spring BeanProcessor接口詳解
1. 簡單認識BeanProcessor
BeanProcessor的理解
BeanProcessor是spring中的一個重要接口，他有兩個接口方法一個是postProcessBeforeInitialization前置初始化，另一個是postProcessAfterInitialization後置初始化。從名稱上就可以大概清楚這個接口的作用：在一個業務流程的前後加入兩個接口方法，當執行這個業務流程時，就會觸發這兩個接口方法的執行。簡單的總結一下有兩個要點：
- 在業務流程中，根據BeanProcessor接口方法加在不同的位置(一般是前後)，可以實現對業務邏輯的擴展。
- 在業務邏輯執行前，BeanProcessor的實現類必須已經被創建完成(BeanProcessor接口類必須要優先實例化)。
而在spring中，就有很多實現瞭BeanProcessor的bean，通過在重要的業務流程(如bean的生命周期流程)的前後加上BeanProcessor接口方法，就可以對業務邏輯進行修改或補充。
一個BeanProcessor的使用實例
在spring的bean生命周期中，BeanProcessor接口方法會在bean創建後的初始化方法(init-method或@PostConstruct指向的方法)前後執行before和after方法；那有沒有在bean創建前後執行的接口方法呢？答案是肯定有的，這個功能是由BeanProcessor的子接口InstantiationAwareBeanPostProcessor來實現的，他也是有before和after方法，會在bean實例化前後執行。
我們先定義一個BeanProcessor接口實現類和一個InstantiationAwareBeanPostProcessor接口實現類。
BeanPostProcessor實現類:
//net.postProcessor.CustomerPostProcessor
@Component
public class CustomerPostProcessor implements BeanPostProcessor {
@PostConstruct
public void init(){
System.out.println("執行CustomerPostProcessor的PostConstruct");
}
public CustomerPostProcessor(){
System.out.println("執行CustomerPostProcessor的構造方法");
}
@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實現類:
//net.postProcessor.CustomerInitialPostProcessor
@Component
public class CustomerInitialPostProcessor implements InstantiationAwareBeanPostProcessor {
@PostConstruct
public void init(){
System.out.println("執行CustomerInitialPostProcessor的PostConstruct");
}
public CustomerInitialPostProcessor(){
System.out.println("執行CustomerInitialPostProcessor的構造方法");
}
@Override
public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
System.out.println("bean初始化前執行：class為"+beanClass.getName()+"|beanName為"+beanName);
return null;
}
@Override
public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
System.out.println("bean初始化後執行：Object為"+bean+"|beanName為"+beanName);
return false;
}
}
再創建一個普通的bean對象：
//net.postProcessor.FirstBean
@Component
public class FirstBean implements InitializingBean {
private String msg = "hello";
@PostConstruct
public void init(){
System.out.println("執行FirstBean的PostConstruct");
}
public FirstBean(){
System.out.println("FirstBean構造方法！"+msg);
}
public String getMsg() {
return msg;
}
public void setMsg(String msg) {
this.msg = msg;
}
@Override
public void afterPropertiesSet() throws Exception {
System.out.println("執行FirstBean的afterPropertiesSet");
}
}
我們創建一個spring工廠對象將上述bean加載進去：
@Test
public void test(){
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext("net.postProcessor");
}
//執行得到以下結果：
執行CustomerInitialPostProcessor的構造方法
執行CustomerInitialPostProcessor的PostConstruct
執行CustomerPostProcessor的構造方法
執行CustomerPostProcessor的PostConstruct
bean初始化前執行：class為net.postProcessor.FirstBean|beanName為firstBean
FirstBean構造方法！hello
bean初始化後執行：Object為net.postProcessor.FirstBean@79179359|beanName為firstBean
net.postProcessor.FirstBean@79179359======BeforeInitialization======firstBean
執行FirstBean的PostConstruct
執行FirstBean的afterPropertiesSet
net.postProcessor.FirstBean@79179359======AfterInitialization======firstBean
通過上述結果證明瞭我們之前的說法是正確的：
1.BeanPostProcessor接口類會優先實例化，且在實例化中無法不會調用BeanPostProcessor接口方法的
2.InstantiationAwareBeanPostProcessor接口方法會在FirstBean構造方法構造方法前後執行
3.BeanPostProcessor接口方法會在FirstBean實例化後進行初始化的前後執行
