SqlSessionFactoryBean注入分析

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我是靠谱客的博主落寞诺言，最近开发中收集的这篇文章主要介绍SqlSessionFactoryBean注入分析，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

通过xml装配mybatis的SqlSessionTemplate时通常采用如下方法：


<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="dataSource" ref="dataSource"/>
<property name="mapperLocations" value="classpath:*-mapper.xml"/>
</bean>
<bean id="sqlSessionTemplate" class="org.mybatis.spring.SqlSessionTemplate">
<constructor-arg index="0" ref="sqlSessionFactory"/>
</bean>

然而SqlSessionTemplate中需要的是SqlSessionFactory，而不是SqlSessionFactoryBean。这个是因为SqlSessionFactoryBean继承了FactoryBean<SqlSessionFactory>。

在spring装配SqlSessionFactoryBean的时候会从FactoryBean的getObject()方法中获取SqlSessionFactory，因为工厂Bean跟普通Bean不同，其返回的对象不是指定类的一个实例，其返回的是该工厂Bean的getObject方法所返回的对象。

补充一点：SqlSessionFactoryBean还继承了InitializingBean, ApplicationListener<ApplicationEvent>

InitializingBean的初始化方法就是afterPropertiesSet()，这个方法的执行之前顾名思义，在所有属性都set了之后就执行，所以在mabatis中会检查dataSource和sqlSessionFactoryBuilder，如下：


public void afterPropertiesSet() throws Exception {
notNull(dataSource, "Property 'dataSource' is required");
notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");
this.sqlSessionFactory = buildSqlSessionFactory();
}

InitializingBean和init-method：

但是，一但该bean实现了InitializingBean接口，那么这个bean的代码就和Spring耦合到一起了。这样也不好，所以可以使用Spring提供的init-method的功能来执行一个bean 子定义的初始化方法，这样就解耦了。当然，InitializingBean和init-method可以一起使用，Spring会先处理InitializingBean再处理init-method，如下：

/**
* Give a bean a chance to react now all its properties are set,
* and a chance to know about its owning bean factory (this object).
* This means checking whether the bean implements InitializingBean or defines
* a custom init method, and invoking the necessary callback(s) if it does.
* @param beanName the bean name in the factory (for debugging purposes)
* @param bean the new bean instance we may need to initialize
* @param mbd the merged bean definition that the bean was created with
* (can also be {@code null}, if given an existing bean instance)
* @throws Throwable if thrown by init methods or by the invocation process
* @see #invokeCustomInitMethod
*/
protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd)
throws Throwable {
boolean isInitializingBean = (bean instanceof InitializingBean);
if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
if (logger.isDebugEnabled()) {
logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
}
if (System.getSecurityManager() != null) {
try {
AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
@Override
public Object run() throws Exception {
((InitializingBean) bean).afterPropertiesSet();
return null;
}
}, getAccessControlContext());
}
catch (PrivilegedActionException pae) {
throw pae.getException();
}
}
else {
((InitializingBean) bean).afterPropertiesSet();
}
}
if (mbd != null) {
String initMethodName = mbd.getInitMethodName();
if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
!mbd.isExternallyManagedInitMethod(initMethodName)) {
invokeCustomInitMethod(beanName, bean, mbd);
}
}
}

/**
* Invoke the specified custom init method on the given bean.
* Called by invokeInitMethods.
* <p>Can be overridden in subclasses for custom resolution of init
* methods with arguments.
* @see #invokeInitMethods
*/
protected void invokeCustomInitMethod(String beanName, final Object bean, RootBeanDefinition mbd) throws Throwable {
String initMethodName = mbd.getInitMethodName();
final Method initMethod = (mbd.isNonPublicAccessAllowed() ?
BeanUtils.findMethod(bean.getClass(), initMethodName) :
ClassUtils.getMethodIfAvailable(bean.getClass(), initMethodName));
if (initMethod == null) {
if (mbd.isEnforceInitMethod()) {
throw new BeanDefinitionValidationException("Couldn't find an init method named '" +
initMethodName + "' on bean with name '" + beanName + "'");
}
else {
if (logger.isDebugEnabled()) {
logger.debug("No default init method named '" + initMethodName +
"' found on bean with name '" + beanName + "'");
}
// Ignore non-existent default lifecycle methods.
return;
}
}
if (logger.isDebugEnabled()) {
logger.debug("Invoking init method
'" + initMethodName + "' on bean with name '" + beanName + "'");
}
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
@Override
public Object run() throws Exception {
ReflectionUtils.makeAccessible(initMethod);
return null;
}
});
try {
AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
@Override
public Object run() throws Exception {
initMethod.invoke(bean);
return null;
}
}, getAccessControlContext());
}
catch (PrivilegedActionException pae) {
InvocationTargetException ex = (InvocationTargetException) pae.getException();
throw ex.getTargetException();
}
}
else {
try {
ReflectionUtils.makeAccessible(initMethod);
//反射执行init-method的方法
initMethod.invoke(bean);
}
catch (InvocationTargetException ex) {
throw ex.getTargetException();
}
}
}

afterPropertiesSet是直接执行的，而init-method是通过反射执行的。afterPropertiesSet效率更高，init-method耦合更低。

ApplicationListener<ApplicationEvent>

其实这就是标准的Oberver设计模式

另外，关于在spring容器初始化bean和销毁前所做的操作定义方式有三种：
第一种：通过@PostConstruct 和 @PreDestroy 方法实现初始化和销毁bean之前进行的操作
第二种是：通过在xml中定义init-method 和 destory-method方法
第三种是：通过bean实现InitializingBean和 DisposableBean接口