Mybatis入门篇，带你感受一下mybatis独特的魅力！

本篇的技术栈

• mysql5.7.25
• maven3.6.1
• jdk1.8
• idea2019
• mybatis

案例

准备数据库
mysql中运行下面脚本：

DROP DATABASE IF EXISTS `javacode2018`;
CREATE DATABASE `javacode2018`;
USE `javacode2018`;

/*创建表结构*/
DROP TABLE IF EXISTS `t_user`;
CREATE TABLE t_user (
  id BIGINT AUTO_INCREMENT PRIMARY KEY COMMENT '主键，用户id，自动增长',
  `name` VARCHAR(32) NOT NULL DEFAULT '' COMMENT '姓名',
  `age` SMALLINT NOT NULL DEFAULT 1 COMMENT '年龄',
  `salary` DECIMAL(12,2) NOT NULL DEFAULT 0 COMMENT '薪水'
) COMMENT '用户表';

SELECT * FROM t_user;

我们的需求:

对t_user表，我们有以下这些需求：

• 实现一个通用的插入操作：支持动态插入，可以根据传入的字段的值，动态生成所需要的各种insert语句

• 批量插入功能

• 实现一个通用的更新操作：支持动态更新操作，可以根据传入的字段，动态生成所需要的各种update语句

• 实现一个通用的查询操作：支持各种组合条件查询、支撑排序、分页、支持返回列的控制等各种复杂的查询需求

引入mybatis依赖:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.javacode2018</groupId>
    <artifactId>mybatis-series</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>pom</packaging>

    <modules>
        <module>chat01</module>
    </modules>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <!-- 配置maven编译的时候采用的编译器版本 -->
        <maven.compiler.compilerVersion>1.8</maven.compiler.compilerVersion>
        <!-- 指定源代码是什么版本的，如果源码和这个版本不符将报错，maven中执行编译的时候会用到这个配置，默认是1.5，这个相当于javac命令后面的-source参数 -->
        <maven.compiler.source>1.8</maven.compiler.source>
        <!-- 该命令用于指定生成的class文件将保证和哪个版本的虚拟机进行兼容，maven中执行编译的时候会用到这个配置，默认是1.5，这个相当于javac命令后面的-target参数 -->
        <maven.compiler.target>1.8</maven.compiler.target>
        <mybatis.version>3.5.3</mybatis.version>
        <mysql.version>5.1.47</mysql.version>
        <lombok.version>1.18.10</lombok.version>
    </properties>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.mybatis</groupId>
                <artifactId>mybatis</artifactId>
                <version>${mybatis.version}</version>
            </dependency>
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>${mysql.version}</version>
            </dependency>
            <dependency>
                <groupId>org.projectlombok</groupId>
                <artifactId>lombok</artifactId>
                <version>${lombok.version}</version>
                <scope>provided</scope>
            </dependency>
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>4.12</version>
                <scope>test</scope>
            </dependency>
            <dependency>
                <groupId>ch.qos.logback</groupId>
                <artifactId>logback-classic</artifactId>
                <version>1.2.3</version>
                
            </dependency>
        </dependencies>
    </dependencyManagement>

</project>

子项目为：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>mybatis-series</artifactId>
        <groupId>com.javacode2018</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>chat01</artifactId>

    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
        </dependency>
    </dependencies>

</project>

创建mybatis相关文件

user.xml

chat01/src/main/resources目录中新建user.xml，内容如下：

<?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.javacode2018.mybatis.chat01.UserMapper">

    <!-- 插入 -->
    <insert id="insert" parameterType="com.javacode2018.mybatis.chat01.UserModel" keyProperty="id" useGeneratedKeys="true">
        <![CDATA[ INSERT INTO `t_user` ]]>
        <trim prefix="(" suffix=")" suffixOverrides=",">
            <if test="id!=null">
                <![CDATA[ `id`, ]]>
            </if>
            <if test="name!=null">
                <![CDATA[ `name`, ]]>
            </if>
            <if test="age!=null">
                <![CDATA[ `age`, ]]>
            </if>
            <if test="salary!=null">
                <![CDATA[ `salary`, ]]>
            </if>
        </trim>
        <![CDATA[ VALUES ]]>
        <trim prefix="(" suffix=")" suffixOverrides=",">
            <if test="id!=null">
                <![CDATA[ #{id}, ]]>
            </if>
            <if test="name!=null">
                <![CDATA[ #{name}, ]]>
            </if>
            <if test="age!=null">
                <![CDATA[ #{age}, ]]>
            </if>
            <if test="salary!=null">
                <![CDATA[ #{salary}, ]]>
            </if>
        </trim>
    </insert>

