spring源码-value,PostConstruct,PreDestroy,InitializingBean,DisposableBean,init-method,destroy-method顺序

项目中用到value注解，再根据value值初始化一些配置，所以就看了下spring源码关于这几个的调用顺序。

demo

application.properties

request.order.service=orderService
request.order.method=queryOrder

beans-auto.xml

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="  
           http://www.springframework.org/schema/beans  
           http://www.springframework.org/schema/beans/spring-beans-3.0.xsd  
           http://www.springframework.org/schema/context  
           http://www.springframework.org/schema/context/spring-context-3.0.xsd">

    <context:property-placeholder location="classpath:/conf/application.properties" />

    
    
    
    <bean class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor" />
    <bean class="org.springframework.context.annotation.CommonAnnotationBeanPostProcessor" />


    <bean id="orderService" class="com.chris.test.OrderService" init-method="myInit" destroy-method="myDetory"/>

beans>

OrderService.java

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.annotation.Value;

/**
 * OrderService

 */
public class OrderService implements InitializingBean, DisposableBean{

    @Value("${request.order.service}")
    private String requestService;

    @Value("${request.order.method}")
    private String requestOrderMethod;

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("call-InitializingBean-afterPropertiesSet");
    }

    @Override
    public void destroy() throws Exception {
        System.out.println("call-destroy");
    }

    @PostConstruct
    private void showPostConstruct(){
        System.out.println("Value-requestService"+requestService);
        System.out.println("Value-requestOrderMethod"+requestOrderMethod);
        System.out.println("call-PostConstruct");
    }

    @PreDestroy
    private void showPreDestroy(){
        System.out.println("call-PreDestroy");
    }

    private void myInit(){
        System.out.println("call-myInit");
    }

    private void myDetory(){
        System.out.println("call-myDetory");
    }

}

OrderServiceTest.java

import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * OrderServiceTest

 */
public class OrderServiceTest {

    public static void main(String[] args){
        ClassPathXmlApplicationContext  ctx=new ClassPathXmlApplicationContext("beans-auto.xml");
        ctx.close();
    }
}

测试结果：

这里我们可以调用顺序：
初始化顺序：
value–>postConstruct–>InitializingBean–>自定义的init-method
销毁时的顺序：
PreDestroy–>DisposableBean–>destroy-method

Value注解

properties配置解析

xml中配置properties：

    <context:property-placeholder location="classpath:/conf/application.properties" />

如果你熟悉spring的标签解析，你就会明白必然会有个XXXNamespaceHandler来处理这个。这里使用的是ContextNamespaceHandler来处理。

ContextNamespaceHandler：

public class ContextNamespaceHandler extends NamespaceHandlerSupport {

    public void init() {
        // 这里专注properties标签处理
        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());
    }

}

这里不关心标签的解析，大部分的套路基本上都是对标签属性的取值然后设置到bean里面去，我们要关心的是这个bean是谁，通过PropertyPlaceholderBeanDefinitionParser的方法getBeanClass根据配置得到这个beanPropertySourcesPlaceholderConfigurer或PropertyPlaceholderConfigurer，我们只分析下PropertyPlaceholderConfigurer。

PropertyPlaceholderConfigurer

看下类继承关系：

我们看到这个类实现了BeanFactoryPostProcessor接口，而这个接口是spring的beanFactory后置处理器，在获取beanfactory后调用硬编码或配置所有实现这个接口的process(希望你知道我说的是啥)，如果对这里不清楚的，可以看下AbstractApplicationContext的refresh方法。

我们看下PropertyResourceConfigurer对这个接口的实现：

public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        try {
            // 加载properties文件
            Properties mergedProps = mergeProperties();

            // Convert the merged properties, if necessary.
            convertProperties(mergedProps);

            // Let the subclass process the properties.
            // 子类处理properties
            processProperties(beanFactory, mergedProps);
        }
        catch (IOException ex) {
            throw new BeanInitializationException("Could not load properties", ex);
        }
    }

PropertyPlaceholderConfigurer:

@Override
    protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props)
            throws BeansException {

