spring源码-Aware-3.4

　　一、Aware接口，这个也是spring的拓展之一，为啥要单独拿出来讲呢，因为他相比于BeanFactoryPostProcessor，BeanPostProcessor的实用性更加高，并且在具体的业务中也可以灵活使用，主要是能够达到解耦的目的。

　　二、常用的Aware接口有：第一类：BeanNameAware/BeanClassLoaderAware/BeanFactoryAware。 第二类：EmbeddedValueResolverAware/ResourceLoaderAware/ApplicationEventPublisherAware/MessageSourceAware/ApplicationContextAware。这两类到底有啥区别类，其实没有太大的区别。但是在源码实现中还是存在很大的差别的（后面统一说道）。

　　三、源码实现：

　　1、第一类：BeanNameAware/BeanClassLoaderAware/BeanFactoryAware

　　1）实现方式：

import org.springframework.beans.factory.BeanNameAware;

/**
 * BeanNameAware/BeanClassLoaderAware/BeanFactoryAware类似
 */
public class TestBeanAware implements BeanNameAware{

    private String beanName;
    @Override
    public void setBeanName(String beanName) {
        System.out.println(beanName);
        this.beanName = beanName;
    }

    public String getBeanName() {
        return beanName;
    }
}

　　2）有啥区别

　　这里简单说明一下：相对于普通的bean，这里可以获取到beanName/classLoader/beanFactory。是对普通bean的一种增强，然后合理的应用才是关键

　　3）源码实现部分：

protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
        if (System.getSecurityManager() != null) {
            AccessController.doPrivileged(new PrivilegedAction<Object>() {
                public Object run() {
                    AbstractAutowireCapableBeanFactory.this.invokeAwareMethods(beanName, bean);
                    return null;
                }
            }, this.getAccessControlContext());
        } else {
            this.invokeAwareMethods(beanName, bean);
        }

        Object wrappedBean = bean;
        if (mbd == null || !mbd.isSynthetic()) {
            wrappedBean = this.applyBeanPostProcessorsBeforeInitialization(bean, beanName);
        }

        try {
            this.invokeInitMethods(beanName, wrappedBean, mbd);
        } catch (Throwable var6) {
            throw new BeanCreationException(mbd != null ? mbd.getResourceDescription() : null, beanName, "Invocation of init method failed", var6);
        }

        if (mbd == null || !mbd.isSynthetic()) {
            wrappedBean = this.applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        }

        return wrappedBean;
    }

    private void invokeAwareMethods(String beanName, Object bean) {
        if (bean instanceof BeanNameAware) {
            ((BeanNameAware)bean).setBeanName(beanName);
        }

        if (bean instanceof BeanClassLoaderAware) {
            ((BeanClassLoaderAware)bean).setBeanClassLoader(this.getBeanClassLoader());
        }

        if (bean instanceof BeanFactoryAware) {
            ((BeanFactoryAware)bean).setBeanFactory(this);
        }

    }

　　4）何时调用：spring源码-bean之加载-2 的3）点d.3 doCreateBean中的initializeBean（）部分开始，所以这个其实是在getBean的时候才会调用。

　　5）测试的时候发现：在增强容器中refresh方法中finishBeanFactoryInitializationh会完成这部分的调用

　　

　　2、第二类：EmbeddedValueResolverAware/ResourceLoaderAware/ApplicationEventPublisherAware/MessageSourceAware/ApplicationContextAware

　　1）实现方式：这里举两个例子EmbeddedValueResolverAware，ApplicationEventPublisherAware　　

　　a.EmbeddedValueResolverAware

import org.springframework.context.EmbeddedValueResolverAware;
import org.springframework.util.StringValueResolver;

import javax.annotation.PostConstruct;

public class TestEmbeddedValueResolverAware implements EmbeddedValueResolverAware {

    private StringValueResolver stringValueResolver;

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

    public String getProperties (String name) {
        String elName = "${"+ name +"}";
        return stringValueResolver.resolveStringValue(elName);
    }

    @PostConstruct
    public void test() {
        System.out.println(getProperties("name"));
    }
}

　　注意：这里是读取方式配置

　　<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="locations">
            <list>
                <value>aware.properties</value>
            </list>
        </property>
    </bean>

　　aware.properties

name=test
age=25
sex=boy

　　疑问：和这个有啥关系，看在StringValueResolver可以知道，这里的StringValueResolver指向的是PropertyPlaceholderConfigurer的内部类PlaceholderResolvingStringValueResolver，当然具体的实现有不同的方式

　　private class PlaceholderResolvingStringValueResolver implements StringValueResolver {
        private final PropertyPlaceholderHelper helper;
        private final PlaceholderResolver resolver;

        public PlaceholderResolvingStringValueResolver(Properties props) {
            this.helper = new PropertyPlaceholderHelper(PropertyPlaceholderConfigurer.this.placeholderPrefix, PropertyPlaceholderConfigurer.this.placeholderSuffix, PropertyPlaceholderConfigurer.this.valueSeparator, PropertyPlaceholderConfigurer.this.ignoreUnresolvablePlaceholders);
            this.resolver = PropertyPlaceholderConfigurer.this.new PropertyPlaceholderConfigurerResolver(props, (PropertyPlaceholderConfigurer.PropertyPlaceholderConfigurerResolver)null);
        }

        public String resolveStringValue(String strVal) throws BeansException {
            String value = this.helper.replacePlaceholders(strVal, this.resolver);
            return value.equals(PropertyPlaceholderConfigurer.this.nullValue) ? null : value;
        }
    }

　　b.ApplicationEventPublisherAware

import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationEventPublisherAware;

import javax.annotation.PostConstruct;

public class TestApplicationEventPublisherAware implements ApplicationEventPublisherAware {

    private ApplicationEventPublisher publisher;