註意：若@PostConstruct註解方法方法未執行，請加入javax.annotation:javax.annotation-api:1.3.2jar包依賴，原因是@PostConstruct是J2EE標準的註解，不是spring自己的接口，而在JDK8往上的版本中設計者打算棄用這些註解，所以做瞭處理，我們是沒有辦法直接使用J2EE標準註解的(@Resource、@PostConstruct、@PreDestroy等幾個註解)，為瞭兼容這種情況，所以有瞭javax.annotation-apijar包的產生(或者降低JDK版本)。
2. BeanProcessor的實現思路和簡化實例
BeanProcessor大概的實現思路
通過之前的瞭解BeanProcessor的使用，我們可以知道BeanProcessor並不復雜，但是卻十分的重要，下面來分析下BeanProcessor的實現思路：
- 創建個接口A，接口包含一些切點方法(Before、After、Around之類的)，實現這個接口A的類要在使用前就創建好
- 我們需要有個業務流程，這個業務流程由若幹步組成；將接口A的接口方法插入到這些業務步驟之間(需要擴展的地方)
- 要執行這個業務流程時，把接口A的實現類對象賦值到業務流程中，在執行業務流程中，就會觸發接口方法的執行完成功能擴展
當我們更換賦值到業務流程中的接口A的實現類時，對應的擴展邏輯也會隨之變化，這樣就實現瞭可插拔式的擴展邏輯(策略模式)。
一個BeanProcessor的簡化邏輯實例
在spring中我們可以創建任意數量的bean實現BeanProcessor接口，所以實際上我們是要一個全局的beanProcessorList對象用來存儲這些BeanProcessor對象；在執行業務代碼時，要循環這個beanProcessorList對象，獲取你需要的BeanProcessor對象來執行接口方法。下面是一個模擬spring bean生命周期的簡化版，來幫助你理解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構造方法！"+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("執行CustomerPostProcessor的PostConstruct");
}
public CustomerPostProcessor(){
System.out.println("執行CustomerPostProcessor的構造方法");
}
@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 {
//模擬掃描到的bean信息<"SecondBean", "net.postProcessor.SecondBean">
Map<String, String> scanBeanMap = new HashMap<>();
//模擬spring的beanPostProcessors列表
List<BeanPostProcessor> processorBeanList = new ArrayList<>();
//模擬bean對象緩存
Map<String, Object> beanCache = new HashMap<>();
//添加掃描的bean信息
public PostProcessor addBeanInfo(String beanName, String classPath){
this.scanBeanMap.put(beanName, classPath);
return this;
}
//模擬bean創建流程
public Object execute(){
try {
//先臨時存儲實現瞭postProcessor接口的bean對象
List<BeanPostProcessor> postProcessorStrList = new ArrayList<>();
//循環scanBeanMap，獲取bean列表中實現瞭postProcessor接口的類，加入processorBeanList中
for(String temp: scanBeanMap.keySet()){
Class<?> clazz = Class.forName(scanBeanMap.get(temp));
//判斷是否實現瞭BeanPostProcessor接口
if(BeanPostProcessor.class.isAssignableFrom(clazz)){
//實例化讓如臨時容器
postProcessorStrList.add((BeanPostProcessor)createBean(temp));
}
}
//將實現瞭postProcessor接口的bean加入processorBeanList中
for(BeanPostProcessor obj: postProcessorStrList){
processorBeanList.add(obj);
}
//再次循環scanBeanMap初始化所用bean
for(String temp: scanBeanMap.keySet()){
createBean(temp);
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
return null;
}
//bean實例化
public Object createBean(String beanName){
//從緩存中獲取
if(beanCache.containsKey(beanName)){
return beanCache.get(beanName);
}else{
//緩存中取不到，則進行創建後加入緩存
try {
Class<?> clazz = Class.forName(scanBeanMap.get(beanName));
//processor前置方法執行
for(BeanPostProcessor processor : processorBeanList){
processor.postProcessBeforeInitialization(clazz, beanName);
}
//bean實例化
Object result = clazz.getConstructor().newInstance();
//processor後置方法執行
for(BeanPostProcessor processor : processorBeanList){
processor.postProcessAfterInitialization(result, beanName);
}
//將bean加入緩存
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;
}
}
代碼調用
public static void main(String[] args) {
PostProcessor postProcessor = new PostProcessor();
//添加掃描到的bean
postProcessor
.addBeanInfo("SecondBean", "net.postProcessor.SecondBean")
.addBeanInfo("CustomerPostProcessor", "net.postProcessor.CustomerPostProcessor");
postProcessor.execute();
}
//執行結果
執行CustomerPostProcessor的構造方法
class net.postProcessor.SecondBean======BeforeInitialization======SecondBean
