Spring扩展点系列-ApplicationContextAwareProcessor

文章目录

- 简介
- 源码分析
- 示例代码
- - 示例一：扩展点的执行顺序
  - - 运行示例一
  - 示例二：获取配置文件值
  - - 配置文件application.properties内容
    - 定义工具类ConfigUtil
    - controller测试调用
    - 运行示例二
  - 示例三：实现ResourceLoaderAware读取文件
  - - ExtendResourceLoaderAware 文件内容
    - token.json 文件
    - controller测试代码
    - 运行示例三

简介

spring容器中Bean的生命周期内所有可扩展的点的调用顺序

扩展接口	实现接口
ApplicationContextlnitializer	initialize
AbstractApplicationContext	refreshe
BeanDefinitionRegistryPostProcessor	postProcessBeanDefinitionRegistry
BeanDefinitionRegistryPostProcessor	postProcessBeanFactory
BeanFactoryPostProcessor	postProcessBeanFactory
instantiationAwareBeanPostProcessor	postProcessBeforelnstantiation
SmartlnstantiationAwareBeanPostProcessor	determineCandidateConstructors
MergedBeanDefinitionPostProcessor	postProcessMergedBeanDefinition
InstantiationAwareBeanPostProcessor	postProcessAfterlnstantiation
SmartInstantiationAwareBeanPostProcessor	getEarlyBeanReference
BeanFactoryAware	postProcessPropertyValues
ApplicationContextAwareProcessor	invokeAwarelnterfaces
BeanNameAware	setBeanName
InstantiationAwareBeanPostProcessor	postProcessBeforelnstantiation
@PostConstruct
InitializingBean	afterPropertiesSet
FactoryBean	getobject
SmartlnitializingSingleton	afterSingletonslnstantiated
CommandLineRunner	run
DisposableBean	destroy

今天要介绍的是ApplicationContextAwareProcessor ，ApplicationContextAwareProcessor 本身是没有扩展点的，但其内部却有7个扩展点可供实现，分别为

EnvironmentAware
EmbeddedValueResolverAware
ResourceLoaderAware
ApplicationEventPublisherAware
MessageSourceAware
ApplicationStartupAware
ApplicationContextAware

这些内部扩展点触发的时机在bean实例化之后，初始化之前。

1、EnvironmentAware：凡注册到Spring容器内的bean，实现了EnvironmentAware接口重写setEnvironment方法后，在工程启动时可以获得application.properties的配置文件配置的属性值。
2、EmbeddedValueResolverAware：用于获取StringValueResolver的一个扩展类， StringValueResolver用于获取基于String类型的properties的变量
3、ResourceLoaderAware：用于获取ResourceLoader的一个扩展类，ResourceLoader可以用于获取classpath内所有的资源对象，可以扩展此类来拿到ResourceLoader对象。
4、ApplicationEventPublisherAware：用于获取ApplicationEventPublisher的一个扩展类，ApplicationEventPublisher可以用来发布事件，结合ApplicationListener来共同使用
5、MessageSourceAware：用于获取MessageSource的一个扩展类，MessageSource主要用来做国际化
6、ApplicationStartupAware：要开始收集定制的StartupStep，组件可以实现ApplicationStartupAware接口直接获得ApplicationStartup实例或者在注入点请求ApplicationStartup类型。
7、ApplicationContextAware：可以用来获取ApplicationContext的一个扩展类，也就是spring上下文管理器，可以手动的获取任何在spring上下文注册的bean

源码分析

从下列源码的invokeAwareInterfaces方法可知，ApplicationContextAwareProcessor关联了大部分Spring内置Aware接口,它们的执行顺序如
下源码码所示从上到下，最开始是EnvironmentAware，最后是ApplicationContextAware

package org.springframework.context.support;

class ApplicationContextAwareProcessor implements BeanPostProcessor {

	private final ConfigurableApplicationContext applicationContext;

	private final StringValueResolver embeddedValueResolver;

	/**
	 * Create a new ApplicationContextAwareProcessor for the given context.
	 */
	public ApplicationContextAwareProcessor(ConfigurableApplicationContext applicationContext) {
		this.applicationContext = applicationContext;
		this.embeddedValueResolver = new EmbeddedValueResolver(applicationContext.getBeanFactory());
	}

	@Override
	@Nullable
	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
				bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
				bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware ||
				bean instanceof ApplicationStartupAware)) {
			return bean;
		}

