【SSM-Mybatis】Mybatis配置方式（不用接口，用mapper，使用注解）

Mybatis配置方式：
方式一：不用接口：表对应类+.xml

方式二：用mapper：表对应类+类Mapper接口+.xml

方式三：使用注解：表对应类+类Mapper接口

当然还有SQL语句方式，在另一篇文章

https://blog.youkuaiyun.com/beauman/article/details/90751393
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开始

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用最简单的只有 id 和name的表演示
对应World类

public class World {
    int id;
    String name;
    @Override
    public String toString() {
        return "World{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
    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;
        }
    }

方式一：

不用mapper 只用表对应World类+World.xml

因为我的类创建再pojo文件下，我为了好看在resources下创建了一个pojo而真正决定起作用的和路径无关，只要在mybatis下

world.xml直接放在resources也可以
1.world.xml代码：
只演示一个select

<?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="M2.pojo">

    <select id="listWorld" resultType="World">
        select * from world
    </select>

</mapper>

2.mybatis.xml配置

<?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>

  <!--  使用LOG4J-->
    <settings>
        <setting name="logImpl" value="LOG4J"/>
    </settings>

        <!--别名-->
    <typeAliases>
        <package name="M2.pojo"/>
    </typeAliases>


        <!-- environmengs
            transactionMapper
            dataSource
        -->

    <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/how2java?useSSL=false
&amp;serverTimezone=UTC"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>

        <mapper resource="pojo/World.xml"/>
    </mappers>
</configuration>

3.Test

public class WorldTest {
    @Test
    public void worldt() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
        CategoryMapper mapper = session.getMapper(CategoryMapper.class);

        List<World> worlds = session.selectList("listWorld");
        for (World w:worlds
             ) {
            System.out.println(w);
        }
        session.commit();
        session.close();
    }
}

方式二：

使用mapper接口方式 那么需要World类+WorldMapper接口+WorldMapper.xml

1.worldMapper

public interface WorldMapper {
    void addWorld();

    List<World> listWorld();
}

2.WorldMapper.xml
注意点：
1.还是那句话，名字和位置是随便起，随便放，但是 你得在 mybatis.xml中对应准确：

<mappers>
    <mapper resource="mapper/World.xml"/>
</mappers>

2.此时的namespace的值必须为WorldMapper接口

---

代码：

<?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="M1.mapper.WorldMapper"> 

    <select id="listWorld" resultType="World">
        select * from world
    </select>
</mapper>

3.Mybatis.xml
只需要改

<mappers>
    <mapper resource="mapper/World.xml"/>
</mappers>

全部代码：

<?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>

  <!--  使用LOG4J-->
    <settings>
        <setting name="logImpl" value="LOG4J"/>
    </settings>

        <!--别名-->
    <typeAliases>
        <package name="M2.pojo"/>
    </typeAliases>

        <!-- environmengs
            transactionMapper
            dataSource
        -->

    <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/how2java?useSSL=false
&amp;serverTimezone=UTC"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="mapper/World.xml"/>
    </mappers>
</configuration>

4.Test

public class WorldTest {
    @org.junit.Test
    public void test1() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        //读取配置文件的配置信息，利用SqlSessionFactoryBuilder创建sqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //利用sqlSessionFactory打开与数据库的会话
        SqlSession sqlSession = sqlSessionFactory.openSession();

        WorldMapper worldMapper = sqlSession.getMapper(WorldMapper.class);
        List<World> lists = worldMapper.listWorld();
        for (World w : lists
                ) {
            System.out.println(w);
        }
		 sqlSession.commit();
  	  		sqlSession.close();
}

方式三

使用注解 只有World类 + WorldMapper（注解）

1.WorldMapper2

public interface WorldMapper2 {

    @Select("select * from world")
    List<World> listWorld2();
}

2.mybatis.xml配置
只修改下面就行了

<mappers>
    <mapper class="M1.mapper.WorldMapper2"/>
</mappers>

3.Test

public class WorldMapperTest {
    @Test
    public void t() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        //读取配置文件的配置信息，利用SqlSessionFactoryBuilder创建sqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //利用sqlSessionFactory打开与数据库的会话
        SqlSession sqlSession = sqlSessionFactory.openSession();
        WorldMapper2 mapper2 = sqlSession.getMapper(WorldMapper2.class);


        listWorld(mapper2);
        sqlSession.close();
    }
    private static void listWorld(WorldMapper2 mapper2){
        List<World> ws = mapper2.listWorld2();
        for (World w:ws
             ) {
            System.out.println(w);
        }
    }
}

总结：

1.用session启动和用mapper启动

方式一的启动方式是session.

方式三的启动方式是
先getMapper

WorldMapper mapper = sqlSession.getMapper(WorldMapper.class);

再调用mapper. 在WorldMapper中自己设置的方法。

方式二因为既有mapper又有xml所以
session和mapper都可以启动，
上面代码给的是mapper启动，这是session启动，效果一样，看你想用哪个

 SqlSession sqlSession = sqlSessionFactory.openSession();
        List<World> worlds = sqlSession.selectList("listWorld");
        for (World w:worlds
        ) {
            System.out.println(w);
        }

2.在mybatis.xml中的配置不同

方式一、二是xml配置方式
在mybatis.xm需要用

 <mappers>
        <mapper resource="    /    .xml"/>
</mapper>

而方式三不用xml只保留了mapper

 <mappers>
        <mapper class="    .    .xml"/>
</mapper>

3.namespace中的指定

方式二中xml的

<mapper namespace="M2.mapper.WorldMapper">

必须指定到mapper