javaweb：mybatis：mapper(sql映射+代理开发+配置文件之设置别名、多环境配置、顺序+注解开

1.0版本 sql映射文件实现 流程

首先程序进入启动类MyBatisDemo.java中，读取配置文件mybatis-config.xml 再由mybatis-config的mappers属性

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

找到sql映射文件UserMapper.xml文件，通过其中的namespace属性，

<mapper namespace="test">

找到User类，并和数据库表做映射。

项目结构

User.java package com.itheima.pojo; public class User { String id; public String getId() { return id; } public void setId(String id) { this.id = id; } @Override public String toString() { return "User{" + "id='" + id + '\'' + '}'; } } MyBatisDemo.java package com.itheima; import com.itheima.pojo.User; 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; import java.util.List; public class MyBatisDemo { public static void main(String[] args) throws IOException { // 加载mybatis核心配置文件，获取SqlSessionFactory String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); // SqlSession，用它执行sql SqlSession sqlSession = sqlSessionFactory.openSession(); // 执行sql List<User> users = sqlSession.selectList("test.selectAll"); System.out.println(users); // 释放资源 sqlSession.close(); } } 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属性可以切换不同的environment --> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"></transactionManager> <dataSource type="POOLED"> <!-- 数据库连接信息 --> <property name="driver" value="com.mysql.jdbc.Driver"></property> <property name="url" value="jdbc:mysql:///mybatis?useSSL=false"></property> <property name="username" value="root"></property> <property name="password" value="1234"></property> </dataSource> </environment> </environments> <mappers> <mapper resource="UserMapper.xml"></mapper> </mappers> </configuration>

这里的

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

是因为UserMapper和mybatis-config同处于一个包，所以可以只写名字。但是如果UserMapper不和其同处于一个包的话，就需要写全路径。

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"> <mapper namespace="test"> <select id = "selectAll" resultType ="com.itheima.pojo.User"> select * from tb_user; </select> </mapper>

这里的namespace

<mapper namespace="test">

相当于这个mapper文件的唯一标识，不能与其他mapper文件的重复，就相当于外面套了一个test包，在其他地方调用，譬如启动类MyBatisDemo.java中调用时，要用test.方法名。

2.0版本 mapper代理开发 注意

想在resources包下面创建多级目录，譬如"com.itheima.mapper"，不能直接创建一个目录，然后名称写"com.itheima.mapper"，这样只会默认创建一个"com.itheima.mapper"的目录，而不会自动分级。 如果想要自动分级，需要写"com/itheima/mapper"

整体流程

首先程序进入启动类MyBatisDemo中，读取配置文件mybatis-config.xml 再由mybatis-config的mappers属性

<mappers> <package name="com.itheima.mapper"/> </mappers>

找到mapper包下面的mapper接口。 因为mapper接口和sql映射文件属于同一个包层次结构，所以由mapper接口可以找到sql映射文件UserMapper.xml。再由其中的resultType字段

<select id = "selectAll" resultType ="com.itheima.pojo.User">

找到pojo类，并映射对应的数据库表结构。

项目结构

mapper包下的UserMapper.java package com.itheima.mapper; import com.itheima.pojo.User;·54 import java.util.List; public interface UserMapper { List<User> selectAll(); } pojo包下的User类 package com.itheima.pojo; public class User { String id; public String getId() { return id; } public void setId(String id) { this.id = id; } @Override public String toString() { return "User{" + "id='" + id + '\'' + '}'; } } UserMapper.xml