    @Override
    public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
        this.publisher = applicationEventPublisher;
    }

    public ApplicationEventPublisher getPublisher() {
        return publisher;
    }

    public class TestEvent extends ApplicationEvent {

        private Object object;

        public TestEvent(Object source, Object object) {
            super(source);
            this.object = object;
        }

        public Object getObject() {
            return object;
        }
    }

    @PostConstruct
    public void test() {
        publisher.publishEvent(new TestEvent(this, "test"));
    }

import org.springframework.context.ApplicationListener;

public class TestListener implements ApplicationListener<TestApplicationEventPublisherAware.TestEvent>{

    @Override
    public void onApplicationEvent(TestApplicationEventPublisherAware.TestEvent testEvent) {
        System.out.println("TestEvent is Happen" + testEvent.getObject());
    }
}

　　发布，监听的过程相信。在实际业务中很常用吧。这里监听过程后面会讲，这里不细说。

　　注意：这里用aware的接口方式实现发布，监听过程，会比直接调用的方式更加解耦。

　　2）重点来了，这玩意在哪里调用的呢。其实我们之前我们忽略了一个重点。

　　a.先看调用方式

　　

　　看到postProcessBeforeInitialization应该感到高兴了，因为这不就是实现了BeanPostProcessor接口的前置调用过程吗。

　　有问题可以参考：spring源码-BeanPostProcessor-3.3

　　b.疑问：我们并没有手动去实现BeanPostProcessor的接口并且对aware接口做处理啊。

　　通过debug和查看堆栈信息可以知道方法调用在ApplicationContextAwareProcessor类里面

package org.springframework.context.support;

import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedAction;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.ApplicationEventPublisherAware;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.EmbeddedValueResolverAware;
import org.springframework.context.MessageSourceAware;
import org.springframework.context.ResourceLoaderAware;
import org.springframework.util.StringValueResolver;

class ApplicationContextAwareProcessor implements BeanPostProcessor {
    private final ConfigurableApplicationContext applicationContext;

    public ApplicationContextAwareProcessor(ConfigurableApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }

    public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {
        AccessControlContext acc = null;
        if (System.getSecurityManager() != null && (bean instanceof EmbeddedValueResolverAware || bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware || bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) {
            acc = this.applicationContext.getBeanFactory().getAccessControlContext();
        }

        if (acc != null) {
            AccessController.doPrivileged(new PrivilegedAction<Object>() {
                public Object run() {
                    ApplicationContextAwareProcessor.this.invokeAwareInterfaces(bean);
                    return null;
                }
            }, acc);
        } else {
            this.invokeAwareInterfaces(bean);
        }

        return bean;
    }

    private void invokeAwareInterfaces(Object bean) {
        if (bean instanceof EmbeddedValueResolverAware) {
            ((EmbeddedValueResolverAware)bean).setEmbeddedValueResolver(new ApplicationContextAwareProcessor.EmbeddedValueResolver(this.applicationContext.getBeanFactory()));
        }

        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 ApplicationContextAware) {
            ((ApplicationContextAware)bean).setApplicationContext(this.applicationContext);
        }

    }

    public Object postProcessAfterInitialization(Object bean, String beanName) {
        return bean;
    }

    private static class EmbeddedValueResolver implements StringValueResolver {
        private final ConfigurableBeanFactory beanFactory;

        public EmbeddedValueResolver(ConfigurableBeanFactory beanFactory) {
            this.beanFactory = beanFactory;
        }

        public String resolveStringValue(String strVal) {
            return this.beanFactory.resolveEmbeddedValue(strVal);
        }
    }
}

　　c、还有一个问题ApplicationContextAwareProcessor在哪里注册的呢？

　　通过源码方式查看到在refresh()的this.prepareBeanFactory(beanFactory);中提前准备了ApplicationContextAwareProcessor

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        beanFactory.setBeanClassLoader(this.getClassLoader());
        beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver());
        beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this));
        beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
        beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
        beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
        beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
        beanFactory.registerResolvableDependency(ResourceLoader.class, this);
        beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
        beanFactory.registerResolvableDependency(ApplicationContext.class, this);
        if (beanFactory.containsBean("loadTimeWeaver")) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }

        Object systemEnvironment;
        if (!beanFactory.containsBean("systemProperties")) {
            try {
                systemEnvironment = System.getProperties();
            } catch (AccessControlException var4) {
                systemEnvironment = new ReadOnlySystemAttributesMap() {
                    protected String getSystemAttribute(String propertyName) {
                        try {
                            return System.getProperty(propertyName);
                        } catch (AccessControlException var3) {
                            if (AbstractApplicationContext.this.logger.isInfoEnabled()) {
                                AbstractApplicationContext.this.logger.info("Not allowed to obtain system property [" + propertyName + "]: " + var3.getMessage());
                            }

                            return null;
                        }
                    }
                };
            }

            beanFactory.registerSingleton("systemProperties", systemEnvironment);
        }

　　四：Aware接口部分就这么多吧，这里没有具体些实现和用法，但是相对于BeanFactoryPostProcessor，BeanPostProcessor。Aware在实际应用中会更加常用，这一部分是spring提供出来的拓展，也是必要重要的一个部分。

　　当然，我这里可能还存在一些纰漏，还请大佬指出来！