還記的我們?cè)?CreateBean(...)方法中其中有一個(gè)過(guò)程是初始化bean的過(guò)程,在初始化的方法中我們其中有一個(gè)過(guò)程是激活A(yù)ware的方法的過(guò)程,這節(jié)我們來(lái)看看Aware到底是什么

Aware接口

該接口位于org.springframework.beans.factory包下

/**
 * A marker superinterface indicating that a bean is eligible to be notified by the
 * Spring container of a particular framework object through a callback-style method.
 * The actual method signature is determined by individual subinterfaces but should
 * typically consist of just one void-returning method that accepts a single argument.
 *
 * <p>Note that merely implementing {@link Aware} provides no default functionality.
 * Rather, processing must be done explicitly, for example in a
 * {@link org.springframework.beans.factory.config.BeanPostProcessor}.
 * Refer to {@link org.springframework.context.support.ApplicationContextAwareProcessor}
 * for an example of processing specific {@code *Aware} interface callback
 */
  public interface Aware {

}

該接口主要的作用是一個(gè)標(biāo)記超級(jí)接口,實(shí)現(xiàn)了該接口的bean是具有回調(diào)spring容器的能力,我們可以看到,是一個(gè)空接口,實(shí)際方法的簽名是由各個(gè)子接口來(lái)實(shí)現(xiàn),通常只接受返回單個(gè)參數(shù)的seter方法,我們來(lái)看一下我們的激活A(yù)ware方法的代碼:

AbstractAutowireCapableBeanFactory.java
private void invokeAwareMethods(final String beanName, final Object bean) {
    if (bean instanceof Aware) {
        if (bean instanceof BeanNameAware) {
            ((BeanNameAware) bean).setBeanName(beanName);
        }
        if (bean instanceof BeanClassLoaderAware) {
            ClassLoader bcl = getBeanClassLoader();
            if (bcl != null) {
                ((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);
            }
        }
        if (bean instanceof BeanFactoryAware) {
            ((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
        }
    }
}

代碼簡(jiǎn)單:

• 如果是BeanNameAware類(lèi)型的話,調(diào)用setXX方法設(shè)置屬性
• 如果是BeanClassLoaderAware類(lèi)型的話,調(diào)用setBeanClassLoader設(shè)置屬性
• 如果是beanFactoryAware類(lèi)型的話,調(diào)用setBeanFactory設(shè)置屬性

Aware的實(shí)現(xiàn)類(lèi)

我們來(lái)看一下實(shí)現(xiàn)了Aware接口的子類(lèi)

image

這只是其中的一部分實(shí)現(xiàn),圖來(lái)自大佬芋艿的博客,大家可以去看看,接下來(lái)我們自己可以實(shí)現(xiàn)自己的Aware方法:

''''''
public interface BeanClassLoaderAware extends Aware {

/**
* 將 BeanClassLoader 提供給 bean 實(shí)例回調(diào)
* 在 bean 屬性填充之后、初始化回調(diào)之前回調(diào)，
* 例如InitializingBean的InitializingBean.afterPropertiesSet（）方法或自定義init方法
*/
void setBeanClassLoader(ClassLoader classLoader);


public interface BeanFactoryAware extends Aware {

   /**
* 將 BeanFactory 提供給 bean 實(shí)例回調(diào)
* 調(diào)用時(shí)機(jī)和 setBeanClassLoader 一樣
*/
void setBeanFactory(BeanFactory beanFactory) throws BeansException;

public interface BeanNameAware extends Aware {

/**
* 在創(chuàng)建此 bean 的 bean工廠中設(shè)置 beanName
*/
void setBeanName(String name);

}


public interface ApplicationContextAware extends Aware {

/**
 * 設(shè)置此 bean 對(duì)象的 ApplicationContext逸雹，通常，該方法用于初始化對(duì)象
 */
void setApplicationContext(ApplicationContext applicationContext) throws BeansException;

