Mybatis系列十八：源码解析-getMapper

喜欢ヅ旅行 2022-02-13 07:27 286阅读 0赞

mybatis全局配置文件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" />
    			<dataSource type="POOLED">
    				<property name="driver" value="com.mysql.jdbc.Driver" />
    				<property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
    				<property name="username" value="root" />
    				<property name="password" value="root" />
    			</dataSource>
    		</environment>
    	</environments>
    	
    	<mappers>
    		<mapper resource="EmployeeMapper.xml" />
    	</mappers>
    </configuration>

mapper映射文件EmployeeMapper.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.atguigu.mybatis.dao.EmployeeMapper">
    
    
    	<select id="getEmpById" resultType="com.atguigu.mybatis.bean.Employee">
    		select id,last_name lastName,email,gender from tbl_employee where id = #{id}
    	</select>
    </mapper>

测试方法：

/**
    	 * 1、获取sqlSessionFactory对象
    	 * 		解析文件的每一个信息保存在Configuration中，然后返回包含Configuration的DefaultSqlSession。
    	 * 		MappedStatement：代表一个增删改查的详细信息。
    	 * 2、获取sqlSession对象
    	 * 		 返回一个SqlSession 的实现类DefaultSqlSession对象。
    	 * 		 这一步会创建Executor 对象。
    	 * 3、获取接口的代理对象（MapperProxy）
    	 *  	getMapper，使用MapperProxyFactory创建一个MapperProxy的代理对象。
    	 *  	代理对象里面包含了，DefaultSqlSession（Executor ）
    	 * 4、执行增删改查方法
    	 * @throws IOException
    	 */
    	@Test
    	public void test() throws IOException {
    		//1、获取sqlSessionFactory对象
    		String resource = "mybatis-config.xml";
    		InputStream inputStream = Resources.getResourceAsStream(resource);
    		SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    		//2、获取sqlSession对象
    		SqlSession openSession = sqlSessionFactory.openSession();
    		try {
    			//3、获取接口的代理对象
    			//会为接口自动创建一个代理对象，代理对象去执行增删改查方法
    			EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
    			//4、执行增删改查方法
    			Employee employee = mapper.getEmpById(1);
    			System.out.println(mapper);
    			System.out.println(employee);
    		} finally {
    			openSession.close();
    		}
    	}

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源码解析：  
三、获取到接口的代理对象

EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);

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1、DefaultSqlSession

public <T> T getMapper(Class<T> type) {
            return this.configuration.getMapper(type, this);
        }

2、Configuration

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
            return this.mapperRegistry.getMapper(type, sqlSession);
        }

3、MapperRegistry

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    		//获取Mapper的代理工厂MapperProxyFactory
            MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory)this.knownMappers.get(type);
            if (mapperProxyFactory == null) {
                throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
            } else {
                try {
                	//传入sqlSession创建一个MapperProxy
                    return mapperProxyFactory.newInstance(sqlSession);
                } catch (Exception var5) {
                    throw new BindingException("Error getting mapper instance. Cause: " + var5, var5);
                }
            }
        }

4、MapperProxyFactory

//根据传入的MapperProxy创建一个MapperProxy的代理对象
     	protected T newInstance(MapperProxy<T> mapperProxy) {
            return Proxy.newProxyInstance(this.mapperInterface.getClassLoader(), new Class[]{this.mapperInterface}, mapperProxy);
        }
        
    	public T newInstance(SqlSession sqlSession) {
            MapperProxy<T> mapperProxy = new MapperProxy(sqlSession, this.mapperInterface, this.methodCache);
            return this.newInstance(mapperProxy);
        }

5、MapperProxy

//MapperProxy实现了InvocationHandler。InvocationHandler是Jdk用来创建动态代理的
    public class MapperProxy<T> implements InvocationHandler, Serializable {
        private static final long serialVersionUID = -6424540398559729838L;
        private final SqlSession sqlSession;
        private final Class<T> mapperInterface;
        private final Map<Method, MapperMethod> methodCache;
    
        public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) {
            this.sqlSession = sqlSession;
            this.mapperInterface = mapperInterface;
            this.methodCache = methodCache;
        }
    
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            if (Object.class.equals(method.getDeclaringClass())) {
                try {
                    return method.invoke(this, args);
                } catch (Throwable var5) {
                    throw ExceptionUtil.unwrapThrowable(var5);
                }
            } else {
                MapperMethod mapperMethod = this.cachedMapperMethod(method);
                return mapperMethod.execute(this.sqlSession, args);
            }
        }
    
        private MapperMethod cachedMapperMethod(Method method) {
            MapperMethod mapperMethod = (MapperMethod)this.methodCache.get(method);
            if (mapperMethod == null) {
                mapperMethod = new MapperMethod(this.mapperInterface, method, this.sqlSession.getConfiguration());
                this.methodCache.put(method, mapperMethod);
            }
    
            return mapperMethod;
        }
    }

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