spring BeanProcessor接口详解

spring BeanProcessor接口详解

1. 简单认识BeanProcessor

BeanProcessor的理解

BeanProcessor是spring中的一个重要接口，他有两个接口方法一个是postProcessBeforeInitialization前置初始化，另一个是postProcessAfteilxExOHcFtrInitialization后置初始化。从名称上就可以大概清楚这个接口的作用：在一个业务流程的前后加入两个接口方法，当执行这个业务流程时，就会触发这两个接口方法的执行。简单的总结一下有两个要点：

在业务流程中，根据BeanProcessor接口方法加在不同的位置(一般是前后)，可以实现对业务逻辑的扩展。

在业务逻辑执行前，BeanProcessor的实现类必须已经被创建完成(BeanProcessor接口类必须要优先实例化)。

而在spring中，就有很多实现了BeanProcessor的bean，通过在重要的业务流程(如bean的生命周期流程)的前后加上BeanProcessor接口方法，就可以对业务逻辑进行修改或补充。

一个BeanProcessor的使用实例

在spring的bean生命周期中，BeanProcessor接口方法会在bean创建后的初始化方法(init-method或@PostConstruct指向的方法)前后执行before和after方法；那有没有在bean创建前后执行的接口方法呢？答案是肯定有的，这个功能是由BeanProcessor的子接口InstantiationAwareBeanPostProcessor来实现的，他也是有before和after方法，会在bean实例化前后执行。

我们先定义一个BeanProcessor接口实现类和一个InstantiationAwareBeanPostProcessor接口实现类。

BeanPostProcessor实现类:

//net.postProcessor.CustomerPostProcessor

@Component

public class CustomerPostProcessor implements BeanPostProcessor {

@PostConstruct

public void init(){

System.out.println("执行CustomerPostProcessor的PostConstruct");

}

public CustomerPostProcessor(){

System.out.println("执行CustomerPostProcessor的构造方法");

}

@Override

public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {

System.out.println(bean+"======BeforeInitialization======"+ beanName);

return bean;

}

@Override

public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {

System.out.println(bean+"======AfterInitialization======"+ beanName);

return bean;

}

}

InstantiationAwareBeanPostProcessor实现类:

//net.postProcessor.CustomerInitialPostProcessor

@Component

public class CustomerInitialPostProcessor implements InstantiationAwareBeanPostProcessor {

@PostConstruct

public void init(){

System.out.println("执行CustomerInitialPostProcessor的PostConstruct");

}

public CustomerInitialPostProcessor(){

System.out.println("执行CustomerInitialPostProcessor的构造方法");

}

@Override

public Object postProcessBeforeInstantiation(Class> beanClass, String beanName) throws BeansException {

System.out.println("bean初始化前执行：class为"+beanClass.getName()+"|beanName为"+beanName);

return null;

}

@Override

public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {

System.out.println("bean初始化后执行：Object为"+bean+"|beanName为"+beanName);

return false;

}

}

再创建一个普通的bean对象：

//net.postProcessor.FirstBean

@Component

public class FirstBean implements InitializingBean {

private String msg = "hello";

@PostConstruct

public void init(){

System.out.println("执行FirstBean的PostConstruct");

}

public FirstBean(){

System.out.println("FirstBean构造方法！"+msg);

}

public String getMsg() {

return msg;

}

public void setMsg(String msg) {

this.msg = msg;

}

@Override

public void afterPropertiesSet() throws Exception {

System.out.println("执行FirstBean的afterPropertiesSet");

}

}

我们创建一个spring工厂对象将上述bean加载进去：

@Test

public void test(){

AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext("net.postProcessor");

