spring BeanProcessor接口详解

时间：2022-12-07 12:39:50

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：

  1. 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。
  2. 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。

spring BeanProcessor接口详解

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)。

spring BeanProcessor接口详解

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：

  1. 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
  2. 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)
  3. 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：

  1. 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。
  2. 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
  3. 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：

  1. postprocessbeanfactory(beanfactory)，这个是一共空的扩展方法，显然无关
  2. 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
  3. 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：

  1. 循环扫描到的bean列表，获取实现了beanpostprocessor接口的beanname数组
  2. 循环beanname数组数组，调用beanfactory.getbean()将bean实例化，并放入priorityorderedpostprocessors列表中
  3. 调用sortpostprocessors对priorityorderedpostprocessors列表进行排序(处理beanpostprocessor调用的顺序)
  4. 调用registerbeanpostprocessors将priorityorderedpostprocessors列表中的bean对象赋值到全局列表beanpostprocessors中
  5. 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

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