Spring中初始化方法的执行顺序
首先通过一个例子来看其顺序
/**
* 调用顺序 init2(PostConstruct注解) --> afterPropertiesSet(InitializingBean接口) --> init3(init-method配置)
*/
public class Test implements InitializingBean {
public void init3(){
System.out.println("init3");
}
@PostConstruct
public void init2(){
System.out.println("init2");
}
@Override
public void afterPropertiesSet() throws Exception {
System.out.println("afterPropertiesSet");
}
}
配置
<context:annotation-config/>
<bean class="com.cyy.spring.lifecycle.Test" id="test" init-method="init3"/>
通过运行,我们得出其执行顺序为init2(PostConstruct注解) --> afterPropertiesSet(InitializingBean接口) --> init3(init-method配置)。但是为什么是这个顺序呢?我们可以通过分析其源码得出结论。
首先在解析配置文件的时候,碰到context:annotation-config/自定义标签会调用其自定义解析器,这个自定义解析器在哪儿呢?在spring-context的spring.handlers中有配置
http\://www.springframework.org/schema/context=org.springframework.context.config.ContextNamespaceHandler
我们进入这个类看
public class ContextNamespaceHandler extends NamespaceHandlerSupport {
@Override
public void init() {
registerBeanDefinitionParser("property-placeholder", new PropertyPlaceholderBeanDefinitionParser());
registerBeanDefinitionParser("property-override", new PropertyOverrideBeanDefinitionParser());
registerBeanDefinitionParser("annotation-config", new AnnotationConfigBeanDefinitionParser());
registerBeanDefinitionParser("component-scan", new ComponentScanBeanDefinitionParser());
registerBeanDefinitionParser("load-time-weaver", new LoadTimeWeaverBeanDefinitionParser());
registerBeanDefinitionParser("spring-configured", new SpringConfiguredBeanDefinitionParser());
registerBeanDefinitionParser("mbean-export", new MBeanExportBeanDefinitionParser());
registerBeanDefinitionParser("mbean-server", new MBeanServerBeanDefinitionParser());
}
}
我们看到了annotation-config了,我们只关心这个标签,那我们就进入AnnotationConfigBeanDefinitionParser类中,看它的parse方法
public BeanDefinition parse(Element element, ParserContext parserContext) {
Object source = parserContext.extractSource(element);
// Obtain bean definitions for all relevant BeanPostProcessors.
Set<BeanDefinitionHolder> processorDefinitions =
AnnotationConfigUtils.registerAnnotationConfigProcessors(parserContext.getRegistry(), source);
// Register component for the surrounding element.
CompositeComponentDefinition compDefinition = new CompositeComponentDefinition(element.getTagName(), source);
parserContext.pushContainingComponent(compDefinition);
// Nest the concrete beans in the surrounding component.
for (BeanDefinitionHolder processorDefinition : processorDefinitions) {
parserContext.registerComponent(new BeanComponentDefinition(processorDefinition));
}
// Finally register the composite component.
parserContext.popAndRegisterContainingComponent();
return null;
}
我们重点看下这行代码
Set<BeanDefinitionHolder> processorDefinitions = AnnotationConfigUtils.registerAnnotationConfigProcessors(parserContext.getRegistry(), source);
我们追踪进去(其中省略了一些我们不关心的代码)
public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
BeanDefinitionRegistry registry, Object source) {
...
// Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
}
...
}
在这个方法其中注册了一个CommonAnnotationBeanPostProcessor类,这个类是我们@PostConstruct这个注解发挥作用的基础。
在bean实例化的过程中,会调用AbstractAutowireCapableBeanFactory类的doCreateBean方法,在这个方法中会有一个调用initializeBean方法的地方,我们直接看initializeBean这个方法
protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
invokeAwareMethods(beanName, bean);
return null;
}
}, getAccessControlContext());
}
else {
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
// 调用@PostConstruct方法注解的地方
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);//①
}
try {
// 调用afterPropertiesSet和init-method地方
invokeInitMethods(beanName, wrappedBean, mbd);// ②
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
先看①这行,进入applyBeanPostProcessorsBeforeInitialization方法
public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
result = beanProcessor.postProcessBeforeInitialization(result, beanName);
if (result == null) {
return result;
}
}
return result;
}
我们还记得前面注册的一个类CommonAnnotationBeanPostProcessor,其中这个类间接的实现了BeanPostProcessor接口,所以此处会调用CommonAnnotationBeanPostProcessor类的postProcessBeforeInitialization方法,它本身并没有实现这个方法,但他的父类InitDestroyAnnotationBeanPostProcessor实现了postProcessBeforeInitialization的方法,其中这个方法就实现调用目标类上有@PostConstruct注解的方法
// 获取目标类上有@PostConstruct注解的方法并调用
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
LifecycleMetadata metadata = findLifecycleMetadata(bean.getClass());
try {
metadata.invokeInitMethods(bean, beanName);
}
catch (InvocationTargetException ex) {
throw new BeanCreationException(beanName, "Invocation of init method failed", ex.getTargetException());
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Failed to invoke init method", ex);
}
return bean;
}
然后接着看initializeBean方法中②这一行代码,首先判断目标类有没有实现InitializingBean,如果实现了就调用目标类的afterPropertiesSet方法,然后如果有配置init-method就调用其方法
protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd)
throws Throwable {
// 1、调用afterPropertiesSet方法
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();
}
}
// 2、调用init-method方法
if (mbd != null) {
String initMethodName = mbd.getInitMethodName();
if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
!mbd.isExternallyManagedInitMethod(initMethodName)) {
invokeCustomInitMethod(beanName, bean, mbd);
}
}
}
至此Spring的初始化方法调用顺序的解析就已经完了。