SSM之Mybatis_ch1——入门

SSM之Mybatis_ch1

准备工作

数据库方面

新建数据库mybatis，并创建user表。

CREATE DATABASE IF NOT EXISTS `mybatis`;

USE `mybatis`;

CREATE TABLE `user` ( 
`id` int PRIMARY KEY,
`name` VARCHAR(100) NOT NULL,
`pwd` VARCHAR(100) NOT NULL
) ENGINE=INNODB DEFAULT CHARSET=utf8;

向其中插入数据

INSERT INTO `user` VALUES
(1,'reflect111','pwd123456'),
(2,'reflect222','pwd123456'),
(3,'reflect333','pwd123456'),
(4,'reflect444','pwd123456'),
(5,'reflect555','pwd123456');

IDEA方面

1.新建Maven项目

File -> New -> Project -> Maven

取名为Mybatis_ch1，groupId可更改，如com.study

2.添加所需依赖

打开浏览器搜索Maven Repository，分别搜索mybatis和mysql

打开pom.xml文件，将Mybatis和MySQL的依赖导入，以及junit单元测试

<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.6</version>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.21</version>
</dependency>
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
    <scope>test</scope>
</dependency>

3.新建所需的包和类

开始测试

1.在pojo包下新建实体类User.java

public class User {
    private int id;
    private String name;
    private String pwd;

    public User() {
    }

    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    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 getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                '}';
    }
}

2.在Mapper包下新建一个mapper所对应的接口：UserMapper.java

public interface UserMapper {

    // 查询全部用户
    List<User> getUserList();
}

3.在UserMapper接口的同一位置新建UserMapper.xml（此处即在mapper包下）

<?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">

<!--namespace绑定一个对应的mapper接口-->
<mapper namespace="com.reflect.mapper.UserMapper">

<!--    每个select/insert/update/delete的id都对应mapper接口中的方法名-->
<!--    resultType：sql执行后返回值的类型-->
<!--    resultMap：sql执行后返回的不止一个元素，需要对齐自定义解释-->
    <select id="getUserList" resultType="com.reflect.pojo.User">
        select * from mybatis.user
    </select>
</mapper>

4.新建Mybatis的工具类，避免以后繁琐进行SqlSession的创建

/**
 * 建议将Mybatis打开SqlSession这一操作
 * 直接在静态方法块中加载配置文件，
 * 最后使用静态方法对外返回(暴露)SqlSession
 */
public class MybatisUtils {

    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

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

5.新建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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <!--此处url记得换成localhost，或者自己虚拟机所在的ip-->
                <property name="url" value="jdbc:mysql://192.168.199.131:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <!--此处注意换成自己的mysql密码-->
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
<!--    此处的resource要注意是'/'，而不是'.'-->
    <mappers>
        <mapper resource="com/reflect/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

6.最后新建测试类MyTest

public class MyTest {

    // 查询全部用户
    @Test
    public void getUserList() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        try {
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            List<User> userList = mapper.getUserList();
            for (User user : userList) {
                System.out.println(user);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            sqlSession.close();
        }
    }
}

7.测试运行

单击@Test左边的绿色按钮运行，或者直接右键运行测试

最后得到的结果如下所示，即代表成功

8.错误分析

①出现如下所示，一般是Test类中对应的getUserList在UserMapper.xml未找到对应方法，即UserMapper.xml中的id不正确，请确定与UserMapper.java中的方法名一致。

②出现如下所示，一般是mybatis-config.xml中的数据库配置不正确，导致数据库无法正确连接，特别是url一定要注意修改。

测试总结

以上就是我重归SSM学习回顾mybatis的第一次测试。

接下来就不细说了，直接上我我第一次所写的所有代码了。有兴趣的朋友可以对着自己动手做做，只要修改了我上面所说的地方，都能成功。

全部代码

1.实体类User.java

package com.reflect.pojo;

