Spring 中的几个常用的钩子接口

1.Aware接口

Awear 这个单词的意思是知道的，所以可以猜想以Awear 结尾的接口意思可以把他知道的东西告诉我们。常用的Awear接口有 ApplicationContextAware和 BeanFactoryAware，另外还有BeanNameAware 和EnvironmentAware

（1）ApplicationContextAware 接口 可以返回  ApplicationContext，也就是容器本身，我们可以通过ApplicationContext 这个容器对象做很多事，最常见的是获取Bean，和判断当前容器是否包含某个组件。下面的示例是通过ApplicationContext 获取Bean的示例（工程基于SpringBoot2.2.1.RELEASE）

package com.spring.hook.compent;

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

/**
 * @Author lizhilong
 * @create 2019/11/28 13:51
 * @desc
 */
@Component
public class SpringContextAware implements ApplicationContextAware {

    private static ApplicationContext app;
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
         app  = applicationContext;
    }

    public  static<T> T getBeanByClass(Class<T> clazz){
        return  app.getBean(clazz);
    }

    public static Class<?>  getBeanByType(String type){
        return  app.getType(type);
    }

    @SuppressWarnings("unchecked")
    public static <T> T getBeanByName(String name){
        return  (T) app.getBean(name);
    }
}

（2）BeanFactoryAware 。通过实现 BeanFactoryAware 可以获取BeanFactory。Beanfactory 作用和ApplicationContext 类似，BeanFactory 比ApplicationContext更底层一些， 当然功能更加单一一些，ApplicationContext 在此基础做了一些加强，比如多了国际化等一些信息。

package com.spring.hook.compent;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.stereotype.Component;

/**
 * @Author lizhilong
 * @create 2019/11/28 16:48
 * @desc
 */
@Component
public class BeanFactoryContext implements BeanFactoryAware{

    private  static  BeanFactory beanFactory;
    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        BeanFactoryContext.beanFactory = beanFactory;
    }

    public  static<T> T getBeanByClass(Class<T> clazz){
        return  beanFactory.getBean(clazz);
    }
}

（3）BeanNameAware。这个接口个人感觉作用不明显，通过实现这个接口可以获取当前Bean的名称。

package com.spring.hook.compent;

import org.springframework.beans.factory.BeanNameAware;
import org.springframework.stereotype.Component;

/**
 * @Author lizhilong
 * @create 2019/11/28 14:19
 * @desc
 */
@Component
public class Car implements BeanNameAware{

    @Override
    public void setBeanName(String s) {
        System.out.println("BeanName:"+s);
    }

    private  String brand;

    private String color;

    public String getCarAttr(){
        return "品牌："+brand+"    颜色："+color;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public void setColor(String color) {
        this.color = color;
    }
}

（4）EnvironmentAware 通过实现这个接口可以获取当前运行环境的一些信息。

package com.spring.hook.compent;

import org.springframework.context.EnvironmentAware;
import org.springframework.core.env.Environment;
import org.springframework.stereotype.Component;

/**
 * @Author lizhilong
 * @create 2019/11/28 17:25
 * @desc
 */
@Component
public class EnvironmentContext implements EnvironmentAware {
    @Override
    public void setEnvironment(Environment environment) {
        String[] activeProfile = environment.getActiveProfiles();
        String[] defaultProfile = environment.getDefaultProfiles();
        String port = environment.getProperty("dog.type");
    }
}

2.InitializingBean,DisposableBean 通过实现这两个接口可以在Bean初始化后和摧毁钱做一些事。InitializingBean 接口的afterPropertiesSet() 方法在set属性完成后执行，DisposableBean 的 destroy() 方法在bean摧毁前BeanFactory执行

package com.spring.hook.compent;

import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.stereotype.Component;

/**
 * @Author lizhilong
 * @create 2019/11/28 17:45
 * @desc
 */
@Component
public class Fruit implements InitializingBean,DisposableBean{
    @Override
    public void destroy() throws Exception {
        System.out.println("我要被销毁了");
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("我原来的名字叫："+name);
        name = "苹果";
    }

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

3.PostProcessor 这个接口被称为后置处理器，常见的有：BeanPostProcessor，BeanFactoryPostProcessor ，分别为Bean的后置处理器和BeanFactory的后置处理器。

（1）BeanPostProcessor 能再Bean的初始化前后做一些事，但是个人感觉很功能很单一，无法返回具体的Bean

package com.spring.hook.compent;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;

/**
 * @Author lizhilong
 * @create 2019/11/28 18:19
 * @desc
 */
@Component
public class BeanPostProcessorImpl implements BeanPostProcessor{
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("初始化前BeanName:"+beanName);
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("初始化后BeanName:"+beanName);
        return bean;
    }

}

（2）BeanFactoryPostProcessor

package com.spring.hook.compent;

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.stereotype.Component;

/**
 * @Author lizhilong
 * @create 2019/11/28 18:29
 * @desc
 */
@Component
public class BeanPostFactoryContextImpl implements BeanFactoryPostProcessor {

    private static  ConfigurableListableBeanFactory beanFactory;

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {
        beanFactory = configurableListableBeanFactory;
        if(beanFactory.containsBean("fruit")){
            BeanDefinition fruit = beanFactory.getBeanDefinition("fruit");
            MutablePropertyValues propertyValues = fruit.getPropertyValues();
            propertyValues.add("name","香蕉");

        }
        Fruit fruit = (Fruit)beanFactory.getBean("fruit");
        System.out.println("我现在的名字叫："+fruit.getName());
    }
}

示例中我们在不同的时刻为 Fruit 的name属性赋值，运行结果：

我原来的名字叫：香蕉
我现在的名字叫：苹果