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postprocessafterinitialization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:
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//net.postprocessor.customerpostprocessor@componentpublic 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:
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//net.postprocessor.customerinitialpostprocessor@componentpublic 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：
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//net.postprocessor.firstbean@componentpublic 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：
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@testpublic 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firstbeanfirstbean构造方法！hellobean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afterpropertiessetnet.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
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@componentpublic 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
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@componentpublic 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
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public class postprocessor { //模拟扫描到的bean信息<"secondbean", "net.postprocessor.secondbean"> map<string, string> scanbeanmap = new hashmap<>(); //模拟spring的beanpostprocessors列表 list<beanpostprocessor> processorbeanlist = new arraylist<>(); //模拟bean对象缓存 map<string, object> 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<beanpostprocessor> 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
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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======secondbeansecondbean构造方法！worldnet.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：
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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()：
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//abstractapplicationcontext#registerbeanpostprocessorsprotected void registerbeanpostprocessors(configurablelistablebeanfactory beanfactory) { //委托给postprocessorregistrationdelegate.registerbeanpostprocessors进行处理 postprocessorregistrationdelegate.registerbeanpostprocessors进行处理(beanfactory, this);} |
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public static void registerbeanpostprocessors( configurablelistablebeanfactory beanfactory, abstractapplicationcontext applicationcontext) { //查询实现了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<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接口的资料请关注服务器之家其它相关文章！
原文链接：https://juejin.cn/post/6844904196026843149
