Introduction

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Talk about the BeanPostProcessor interface in Spring

Description

All beans will go to the postProcessBeforeInitialization and postProcessAfterInitialization methods of the BeanPostProcessor interface.

See the life cycle process of Bean : Bean life cycle-summary_feiying0canglang的博客-CSDN博客

Simple example

Other URL

BeanPostProcessor use-简书

Code

package com.example.processor;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;

@Component
public class TestProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("postProcessBeforeInitialization==> " + "bean:" + bean + "; " + "beanName:" + beanName);
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("postProcessAfterInitialization==> " + "bean:" + bean + "; " + "beanName:" + beanName);
        return bean;
    }
}

Running result (too long, only part of it)

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.3.0.RELEASE)

2021-03-04 23:40:59.246  INFO 5820 --- [           main] com.example.DemoApplication              : Starting DemoApplication on DESKTOP-QI6B9ME with PID 5820 (E:\work\Idea_proj\demo_JAVA\demo_SpringBoot\target\classes started by Liu in E:\work\Idea_proj\demo_JAVA\demo_SpringBoot)
2021-03-04 23:40:59.248  INFO 5820 --- [           main] com.example.DemoApplication              : No active profile set, falling back to default profiles: default
postProcessBeforeInitialization==> bean:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryConfiguration$EmbeddedTomcat@1136b469; beanName:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryConfiguration$EmbeddedTomcat
postProcessAfterInitialization==> bean:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryConfiguration$EmbeddedTomcat@1136b469; beanName:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryConfiguration$EmbeddedTomcat
postProcessBeforeInitialization==> bean:org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory@512d4583; beanName:tomcatServletWebServerFactory
postProcessBeforeInitialization==> bean:org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration$TomcatWebSocketConfiguration@2abc224d; beanName:org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration$TomcatWebSocketConfiguration
postProcessAfterInitialization==> bean:org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration$TomcatWebSocketConfiguration@2abc224d; beanName:org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration$TomcatWebSocketConfiguration
postProcessBeforeInitialization==> bean:org.springframework.boot.autoconfigure.websocket.servlet.TomcatWebSocketServletWebServerCustomizer@2b97cc1f; beanName:websocketServletWebServerCustomizer
postProcessAfterInitialization==> bean:org.springframework.boot.autoconfigure.websocket.servlet.TomcatWebSocketServletWebServerCustomizer@2b97cc1f; beanName:websocketServletWebServerCustomizer
postProcessBeforeInitialization==> bean:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration@64f555e7; beanName:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration
postProcessAfterInitialization==> bean:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration@64f555e7; beanName:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration

Advanced application: injecting properties

Other URL

Spring combat series (three)-the magical use of BeanPostProcessor_jokeHello's column -CSDN blog_beanpostprocessor

Introduction

When developing Spring, you will encounter multiple implementation classes for the same interface, usually the following methods:

Introduce the interface through @Autowired+@Qualify: @Autowired @Qualify("helloServiceImpl2") private HelloService helloService;

Via @Autowired+@Primary: Mark @Primary on a certain implementation class

In the specific call place, different interface implementation classes can be selected according to the needs of the business through the ApplicationContext. Although a factory method can be abstracted, it still feels not elegant enough, otherwise an error will be reported.

In fact, the above methods can already meet the development needs, and method 1 is recommended. Here, BeanPostProcessor+custom annotations are used to achieve the same effect. Of course, writing this way is a reinvention of the wheel, which is essentially meaningless. However, we can learn the following points from this example:

Method of assigning values to attributes using custom annotations

Usage of the proxy factory class

Usage of BeanPostProcessor

interface

package com.example.service;

public interface HelloService {
    void sayHello();
}

Implementation class

package com.example.service.impl;

import com.example.service.HelloService;
import org.springframework.stereotype.Service;

@Service
public class HelloServiceImpl1 implements HelloService {
    @Override
    public void sayHello() {
        System.out.println("我是HelloServiceImpl1");
    }
}

package com.example.service.impl;

import com.example.service.HelloService;
import org.springframework.stereotype.Service;

@Service
public class HelloServiceImpl2 implements HelloService {
    @Override
    public void sayHello() {
        System.out.println("我是HelloServiceImpl2");
    }
}

Custom annotation

package com.example.annotation;

import org.springframework.stereotype.Component;

import java.lang.annotation.*;

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface RountingInjected {
    String value() default "helloServiceImpl1";
}

Custom BeanPostProcessor implementation class

package com.example.processor;

import com.example.annotation.RountingInjected;
import com.example.factory.RoutingBeanProxyFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanCreationException;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.context.ApplicationContext;
import org.springframework.stereotype.Component;

import java.lang.reflect.Field;
import java.util.Map;

@Component
public class HelloServiceInjectProcessor implements BeanPostProcessor {
    @Autowired
    private ApplicationContext applicationContext;

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        Class<?> targetCls = bean.getClass();
        Field[] targetFld = targetCls.getDeclaredFields();
        for (Field field : targetFld) {
            //找到指定目标的注解类
            if (field.isAnnotationPresent(RountingInjected.class)) {
                if (!field.getType().isInterface()) {
                    throw new BeanCreationException("RoutingInjected field must be declared as an interface:" 
                                                     + field.getName() + " @Class " + targetCls.getName());
                }
                try {
                    this.handleRoutingInjected(field, bean, field.getType());
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
            }
        }
        return bean;
    }

    private void handleRoutingInjected(Field field, Object bean, Class type) throws IllegalAccessException {
        Map<String, Object> candidates = this.applicationContext.getBeansOfType(type);
        field.setAccessible(true);
        if (candidates.size() == 1) {
            field.set(bean, candidates.values().iterator().next());
        } else if (candidates.size() == 2) {
            String injectVal = field.getAnnotation(RountingInjected.class).value();
            Object proxy = RoutingBeanProxyFactory.createProxy(injectVal, type, candidates);
            field.set(bean, proxy);
        } else {
            throw new IllegalArgumentException("Find more than 2 beans for type: " + type);
        }
    }
}

Proxy implementation class

package com.example.factory;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
import org.springframework.aop.framework.ProxyFactory;

import java.util.Map;

public class RoutingBeanProxyFactory {
 
    private final static String DEFAULT_BEAN_NAME = "helloServiceImpl1";
 
    public static Object createProxy(String name, Class type, Map<String, Object> candidates) {
        ProxyFactory proxyFactory = new ProxyFactory();
        proxyFactory.setInterfaces(type);
        proxyFactory.addAdvice(new VersionRoutingMethodInterceptor(name, candidates));
        return proxyFactory.getProxy();
    }
 
    static class VersionRoutingMethodInterceptor implements MethodInterceptor {
        private Object targetObject;
 
        public VersionRoutingMethodInterceptor(String name, Map<String, Object> beans) {
            this.targetObject = beans.get(name);
            if (this.targetObject == null) {
                this.targetObject = beans.get(DEFAULT_BEAN_NAME);
            }
        }
 
        @Override
        public Object invoke(MethodInvocation invocation) throws Throwable {
            return invocation.getMethod().invoke(this.targetObject, invocation.getArguments());
        }
    }
}

Test class

package com.example.controller;

import com.example.annotation.RountingInjected;
import com.example.service.HelloService;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {
    @RountingInjected(value = "helloServiceImpl2")
    private HelloService helloService;

    @GetMapping("/test1")
    public String test1() {
        helloService.sayHello();
        return "test1 success";
    }
}

test

Visit: http://localhost:8080/test1

Back-end results:
我是HelloServiceImpl2

Bean life cycle--BeanPostProcessor application

Introduction

Simple example

Advanced application: injecting properties

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