Mybatis步骤分解实现一个增删改查程序

2022-05-20 10:45:45 作者：张志明(努力奋斗版)

MybatisPlus是国产的第三方插件，它封装了许多常用的CURDapi，免去了我们写mapper.xml的重复劳动。本文将整合MybatisPlus实现增删改查功能，感兴趣的可以了解一下

1.idea新建Maven项目Mybatis-study 将项目里的src文件夹删掉依次将此项目作为父项目

2.在Mybatis-study中新建模块mybatis-01

在mybatis的pom文件中可以看到其父项目为ybatis-study

<parent>
<artifactId>MyBatis-study</artifactId>
<groupId>org.example</groupId>
<version>1.0-SNAPSHOT</version>
</parent>

3. 在Mybatis-study的pom.xml中引入如下jar包

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
    <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.5.9</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>8.0.29</version>
    </dependency>
  </dependencies>

4.将IDEA和MySQL数据库建立连接：

根据实际情况填写user和password 填写之后点击Test Connection

测试成功之后点击Schemas选择你要链接的数据库

5.新建mybatis-config.xml配置文件引入数据库资源

<?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">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/smbms?useSSL=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/kero/dao/UserMapper.xml" />
    </mappers>
</configuration>

6.创建实体类User 注意:实体类中成员变量名要和数据库表中字段名完全一致

package com.kero.pojo;
public class User {
    private int id;
    private String name;
    private String password;
    public User() {
    }
    public User(int id, String name, String password) {
        this.id = id;
        this.name = name;
        this.password = password;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getpassword() {
        return password;
    }
    public void setpassword(String pwd) {
        this.password = pwd;
    }
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + password + '\'' +
                '}';
    }
}

7.编写工具类Utils

package com.kero.utils;
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;
//sqlSessionFactory
public class MyBatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
    static {
        try {
            //使用Mybatis第一步 获取sqlSessionFactory对象
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
/*
既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例。SqlSession
 提供了在数据库执行 SQL 命令所需的所有方法。你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句。例如：
 */
        public static SqlSession getSqlSession(){
            return sqlSessionFactory.openSession();
        }
}

8.定义接口

package com.kero.dao;
import com.kero.pojo.User;
import java.util.List;
public interface UserMapper {
  //查询全部用户
    List<User> getUserList();
    //根据ID查询用户
    User getUserByID(int id);
    //insert一个用户
    int addUser(User user);
  //修改一个用户
  int updateUser(User user);
  //删除一个用户
  int deleteUser(int id);
}

9.定义Mapper文件这里的Mapper文件相当于原来传统方式中接口的实现类

<?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">
<!--namespace会绑定一个对应的Mapper接口-->
<mapper namespace="com.kero.dao.UserMapper">
    <select id="getUserList" resultType="com.kero.pojo.User">
        select * from smbms.user
    </select>
        <select id="getUserByID" parameterType="int" resultType="com.kero.pojo.User">
            select * from smbms.user where id = #{id}
        </select>
    <insert id="addUser" parameterType="com.kero.pojo.User">
        insert into smbms.user (id, name, password) VALUES (#{id},#{name},#{password})
    </insert>
    <update id="updateUser" parameterType="com.kero.pojo.User">
       update smbms.user set name=#{name},password=#{password} where id = #{id}
    </update>
    <delete id="deleteUser" parameterType="int">
        delete from smbms.user where id = #{id}
    </delete>
</mapper>

10.编写测试类

import com.kero.dao.UserMapper;
import com.kero.pojo.User;
import com.kero.utils.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
public class test {
    @Test
    public void test(){
        SqlSession session = MyBatisUtils.getSqlSession();
        UserMapper mapper = session.getMapper(UserMapper.class);
        List<User> userList = mapper.getUserList();
        for (User l:userList) {
            System.out.println(l.toString());
        }
        session.close();
    }
    @Test
    public void testgetUserByID(){
        SqlSession session = MyBatisUtils.getSqlSession();
        UserMapper mapper = session.getMapper(UserMapper.class);
        User userByID = mapper.getUserByID(1);
        System.out.println(userByID);
        session.close();
    }
    //增删改需要提交事务
    @Test
    public void testaddUser(){
        SqlSession session = MyBatisUtils.getSqlSession();
        UserMapper mapper = session.getMapper(UserMapper.class);
        int zhhgf = mapper.addUser(new User(10, "zhhgf", "1k23jbjk"));
        System.out.println(zhhgf);
        session.commit();
        //提交事务
        session.close();
    }
    @Test
    public void testupdateUser(){
        SqlSession session = MyBatisUtils.getSqlSession();
        UserMapper mapper = session.getMapper(UserMapper.class);
        int i = mapper.updateUser(new User(8,"asdfsdf","234sdfs"));
        session.commit();
        //提交事务
        session.close();
    }
    @Test
    public void testdeleteUser(){
        SqlSession session = MyBatisUtils.getSqlSession();
        UserMapper mapper = session.getMapper(UserMapper.class);
        int i = mapper.deleteUser(8);
        session.commit();
        //提交事务
        session.close();
    }
}

11.测试查询功能 : 输出结果与数据库表中数据

User{id=1, name='Sugawara Ryota', pwd='8X8Jq7HVNs'}

User{id=2, name='Shawn Mills', pwd='R78IHGDSXr'}

User{id=3, name='Matsuda Hina', pwd='mUi3CVA7mc'}

User{id=4, name='Cynthia Hawkins', pwd='NO1EwWbOs9'}

User{id=5, name='Rachel Bennett', pwd='YefuPVxzb9'}

tips:

如果一切配置正常但出现java.lang.ExceptionInInitializerError

Caused by org.apache.ibatis.execeptions.PersistenceExecepyion错误

是因为:maven由于它的约定大于配置我们写的配置文件可能会出现无法被导出或者生效的问题解决方案在pom.xml文件中添加如下代码

<build>
  <resources>
    <resource>
      <directory>src/main/resources</directory>
      <includes>
        <include>**/*.properties</include>
        <include>**/*.xml</include>
      </includes>
      <filtering>true</filtering>
    </resource>
    <resource>
      <directory>src/main/java</directory>
      <includes>
        <include>**/*.properties</include>
        <include>**/*.xml</include>
      </includes>
      <filtering>true</filtering>
    </resource>
  </resources>
</build>

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Mybatis步骤分解实现一个增删改查程序

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