本章我们继续实战spring的扩展能力,通过自定义BeanFactoryPostProcessor接口的实现类,来对bean实例做一些控制;
原文地址:https://blog.csdn.net/boling_cavalry/article/details/82083889
spring容器初始化时,从资源中读取到bean的相关定义后,保存在beanFactory的成员变量中(参考DefaultListableBeanFactory类的成员变量beanDefinitionMap),在实例化bean的操作就是依据这些bean的定义来做的,而在实例化之前,spring允许我们通过自定义扩展来改变bean的定义,定义一旦变了,后面的实例也就变了,而beanFactory后置处理器,即BeanFactoryPostProcessor就是用来改变bean定义的;
一起来看看上述功能对应的源码,从AbstractApplicationContext类的refresh方法看起,这里面对应着容器初始化的基本操作;
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
}
@Override
public void addBeanFactoryPostProcessor(BeanFactoryPostProcessor postProcessor) {
Assert.notNull(postProcessor, "BeanFactoryPostProcessor must not be null");
this.beanFactoryPostProcessors.add(postProcessor);
}
@Override
public void initialize(ConfigurableApplicationContext context) {
context.addBeanFactoryPostProcessor(
new ConfigurationWarningsPostProcessor(getChecks()));
}
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
List<String> orderedPostProcessorNames = new ArrayList<String>();
List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
for (String ppName : postProcessorNames) {
if (processedBeans.contains(ppName)) {
// skip - already processed in first phase above
}
else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
第七段,priorityOrderedPostProcessors和orderedPostProcessorNames这两个集合,都是先做排序再调用invokeBeanDefinitionRegistryPostProcessors方法,最后是nonOrderedPostProcessorNames集合,也被传入invokeBeanDefinitionRegistryPostProcessors方法;
private static void invokeBeanDefinitionRegistryPostProcessors(
Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry) {
for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
postProcessor.postProcessBeanDefinitionRegistry(registry);
}
}
/**
* Invoke the given BeanFactoryPostProcessor beans.
*/
private static void invokeBeanFactoryPostProcessors(
Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) {
for (BeanFactoryPostProcessor postProcessor : postProcessors) {
postProcessor.postProcessBeanFactory(beanFactory);
}
}
如上所示,两个方法都很简单,对每个BeanFactoryPostProcessor接口的实现类,都调用了其接口方法,不同的是,对于实现了BeanDefinitionRegistryPostProcessor接口的bean,调用其postProcessBeanDefinitionRegistry方法的时候,入参是BeanDefinitionRegistry,而非BeanFactory,因此,实现了BeanDefinitionRegistryPostProcessor接口的bean,其postProcessBeanDefinitionRegistry在被调用时,可以通过入参BeanDefinitionRegistry来做更多和bean的定义有关的操作,例如注册bean;
至此,对BeanFactoryPostProcessor的处理流程就全部分析完了,这里小结一下:
本次实战的内容是创建一个springboot工程,在里面自定义一个BeanFactoryPostProcessor接口的实现类,如果您不想敲代码,也可以去github下载源码,地址和链接信息如下表所示:
名称 | 链接 | 备注 |
---|---|---|
项目主页 | 该项目在GitHub上的主页 | |
git仓库地址(https) | 该项目源码的仓库地址,https协议 | |
git仓库地址(ssh) | git@github.com:zq2599/blog_demos.git | 该项目源码的仓库地址,ssh协议 |
这个git项目中有多个文件夹,本章源码在文件夹customizebeanfactorypostprocessor下,如下图红框所示:
接下来开始实战吧:
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.bolingcavalry</groupId>
<artifactId>customizebeanfactorypostprocessor</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>customizebeanfactorypostprocessor</name>
<description>Demo project for Spring Boot</description>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.5.15.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
package com.bolingcavalry.customizebeanfactorypostprocessor.service;
public interface CalculateService {
/**
* 整数加法
* @param a
* @param b
* @return
*/
int add(int a, int b);
/**
* 返回当前实现类的描述信息
* @return
*/
String getServiceDesc();
}
package com.bolingcavalry.customizebeanfactorypostprocessor.service.impl;
import com.bolingcavalry.customizebeanfactorypostprocessor.service.CalculateService;
import org.springframework.stereotype.Service;
@Service("calculateService")
public class CalculateServiceImpl implements CalculateService {
private String desc = "desc from class";
public void setDesc(String desc) {
this.desc = desc;
}
@Override
public int add(int a, int b) {
return a + b;
}
@Override
public String getServiceDesc() {
return desc;
}
}
package com.bolingcavalry.customizebeanfactorypostprocessor.beanfactorypostprocessor;
import org.springframework.beans.BeansException;
import org.springframework.beans.MutablePropertyValues;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.AbstractBeanDefinition;
import org.springframework.stereotype.Component;
@Component
public class CustomizeBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
AbstractBeanDefinition abstractBeanDefinition = (AbstractBeanDefinition) beanFactory.getBeanDefinition("calculateService");
MutablePropertyValues pv = abstractBeanDefinition.getPropertyValues();
pv.addPropertyValue("desc", "Desc is changed from bean factory post processor");
abstractBeanDefinition.setScope(BeanDefinition.SCOPE_SINGLETON);
}
}
上述代码的功能很简单,找到名为”calculateService”的bean的定义对象,通过调用addPropertyValue方法,将定义中的desc属性值改为”Desc is changed from bean factory post processor”,这样等名为”calculateService”的bean被实例化出来后,其成员变量desc的值就是”Desc is changed from bean factory post processor”;
package com.bolingcavalry.customizebeanfactorypostprocessor;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class CustomizebeanfactorypostprocessorApplication {
public static void main(String[] args) {
SpringApplication.run(CustomizebeanfactorypostprocessorApplication.class, args);
}
}
至此,BeanFactoryPostProcessor的源码分析和扩展实战就结束了,通过本次实战,除了对spring扩展的认识加深,又掌握了一种控制bean的方式;