【 MyBatis 的 Dao 编写（mapper 代理方式实现） 】
Mapper代理的开发方式，程序员只需要编写mapper接口（相当于dao接口）即可。Mybatis会自动的为mapper接口生成动态代理实现类。
不过要实现mapper代理的开发方式，需要遵循一些开发规范。
开发规范
1. mapper接口的全限定名要和mapper映射文件的namespace的值相同。
2. mapper接口的方法名称要和mapper映射文件中的statement的id相同；
3. mapper接口的方法参数只能有一个，且类型要和mapper映射文件中statement的parameterType的值保持一致。
4. mapper接口的返回值类型要和mapper映射文件中statement的resultType值或resultMap中的type值保持一致；
通过规范式的开发mapper接口，可以解决原始dao开发当中存在的问题：
- 模板代码已经去掉；
- 剩下去不掉的操作数据库的代码，其实就是一行代码。这行代码中硬编码的部分，通过第一和第二个规范就可以解决。
编写步骤
第一步：重新写个 UserMapper 配置文件和定义 mapper 映射文件UserMapper.xml（内容同Users.xml，除了namespace的值），放到新创建的目录mapper下。
package cn.ys.mapper;
import cn.ys.model.User;
public interface UserMapper {
/**
*
* @param user
* @return 受影响的行数
*/
public int save(User user);
public User findUserById(int id);
}
<?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="cn.ys.mapper.UserMapper">
<insert id="save" parameterType="cn.ys.model.User">
INSERT INTO user (username,sex,birthday,address)
VALUE (#{username},#{sex},#{birthday},#{address})
</insert>
<select id="findUserById" parameterType="int" resultType="cn.ys.model.User">
SELECT * FROM user WHERE id = #{id}
</select>
</mapper>
db.properties
driverClass=com.mysql.jdbc.Driver
url=jdbc:mysql://yangnanxi.cn:3306/mybatis?useUnicode=true&characterEncoding=utf8
name=yang
password=123456
创建 SqlMapConfig.xml
在 classpath(src) 下，创建 SqlMapConfig.xml 文件【SqlMapConfig.xml（文件头可以从mybatis-3.2.7.pdf文档的2.1.2小节中拷贝）】
<?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>
<properties resource="db.properties"/>
<!-- 配置mybatis的环境信息 -->
<environments default="development">
<environment id="development">
<!-- 配置JDBC事务控制，由mybatis进行管理 -->
<transactionManager type="JDBC"></transactionManager>
<!-- 配置数据源，采用dbcp连接池 -->
<dataSource type="POOLED">
<property name="driver" value="${driverClass}"/>
<property name="url" value="${url}"/>
<property name="username" value="${name}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<!-- 告诉mybatis加载映射文件 -->
<mappers>
<mapper resource="cn/ys/mapper/UserMapper.xml"></mapper>
</mappers>
</configuration>
测试
package cn.ys.test;
import cn.ys.mapper.UserMapper;
import cn.ys.model.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 org.junit.After;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import java.util.Date;
public class Demo04 {
SqlSession session;
@Before
public void before() throws IOException {
System.out.println("before.....获取session");
// a)读取配置文件；
InputStream is = Resources.getResourceAsStream("SqlMapConfig.xml");
//b)通过SqlSessionFactoryBuilder创建SqlSessionFactory会话工厂。
SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
session = sessionFactory.openSession();
}
@After
public void after(){
session.close();
}
@Test
public void test1() throws IOException {
UserMapper userMapper = session.getMapper(UserMapper.class);
//System.out.println(obj.getClass());
//获取数据
System.out.println(userMapper.findUserById(1));
//保存
User user2 = new User();
user2.setUsername("xxx");
user2.setSex("x");
user2.setBirthday(new Date());
user2.setAddress("xx");
userMapper.save(user2);
session.commit();
}
}
控制台打印