/**
 * author: Administrator
 * date: 2020/12/30 - 10:08
 */
public class User {
    private int id;
    private String name;
    private String pwd;

    public User() {
    }

    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    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 getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                '}';
    }
}

2.映射接口UserMapper.java

package com.reflect.mapper;

import com.reflect.pojo.User;

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

/**
 * author: Administrator
 * date: 2020/12/30 - 10:18
 */

/**
 * 通过Mapper接口来写需要执行的操作
 * 映射到Mapper.xml来执行sql语句
 */
public interface UserMapper {

    // 查询全部用户
    List<User> getUserList();

    // 查询单个用户
    User getUser(int id);

    // 新增一个用户
    boolean insertUser(User user);

    // 修改一个用户
    boolean updateUser(User user);

    // 删除一个用户
    boolean deleteUser(int id);

    // 万能Map？？？
    User getMapUser(Map<String,Object> map);
    boolean insertMapUser(Map<String,Object> map);
    boolean updateMapUser(Map<String,Object> map);
    boolean deleteMapUser(Map<String,Object> map);

    // 模糊查询
    List<User> getUserLike(String vale);

}

3.Mapper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">

<!--namespace绑定一个对应的mapper接口-->
<mapper namespace="com.reflect.mapper.UserMapper">

<!--    每个select/insert/update/delete的id都对应mapper接口中的方法名-->
<!--    resultType：sql执行后返回值的类型-->
<!--    resultMap：sql执行后返回的不止一个元素，需要对齐自定义解释-->
    <select id="getUserList" resultType="com.reflect.pojo.User">
        select * from mybatis.user
    </select>

<!--    #{}可防止sql注入、推荐使用，${}一般不推荐使用-->
    <select id="getUser" parameterType="int" resultType="com.reflect.pojo.User">
        select *
        from mybatis.user where id = #{id};
    </select>

<!--    parameterType：sql语句的参数类型-->
    <insert id="insertUser" parameterType="com.reflect.pojo.User">
        insert into mybatis.user (id,name,pwd) values (#{id},#{name},#{pwd})
    </insert>

    <update id="updateUser" parameterType="com.reflect.pojo.User">
        update mybatis.user set name=#{name},pwd=#{pwd} where id=#{id}
    </update>

    <delete id="deleteUser" parameterType="com.reflect.pojo.User">
        delete from mybatis.user where id=#{id}
    </delete>
    
<!--    万能Map合集-->
<!--    参数可以自定义，此处将参数id改为reflect为例-->
    <select id="getMapUser" parameterType="map" resultType="com.reflect.pojo.User">
        select * from mybatis.user where id=#{reflect} and name=#{name}
    </select>
    <insert id="insertMapUser" parameterType="map">
        insert into mybatis.user (id,name,pwd) values (#{id},#{name},#{pwd})
    </insert>
    <update id="updateMapUser" parameterType="map">
        update mybatis.user set name=#{name},pwd=#{pwd} where id=#{id}
    </update>
    <delete id="deleteMapUser" parameterType="map">
        delete from mybatis.user where id=#{id}
    </delete>

<!--    模糊查询-->
    <select id="getUserLike" parameterType="String" resultType="com.reflect.pojo.User">
        select * from mybatis.user where name like #{value};
    </select>

</mapper>

4.Mybatis工具类MybatisUtils.java

package com.reflect.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;

/**
 * author: Administrator
 * date: 2020/12/29 - 23:47
 */

/**
 * 建议将Mybatis打开SqlSession这一操作
 * 直接在静态方法块中加载配置文件，
 * 最后使用静态方法对外返回(暴露)SqlSession
 */
public class MybatisUtils {

    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

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

5.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>
    <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/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
<!--    此处的resource要注意是'/'，而不是'.'-->
    <mappers>
        <mapper resource="com/reflect/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

6.测试类MyTest

import com.reflect.mapper.UserMapper;
import com.reflect.pojo.User;
import com.reflect.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.*;