常見(jiàn)的四種實(shí)現(xiàn)Aware接口的子類(lèi),我們來(lái)看case

  public class MyAwareCase implements
    BeanNameAware, BeanFactoryAware, BeanClassLoaderAware, ApplicationContextAware {

private String beanName;
private ClassLoader classLoader;
private BeanFactory beanFactory;
private ApplicationContext applicationContext;
public void setBeanClassLoader(ClassLoader classLoader) {

    this.classLoader = classLoader;
    System.out.println("調(diào)用:BeanClassLoaderAware的setBeanClassLoader方法");

}

public void setBeanFactory(BeanFactory beanFactory) throws BeansException {

    this.beanFactory = beanFactory;
    System.out.println("調(diào)用:BeanFactoryAware的setBeanFactory方法");

}

public void setBeanName(String name) {
    this.beanName = name;
    System.out.println("調(diào)用:BeanNameAware的setBeanName方法");

}

public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {

    this.applicationContext = applicationContext;
    System.out.println("調(diào)用:ApplicationContextAware的setApplicationContext方法");

}

public void display(){
    System.out.println("beanName:" + beanName);
    System.out.println("是否為單例：" + beanFactory.isSingleton(beanName));
    System.out.println("系統(tǒng)環(huán)境為：" + applicationContext.getEnvironment());
}

測(cè)試方法如下:

public class AwareTest {

public static void main(String[] args) {

    ClassPathResource resource = new ClassPathResource("awareConfig.xml");
    DefaultListableBeanFactory factory = new DefaultListableBeanFactory();
    XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory);
     reader.loadBeanDefinitions(resource);
    MyAwareCase myAwareCase = (MyAwareCase)factory.getBean("myAwareCase");
    myAwareCase.display();
}

配置文件如下:

<?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 id="myAwareCase" class="com.sgcc.aware.MyAwareCase">
    <property name="beanName" value="beanName"/>
    <property name="beanFactory" value="beanFactory"/>
    <property name="beanClassLoader" value="beanClassLoader"/>
    <property name="applicationContext" value="applicationContext"/>
</bean>
</beans>

很意外,我運(yùn)行時(shí)報(bào)了一個(gè)錯(cuò)誤,大概知道問(wèn)題所在,這里我把錯(cuò)誤貼出來(lái),有知道解決的可以留個(gè)言,在這里我先謝過(guò)了

Caused by: org.springframework.beans.ConversionNotSupportedException: Failed to convert property value of type 'java.lang.String' to required type 'org.springframework.beans.factory.BeanFactory' for property 'beanFactory'; nested exception is java.lang.IllegalStateException: Cannot convert value of type 'java.lang.String' to required type 'org.springframework.beans.factory.BeanFactory' for property 'beanFactory': no matching editors or conversion strategy found
at org.springframework.beans.AbstractNestablePropertyAccessor.convertIfNecessary(AbstractNestablePropertyAccessor.java:590)
at org.springframework.beans.AbstractNestablePropertyAccessor.convertForProperty(AbstractNestablePropertyAccessor.java:604)
at org.springframework.beans.BeanWrapperImpl.convertForProperty(BeanWrapperImpl.java:219)

從異常信息來(lái)看是因?yàn)閷傩詁eanFactory在匹配類(lèi)型的過(guò)程中出現(xiàn)的問(wèn)題.它需要的是一個(gè)BeanFactory類(lèi)型的屬性value,我這里是String,可能是這個(gè)原因造成的

總結(jié)

經(jīng)過(guò)簡(jiǎn)單的case,我們發(fā)現(xiàn)Aware接口的實(shí)質(zhì),spring主要來(lái)檢測(cè)當(dāng)前bean是否實(shí)現(xiàn)了Aware接口,如果實(shí)現(xiàn)了,則通過(guò)setxxx設(shè)置對(duì)應(yīng)的屬性給bean,之后我們的bean就有了從spring容器中獲取資源的權(quán)限了......