mybatis教程1【基本使用】

阳光穿透心脏的1/2处 2022-02-14 05:09 252阅读 0赞

## 什么是MyBatis？ ##

MyBatis 是一款优秀的持久层框架，它支持定制化 SQL、存储过程以及高级映射。MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。MyBatis 可以使用简单的 XML 或注解来配置和映射原生信息，将接口和 Java 的 POJOs(Plain Old Java Objects,普通的 Java对象)映射成数据库中的记录。

## mybatis和hibernate的比较 ##

<table> 
 <thead> 
  <tr> 
   <th>mybatis</th> 
   <th>hibernate</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>半自动ORM框架</td> 
   <td>全自动ORM框架</td> 
  </tr> 
  <tr> 
   <td>必须写sql</td> 
   <td>可以不写sql</td> 
  </tr> 
  <tr> 
   <td>事务处理</td> 
   <td>事务处理</td> 
  </tr> 
  <tr> 
   <td>缓存都支持</td> 
   <td>缓存都支持，二级缓存比mybatis更好</td> 
  </tr> 
 </tbody> 
</table>

## 入门案例 ##

## 创建maven工程，添加对应jar包 ##

<dependencies>
    	<dependency>
    		<groupId>org.mybatis</groupId>
    		<artifactId>mybatis</artifactId>
    		<version>3.4.6</version>
    	</dependency>
    	<dependency>
    		<groupId>mysql</groupId>
    		<artifactId>mysql-connector-java</artifactId>
    		<version>5.1.27</version>
    	</dependency>
    </dependencies>

## 创建全局配置文件 ##

该配置文件包含了对MyBatis系统的核心设置，包含获取数据库连接实例的数据源，和决定事务作用域和控制方式的事务功能。XML配置文件的详细内容后面在讨论，这里先给出一个简单案例

<?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.jdbc.Driver"/>
            <property name="url" value="jdbc:mysql://localhost:3306/pms?characterEncoding=utf-8"/>
            <property name="username" value="root"/>
            <property name="password" value="123456"/>
          </dataSource>
        </environment>
      </environments>
    </configuration>

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMwOTg0NTYx_size_16_color_FFFFFF_t_70]

## 定义User对像 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMwOTg0NTYx_size_16_color_FFFFFF_t_70 1]

## 创建映射文件 ##

<?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="dpb">
    	<insert id="addUser" parameterType="com.sxt.dao.User">
    		insert into t_user(name,age)values(#{name},#{age})
    	</insert>
    	<delete id="deleteUserById" parameterType="java.lang.Integer"> 
    		delete from t_user where id=#{id}    
    	</delete>
    	<update id="updateUserById" parameterType="com.sxt.dao.User"> 
    		update t_user set name = #{name} where id=#{id}    
    	</update>
    	<select id="getUserById" parameterType="java.lang.Integer" resultType="com.sxt.dao.User"> 
    		select * from t_user where id=#{id}   
    	</select>
    </mapper>

## 将配置文件添加到主配置文件中 ##

## 测试查询 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMwOTg0NTYx_size_16_color_FFFFFF_t_70 2]

@Test
    	public void add() throws IOException {
    		// 1.通过Resources对象加载配置文件
    		InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
    		// 2.获取SqlSessionFactory对象
    		SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream );
    		// 3.通过SqlSessionFactory对象获取SQLSession对象
    		SqlSession session = factory.openSession();
    		User user = new User();
    		user.setName("dpb");
    		user.setAge(22);
    		// dpb.addUser  是映射文件中 namespace的内容加 id的内容，定位要执行的SQL
    		int count = session.insert("dpb.addUser", user);
    		System.out.println("影响的行数："+count);
    		// 需要显示的提交
    		session.commit();
    		session.close();
    	}
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMwOTg0NTYx_size_16_color_FFFFFF_t_70 3]

## 查询，修改，删除操作 ##

public class Test02 {
    	private SqlSession sqlSession;
    
    	@Before
    	public void before() throws IOException {
    		// 1. 加载配置文件
    		InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
    		// 2. 根据配置文件获取一个SqlSessionFactory对象，这个对象相当于连接工厂
    		SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
    		// 3. 获取一个sqlsession，sqlsession类似于之前学过的Connection
    		sqlSession = sqlSessionFactory.openSession();
    	}
    
    	@After
    	public void after() {
    		sqlSession.commit();
    		sqlSession.close();
    	}
    
    	@Test
    	public void test1() {
    		User user = new User();
    		user.setId(7);
    		user.setName("里斯1");
    		int update = sqlSession.update("dpb.updateUserById", user);
    		System.out.println(update);
    	}
    
    	@Test
    	public void test2() {
    		int delete = sqlSession.delete("dpb.deleteUserById", 7);
    		System.out.println(delete);
    	}
    
    	@Test
    	public void test3() {
    		User user = (User) sqlSession.selectOne("dpb.getUserById", 8);
    		System.out.println(user);
    	}
    