		AccessControlContext acc = null;

		if (System.getSecurityManager() != null) {
			acc = this.applicationContext.getBeanFactory().getAccessControlContext();
		}

		if (acc != null) {
			AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
				invokeAwareInterfaces(bean);
				return null;
			}, acc);
		}
		else {
			invokeAwareInterfaces(bean);
		}

		return bean;
	}

	private void invokeAwareInterfaces(Object bean) {
		if (bean instanceof EnvironmentAware) {
			((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
		}
		if (bean instanceof EmbeddedValueResolverAware) {
			((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
		}
		if (bean instanceof ResourceLoaderAware) {
			((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
		}
		if (bean instanceof ApplicationEventPublisherAware) {
			((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
		}
		if (bean instanceof MessageSourceAware) {
			((MessageSourceAware) bean).setMessageSource(this.applicationContext);
		}
		if (bean instanceof ApplicationStartupAware) {
			((ApplicationStartupAware) bean).setApplicationStartup(this.applicationContext.getApplicationStartup());
		}
		if (bean instanceof ApplicationContextAware) {
			((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
		}
	}
}

示例代码

示例一：扩展点的执行顺序

示例一展示的是7个内部扩展点所执行的顺序

@Slf4j
@Configuration
public class ExtendInvokeAware implements EnvironmentAware, EmbeddedValueResolverAware, ResourceLoaderAware,
        ApplicationEventPublisherAware, MessageSourceAware, ApplicationStartupAware, ApplicationContextAware, BeanNameAware {

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        log.info("setApplicationContext--Extend--run {}",applicationContext);
    }

    @Override
    public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
        log.info("setApplicationEventPublisher--Extend--run {}",applicationEventPublisher);
    }

    @Override
    public void setApplicationStartup(ApplicationStartup applicationStartup) {
        log.info("setApplicationStartup--Extend--run {}",applicationStartup);
    }

    @Override
    public void setEmbeddedValueResolver(StringValueResolver resolver) {
        log.info("setEmbeddedValueResolver--Extend--run {}",resolver);
    }

    @Override
    public void setEnvironment(Environment environment) {
        log.info("setEnvironment--Extend--run {}",environment);
    }

    @Override
    public void setMessageSource(MessageSource messageSource) {
        log.info("setMessageSource--Extend--run {}",messageSource);
    }

    @Override
    public void setResourceLoader(ResourceLoader resourceLoader) {
        log.info("setResourceLoader--Extend--run {}",resourceLoader);
    }

    @Override
    public void setBeanName(String name) {
        log.info("setBeanName--Extend--run {}",name);
    }
}

运行示例一

在这里插入图片描述

示例二：获取配置文件值

展示如何利用实现EmbeddedValueResolverAware来获取配置文件的属性值

配置文件application.properties内容

db.user=navicat
db.password=navicat
db.driverClass=com.mysql.jdbc.Driver

定义工具类ConfigUtil

该工具类功能为传入的key获取对应value

@Component
public class ConfigUtil implements EmbeddedValueResolverAware {

    private StringValueResolver resolver;

    @Override
    public void setEmbeddedValueResolver(StringValueResolver resolver) {
        this.resolver = resolver;
    }

    /**
     * 获取属性，直接传入属性名称即可
     * @param key
     * @return
     */
    public String getPropertiesValue(String key) {
        StringBuilder name = new StringBuilder("${").append(key).append("}");
        return resolver.resolveStringValue(name.toString());
    }

}

controller测试调用

@GetMapping("/testConfig")
public void testConfig() {
    String s = configUtil.getPropertiesValue("db.user");
    System.out.println(s);
}

运行示例二

在这里插入图片描述

示例三：实现ResourceLoaderAware读取文件

ExtendResourceLoaderAware 文件内容

实现ResourceLoaderAware 接口，并读取文件内容进行打印

@Slf4j
@Configuration
public class ExtendResourceLoaderAware implements ResourceLoaderAware {

    private ResourceLoader resourceLoader;

    @Override
    public void setResourceLoader(ResourceLoader resourceLoader) {
        this.resourceLoader = resourceLoader;
        log.info("ApplicationContextAware--Extend--run {}",resourceLoader);
    }


    public void showResourceData() throws IOException
    {
        //This line will be changed for all versions of other examples
        Resource banner = resourceLoader.getResource("file:d:/token.json");

        InputStream in = banner.getInputStream();

        BufferedReader reader = new BufferedReader(new InputStreamReader(in));

        while (true) {
            String line = reader.readLine();
            if (line == null)
                break;
            System.out.println(line);
        }
        reader.close();
    }
}

token.json 文件

{"name":"张三"}

controller测试代码

@Autowired
ApplicationContext context;

@SuppressWarnings("resource")
@GetMapping("/testResource")
public void testResource() throws Exception{
    ExtendResourceLoaderAware extendResourceLoaderAware = (ExtendResourceLoaderAware) context.getBean("extendResourceLoaderAware");

    extendResourceLoaderAware.showResourceData();
}