<!-- 批量插入 -->
<insert id="insertBatch" parameterType="map">
    <![CDATA[ INSERT INTO `t_user` (`id`, `name`, `age`, `salary`) VALUES ]]>
    <foreach collection="list" separator="," item="item">
        (#{item.id}, #{item.name}, #{item.age}, #{item.salary})
    </foreach>
</insert>

    <!-- 更新 -->
    <update id="update" parameterType="com.javacode2018.mybatis.chat01.UserModel">
        <![CDATA[ UPDATE `t_user` ]]>
        <set>
            <if test="name!=null">
                <![CDATA[ `name` = #{name}, ]]>
            </if>
            <if test="age!=null">
                <![CDATA[ `age` = #{age}, ]]>
            </if>
            <if test="salary!=null">
                <![CDATA[ `salary` = #{salary}, ]]>
            </if>
        </set>
        <where>
            <if test="id!=null">
                <![CDATA[ AND `id` = #{id} ]]>
            </if>
        </where>
    </update>

    <!-- 更新 -->
    <update id="updateByMap" parameterType="map">
        <![CDATA[ UPDATE `t_user` ]]>
        <set>
            <if test="name!=null">
                <![CDATA[ `name` = #{name}, ]]>
            </if>
            <if test="age!=null">
                <![CDATA[ `age` = #{age}, ]]>
            </if>
            <if test="salary!=null">
                <![CDATA[ `salary` = #{salary}, ]]>
            </if>
        </set>
        <where>
            <if test="id!=null">
                <![CDATA[ AND `id` = #{id} ]]>
            </if>
        </where>
    </update>

    <!-- 删除 -->
    <delete id="delete" parameterType="map">
        <![CDATA[
            DELETE FROM `t_user`
        ]]>
        <where>
            <if test="id!=null">
                <![CDATA[ AND `id` = #{id} ]]>
            </if>
        </where>
    </delete>


    <!-- 查询记录 -->
    <select id="getModelList" parameterType="map" resultType="com.javacode2018.mybatis.chat01.UserModel">
        <![CDATA[
        SELECT
        ]]>
        <choose>
            <when test="tableColumnList!=null and tableColumnList.size() >= 1">
                <foreach collection="tableColumnList" item="item" separator=",">
                    <![CDATA[ ${item} ]]>
                </foreach>
            </when>
            <otherwise>
                <![CDATA[
                `id`,
                `name`,
                `age`,
                `salary`
                ]]>
            </otherwise>
        </choose>
        <![CDATA[
        FROM
        `t_user` a
        ]]>
        <where>
            <if test="id!=null and id.toString()!=''">
                <![CDATA[ AND a.`id` = #{id} ]]>
            </if>
            <if test="idList!=null and idList.size() >= 1">
                <![CDATA[ AND a.`id` IN ]]>
                <foreach collection="idList" item="item" open="(" separator="," close=")">
                    <![CDATA[ #{item} ]]>
                </foreach>
            </if>
            <if test="name!=null and name.toString()!=''">
                <![CDATA[ AND a.`name` = #{name} ]]>
            </if>
            <if test="age!=null and age.toString()!=''">
                <![CDATA[ AND a.`age` = #{age} ]]>
            </if>
            <if test="salary!=null and salary.toString()!=''">
                <![CDATA[ AND a.`salary` = #{salary} ]]>
            </if>
            <if test="nameLike!=null and nameLike.toString()!=''">
                <![CDATA[ AND a.`name` like '%${nameLike}%' ]]>
            </if>
            <if test="salaryGte!=null and salaryGte.toString()!=''">
                <![CDATA[ AND a.`salary` >= #{salaryGte} ]]>
            </if>
        </where>
        <if test="sort!=null and sort.toString()!=''">
            <![CDATA[ order by ${sort} ]]>
        </if>
        <if test="skip!=null and pageSize!=null">
            <![CDATA[ LIMIT #{skip},#{pageSize} ]]>
        </if>
    </select>

</mapper>

mybatis-config.xml

chat01/src/main/resources目录中新建mybatis-config.xml，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>
    <properties>
        <property name="driver" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/javacode2018?characterEncoding=UTF-8"/>
        <property name="username" value="root"/>
        <property name="password" value="root123"/>
    </properties>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <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="mapper/user.xml"/>
    </mappers>
</configuration>