}

//执行得到以下结果：

执行CustomerInitialPostProcessor的构造方法

执行CustomerInitialPostProcessor的PostConstruct

执行CustomerPostProcessor的构造方法

执行CustomerPostProcessor的PostConstruct

bean初始化前执行：class为net.postProcessor.FirstBean|beanName为firstBean

FirstBean构造方法！hello

bean初始化后执行：Object为net.postProcessor.FirstBean@79179359|beanName为firstBean

net.postProcessor.FirstBean@79179359======BeforeInitialization======firstBean

执行FirstBean的PostConstruct

执行FirstBean的afterPropertiesSet

net.postProcessor.FirstBean@79179359======AfterInitialization======firstBean

通过上述结果证明了我们之前的说法是正确的：

1.BeanPostProcessor接口类会优先实例化，且在实例化中无法不会调用BeanPostProcessor接口方法的

2.InstantiationAwareBeanPostProcessor接口方法会在FirstBean构造方法构造方法前后执行

3.BeanPostProcessor接口方法会在FirstBean实例化后进行初始化的前后执行

注意：若@PostConstruct注解方法方法未执行，请加入javax.annotation:javax.annotation-api:1.3.2jar包依赖，原因是@PostConstruct是J2EE标准的注解，不是spring自己的接口，而在JDK8往上的版本中设计者打算弃用这些注解，所以做了处理，我们是没有办法直接使用J2EE标准注解的(@Resource、@PostConstruct、@PreDestroy等几个注解)，为了兼容这种情况，所以有了javax.annotation-apijar包的产生(或者降低JDK版本)。

2. BeanProcessor的实现思路和简化实例

BeanProcessor大概的实现思路

通过之前的了解BeanProcessor的使用，我们可以知道BeanProcessor并不复杂，但是却十分的重要，下面来分析下BeanProcessor的实现思路：

创建个接口A，接口包含一些切点方法(Before、After、Around之类的)，实现这个接口A的类要在使用前就创建好

我们需要有个业务流程，这个业务流程由若干步组成；将接口A的接口方法插入到这些业务步骤之间(需要扩展的地方)

要执行这个业务流程时，把接口A的实现类对象赋值到业务流程中，在执行业务流程中，就会触发接口方法的执行完成功能扩展

当我们更换赋值到业务流程中的接口A的实现类时，对应的扩展逻辑也会随之变化，这样就实现了可插拔式的扩展逻辑(策略模式)。

一个BeanProcessor的简化逻辑实例

在spring中我们可以创建任意数量的bean实现BeanProcessor接口，所以实际上我们是要一个全局的beanProcessorList对象用来存储这些BeanProcessor对象；在执行业务代码时，要循环这个beanProcessorList对象，获取你需要的BeanProcessor对象来执行接口方法。下面是一个模拟spring bean生命周期的简化版，来帮助你理解spring中BeanProcessor的工作原理。

net.postProcessor.SecondBean.java

@Component

public class SecondBean {

private String msg = "world";

public SecondBean(){

System.out.println("SecondBean构造方法！"+msg);

}

public String getMsg() {

return msg;

}

public void setMsg(String msg) {

this.msg = msg;

}

}

net.postProcessor.CustomerPostProcessor.java

@Component

public class CustomerPostProcessor implements BeanPostProcessor {

@PostConstruct

public void init(){

System.out.println("执行CustomerPostProcessor的PostConstruct");

}

public CustomerPostProcessor(){

System.out.println("执行CustomerPostProcessor的构造方法");

}

@Override

public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {

System.out.println(bean+"======BeforeInitialization======"+ beanName);

return bean;

}

@Override

public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {

System.out.println(bean+"======AfterInitialization======"+ beanName);

return bean;

}

}

net.postProcessor.PostProcessor.java

public class PostProcessor {

//模拟扫描到的bean信息<"SecondBean", "net.postProcessor.SecondBean">

Map scanBeanMap = new HashMap<>();

//模拟spring的beanPostProcessors列表

List processorBeanList = new ArrayList<>();

//模拟bean对象缓存

Map beanCache = new HashMap<>();

//添加扫描的bean信息

public PostProcessor addBeanInfo(String beanName, String classPath){

this.scanBeanMap.put(beanName, classPath);

return this;

}

//模拟bean创建流程

public Object execute(){

try {

//先临时存储实现了postProcessor接口的bean对象

List postProcessorStrList = new ArrayList<>();

//循环scanBeanMap，获取bean列表中实现了postProcessor接口的类，加入processorBeanList中

for(String temp: scanBeanMap.keySet()){

Class> clazz = Class.forName(scanBeanMap.get(temp));

//判断是否实现了BeanPostProcessor接口

if(BeanPostProcessor.class.isAssignableFrom(clazz)){

//实例化让如临时容器

postProcessorStrList.add((BeanPostProcessor)createBean(temp));

}

}

//将实现了postProcessor接口的bean加入processorBeanList中

for(BeanPostProcessor obj: postProcessorStrList){

processorBeanList.add(obj);

