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LiAngJava2023年11月16日MyBatisJava大约 12 分钟约 2368 字

需求说明

开发一个 MyBatis 项目，通过 MyBatis 的方式可以完成对 monster 表的 crud 操作。

代码实现

创建 mybatis 数据库 - monster 表

CREATE DATABASE `mybatis`

CREATE TABLE `monster` (
	`id` INT NOT NULL AUTO_INCREMENT, 
    `age` INT NOT NULL, 
    `birthday` DATE DEFAULT NULL, 
    `email` VARCHAR(255) NOT NULL, 
    `gender` TINYINT NOT NULL, 
    `name` VARCHAR(255) NOT NULL, 
    `salary` DOUBLE NOT NULL, 
    PRIMARY KEY (`id`)
)CHARSET=utf8

创建 maven 项目

image-20220630091313985
image-20220630091313985
image-20220630091424110
image-20220630091424110
image-20220630091726849
image-20220630091726849

修改父项目 pom.xml

<?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>

    <!--
        1. 将mybatis作为父项目管理多个子模块/子项目
        2. 父项目的完整的坐标 groupId[组织名]+artifactId[项目名]
        3. 后面该父项目会管理多个子模块/子项目 , 将来父项目中的引入的依赖可以直接给子项目用, 这样开发简单，提高复用性，也便于管理
    -->
    <groupId>com.lzw</groupId>
    <artifactId>mybatis</artifactId>
    <version>1.0-SNAPSHOT</version>


    <!--加入依赖-->
    <dependencies>
        <!--mysql依赖-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.49</version>
        </dependency>
        <!--mybatis依赖-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.7</version>
        </dependency>
        <!--junit依赖-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <!--如果这里有一个scope-test 表示该jar的作用范围在test目录 -->
            <!--<scope>test</scope>-->
        </dependency>
    </dependencies>

</project>

创建子项目

image-20220630092503986
image-20220630092503986
image-20220630092521042
image-20220630092521042
image-20220630092608970
image-20220630092608970
image-20220630093148576
image-20220630093148576

创建 resources/mybatis-config.xml

image-20220630093805664
image-20220630093805664
<?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="development">
        <environment id="development">
            <!--配置事务管理器-->
            <transactionManager type="JDBC"/>
            <!--配置数据源-->
            <dataSource type="POOLED">
                <!--配置驱动-->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <!--配置连接mysql-url
                1. jdbc:mysql 协议
                2. 127.0.0.1:3306 : 指定连接mysql的ip+port
                3. mybatis: 连接的DB
                4. useSSL=true 表示使用安全连接
                5. &amp; 表示 & 防止解析错误
                6. useUnicode=true : 使用unicode 作用是防止编码错误
                7. characterEncoding=UTF-8 指定使用utf-8, 防止中文乱码
                8. 温馨提示：不要背，直接使用即可
                -->
                <property name="url" value="jdbc:mysql://127.0.0.1:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
</configuration>

创建 com\lzw\entity\Monster.java

image-20220630094112577
image-20220630094112577
package com.lzw.entity;

import java.util.Date;

/**
 * @author LiAng
 * Monster 和 monster表对应
 */
//1. 一个普通的 Pojo 类
//2. 使用原生态的 sql 语句查询结果还是要封装成对象
//3. 要求这里的实体类属性名和表名字段保持一致。
public class Monster {

    //属性-和表字段有对应关系
    private Integer id;
    private Integer age;
    private String name;
    private String email;
    private Date birthday;
    private double salary;
    private Integer gender;

    public Monster() {
    }

    public Monster(Integer id, Integer age, String name, String email, Date birthday, double salary, Integer gender) {
        this.id = id;
        this.age = age;
        this.name = name;
        this.email = email;
        this.birthday = birthday;
        this.salary = salary;
        this.gender = gender;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }

    public Integer getGender() {
        return gender;
    }

    public void setGender(Integer gender) {
        this.gender = gender;
    }

    @Override
    public String toString() {
        return "Monster{" +
                "id=" + id +
                ", age=" + age +
                ", name='" + name + '\'' +
                ", email='" + email + '\'' +
                ", birthday=" + birthday +
                ", salary=" + salary +
                ", gender=" + gender +
                '}';
    }
}

创建 MonsterMapper.java

image-20220630094508275
image-20220630094508275
package com.lzw.mapper;

import com.lzw.entity.Monster;

/**
 * @author LiAng
 * 1. 这是一个接口
 * 2. 该接口用于声明操作monster表的方法
 * 3. 这些方法可以通过注解或者xml文件来实现
 */
public interface MonsterMapper {

    //添加monster
    public void addMonster(Monster monster);

}

创建 MonsterMapper.xml

image-20220630095853208
image-20220630095853208
<?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">