C:\Java\jdk1.8.0_181\bin\java.exe -ea -Didea.test.cyclic.buffer.size=1048576 "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2018.2.1\lib\idea_rt.jar=63975:C:\Program Files\JetBrains\IntelliJ IDEA 2018.2.1\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\JetBrains\IntelliJ IDEA 2018.2.1\lib\idea_rt.jar;C:\Program Files\JetBrains\IntelliJ IDEA 2018.2.1\plugins\junit\lib\junit-rt.jar;C:\Program Files\JetBrains\IntelliJ IDEA 2018.2.1\plugins\junit\lib\junit5-rt.jar;C:\Java\jdk1.8.0_181\jre\lib\charsets.jar;C:\Java\jdk1.8.0_181\jre\lib\deploy.jar;C:\Java\jdk1.8.0_181\jre\lib\ext\access-bridge-64.jar;C:\Java\jdk1.8.0_181\jre\lib\ext\cldrdata.jar;C:\Java\jdk1.8.0_181\jre\lib\ext\dnsns.jar;C:\Java\jdk1.8.0_181\jre\lib\ext\jaccess.jar;C:\Java\jdk1.8.0_181\jre\lib\ext\jfxrt.jar;C:\Java\jdk1.8.0_181\jre\lib\ext\localedata.jar;C:\Java\jdk1.8.0_181\jre\lib\ext\nashorn.jar;C:\Java\jdk1.8.0_181\jre\lib\ext\sunec.jar;C:\Java\jdk1.8.0_181\jre\lib\ext\sunjce_provider.jar;C:\Java\jdk1.8.0_181\jre\lib\ext\sunmscapi.jar;C:\Java\jdk1.8.0_181\jre\lib\ext\sunpkcs11.jar;C:\Java\jdk1.8.0_181\jre\lib\ext\zipfs.jar;C:\Java\jdk1.8.0_181\jre\lib\javaws.jar;C:\Java\jdk1.8.0_181\jre\lib\jce.jar;C:\Java\jdk1.8.0_181\jre\lib\jfr.jar;C:\Java\jdk1.8.0_181\jre\lib\jfxswt.jar;C:\Java\jdk1.8.0_181\jre\lib\jsse.jar;C:\Java\jdk1.8.0_181\jre\lib\management-agent.jar;C:\Java\jdk1.8.0_181\jre\lib\plugin.jar;C:\Java\jdk1.8.0_181\jre\lib\resources.jar;C:\Java\jdk1.8.0_181\jre\lib\rt.jar;C:\Users\ys951\Desktop\JavaSETest\JavaEE\out\production\mybatis;C:\Users\ys951\Desktop\JavaSETest\JavaEE\mybatis\lib\asm-3.3.1.jar;C:\Users\ys951\Desktop\JavaSETest\JavaEE\mybatis\lib\cglib-2.2.2.jar;C:\Users\ys951\Desktop\JavaSETest\JavaEE\mybatis\lib\commons-logging-1.1.1.jar;C:\Users\ys951\Desktop\JavaSETest\JavaEE\mybatis\lib\javassist-3.17.1-GA.jar;C:\Users\ys951\Desktop\JavaSETest\JavaEE\mybatis\lib\junit-4.8.2.jar;C:\Users\ys951\Desktop\JavaSETest\JavaEE\mybatis\lib\log4j-1.2.17.jar;C:\Users\ys951\Desktop\JavaSETest\JavaEE\mybatis\lib\log4j-api-2.0-rc1.jar;C:\Users\ys951\Desktop\JavaSETest\JavaEE\mybatis\lib\log4j-core-2.0-rc1.jar;C:\Users\ys951\Desktop\JavaSETest\JavaEE\mybatis\lib\mybatis-3.2.7.jar;C:\Users\ys951\Desktop\JavaSETest\JavaEE\mybatis\lib\mysql-connector-java-5.1.7-bin.jar;C:\Users\ys951\Desktop\JavaSETest\JavaEE\mybatis\lib\slf4j-api-1.7.5.jar;C:\Users\ys951\Desktop\JavaSETest\JavaEE\mybatis\lib\slf4j-log4j12-1.7.5.jar" com.intellij.rt.execution.junit.JUnitStarter -ideVersion5 -junit4 cn.ys.test.Demo04,test1
before.....获取session
DEBUG [main] - Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - Opening JDBC Connection
DEBUG [main] - Created connection 157683534.
DEBUG [main] - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@9660f4e]
DEBUG [main] - ==> Preparing: SELECT * FROM user WHERE id = ?
DEBUG [main] - ==> Parameters: 1(Integer)
DEBUG [main] - <== Total: 1
User [id=1, username=王五, sex=2, birthday=null, address=null]
DEBUG [main] - ==> Preparing: INSERT INTO user (username,sex,birthday,address) VALUE (?,?,?,?)
DEBUG [main] - ==> Parameters: xxx(String), x(String), 2019-02-28 21:04:14.146(Timestamp), xx(String)
DEBUG [main] - <== Updates: 1
DEBUG [main] - Committing JDBC Connection [com.mysql.jdbc.JDBC4Connection@9660f4e]
DEBUG [main] - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@9660f4e]
DEBUG [main] - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@9660f4e]
DEBUG [main] - Returned connection 157683534 to pool.
Process finished with exit code 0