    }

## 案例优化 ##

## 获取SqlSessionFactory ##

SqlSessionFactory在一个服务中只需要有一个实例就可以了，此时可以通过单例的模式获取

/**
     * 工具类  对外提供SqlSessionFactory的单例对象
     * @author dengp
     *
     */
    public class DbUtils {
    
    	private static  SqlSessionFactory factory ;
    	
    	public static SqlSessionFactory getInstace(){
    		if(factory ==null){
    			InputStream in = null;
    			try{
    				in = Resources.getResourceAsStream("mybatis-config.xml");
    			}catch(Exception e){
    				e.printStackTrace();
    			}
    			synchronized (DbUtils.class) {
    				if(factory ==null){
    					factory = new SqlSessionFactoryBuilder().build(in);
    				}
    			}
    		}
    		return factory;
    	}
    }

## 整理CRUD操作 ##

public interface UserMapper {
    
    	public int addUser(User user);
    	
    	public int updateById(User user);
    	
    	public int deleteById(int id);
    	
    	public User queryById(int id);
    }

public class UserDao implements UserMapper {
    
    	@Override
    	public int addUser(User user) {
    		
    		return DBUtils.getInstall().openSession().insert("com.sxt.dao.UserMapper.addUser", user);
    	}
    
    	@Override
    	public int updateById(User user) {
    		// TODO Auto-generated method stub
    		return DBUtils.getInstall().openSession().update("com.sxt.dao.UserMapper.updateById", user);
    	}
    
    	@Override
    	public int deleteById(int id) {
    		// TODO Auto-generated method stub
    		return DBUtils.getInstall().openSession().delete("com.sxt.dao.UserMapper.deleteById", id);
    	}
    
    	@Override
    	public User queryById(int id) {
    		// TODO Auto-generated method stub
    		return DBUtils.getInstall().openSession().selectOne("com.sxt.dao.UserMapper.queryById", 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="com.sxt.dao.UserMapper">
    	<insert id="addUser" parameterType="com.sxt.bean.User">
    		insert into t_user(name,age)values(#{name},#{age})		
    	</insert>
    	
    	<delete id="deleteById" parameterType="java.lang.Integer">
    		delete from t_user where id=#{id}
    	</delete>
    	
    	<update id="updateById" parameterType="com.sxt.bean.User">
    		update t_user 
    		set name=#{name},age=#{age}
    		where id=#{id}
    	</update>
    	
    	<select id="queryById" parameterType="java.lang.Integer"
    		resultType="com.sxt.bean.User">
    		select * from t_user where id=#{id}
    	</select>
    </mapper>

/**
     * 代理方式
     */
    @Test
    public void test(){
    	UserMapper mapper = (UserMapper) Proxy.newProxyInstance(UserMapper.class.getClassLoader()
    			, new Class[]{UserMapper.class},new InvocationHandler() {
    				@Override
    				public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    					System.out.println(UserMapper.class.getName()+"."+method.getName());
    					Object id = null;
    					for (Object object : args) {
    						System.out.println(object);
    						id = object;
    					}
    					
    					// 实现逻辑
    					return DBUtils.getInstall().openSession().selectOne(UserMapper.class.getName()+"."+method.getName(), id);
    				}
    			} );
    	System.out.println(mapper.queryById(5));
    }

![在这里插入图片描述][20190425201137132.]

## mybatis接口的使用方式 ##

通过前面UserDao的设计，可以发现，UserDao中的代码都是模板化代码，都可以通过配置自动生成，因此，在实际开发中，Mapper可以按照如下方式设计

## 定义Mapper接口 ##

Mapper接口中，只需要声明方法名，方法参数、方法返回等信息

public interface UserMapper {
    
    	public int addUser(User user);
    }

## 定义映射文件 ##

<?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.sxt.dao.UserMapper">
    	
    	<insert id="addUser" parameterType="com.sxt.bean.User">
    		insert into t_user(name,age)values(#{name},#{age})
    	</insert>
    </mapper>

## 测试 ##

@Test
    public void add() throws IOException {
    	// 1.通过Resources对象加载配置文件
    	InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
    	// 2.获取SqlSessionFactory对象
    	SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream );
    	// 3.通过SqlSessionFactory对象获取SQLSession对象
    	SqlSession session = factory.openSession();
    	User user = new User();
    	user.setName("dpb");
    	user.setAge(22);
    	//通过Java动态代理自动提供了UserMapper的实现类
    	UserMapper mapper = session.getMapper(UserMapper.class);
    	int count = mapper.addUser(user);
    	System.out.println("影响的行数:"+count);
    	session.commit();
    }

注意：  
使用mapper接口方式必须满足:

<table> 
 <thead> 
  <tr> 
   <th>序号</th> 
   <th>注意点</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>1</td> 
   <td>映射文件的namespace的值必须是接口的全路径名称 比如：com.dpb.dao.UserMapper</td> 
  </tr> 
  <tr> 
   <td>2</td> 
   <td>接口中的方法名在映射文件中必须有一个id值与之对应。</td> 
  </tr> 
  <tr> 
   <td>3</td> 
   <td>映射文件的名称必须和接口的名称一致</td> 
  </tr> 
 </tbody> 
</table>

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[20190425201137132.]: /images/20220214/9c476d30025c4d11adbce67796a51a93.png