<!--
1. 这是一个mapper xml 文件
2. 该文件可以去实现对应的接口的方法
3. namespace 指定该xml文件和哪个接口对应!!!
-->
<mapper namespace="com.lzw.mapper.MonsterMapper">
    <!--配置addMonster
       1. id="addMonster" 就是接口的方法名
       2. parameterType="com.lzw.entity.Monster" 放入的形参的类型
       3. 注意"com.lzw.entity.Monster" 可以简写
       4. 写入sql语句=> 建议，先在sqlyog 写完成-测试通过，再拿过来
       5. (`age`, `birthday`, `email`, `gender`, `name`, `salary`) 表的字段
       6. (#{age}, #{birthday}, #{email}, #{gender}, #{name}, #{salary}) 是从传入的monster对象属性值
       7. 这里 #{age} age 对应monster对象的属性名，其它一样
   -->
    <insert id="addMonster" parameterType="com.lzw.entity.Monster">
        insert into `monster`(`age`, `birthday`, `email`, `gender`, `name`, `salary`)
         values(#{age}, #{birthday}, #{email}, #{gender}, #{name}, #{salary})
    </insert>

</mapper>

修改 mybatis-config.xml

image-20220630100036983
image-20220630100036983
	<!--
    1. 这里我们配置需要关联的Mapper.xml
    2. 这里我们可以通过菜单 Path from source root
    -->
    <mappers>
        <mapper resource="com/lzw/mapper/MonsterMapper.xml"/>
    </mappers>

创建工具类 MyBatisUtils.java

package com.lzw.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;

/**
 * @author LiAng
 */
public class MyBatisUtils {

    private static SqlSessionFactory sqlSessionFactory;

    //编写静态代码块，初始化 sqlSessionFactory
    static {
        try {
            //指定资源文件，配置文件 mybatis-config.xml
            String resource = "mybatis-config.xml";
            //获取到配置文件 mybatis-config.xml 对应的 inputStream
            //加载文件时，默认到 resources目录=>运行后的工作目录
            InputStream resourceAsStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
            System.out.println("sqlSessionFactory = " + sqlSessionFactory);

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


    //编写方法，返回SqlSession对象-会话
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }

}
image-20220630100612166
image-20220630100612166

创建 MonsterMapperTest.java

image-20220630101329675
image-20220630101329675
package com.lzw.mapper;

import com.lzw.util.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Before;
import org.junit.Test;

/**
 * @author LiAng
 */
public class MonsterMapperTest {
    private SqlSession sqlSession;
    private MonsterMapper monsterMapper;

    /**
     * 方法标注 @Before, 表示在执行你的目标测试方法前，会先执行该方法
     */
    //编写方法，完成初始化
    @Before
    public void init(){
        //获取到 sqlSession
        sqlSession = MyBatisUtils.getSqlSession();
         //获取到到MonsterMapper对象 class com.sun.proxy.$Proxy7 代理对象
        //, 底层是使用了动态代理机制
        monsterMapper = sqlSession.getMapper(MonsterMapper.class);
        System.out.println("monsterMapper = " + monsterMapper.getClass());
    }

    @Test
    public void t1(){
        System.out.println("t1()...");
    }

}

测试 t1方法，会出下列异常

image-20220630102142965
image-20220630102142965
image-20220630102430998
image-20220630102430998

解决该问题

在父工程的 pom.xml文件中加入以下内容，加在 <project> 中

	<!--在build中配置resources，来防止我们资源导出失败的问题
        1. 不同的idea/maven 可能提示的错误不一样
        2. 不变应万变，少什么文件，就增加相应配置即可
        3. 含义是将 src/main/java目录和子目录 和 src/main/resources目录和子目录
        的资源文件 xml 和 properties在build项目时，导出到对应的target目录下
    -->
    <build>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.xml</include>
                </includes>
            </resource>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.xml</include>
                    <include>**/*.properties</include>
                </includes>
            </resource>
        </resources>
    </build>

方案1

clean一下

image-20220630103017052
image-20220630103017052

Build Project

image-20220630103038083
image-20220630103038083

有的版本的IDEA到这已经可以正常运行了。

方案2

image-20220630103258429
image-20220630103258429

image-20220630103017052image-20220630103038083

成功解决

image-20220630103629764
image-20220630103629764
image-20220630103515306
image-20220630103515306

修改 MonsterMapperTest.java

	@Test
    public void addMonster(){

        for (int i = 0; i < 2; i++) {
            Monster monster = new Monster();
            monster.setAge(10 + i);
            monster.setBirthday(new Date());
            monster.setEmail("kate@sohu.com");
            monster.setGender(1);
            monster.setName("松鼠精" + i);
            monster.setSalary(1000 + i * 10);
            monsterMapper.addMonster(monster);
            System.out.println("添加对象--" + monster);
        }

        //如果是增删改，需要提交事务
        if(sqlSession != null){
            sqlSession.commit();
            sqlSession.close();
        }

        System.out.println("保存成功");

    }

测试添加

image-20220630113830979
image-20220630113830979
image-20220630113839926
image-20220630113839926

返回自增长id

修改 MonsterMapper.xml

	<insert id="addMonster" parameterType="com.lzw.entity.Monster" useGeneratedKeys="true" keyProperty="id">
        insert into `monster`(`age`, `birthday`, `email`, `gender`, `name`, `salary`)
        values(#{age}, #{birthday}, #{email}, #{gender}, #{name}, #{salary})
    </insert>

