Spring boot BeanPostProcessor优先级

前言

其实是一个老项目，项目中有aop，有BeanPostProcessor注入Spring bean的属性。当orader一样时，那么加载顺序就很重要。如何保证绝对的加载逻辑就与Spring的原理相关了。源码简单分析即可明白Spring的设计。

 

1. demo构造

1.1 demo

pom

    4.0.0

    org.example
    spring-boot-demo
    1.0-SNAPSHOT

    
        
            org.springframework.boot
            spring-boot-starter-web
            2.3.5.RELEASE
        
        
            org.springframework.boot
            spring-boot-starter-test
            2.3.5.RELEASE
            test
        
        
            org.springframework.boot
            spring-boot-starter-aop
            2.3.5.RELEASE
        

    

构建aop一个，controller一个，BeanPostProcessor逻辑一个

package com.feng.boot.aop;

import org.aspectj.lang.annotation.Aspect;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.EnableAspectJAutoProxy;

//@Aspect
@Configuration
@EnableAspectJAutoProxy
public class AopConfig {

    @Bean
    public DemoAspect getAspectDemo(){
        return new DemoAspect();
    }
}

package com.feng.boot.aop;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;

@Aspect
public class DemoAspect {

    @Around("execution(* com.feng.boot.bean.DemoController.*(..))")
    public Object around(ProceedingJoinPoint pjp) {
        try {
            Object o =  pjp.proceed();
            return o;
        } catch (Throwable e) {
            return null;
        }
    }
}

package com.feng.boot.bean;

import com.feng.boot.anno.InjectFieldAnno;
import com.feng.boot.anno.InjectFieldBean;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class DemoController {

    @InjectFieldAnno(name = "feng")
    private InjectFieldBean injectFieldBean;

    @RequestMapping("/hello")
    public String testDemo(String param){
        return injectFieldBean.invokeMethod(param);
    }
}

package com.feng.boot.processor;

import com.feng.boot.anno.InjectFieldAnno;
import com.feng.boot.anno.InjectFieldBean;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.core.Ordered;
import org.springframework.stereotype.Component;

import java.lang.reflect.Field;

@Component
public class FieldInjectBean implements BeanPostProcessor, Ordered {
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        Field[] fields = bean.getClass().getDeclaredFields();
        InjectFieldAnno injectFieldAnno;
        for (Field field : fields) {
            injectFieldAnno = field.getAnnotation(InjectFieldAnno.class);
            if (injectFieldAnno != null) {
                InjectFieldBean injectFieldBean = new InjectFieldBean();
                injectFieldBean.setName(injectFieldAnno.name());
                field.setAccessible(true);
                try {
                    field.set(bean, injectFieldBean);
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
            }
        }

        return bean;
    }

    public int getOrder() {
        return Ordered.HIGHEST_PRECEDENCE-1;
    }
}

辅助类

package com.feng.boot.anno;

public class InjectFieldBean {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String invokeMethod(String param){
        return this.name;
    }
}

package com.feng.boot.anno;

import java.lang.annotation.*;

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface InjectFieldAnno {
    String name() default "";
}

1.2 运行demo hello

经过AOP

然后发现，自定义属性并没有注入

2. 原因分析

2.1 源码分析原因

Spring创建bean的源码

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory

其中有个核心方法，在初始化bean的对象时，会处理

BeanPostProcessors

源码如下：applyBeanPostProcessorsAfterInitialization

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
		if (System.getSecurityManager() != null) {
			AccessController.doPrivileged((PrivilegedAction