Spring中的FactoryBean及Mybatis中Mapper生成原理解析
2016-07-15 18:11
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一、Spring中的FactoryBean
首先,让我们先来看一看FactoryBean接口的定义,由此可见,FactoryBean也是用来创建bean的,它所创建的bean即为它后面所跟泛型对应的类型的实例。package org.springframework.beans.factory; public abstract interface FactoryBean<T> { public abstract T getObject() throws Exception; public abstract Class<?> getObjectType(); public abstract boolean isSingleton(); }
其中,getObject()方法返回创建的对象,getObjectType()方法返回创建的对象的类型,isSingleton()方法表示此对象是否为单例。
举个例子来看一下:
(1)User.java
先定义一个对象,此对象即为我们即将要实现的FactoryBean要创建的对象。
package com.alan.spring.extensionpoints; public class User { private String name; private Integer age; public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getAge() { return age; } public void setAge(Integer age) { this.age = age; } @Override public String toString() { return "name: "+name+", age: "+age; } }
(2)UserFactoryBean.java
创建上述对象的FactoryBean,实现了FactoryBean、InitializingBean、DisposableBean接口,其中InitializingBean接口主要是为了在UserFactoryBean的初始化方法afterPropertiesSet()中创建User的实例,DisposableBean接口主要与InitializingBean接口配对,并打印销毁日志。
package com.alan.spring.extensionpoints; import org.springframework.beans.factory.DisposableBean; import org.springframework.beans.factory.FactoryBean; import org.springframework.beans.factory.InitializingBean; public class UserFactoryBean implements FactoryBean<User>, InitializingBean, DisposableBean{ private User user; @Override public void destroy() throws Exception { System.err.println("user factory bean destroy"); } @Override public void afterPropertiesSet() throws Exception { user = new User(); user.setName("tangtong"); user.setAge(25); } @Override public User getObject() throws Exception { return user; } @Override public Class<?> getObjectType() { return user==null?User.class:user.getClass(); } @Override public boolean isSingleton() { return true; } @Override public String toString() { return "this is a user factory bean!"; } }
(3)dispatcher.xml
在spring配置文件中配置这个bean,注意,我们配置的是UserFactoryBean。
<bean id="user" class="com.alan.spring.extensionpoints.UserFactoryBean"></bean>
(4)UnitTest.java
从ApplicationContext中取出user,看它到底是什么。
package com.alan.test; import javax.annotation.Resource; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.context.ApplicationContext; import org.springframework.test.context.ContextConfiguration; import org.springframework.test.context.junit4.SpringJUnit4ClassRunner; @RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration(locations="classpath*:META-INF/dispatcher.xml") public class UnitTest { @Resource private ApplicationContext ctx; @Test public void test() { System.err.println("the user factory bean create the user : " + ctx.getBean("user")); //取出的是User的实例 System.err.println("the user factory bean is : " + ctx.getBean("&user")); //取出的是UserFactoryBean的实例 } }
(5)查看输出
如果不出意外,输出结果应该类似下面这样:
the user factory bean create the user : name: tangtong, age: 25 the user factory bean is : this is a user factory bean! user factory bean destroy
从上面的结果可以看到,从ApplicationContext中取出的”user”是User的实例,取出的”&user”却是UserFactoryBean的实例。
二、Mybatis中的Mapper生成原理解析
在Mybatis中如果配置单个Mapper,我们一般使用如下这种形式:<bean id="userMapper" class="org.mybatis.spring.mapper.MapperFactoryBean"> <property name="mapperInterface" value="org.mybatis.spring.sample.mapper.UserMapper"> <property name="sqlSessionFactory" ref="sqlSessionFactory"> </property></property></bean>
可见,这里的userMapper配置的是MapperFactoryBean类的实例,但是我们实际使用的过程中明明就是这么声明的啊:
@Autowired private UserMapper userMapper;
按照配置,它是怎么变成UserMapper的实例的呢?学习了上面关于Spring中的FactoryBean,你可能已经明白了其中一二,下面让我们来看看具体是怎么实现的。
(1)MapperFactoryBean.java
进入MapperFactoryBean源码。
package org.mybatis.spring.mapper; import org.apache.commons.logging.Log; import org.apache.ibatis.executor.ErrorContext; import org.apache.ibatis.session.Configuration; import org.apache.ibatis.session.SqlSession; import org.mybatis.spring.support.SqlSessionDaoSupport; import org.springframework.beans.factory.FactoryBean; import org.springframework.util.Assert; public class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> { private Class<T> mapperInterface; private boolean addToConfig = true; public MapperFactoryBean() { } public MapperFactoryBean(Class<T> mapperInterface) { this.mapperInterface = mapperInterface; } protected void checkDaoConfig() { super.checkDaoConfig(); Assert.notNull(this.mapperInterface, "Property 'mapperInterface' is required"); Configuration configuration = getSqlSession().getConfiguration(); if ((this.addToConfig) && (!configuration.hasMapper(this.mapperInterface))) { try { configuration.addMapper(this.mapperInterface); } catch (Exception e) { this.logger.error("Error while adding the mapper '" + this.mapperInterface + "' to configuration.", e); throw new IllegalArgumentException(e); } finally { ErrorContext.instance().reset(); } } } public T getObject() throws Exception { return getSqlSession().getMapper(this.mapperInterface); } public Class<T> getObjectType() { return this.mapperInterface; } public boolean isSingleton() { return true; } public void setMapperInterface(Class<T> mapperInterface) { this.mapperInterface = mapperInterface; } public Class<T> getMapperInterface() { return this.mapperInterface; } public void setAddToConfig(boolean addToConfig) { this.addToConfig = addToConfig; } public boolean isAddToConfig() { return this.addToConfig; } }
可见,MapperFactoryBean有一个属性叫mapperInterface,即上面的配置中传入的UserMapper接口。然后,找到它的getObject()方法,此方法返回的即是配置中userMapper对应的真实的实例,根据getObject()方法一层层进入。
(2)DefaultSqlSession.xml
public <T> T getMapper(Class<T> type) { return this.configuration.getMapper(type, this); }
(3)Configuration.java
public <T> T getMapper(Class<T> type, SqlSession sqlSession) { return this.mapperRegistry.getMapper(type, sqlSession); }
(4)MapperRegistry.java
public <T> T getMapper(Class<T> type, SqlSession sqlSession) { MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory) this.knownMappers.get(type); if (mapperProxyFactory == null) { throw new BindingException("Type " + type + " is not known to the MapperRegistry."); } try { return mapperProxyFactory.newInstance(sqlSession); } catch (Exception e) { throw new BindingException("Error getting mapper instance. Cause: " + e, e); } }
(5)MapperProxyFactory.java
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 newInstance(mapperProxy); }
到此为止,可见在newInstance(mapperProxy)方法中,最后调用Java原生的代理类Proxy创建了一个mapperInterface接口(即我们所传的UserMapper接口)的实例,所以,我们在代码中可以直接注入UserMapper的实例。
最后,我们可以在单元测试中打印出userMapper的路径:
System.err.println(userInfoMapper.getClass().getName());
得到的结果类似下面这样:
com.sun.proxy.$Proxy28
其中,$Proxy28表示这是一个动态生成的代理类,它继承自java.lang.reflect.Proxy类。
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