修改 MonstermapperTest.java

	@Test
    public void addMonster(){
        for (int i = 0; i < 2; i++) {
            Monster monster = new Monster();
            monster.setAge(10 + i);
            monster.setBirthday(new Date());
            monster.setEmail("kate@sohu.com");
            monster.setGender(1);
            monster.setName("大象精" + i);
            monster.setSalary(1000 + i * 10);
            monsterMapper.addMonster(monster);
            System.out.println("添加对象--" + monster);
            System.out.println("添加到表中后，自增长的id = " + monster.getId());
        }

        //如果是增删改，需要提交事务
        if(sqlSession != null){
            sqlSession.commit();
            sqlSession.close();
        }

        System.out.println("保存成功");

    }
image-20220630114239967
image-20220630114239967

修改 MonsterMapper.java

	//根据di删除一个Monster
    public void delMonster(Integer id);

    //修改Monster
    public void updateMonster(Monster monster);

    //查询-根据id
    public Monster getMonsterById(Integer id);

    //查询所有的Monster
    public List<Monster> findAllMonster();

删除

修改 MonsterMapper.xml

	<!--配置delMonster方法-->
    <delete id="delMonster" parameterType="Integer">
        delete from `monster` where id =  #{id}
    </delete>

修改 MonstermapperTest.java

	@Test
    public void delMonster(){

        monsterMapper.delMonster(2);
        //如果是增删改，需要提交事务
        if(sqlSession != null){
            sqlSession.commit();
            sqlSession.close();
        }
        System.out.println("删除成功");
    }
image-20220630114825197
image-20220630114825197
image-20220630114834259
image-20220630114834259

修改

修改 MonsterMapper.xml

	<!--配置updateMonster方法-->
    <update id="updateMonster" parameterType="com.lzw.entity.Monster">
        UPDATE `monster`
        SET `age`=#{age} , `birthday`= #{birthday}, `email` = #{email},
        `gender` = #{gender} , `name`= #{name}, `salary` = #{salary}
        WHERE id = #{id}
    </update>

修改 MonstermapperTest.java

	@Test
    public void updateMonster(){
        Monster monster = new Monster();
        monster.setAge(50);
        monster.setBirthday(new Date());
        monster.setEmail("kate@sohu.com");
        monster.setGender(1);
        monster.setName("老鼠精");
        monster.setSalary(2000);
        monster.setId(3);
        monsterMapper.updateMonster(monster);

        //如果是增删改，需要提交事务
        if(sqlSession != null){
            sqlSession.commit();
            sqlSession.close();
        }
        System.out.println("修改成功");
    }
image-20220630121400593
image-20220630121400593
image-20220630121514148
image-20220630121514148

parameterType 别名

修改 mybatis-config.xml

为了 MonsterMapper.xml 中 parameterType 简写

	<!--配置别名-->
    <typeAliases>
        <typeAlias type="com.lzw.entity.Monster" alias="Monster"/>
    </typeAliases>
image-20220630122038769
image-20220630122038769
image-20220630122106372
image-20220630122106372

查询

修改 MonsterMapper.xml

	<!--配置getMonsterById-->
    <select id="getMonsterById" resultType="Monster">
        SELECT * FROM `monster` WHERE id = #{id}
    </select>

修改 MonstermapperTest.java

	@Test
    public void getMonsterById(){
        Monster monster = monsterMapper.getMonsterById(1);
        System.out.println(monster);
        if(sqlSession != null){
            sqlSession.close();
        }
        System.out.println("查询成功");
    }
image-20220630122603903
image-20220630122603903

修改 MonsterMapper.xml

	<!--配置findAllMonster-->
    <select id="findAllMonster" resultType="Monster">
        SELECT * FROM `monster`
    </select>

修改 MonstermapperTest.java

	@Test
    public void findAllMonster(){
        List<Monster> monsters = monsterMapper.findAllMonster();
        for (Monster monster : monsters) {
            System.out.println(monster);
        }
        if(sqlSession != null){
            sqlSession.close();
        }
        System.out.println("查询成功");
    }
image-20220630122827069
image-20220630122827069

日志输出-查看SQL

需求

在开发 MyBatis 程序时，比如执行测试方法，程序员往往需要查看程序底层发给 MySQL 的 SQL 语句，到底长什么样？

日志文档

https://mybatis.org/mybatis-3/zh/logging.html

具体操作

查看文档

https://mybatis.org/mybatis-3/zh/configuration.html#settings

image-20220630143453868
image-20220630143453868

修改 mybatis-config.xml

加入日志输出配置，方便分析sql语句

	<!--配置MyBatis自带的日志输出-查看原生的sql-->
    <settings>
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>
image-20220630143701800
image-20220630143701800

运行之前任意测试的代码

image-20220630143835454
image-20220630143835454
上次编辑于: 2023/11/17 23:19:33
贡献者: LiAng