        StringValueResolver valueResolver = new PlaceholderResolvingStringValueResolver(props);

        this.doProcessProperties(beanFactoryToProcess, valueResolver);
    }

记住这里的StringValueResolver，后面对value注解内容替换会使用到这个。

PlaceholderConfigurerSupport：

protected void doProcessProperties(ConfigurableListableBeanFactory beanFactoryToProcess,
            StringValueResolver valueResolver) {

        BeanDefinitionVisitor visitor = new BeanDefinitionVisitor(valueResolver);

        String[] beanNames = beanFactoryToProcess.getBeanDefinitionNames();
        for (String curName : beanNames) {
            // Check that we're not parsing our own bean definition,
            // to avoid failing on unresolvable placeholders in properties file locations.
            // 这里使用visitor模式设置bean的一些配置的value替换，对于开发人员来说很少会用这到这里东西，除非你要自定义bean替换，后面有空单独写个访问者模式的短文
            if (!(curName.equals(this.beanName) && beanFactoryToProcess.equals(this.beanFactory))) {
                BeanDefinition bd = beanFactoryToProcess.getBeanDefinition(curName);
                try {
                    visitor.visitBeanDefinition(bd);
                }
                catch (Exception ex) {
                    throw new BeanDefinitionStoreException(bd.getResourceDescription(), curName, ex.getMessage(), ex);
                }
            }
        }

        // New in Spring 2.5: resolve placeholders in alias target names and aliases as well.
        beanFactoryToProcess.resolveAliases(valueResolver);

        // New in Spring 3.0: resolve placeholders in embedded values such as annotation attributes.
        // 会将上面说的StringvalueResolver加入
            beanFactoryToProcess.addEmbeddedValueResolver(valueResolver);
    }

AbstractBeanFactory：

// 将resolver加入embeddedValueResolvers，后面处理value的时候会for循环使用这个embeddedValueResolvers解析
public void addEmbeddedValueResolver(StringValueResolver valueResolver) {
        Assert.notNull(valueResolver, "StringValueResolver must not be null");
        this.embeddedValueResolvers.add(valueResolver);
    }

value解析

value注解是由xml里面配置的AutowiredAnnotationBeanPostProcessor处理，看下构造方法：

public AutowiredAnnotationBeanPostProcessor() {
        this.autowiredAnnotationTypes.add(Autowired.class);
        this.autowiredAnnotationTypes.add(Value.class);
        ....
    }

发现autowire注解同样由这个类处理。

再来看下这个类继承关系：

红框中这个接口就是处理bean实例化前，实例化后的一个process,后面会讲到在什么地方调用，这里先记得有这个接口，此外这个类还有个方法：

PropertyValues postProcessPropertyValues(
            PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName)
            throws BeansException;

这个就是处理bean属性的注入和propreties替换的东东。

AutowiredAnnotationBeanPostProcessor里面有postProcessPropertyValues的实现，跟源码看就行了。

AutowiredAnnotationBeanPostProcessor:

@Override
    public PropertyValues postProcessPropertyValues(
            PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {

        // 查找上面构造里面加入的注解，autowire和value
        InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass());
        try {
            // 注解注入
            metadata.inject(bean, beanName, pvs);
        }
        catch (Throwable ex) {
            throw new BeanCreationException(beanName, "Injection of autowired dependencies failed", ex);
        }
        return pvs;
    }

会跳转到InjectionMetadata过下，再回到AutowiredAnnotationBeanPostProcessor，回来后我们这里只关注字段上面的inject：

@Override
        protected void inject(Object bean, String beanName, PropertyValues pvs) throws Throwable {
            ....
                    // 解析value的值
                    value = beanFactory.resolveDependency(descriptor, beanName, autowiredBeanNames, typeConverter);
                    ....
                if (value != null) {
                    ReflectionUtils.makeAccessible(field);
                    // 设置值
                    field.set(bean, value);
                }
            ....
    }