UserMapper接口

package com.javacode2018.mybatis.chat01;

import java.util.List;
import java.util.Map;

/**
 * 公众号：路人甲Java，工作10年的前阿里P7分享Java、算法、数据库方面的技术干货！坚信用技术改变命运，让家人过上更体面的生活!
 */
public interface UserMapper {

    /**
     * 插入用户信息
     *
     * @param userModel
     * @return
     */
    void insert(UserModel userModel);

    /**
     * 批量插入用户信息
     *
     * @param userModelList
     */
    void insertBatch(List<UserModel> userModelList);

    /**
     * 更新用户信息
     *
     * @param userModel
     * @return
     */
    int update(UserModel userModel);

    /**
     * 通过map来更新用户记录
     *
     * @param map
     * @return
     */
    int updateByMap(Map<String, Object> map);

    /**
     * 通过map来删除用户记录
     *
     * @param map
     * @return
     */
    int delete(Map<String, Object> map);

    /**
     * 查询用户列表
     *
     * @param map
     * @return
     */
    List<UserModel> getModelList(Map<String, Object> map);

}

UserModel类

package com.javacode2018.mybatis.chat01;

import lombok.*;

/**
 * 公众号：路人甲Java，工作10年的前阿里P7分享Java、算法、数据库方面的技术干货！坚信用技术改变命运，让家人过上更体面的生活!
 */
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Builder
@ToString
public class UserModel {
    private Long id;
    private String name;
    private Integer age;
    private Double salary;
}

UserUtil类

package com.javacode2018.mybatis.chat01;

import lombok.extern.slf4j.Slf4j;
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;

/**
 * 公众号：路人甲Java，工作10年的前阿里P7分享Java、算法、数据库方面的技术干货！坚信用技术改变命运，让家人过上更体面的生活!
 */
@Slf4j
public class UserUtil {
    private static SqlSessionFactory sqlSessionFactory = build();

    public static SqlSessionFactory build() {
        try {
            return new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));
        } catch (IOException e) {
            log.error(e.getMessage(), e);
            throw new RuntimeException(e);
        }
    }

    @FunctionalInterface
    public interface SessionCall<O> {
        O call(SqlSession session) throws Exception;
    }

    @FunctionalInterface
    public interface MapperCall<T, O> {
        O call(T mapper) throws Exception;
    }

    public static <T, O> O callMapper(Class<T> tClass, MapperCall<T, O> mapper) throws Exception {
        return call(session -> mapper.call(session.getMapper(tClass)));
    }

    public static <O> O call(SessionCall<O> sessionCall) throws Exception {
        try (SqlSession session = sqlSessionFactory.openSession(true);) {
            return sessionCall.call(session);
        }
    }
}

创建单元测试类UserMapperTest

chat01\src\test\java\com\javacode2018\mybatis\chat01中创建UserMapperTest，代码如下：

package com.javacode2018.mybatis.chat01;

import lombok.extern.slf4j.Slf4j;
import org.junit.Test;

import java.util.*;
import java.util.stream.Collectors;

/**
 * 公众号：路人甲Java，工作10年的前阿里P7分享Java、算法、数据库方面的技术干货！坚信用技术改变命运，让家人过上更体面的生活!
 */
@Slf4j
public class UserMapperTest {

    //动态插入
    @Test
    public void insert() throws Exception {
        UserModel userModel1 = UserModel.builder().name("路人甲Java").build();
        UserUtil.callMapper(UserMapper.class, mapper -> {
            mapper.insert(userModel1);
            return null;
        });
        log.info("插入结果：{}", this.getModelById(userModel1.getId()));
        log.info("---------------------");
        UserModel userModel2 = UserModel.builder().name("路人").age(30).salary(50000.00).build();
        UserUtil.callMapper(UserMapper.class, mapper -> {
            mapper.insert(userModel2);
            return null;
        });
        log.info("插入结果：{}", this.getModelById(userModel2.getId()));
    }

    //批量插入
    @Test
    public void insertBatch() throws Exception {
        List<UserModel> userModelList = new ArrayList<>();
        for (int i = 1; i <= 5; i++) {
            userModelList.add(UserModel.builder().name("路人甲Java-" + i).age(30 + i).salary(10000.00 * i).build());
            userModelList.add(UserModel.builder().name("javacode2018-" + i).age(30 + i).salary(10000.00 * i).build());
        }
        UserUtil.callMapper(UserMapper.class, mapper -> {
            mapper.insertBatch(userModelList);
            return null;
        });

