency>
           <groupId>mysql</groupId>
           <artifactId>mysql-connector-java</artifactId>
           <version>5.1.38</version>
       </dependency>
   
       <dependency>
           <groupId>org.mybatis</groupId>
           <artifactId>mybatis</artifactId>
           <version>3.5.0</version>
       </dependency>
   
       <dependency>
           <groupId>log4j</groupId>
           <artifactId>log4j</artifactId>
           <version>1.2.17</version>
       </dependency>
   
       <dependency>
           <groupId>junit</groupId>
           <artifactId>junit</artifactId>
           <version>4.12</version>
       </dependency>
   </dependencies>

3. 加入配置文件 db.properties, log4j.properties, mybatis 核心配置文件 mybatis-config.xml,MmalWapper.xml

db.properties

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/test_mybatis
jdbc.username=root
jdbc.password=123456

log4j.properties

log4j.rootLogger=INFO, stdout

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %t %c{2}:%L - %m%n

log4j.category.org.springframework.beans.factory=DEBUG

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>
    <!-- 引入数据库链接配置 -->
    <properties resource="db.properties"></properties>

    <!-- 定义别名 -->
    <typeAliases>
        <!--<package name="com.test.mybatis.pojo"></package>-->
        <typeAlias type="com.test.mybatis.pojo.User" alias="User"></typeAlias>
    </typeAliases>

    <!-- 定义数据源 -->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager>
            <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>

    <!-- 定义映射文件 -->
    <mappers>
        <!--<mapper resource="com/test/mybatis/mapper/MmalWapper.xml"></mapper>-->
        <package name="com.test.mybatis.mapper"></package>
    </mappers>
</configuration>

MmalWapper.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.test.mybatis.mapper.MmalWapper">
    <!-- statement -->
    <select id="selectUser" parameterType="_int" resultType="User">
      select * from mmall_user where id = #{id}
    </select>
    <!--<insert id=""></insert>-->
    <!--<delete id=""></delete>-->
    <!--<update id=""></update>-->
</mapper>

4. 编写接口

MmalWapper.class

package com.test.mybatis.mapper;

import com.test.mybatis.pojo.User;

public interface MmalWapper {
    User selectUser(int id);
}

5. pojo

public class User {
    private int id;
    private String username;
    private String password;
    private String email;
    private String phone;
    private String question;
    private String answer;
    private int role;
    private String createTime;
    private String updateTime;
	// 省略 get set 和 toString
}

6. 创建工具类

MybatisUtil.clss

package com.test.mybatis.util;

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 java.io.IOException;
import java.io.InputStream;


public class MybatisUtil {
    private static SqlSessionFactory sqlSessionFactory = null;

    static {
        try {
			// 从 XML 中构建 SqlSessionFactory
            InputStream in = Resources.getResourceAsStream("com/test/mybatis/mybatis-config.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private MybatisUtil(){}

    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }

}

7. 创建测试用例

MmalWapperTest.class

package com.test.mybatis.mapper;

import com.test.mybatis.pojo.User;
import com.test.mybatis.util.MybatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

public class MmalWapperTest {
	
	
    @Test
    public void testSelectUserNoInterface() {
        SqlSession session = MybatisUtil.getSqlSession();
		
        User user = (User) session.selectOne("com.test.mybatis.mapper.MmalWapper.selectUser",1);

        session.close();

        System.out.println(user);
    }

    @Test
    public void testSelectUser() {
        SqlSession session = MybatisUtil.getSqlSession();

        MmalWapper mmalWapper = session.getMapper(MmalWapper.class);

        User user =  mmalWapper.selectUser(1);

        session.close();

        System.out.println(user);
    }
}

mybatis官方文档