Spring?BeanPostProcessor后處理器源碼解析

更新時(shí)間：2023年09月25日 15:13:16 作者：保持敬畏

這篇文章主要介紹了Spring?BeanPostProcessor后處理器源碼解析,本文通過(guò)實(shí)例代碼給大家介紹的非常詳細(xì),對(duì)大家的學(xué)習(xí)或工作具有一定的參考借鑒價(jià)值,需要的朋友參考下吧

Spring后處理器-BeanPostProcessor

Bean被實(shí)例化后，到最終緩存到名為singletonObjects單例池之前，中間會(huì)經(jīng)過(guò)bean的初始化過(guò)程（（該后處理器的執(zhí)行時(shí)機(jī)）），例如：屬性的填充、初始化方法init的執(zhí)行等，其中有一個(gè)對(duì)外拓展的點(diǎn)BeanPostProcessor，我們稱之為bean后處理器。與上文bean工廠后處理器相似，它也是一個(gè)接口，實(shí)現(xiàn)了該接口并被容器管理的BeanPostProcessor（即在配置文件中對(duì)其進(jìn)行配置），會(huì)在流程節(jié)點(diǎn)上被Spring自動(dòng)調(diào)用。
BeanPostProcessor接口代碼如下

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//
package org.springframework.beans.factory.config;
import org.springframework.beans.BeansException;
import org.springframework.lang.Nullable;
public interface BeanPostProcessor {
    @Nullable
    default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
    @Nullable
    default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
}

創(chuàng)建實(shí)現(xiàn)該接口（BeanPsotProcessor）的類，要在配置文件中進(jìn)行管理

快捷鍵 ctrl + insert 重寫(xiě)接口方法

package com.example.PostProcessor;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
public class MyBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println(beanName + ":postProcessBeforeInitialization");
        return bean;
    }
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println(beanName + ":postProcessAfterInitialization");
        return BeanPostProcessor.super.postProcessAfterInitialization(bean, beanName);
    }
}

測(cè)試類代碼

package com.example.Test;
import com.example.Service.Impl.UserServiceImpl;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class TestApplicationContext {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("application.xml");
        System.out.println(context.getBean(UserServiceImpl.class));
    }
}

運(yùn)行結(jié)果如下

展示了該后處理器的執(zhí)行時(shí)機(jī)

Before和After執(zhí)行時(shí)機(jī)

在Bean實(shí)例化過(guò)程可以配置相關(guān)對(duì)于bean對(duì)象的操作方法，具體間往期文章：Bean的配置

注冊(cè)為bean的類

package com.example.Service.Impl;
import com.example.DAO.UserDAO;
import com.example.Service.UserService;
import org.springframework.beans.factory.InitializingBean;
import java.util.List;
import java.util.Map;
import java.util.Set;
public class UserServiceImpl implements UserService, InitializingBean {
    // todo 無(wú)參構(gòu)造方法
    public UserServiceImpl() {
        System.out.println("UserServiceImpl實(shí)例化");
    }
    // todo 自定義初始化方法
    public void init() {
        System.out.println("自定義初始化方法init()");
    }
    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("屬性設(shè)置之后執(zhí)行afterPropertiesSet()");
    }
}

實(shí)現(xiàn)bean后處理器的類

package com.example.PostProcessor;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
public class MyBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println(beanName + ":postProcessBeforeInitialization");
        return bean;
    }
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println(beanName + ":postProcessAfterInitialization");
        return BeanPostProcessor.super.postProcessAfterInitialization(bean, beanName);
    }
}

配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:util="http://www.springframework.org/schema/util"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/util https://www.springframework.org/schema/util/spring-util.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
    <bean class="com.example.PostProcessor.MyBeanPostProcessor"></bean>
    <bean id="userService" class="com.example.Service.Impl.UserServiceImpl" init-method="init">
</beans>