        List<UserModel> userModelList1 = UserUtil.callMapper(UserMapper.class, mapper -> mapper.getModelList(null));
        log.info("结果:{}", userModelList1);
    }

    //根据用户id删除数据
    @Test
    public void delete() throws Exception {
        Map<String, Object> map = new HashMap<>();
        //需要删除的用户id
        map.put("id", 1);
        Integer count = UserUtil.callMapper(UserMapper.class, mapper -> mapper.delete(map));
        log.info("删除行数：{}", count);
    }

    //动态更新
    @Test
    public void update() throws Exception {
        //将userId=2的name修改为：路人
        Long userId1 = 2L;
        Integer count = UserUtil.callMapper(UserMapper.class, mapper -> mapper.update(UserModel.builder().id(userId1).name("ready").build()));
        log.info("更新行数：{}", count);

        log.info("---------------------");
        //将userId=3的name修改为：路人,薪水为：1000.88
        Long userId2 = 3L;
        count = UserUtil.callMapper(UserMapper.class, mapper -> mapper.update(UserModel.builder().id(userId2).name("ready").salary(1000.88D).build()));
        log.info("更新行数：{}", count);
    }

    //按用户id查询
    public UserModel getModelById(Long userId) throws Exception {
        //查询指定id的数据
        Map<String, Object> map = new HashMap<>();
        map.put("id", userId);
        return UserUtil.callMapper(UserMapper.class, mapper -> {
            List<UserModel> userModelList = mapper.getModelList(map);
            if (userModelList.size() == 1) {
                return userModelList.get(0);
            }
            return null;
        });
    }

    //查询所有数据
    @Test
    public void getModelList1() throws Exception {
        List<UserModel> userModelList = UserUtil.callMapper(UserMapper.class, mapper -> mapper.getModelList(null));
        log.info("结果:{}", userModelList);
    }

    //查询多个用户id对应的数据
    @Test
    public void getModelListByIds() throws Exception {
        List<Integer> idList = Arrays.asList(2, 3, 4).stream().collect(Collectors.toList());
        Map<String, Object> map = new HashMap<>();
        map.put("idList", idList);

        List<UserModel> userModelList = UserUtil.callMapper(UserMapper.class, mapper -> mapper.getModelList(map));
        log.info("结果:{}", userModelList);
    }

    //多条件 & 指定返回的列
    @Test
    public void getModelList2() throws Exception {
        //查询姓名中包含路人甲java以及薪资大于3万的用户id、姓名
        Map<String, Object> map = new HashMap<>();
        map.put("nameLike", "路人甲java");
        map.put("salaryGte", 30000.00D);
        //需要返回的列
        List<String> tableColumnList = new ArrayList<>();
        tableColumnList.add("id");
        tableColumnList.add("name");
        map.put("tableColumnList", tableColumnList);

        List<UserModel> userModelList = UserUtil.callMapper(UserMapper.class, mapper -> mapper.getModelList(map));
        log.info("结果:{}", userModelList);
    }

    //条件过滤 & 排序 & 分页查询数据 & 只返回用户id、salary
    @Test
    public void getPage() throws Exception {
        //查询姓名中包含路人甲java以及薪资大于3万的用户id，按照薪资倒叙，每页5条取第1页
        Map<String, Object> map = new HashMap<>();
        map.put("nameLike", "路人甲java");
        map.put("salaryGte", 30000.00D);

        //加入排序参数
        map.put("sort", "salary desc");

        //加入分页参数
        int page = 1;
        int pageSize = 5;
        map.put("skip", (page - 1) * pageSize);
        map.put("pageSize", pageSize);

        //加入需要返回的列
        List<String> tableColumnList = new ArrayList<>();
        tableColumnList.add("id");
        tableColumnList.add("salary");
        map.put("tableColumnList", tableColumnList);

        List<UserModel> userModelList = UserUtil.callMapper(UserMapper.class, mapper -> mapper.getModelList(map));
        log.info("结果:{}", userModelList);
    }
}

案例总结

上面列举的一些用例基本上包含了我们对db所需的大部分操作，动态sql处理方面体现的最为强劲，如果让我们自己写，我们需要写很多判断，而用mybatis这么简单就实现了，我们在java代码中没有看到一个判断拼接语句，而这些sql的判断拼接都在一个文件中：user.xml中，这个就是mybatis中核心的文件，我们需要写的sql及判断逻辑基本上都在这个xml中，大家可以认真去看一下这个xml文件。