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mybatis入门基础(二)----原始dao的开发和mapper代理开发

阅读目录

　　承接上一篇 mybatis 入门基础 (一)

　　看过上一篇的朋友，肯定可以看出，里面的 MybatisService 中存在大量的重复代码，看起来不是很清楚，但第一次那样写，是为了解 mybatis 的执行步骤，先苦后甜嘛！

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一: 原始 dao 开发方法

　　概要：1. 在上篇中搭建好的框价中编写 dao 接口和 dao 实现类

　　　　　2. 向 dao 接口实现类中注入 SqlSessionFactory, 在方法体内通过 SqlSessionFactory 创建 sqlSession.

  • DAO 接口类 UserDAO.java　　
package com.mybatis.dao;
import java.util.List;
import com.mybatis.entity.User;
/**
 * 
 * @ClassName: UserDAO
 * @Description: TODO(用户管理 DAO 接口)
 * @author warcaft
 * @date 2015-6-27 下午 10:23:42
 * 
 */
public interface UserDAO {
    /** 根据 ID 查询用户信息*/
    public User findUserById(Integer id);

</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">根据用户名称模糊查询用户信息</span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span> List&lt;User&gt;<span style="color: rgba(0, 0, 0, 1)">  findUserByName(String username);

</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)"> 添加用户</span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> insertUser(User user);

</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)"> 根据ID删除用户</span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> deleteUser(Integer id);

</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)"> 根据ID更新用户</span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> updateUser(User user);



}

  • dao 实现类 UserDaoImpl.java　
package com.mybatis.dao;
import java.util.List;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import com.mybatis.entity.User;
/**
 * 
 * @ClassName: UserDaoImpl
 * @Description: TODO(用户管理接口的实现类)
 * @author warcaft
 * @date 2015-6-27 下午 10:29:35
 * 
 */
public class UserDaoImpl implements UserDAO {
    private SqlSessionFactory sqlSessionFactory;
    // 需要向 dao 实现类中注入 SqlSessionFactory
    // 通过构造方法注入
    public UserDaoImpl(SqlSessionFactory sqlSessionFactory) {
        this.sqlSessionFactory = sqlSessionFactory;
    }

@Override
</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> User findUserById(Integer id) {
    SqlSession sqlSession </span>=<span style="color: rgba(0, 0, 0, 1)"> sqlSessionFactory.openSession();
    User user </span>= sqlSession.selectOne("test.findUserById"<span style="color: rgba(0, 0, 0, 1)">, id);
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 释放资源</span>



        sqlSession.close();
return user;
}


@Override
</span><span style="color: rgba(0, 0, 255, 1)">public</span> List&lt;User&gt;<span style="color: rgba(0, 0, 0, 1)"> findUserByName(String username) {
    SqlSession sqlSession </span>=<span style="color: rgba(0, 0, 0, 1)"> sqlSessionFactory.openSession();
    List</span>&lt;User&gt; list =<span style="color: rgba(0, 0, 0, 1)"> sqlSession
            .selectList(</span>"test.findUserByName"<span style="color: rgba(0, 0, 0, 1)">, username);

    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 提交事务</span>



        sqlSession.commit();
// 释放资源
        sqlSession.close();
return list;
}


@Override
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> insertUser(User user) {
    SqlSession sqlSession </span>=<span style="color: rgba(0, 0, 0, 1)"> sqlSessionFactory.openSession();
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 执行插入操作</span>
    sqlSession.insert("test.insertUser"<span style="color: rgba(0, 0, 0, 1)">, user);
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 提交事务</span>



        sqlSession.commit();
// 释放资源
        sqlSession.close();
}


@Override
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> deleteUser(Integer id) {
    SqlSession sqlSession </span>=<span style="color: rgba(0, 0, 0, 1)"> sqlSessionFactory.openSession();
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 执行插入操作</span>
    sqlSession.delete("test.deleteUser"<span style="color: rgba(0, 0, 0, 1)">, id);
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 提交事务</span>



        sqlSession.commit();
// 释放资源
        sqlSession.close();
}


@Override
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> updateUser(User user) {
    SqlSession sqlSession </span>=<span style="color: rgba(0, 0, 0, 1)"> sqlSessionFactory.openSession();
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 执行插入操作</span>
    sqlSession.update("test.updateUser"<span style="color: rgba(0, 0, 0, 1)">, user);
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 提交事务</span>



        sqlSession.commit();
// 释放资源
        sqlSession.close();
}


}

  • JunitTest 测试 UserDaoImplTest.java
package com.mybatis.dao.test;
import java.io.InputStream;
import java.util.Date;
import java.util.List;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;

import com.mybatis.dao.UserDaoImpl;
import com.mybatis.entity.User;


public class UserDaoImplTest {


</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> SqlSessionFactory sqlSessionFactory;