namespace为mapper接口的全限定名。 可以右键点击mapper接口，复制引用，即其全限定名。

<?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.itheima.mapper.UserMapper"> <select id = "selectAll" resultType ="com.itheima.pojo.User"> select * from tb_user; </select> </mapper> 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"></transactionManager> <dataSource type="POOLED"> <!-- 数据库连接信息 --> <property name="driver" value="com.mysql.jdbc.Driver"></property> <property name="url" value="jdbc:mysql:///mybatis?useSSL=false"></property> <property name="username" value="root"></property> <property name="password" value="1234"></property> </dataSource> </environment> </environments> <mappers> <mapper resource="com/itheima/mapper/UserMapper.xml" <package name="com.itheima.mapper"/> </mappers> </configuration> MyBatisDemo package com.itheima; import java.io.IOException; import java.io.InputStream; import java.util.List; import com.itheima.mapper.UserMapper; import com.itheima.pojo.User; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; public class MyBatisDemo { public static void main(String[] args) throws IOException { //加载mybatis核心配置文件，获取SqlSessionFactory String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); // 获取SqlSession对象 SqlSession sqlSession = sqlSessionFactory.openSession(); //获取UserMapper对象，用它直接执行sql方法 UserMapper userMapper = sqlSession.getMapper(UserMapper.class); List<User>users = userMapper.selectAll(); System.out.println(users); //释放资源 sqlSession.close(); } } 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"></transactionManager> <dataSource type="POOLED"> <!-- 数据库连接信息 --> <property name="driver" value="com.mysql.jdbc.Driver"></property> <property name="url" value="jdbc:mysql:///mybatis?useSSL=false"></property> <property name="username" value="root"></property> <property name="password" value="1234"></property> </dataSource> </environment> </environments> <mappers> <!-- <mapper class="com.itheima.mapper.UserMapper"></mapper>--> <package name="com.itheima.mapper"/> </mappers> </configuration>

其中可以使用class=全类名，来找到mapper接口。

<mapper class="com.itheima.mapper.UserMapper"></mapper>

也可以使用包扫描的方式，来找到mapper接口。

<package name="com.itheima.mapper"/> mybatis-config.xml（设置别名+多环境配置+顺序） <?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> <!--设置别名，这样任意xml中出现限定名的地方都不需要加上前面的报名前缀。且类名不区分大小写--> <!--譬如这里配置了后UserMapper中的代码就可以改为 <select id = "selectAll" resultType ="User"> 或者 <select id = "selectAll" resultType ="user"> --> <typeAliases> <package name="com.itheima.pojo"/> </typeAliases> <!-- environments default属性可以切换不同的environment --> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"></transactionManager> <dataSource type="POOLED"> <!-- 数据库连接信息 --> <property name="driver" value="com.mysql.jdbc.Driver"></property> <property name="url" value="jdbc:mysql:///mybatis?useSSL=false"></property> <property name="username" value="root"></property> <property name="password" value="1234"></property> </dataSource> </environment> <environment id="learn"> <transactionManager type="JDBC"></transactionManager> <dataSource type="POOLED"> <!-- 数据库连接信息 --> <property name="driver" value="com.mysql.jdbc.Driver"></property> <property name="url" value="jdbc:mysql:///mybatis?useSSL=false"></property> <property name="username" value="root"></property> <property name="password" value="1234"></property> </dataSource> </environment> </environments> <mappers> <mapper resource="com/itheima/mapper/UserMapper.xml"></mapper> <package name="com.itheima.mapper"/> </mappers> </configuration>

mybatis-config.xml里面的属性是有顺序的，顺序如下：

properties（属性）settings（设置）typeAliases（类型别名）typeHandler（类型处理器）objectFactory（对象工厂）plugins（插件）environments（环境配置） transactionManager（事务管理器）dataSource（数据源） mappers（映射器） 3.0代码 注解开发 流程

和2.0 代理开发一样，但是xml文件里面不需要再写select属性，只需要在pojo的类上面加上对应的注解即可。

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"> <mapper namespace="com.itheima.mapper.UserMapper"></mapper> UserMapper.java package com.itheima.mapper; import com.itheima.pojo.User; import org.apache.ibatis.annotations.Select; import java.util.List; public interface UserMapper { @Select("select * from tb_user") List<User> selectAll(); }