SecondBean構造方法！world
net.postProcessor.SecondBean@1b40d5f0======AfterInitialization======SecondBean
代碼邏輯如下：
- 循環bean信息列表，將BeanPostProcessor接口bean分離出來優先實例化(實例化中緩存bean對象)，並將之放入臨時容器。
- 循環完成，將臨時容器中的BeanPostProcessor接口bean賦值到全局BeanPostProcessor接口列表中
- 再次循環bean信息列表，緩存存在則直接返回緩存對象，不存在則進行bean實例化，期間循環調用全局BeanPostProcessor接口對象方法
3. spring中BeanProcessor的源碼解析
我們要從spring中的refresh()開始看起：
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
//刷新準備
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
//告訴子類刷新內部bean工廠。
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
//為容器準備bean工程
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
//允許在上下文bean的後處理工廠子類。
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
//優先將BeanDefinitionRegistryPostProcessor\BeanFactoryPostProcessor接口的bean對象實例化
//屬於spring內部組件調用
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
//處理用戶自定義PostProcessor接口對象，之後加入spring的beanPostProcessors列表，
// 供之後預實例化其他bean時觸發這些PostProcessor方法
registerBeanPostProcessors(beanFactory);
//...省略代碼
//實例化所有(non-lazy-init)單件。
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銷毀
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...
//重置公共緩存
resetCommonCaches();
}
}
}
其中包含有postProcess字段都有可能和BeanProcessor相關，這裡有三個相關方法：
- postProcessBeanFactory(beanFactory)，這個是一共空的擴展方法，顯然無關
- invokeBeanFactoryPostProcessors(beanFactory)，處理spring中實現瞭BeanProcessor接口的內部組件直接調用接口方法
- registerBeanPostProcessors(beanFactory)，實例化用戶自定義BeanProcessor接口bean組件，之後循環賦值到全局BeanProcessor列表中
所以registerBeanPostProcessors()就是我們要找的對象，來跟進看下registerBeanPostProcessors()：
//AbstractApplicationContext#registerBeanPostProcessors
protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
//委托給PostProcessorRegistrationDelegate.registerBeanPostProcessors進行處理
PostProcessorRegistrationDelegate.registerBeanPostProcessors進行處理(beanFactory, this);
}
public static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
//查詢實現瞭BeanPostProcessor接口的beanName
String[] postProcessorNames = beanFactory.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<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
List<String> orderedPostProcessorNames = new ArrayList<>();
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
//根據beanName循環調用getBean進行實例化
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.
//對BeanPostProcessor接口對象進行排序
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
//將獲取到的PostProcessors接口對象加入到spring的beanPostProcessors列表
registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
// Next, register the BeanPostProcessors that implement Ordered.
List<BeanPostProcessor> 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<BeanPostProcessor> 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));
}
果然這裡就是處理BeanPostProcessor接口的地方，邏輯和之前的思路類似：
- 循環掃描到的bean列表，獲取實現瞭BeanPostProcessor接口的beanName數組
- 循環beanName數組數組，調用beanFactory.getBean()將bean實例化，並放入priorityOrderedPostProcessors列表中
- 調用sortPostProcessors對priorityOrderedPostProcessors列表進行排序(處理BeanPostProcessor調用的順序)
- 調用registerBeanPostProcessors將priorityOrderedPostProcessors列表中的bean對象賦值到全局列表beanPostProcessors中
- 回到refresh()中，當調用finishBeanFactoryInitialization()對所用bean進行預實例化時就會調用這些BeanPostProcessor接口方法
以上就是spring BeanProcessor接口詳解的詳細內容，更多關於spring BeanProcessor接口的資料請關註WalkonNet其它相關文章！
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