@Before
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span> setUp() <span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> Exception {
    String resource </span>= "SqlMapConfig.xml"<span style="color: rgba(0, 0, 0, 1)">;
    InputStream inputStream </span>=<span style="color: rgba(0, 0, 0, 1)"> Resources.getResourceAsStream(resource);
    sqlSessionFactory </span>= <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> SqlSessionFactoryBuilder().build(inputStream);
}

@Test
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> findUserByIdTest() {
    UserDaoImpl userDao </span>= <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> UserDaoImpl(sqlSessionFactory);
    User user </span>= userDao.findUserById(1<span style="color: rgba(0, 0, 0, 1)">);
    System.out.println(user);
}

@Test
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> findUserByNameTest() {
    UserDaoImpl userDao </span>= <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> UserDaoImpl(sqlSessionFactory);
    List</span>&lt;User&gt; list = userDao.findUserByName("小"<span style="color: rgba(0, 0, 0, 1)">);
    System.out.println(list);
}

@Test
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> insertUserTest() {
    UserDaoImpl userDao </span>= <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> UserDaoImpl(sqlSessionFactory);
    User user </span>= <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> User();
    user.setUsername(</span>"张三丰"<span style="color: rgba(0, 0, 0, 1)">);
    user.setSex(</span>"1"<span style="color: rgba(0, 0, 0, 1)">);
    user.setBirthday(</span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> Date());
    user.setAddress(</span>"武当山"<span style="color: rgba(0, 0, 0, 1)">);
    userDao.insertUser(user);
}

@Test
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> deleteUserTest() {
    UserDaoImpl userDao </span>= <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> UserDaoImpl(sqlSessionFactory);
    userDao.deleteUser(</span>8<span style="color: rgba(0, 0, 0, 1)">);
}

@Test
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> updateUserTest() {
    UserDaoImpl userDao </span>= <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> UserDaoImpl(sqlSessionFactory);
    User user </span>= <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> User();
    user.setId(</span>1<span style="color: rgba(0, 0, 0, 1)">);
    user.setUsername(</span>"王六"<span style="color: rgba(0, 0, 0, 1)">);
    user.setSex(</span>"2"<span style="color: rgba(0, 0, 0, 1)">);
    user.setAddress(</span>"天津"<span style="color: rgba(0, 0, 0, 1)">);
    user.setBirthday(</span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> Date());
    userDao.updateUser(user);
}



}

才上面的代码可以看出，比起之前那个 MybatisService.java 类里面的内容稍微清晰了点吧。但依然存在以下几个问题：

　　1.dao 接口中存在大量模版方法，能否把这些代码提出来，减少我们的工作量

　　2. 调用 sqlSession 方法时将 statement 的 id 硬编码了

　　3. 调用 sqlSession 传入的变量，由于 sqlSession 方法使用泛型，即使变量类型传入错误，在编译阶段也不报错，不利于程序开发。

所以我们带着这几个问题看看 mapper 代理开发的方法，是否能解决这些问题呢？

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二：mapper 代理方法 (只需要 mapper 接口，相当于 dao 接口)

1. 概要：(1). 编写 XXXmapper.xml 的映射文件

　　　　(2). 编写 mapper 接口需要遵循一些开发规范，mybatis 可以自动生成 mapper 接口实现类代理对象。

2. 开发规范：

　　(1). 在 XXXmapper.xml 中 namespace 等于 mapper 接口地址；

　　

      (2).XXXmapper.java 接口中的方法和 mapper.xml 中的 statement 的 Id 一致。

　　(3).mapper.java 接口中的方法输入参数和 mapper.xml 中 statement 的 parameterType 指定的类型一致。

　　(4).mapper.java 接口中的方法的返回值类型和 mapper.xml 中 statement 的 resultType 指定的类型一致。

　　

　　

小结：以上的开发规范主要是对下面的代码进行统一生成　

    SqlSession sqlSession = sqlSessionFactory.openSession();
    User user = sqlSession.selectOne("test.findUserById", id);
　　......

3.UserMapper.java 类代码

package com.mybatis.mapper;

import java.util.List;


import com.mybatis.entity.User;


/**
*


    

  • @ClassName: UserDAO
    • 

  • @Description: TODO(用户管理 mapper 接口)
    • 

  • @author warcaft
    • 

  • @date 2015-6-27 下午 10:23:42
    • 

  • 



/
public interface UserMapper {
/** 根据 ID 查询用户信息 /
public User findUserById(int id);


</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)"> 根据用户名称模糊查询用户信息 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span> List&lt;User&gt;<span style="color: rgba(0, 0, 0, 1)"> findUserByName(String username);

</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)"> 添加用户 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> insertUser(User user);

</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)"> 根据ID删除用户 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> deleteUser(Integer id);

</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)"> 根据ID更新用户 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> updateUser(User user);