測(cè)試類

package com.example.Test;
import com.example.Service.Impl.UserServiceImpl;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class TestApplicationContext {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("application.xml");
        System.out.println(context.getBean(UserServiceImpl.class));
    }
}

運(yùn)行結(jié)果

小結(jié)

從上述運(yùn)行結(jié)果來(lái)看，首先完成bean對(duì)象的創(chuàng)建，然后執(zhí)行后處理器中的before方法，然后執(zhí)行屬性設(shè)置之后的方法，然后執(zhí)行自定義的初始化方法，最后執(zhí)行后處理器的after方法

案例

對(duì)Bean方法進(jìn)行執(zhí)行時(shí)間日志增強(qiáng)
要求
- Bean的方法執(zhí)行之前控制臺(tái)打印當(dāng)前時(shí)間
- Bean的方法執(zhí)行之后控制臺(tái)打印當(dāng)前時(shí)間
分析
- 對(duì)方法進(jìn)行增強(qiáng)主要就是代理設(shè)計(jì)模式和包裝設(shè)計(jì)模式
- 由于Bean方法不確定，所以使用動(dòng)態(tài)代理在運(yùn)行期間執(zhí)行增強(qiáng)操作
- 在Bean實(shí)例創(chuàng)建完畢之后，進(jìn)入到單例之前，使用Proxy真實(shí)的目標(biāo)bean
具體代碼如下

代理類（實(shí)現(xiàn)了bean后處理接口）

package com.example.PostProcessor;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;
import java.util.Date;
public class TimeLogBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        // todo 使用動(dòng)態(tài)代理對(duì)目標(biāo)bean進(jìn)行增強(qiáng)，返回proxy對(duì)象，進(jìn)而存儲(chǔ)到單例池singletonObjects中
        Object beanProxy = Proxy.newProxyInstance(bean.getClass().getClassLoader(), bean.getClass().getInterfaces(), (InvocationHandler) (proxy, method, args) -> {
            // 輸出開(kāi)始時(shí)間
            System.out.println("方法" + method.getName() + "開(kāi)始執(zhí)行時(shí)間" + new Date());
            // 執(zhí)行目標(biāo)方法
            Object rs = method.invoke(bean, args);
            // 輸出結(jié)束時(shí)間
            System.out.println("方法" + method.getName() + "結(jié)束執(zhí)行時(shí)間" + new Date());
            return rs;
        });
        return beanProxy;// 將增強(qiáng)的bean存入單例池中
    }
}

bean對(duì)象對(duì)應(yīng)的類

package com.example.Service.Impl;
import com.example.Service.UserService;
public class UserServiceImpl implements UserService {
    public void show() {
        System.out.println("show......");
    }
}

接口類

package com.example.Service;
public interface UserService {
    public void show();
}

配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean class="com.example.PostProcessor.TimeLogBeanPostProcessor"></bean>
    <bean id="userService" class="com.example.Service.Impl.UserServiceImpl">
    </bean>
</beans>

測(cè)試類

package com.example.Test;
import com.example.Service.UserService;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class TestApplicationContext {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("application.xml");
        UserService UserServiceBean = (UserService) context.getBean(UserService.class);
        UserServiceBean.show();
    }
}

運(yùn)行結(jié)果

Bean實(shí)例化基本流程圖

首先通過(guò)Reader讀取配置文件，解析bean標(biāo)簽，然后將每個(gè)bean標(biāo)簽變成beanDefinition對(duì)象存儲(chǔ)到beanDefinitionMap中，然后經(jīng)過(guò)所有的BeanFactoryPostProcessor（bean工廠后處理器），再?gòu)腗ap中取出每個(gè)beanDefiniton對(duì)象，通過(guò)反射變成Object對(duì)象，創(chuàng)建完對(duì)象后，經(jīng)過(guò)beanPoatProcessor中的before方法和after方法（之間還存在bean中的init方法，后面會(huì)講述），最終存入單例池中。

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