}

//再次循环scanBeanMap初始化所用bean

for(String temp: scanBeanMap.keySet()){

createBean(temp);

}

} catch (ClassNotFoundException e) {

e.printStackTrace();

}

return null;

}

//bean实例化

public Object createBean(String beanName){

//从缓存中获取

if(beanCache.containsKey(beanName)){

return beanCache.get(beanName);

}else{

//缓存中取不到，则进行创建后加入缓存

try {

Class> clazz = Class.forName(scanBeanMap.get(beanName));

//processor前置方法执行

for(BeanPostProcessor processor : processorBeanList){

processor.postProcessBeforeInitialization(clazz, beanName);

}

//bean实例化

Object result = clazz.getConstructor().newInstance();

//processor后置方法执行

for(BeanPostProcessor processor : processorBeanList){

processor.postProcessAfterInitialization(result, beanName);

}

//将bean加入缓存

beanCache.put(beanName, result);

return result;

} catch (ClassNotFoundException e) {

e.printStackTrace();

} catch (IllegalAccessException e) {

e.printStackTrace();

} catch (InstantiationException e) {

e.printStackTrace();

} catch (NoSuchMethodException e) {

e.printStackTrace();

} catch (InvocationTargetException e){

e.printStackTrace();

}

}

return null;

}

}

代码调用

public static void main(String[] args) {

PostProcessor postProcessor = new PostProcessor();

//添加扫描到的bean

postProcessor

.addBeanInfo("SecondBean", "net.postProcessor.SecondBean")

.addBeanInfo("CustomerPostProcessor", "net.postProcessor.CustomerPostProcessor");

postProcessor.execute();

}

//执行结果

执行CustomerPostProcessor的构造方法

class net.postProcessor.SecondBean======BeforeInitialization======SecondBean

SecondBean构造方法！world

net.postProcessor.SecondBean@1b40d5f0======AfterInitialization======SecondBean

代码逻辑如下：

循环bean信息列表，将BeanPostProcessor接口bean分离出来优先实例化(实例化中缓存bean对象)，并将之放入临时容器。

循环完成，将临时容器中的BeanPostProcessor接口bean赋值到全局BeanPostProcessor接口列表中

再次循环bean信息列表，缓存存在则直接返回缓存对象，不存在则进行bean实例化，期间循环调用全局BeanPostProcessor接口对象方法

3. spring中BeanProcessor的源码解析

我们要从spring中的refresh()开始看起：

public void refresh() throws BeansException, IllegalStateException {

synchronized (this.startupShutdownMonitor) {

// Prepare this context for refreshing.

//刷新准备

prepareRefresh();

// Tell the subclass to refresh the internal bean factory.

//告诉子类刷新内部bean工厂。

ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

// Prepare the bean factory for use in this context.

//为容器准备bean工程

prepareBeanFactory(beanFactory);

try {

// Allows post-processing of the bean factory in context subclasses.

//允许在上下文bean的后处理工厂子类。

postProcessBeanFactory(beanFactory);

// Invoke factory processors registered as beans in the context.

//优先将BeanDefinitionRegistryPostProcessor\BeanFactoryPostProcessor接口的bean对象实例化

//属于spring内部组件调用

invokeBeanFactoryPostProcessors(beanFactory);

// Register bean processors that intercept bean creation.

//处理用户自定义PostProcessor接口对象，之后加入spring的beanPostProcessors列表，

// 供之后预实例化其他bean时触发这些PostProcessor方法

registerBeanPostProcessors(beanFactory);

//...省略代码

//实例化所有(non-lazy-init)单件。

finishBeanFactoryInitialization(beanFactory);

}

catch (BeansException ex) {

if (logger.isWarnEnabled()) {

logger.warn("Exception encountered during context initialization - " +

"cancelling refresh attempt: " + ex);

}

// Destroy already created singletons to avoid dangling resources.

//bean销毁

destroyBeans();

// Reset 'active' flag.

//取消刷新

cancelRefresh(ex);

// Propagate exception to caller.

throw ex;

}

finally {

// Reset common introspection caches in Spring's core, since we

// might not ever need metadata for singleton beans anymore...