}

View Code

4. 将原来的 User.xml 拷贝修改名称为 UserMapper.xml, 只需修改此行代码即可

<!-- namespace 命名空间, 作用就是对 sql 进行分类化的管理, 理解为 sql 隔离
    注意: 使用 mapper 代理开发时，namespace 有特殊作用,namespace 等于 mapper 接口地址
 -->
<mapper namespace="com.mybatis.mapper.UserMapper">

5. 在 SqlMapConfig.xml 中加载 UserMapper.xml

<!-- 加载映射文件 -->
    <mappers>
        <mapper resource="sqlmap/User.xml"/>
        <mapper resource="mapper/UserMapper.xml"/>
    </mappers>

6.Junit 测试 UserMapperTest.java

package com.mybatis.dao.test;

import java.io.InputStream;
import java.util.Date;
import java.util.List;


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.Before;
import org.junit.Test;


import com.mybatis.entity.User;
import com.mybatis.mapper.UserMapper;


public class UserMapperTest {


</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> SqlSessionFactory sqlSessionFactory;

</span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 此方法是在执行findUserByIdTest之前执行</span>



    @Before
public void setUp() throws Exception {
String resource = "SqlMapConfig.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
// 创建 SqlSessionFcatory
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
}


@Test
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> testFindUserById() {
    SqlSession sqlSession </span>=<span style="color: rgba(0, 0, 0, 1)"> sqlSessionFactory.openSession();
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 创建Usermapper对象，mybatis自动生成mapper代理对象</span>
    UserMapper mapper = sqlSession.getMapper(UserMapper.<span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)">);
    User user </span>= mapper.findUserById(1<span style="color: rgba(0, 0, 0, 1)">);
    System.out.println(user);
    sqlSession.close();
}

@Test
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> testFindUserByName() {
    SqlSession sqlSession </span>=<span style="color: rgba(0, 0, 0, 1)"> sqlSessionFactory.openSession();
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 创建Usermapper对象，mybatis自动生成mapper代理对象</span>
    UserMapper mapper = sqlSession.getMapper(UserMapper.<span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)">);
    List</span>&lt;User&gt; list = mapper.findUserByName("小"<span style="color: rgba(0, 0, 0, 1)">);
    System.out.println(list);
    sqlSession.close();
}

@Test
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> testDeleteUser() {
    SqlSession sqlSession </span>=<span style="color: rgba(0, 0, 0, 1)"> sqlSessionFactory.openSession();
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 创建Usermapper对象，mybatis自动生成mapper代理对象</span>
    UserMapper mapper = sqlSession.getMapper(UserMapper.<span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)">);
    mapper.deleteUser(</span>6<span style="color: rgba(0, 0, 0, 1)">);
    sqlSession.commit();
    sqlSession.close();
}

@Test
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> testInsertUser() {
    SqlSession sqlSession </span>=<span style="color: rgba(0, 0, 0, 1)"> sqlSessionFactory.openSession();
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 创建Usermapper对象，mybatis自动生成mapper代理对象</span>
    User user = <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> User();
    user.setUsername(</span>"者别"<span style="color: rgba(0, 0, 0, 1)">);
    user.setSex(</span>"1"<span style="color: rgba(0, 0, 0, 1)">);
    user.setAddress(</span>"蒙古乞颜部落"<span style="color: rgba(0, 0, 0, 1)">);
    user.setBirthday(</span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> Date());
    UserMapper mapper </span>= sqlSession.getMapper(UserMapper.<span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)">);
    mapper.insertUser(user);
    sqlSession.commit();
    sqlSession.close();
}

@Test
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> testUpdateUser() {
    SqlSession sqlSession </span>=<span style="color: rgba(0, 0, 0, 1)"> sqlSessionFactory.openSession();
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 创建Usermapper对象，mybatis自动生成mapper代理对象</span>
    User user = <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> User();
    user.setId(</span>11);<span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">必须设置Id</span>
    user.setUsername("神箭手者别"<span style="color: rgba(0, 0, 0, 1)">);
    user.setSex(</span>"1"<span style="color: rgba(0, 0, 0, 1)">);
    user.setAddress(</span>"蒙古乞颜部落"<span style="color: rgba(0, 0, 0, 1)">);
    user.setBirthday(</span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> Date());
    UserMapper mapper </span>= sqlSession.getMapper(UserMapper.<span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)">);
    mapper.updateUser(user);
    sqlSession.commit();
    sqlSession.close();
}



}

View Code

7. 小结

　　(1). 代理对象内部调用 selectOne()和 selectList(): 如果 mapper 对象返回单个 pojo 对象 (非集合对象) 代理对象内部通过 selectOne 查询数据库，如果 mapper 方法返回集合对象，代理对象内部通过 selectList 查询数据库。

　　(2).mapper 接口中的方法参数只能有一个是否影响系统开发：

　　mapper 接口方法参数只能有一个，系统是否不利于维护？

　　回答：系统框架中，dao 层的代码是被业务层公用的。机试 mapper 接口只有一个参数，可以使用包装类型的 pojo 满足不同的业务方法的需求。