我们看下resolveDependency方法。
DefaultListableBeanFactory:

public Object resolveDependency(DependencyDescriptor descriptor, String beanName,
        ...
            return doResolveDependency(descriptor, descriptor.getDependencyType(), beanName, autowiredBeanNames, typeConverter);
        ...
    }

protected Object doResolveDependency(DependencyDescriptor descriptor, Class type, String beanName,
            Set autowiredBeanNames, TypeConverter typeConverter) throws BeansException {
    // 这里只关注value注解，获取到value的是value注解的内容${"XXX"}，不是真正的值
        Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor);
        if (value != null) {
            if (value instanceof String) {
                // 获取到properties注入的值
                String strVal = resolveEmbeddedValue((String) value);
                BeanDefinition bd = (beanName != null && containsBean(beanName) ? getMergedBeanDefinition(beanName) : null);
                value = evaluateBeanDefinitionString(strVal, bd);
            }
            ...
    }

AbstractBeanFactory

public String resolveEmbeddedValue(String value) {
        String result = value;
        for (StringValueResolver resolver : this.embeddedValueResolvers) {
            if (result == null) {
                return null;
            }
            result = resolver.resolveStringValue(result);
        }
        return result;
    }

还记得这个StringValueResolver嘛？就是之前properties配置里面解析注入的。
那么到这里这就完成了value的分析，只留下了一疑问：InstantiationAwareBeanPostProcessor这个接口什么时候才会调用？

PostConstruct

xml配置：

    class="org.springframework.context.annotation.CommonAnnotationBeanPostProcessor" />

看下这个类的构造：

public CommonAnnotationBeanPostProcessor() {
        setOrder(Ordered.LOWEST_PRECEDENCE - 3);
        setInitAnnotationType(PostConstruct.class);
        setDestroyAnnotationType(PreDestroy.class);
        ignoreResourceType("javax.xml.ws.WebServiceContext");
    }

so，这个类就是专门用来处理PostConstruct和PreDestroy注解的，我们这里只看PostConstruct，另一个没什么区别。其实这个类也处理其他几个注解，比较常见的就是@Resouce注解，可以按照上面value注解分析的思路，看下这个类，最后重点关注下postProcessPropertyValues方法。

看下类继承：

看到了BeanPostProcessor接口，这个接口是有2个方法，在bean初始化前\后添加个process。

在父类InitDestroyAnnotationBeanPostProcessor中实现了2个接口：

public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
    // 找到class中带有post和pre2个注解的方法，封装了下
        LifecycleMetadata metadata = findLifecycleMetadata(bean.getClass());
        try {
            // 调用带有postConstruct注解的方法
            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, "Couldn't invoke init method", ex);
        }
        return bean;
    }

现在也清除了postConstruct的注解，留下个疑问，BeanPostProcessor这个接口什么时候调用？

bean创建

上面留下2个疑问：
1. InstantiationAwareBeanPostProcessor这个接口什么时候才会调用？
2. BeanPostProcessor这个接口什么时候调用？

要解决这2个问题，需要了解下spring对bean解析创建的整体流程：
1. 加载xml配置文件，解析配置标签，注册bean；
2. 自动创建各种singleton的bean。

是不是有点简单，具体可以看下AbstractApplicationContext类的refresh方法，整个spring的bean加载创建流程都在这里，spring的代码写的真牛逼。

我们现在关注下bean创建流程中对这2个接口的处理部分。
AbstractAutowireCapableBeanFactory：

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
        ....
            // 处理bean的属性
            populateBean(beanName, mbd, instanceWrapper);
            if (exposedObject != null) {
                // 初始化bean
                exposedObject = initializeBean(beanName, exposedObject, mbd);
            }
        ....
        // 注册disposbean
        registerDisposableBeanIfNecessary(beanName, bean, mbd);
        ....
    }

populateBean方法：

protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
        ....

        if (hasInstAwareBpps || needsDepCheck) {
            PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
            if (hasInstAwareBpps) {
                for (BeanPostProcessor bp : getBeanPostProcessors()) {
                    // 这里解决上面value的问题，调用InstantiationAwareBeanPostProcessor所有实现，处理属性解析
                    if (bp instanceof InstantiationAwareBeanPostProcessor) {
                        InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                        pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
                        if (pvs == null) {
                            return;
                        }
                    }
                }
            }
            ....
    }

initializeBean方法：

protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
        if (System.getSecurityManager() != null) {
            AccessController.doPrivileged(new PrivilegedAction