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 @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:
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//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：
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//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：
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@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
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@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
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@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
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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======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：
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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#registerbeanpostprocessors protected 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接口的资料请关注其它相关文章！
原文链接：https://juejin.cn/post/6844904196026843149
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