//重置公共缓存

resetCommonCaches();

}

}

}

其中包含有postProcess字段都有可能和BeanProcessor相关，这里有三个相关方法：

postProcessBeanFactory(beanFactory)，这个是一共空的扩展方法，显然无关

invokeBeanFactoryPostProcessors(beanFactory)，处理spring中实现了BeanProcessor接口的内部组件直接调用接口方法

registerBeanPostProcessors(beanFactory)，实例化用户自定义BeanProcessor接口bean组件，之后循环赋值到全局BeanProcessor列表中

所以registerBeanPostProcessors()就是我们要找的对象，来跟进看下registerBeanPostProcessors()：

//AbstractApplicationContext#registerBeanPostProcessors

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {

//委托给PostProcessorRegistrationDelegate.registerBeanPostProcessors进行处理

PostProcessorRegistrationDelegate.registerBeanPostProcessors进行处理(beanFactory, this);

}

public static void registerBeanPostProcessors(

ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

//查询实现了BeanPostProcessor接口的beanName

String[] postProcessorNames = beanFactorilxExOHcFty.getBeanNamesForType(BeanPostProcessor.class, true, false);

// Register BeanPostProcessorChecker that logs an info message when

// a bean is created during BeanPostProcessor instantiation, i.e. when

// a bean is not eligible for getting processed by all BeanPostProcessors.

int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;

beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

// Separate between BeanPostProcessors that implement PriorityOrdered,

// Ordered, and the rest.

List priorityOrderedPostProcessors = new ArrayList<>();

List internalPostProcessors = new ArrayList<>();

List orderedPostProcessorNames = new ArrayList<>();

List nonOrderedPostProcessorNames = new ArrayList<>();

//根据beanName循环调用getBean进行实例化

for (String ppName : postProcessorNames) {

if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {

BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);

priorityOrderedPostProcessors.add(pp);

if (pp instanceof MergedBeanDefinitionPostProcessor) {

internalPostProcessors.add(pp);

}

}

else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {

orderedPostProcessorNames.add(ppName);

}

else {

nonOrderedPostProcessorNames.add(ppName);

}

}

// First, register the BeanPostProcessors that implement PriorityOrdered.

//对BeanPostProcessor接口对象进行排序

sortPostProcessors(priorityOrderedPostProcessors, beanFactory);

//将获取到的PostProcessors接口对象加入到spring的beanPostProcessors列表

registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

// Next, register the BeanPostProcessors that implement Ordered.

List orderedPostProcessors = new ArrayList<>();

for (String ppName : orderedPostProcessorNames) {

BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);

orderedPostProcessors.add(pp);

if (pp instanceof MergedBeanDefinitionPostProcessor) {

internalPostProcessors.add(pp);

}

}

sortPostProcessors(orderedPostProcessors, beanFactory);

registerBeanPostProcessors(beanFactory, orderedPostProcessors);

// Now, register all regular BeanPostProcessors.

List nonOrderedPostProcessors = new ArrayList<>();

for (String ppName : nonOrderedPostProcessorNames) {

BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);

nonOrderedPostProcessors.add(pp);

if (pp instanceof MergedBeanDefinitionPostProcessor) {

internalPostProcessors.add(pp);

}

}

registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

// Finally, re-register all internal BeanPostProcessors.

sortPostProcessors(internalPostProcessors, beanFactory);

registerBeanPostProcessors(beanFactory, internalPostProcessors);

// Re-register post-processor for detecting inner beans as ApplicationListeners,

// moving it to the end of the processor chain (for picking up proxies etc).

beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));

}

果然这里就是处理BeanPostProcessor接口的地方，逻辑和之前的思路类似：

循环扫描到的bean列表，获取实现了BeanPostProcessor接口的beanName数组

循环beanName数组数组，调用beanFactory.getBean()将bean实例化，并放入priorityOrderedPostProcessors列表中

调用sortPostProcessors对priorityOrderedPostProcessors列表进行排序(处理BeanPostProcessor调用的顺序)

调用registerBeanPostProcessors将priorityOrderedPostProcessors列表中的bean对象赋值到全局列表beanPostProcessors中

回到refresh()中，当调用finishBeanFactoryInitialization()对所用bean进行预实例化时就会调用这些BeanPostProcessor接口方法

以上就是spring BeanProcessor接口详解的详细内容，更多关于spring BeanProcessor接口的资料请关注我们其它相关文章！

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