/**
 * author: Administrator
 * date: 2020/12/30 - 10:27
 */

/**
 * 为了保证SqlSession一定关闭，建议将其放在finally块中。
 * 增删改这三项操作之后，一定要记得Commit提交事务，否则数据库将不会进行相关操作的改动
 */
public class MyTest {

    // 查询全部用户
    @Test
    public void getUserList() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        try {
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            List<User> userList = mapper.getUserList();
            for (User user : userList) {
                System.out.println(user);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            sqlSession.close();
        }
    }

    // 查询单个用户
    @Test
    public void getUser() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        try {
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            User user = mapper.getUser(1);
            System.out.println(user);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            sqlSession.close();
        }
    }

    // 新增一个用户
    @Test
    public void insertUser() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        int id = (int) (Math.random()*1000000000);
        String string = UUID.randomUUID().toString();

        try {
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            boolean res = mapper.insertUser(new User(id, string, "pwd"+string));
            if (res) {
                System.out.println("插入成功！！！");
            }
            // 提交事务（即使打印出成功结果，不提交也是不会插入数据库）
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            sqlSession.close();
        }
    }

    // 修改一个用户
    @Test
    public void updateUser() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        String string = UUID.randomUUID().toString();

        try {
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            boolean res = mapper.updateUser(new User(2,string,"pwd"+string));
            if (res) {
                System.out.println("修改成功！！！");
            }
            // 提交事务
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            sqlSession.close();
        }
    }

    // 删除一个用户
    @Test
    public void deleteUser() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        try {
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            boolean res = mapper.deleteUser(2);
            if (res) {
                System.out.println("删除成功！！！");
            }
            // 提交事务
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            sqlSession.close();
        }
    }

    // 万能Map？？？
    // 查
    @Test
    public void getMapUser() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        try {
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            Map<String,Object> map = new HashMap<>();
            map.put("reflect",1);
            map.put("name","reflect111");
            User user = mapper.getMapUser(map);
            System.out.println(user);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            sqlSession.close();
        }
    }
    // 增
    @Test
    public void insertMapUser() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        int id = (int) (Math.random()*1000000000);
        String string = UUID.randomUUID().toString();

        try {
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            Map<String,Object> map = new HashMap<>();
            map.put("id",id);
            map.put("name",string);
            map.put("pwd","pwd"+string);
            boolean res = mapper.insertMapUser(map);
            if (res) {
                System.out.println("使用Map插入成功！！！");
            }
            // 提交事务
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            sqlSession.close();
        }
    }
    // 改
    @Test
    public void updateMapUser() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        String string = UUID.randomUUID().toString();

        try {
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            Map<String, Object> map = new HashMap<>();
            map.put("id",2);
            map.put("name",string);
            map.put("pwd","pwd"+string);
            boolean res = mapper.updateMapUser(map);
            if (res) {
                System.out.println("使用Map修改成功！！！");
            }
            //提交事务
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            sqlSession.close();
        }
    }
    // 删
    @Test
    public void deleteMapUser() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        try {
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            Map<String, Object> map = new HashMap<>();
            map.put("id",2);
            boolean res = mapper.deleteMapUser(map);
            if (res) {
                System.out.println("使用Map删除成功！！！");
            }
            // 提交事务
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            sqlSession.close();
        }
    }

    // 模糊查询
    @Test
    public void getUserLike() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        try {
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            // value使用%通配符，左右两边都加即代表只要含有"reflect"字符即可查询
            List<User> userLike = mapper.getUserLike("%reflect%");
            for (User user : userLike) {
                System.out.println(user);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            sqlSession.close();
        }
    }
}

全部代码就是这样了，上面所需要修改的就是mysql的配置，之后就肯定能运行起来的。

最后就是希望对大家学习SSM略有帮助。

本文地址：https://blog.csdn.net/A13777852949/article/details/111993362