ApplicationContextAware 的理解和应用

　　当我们在项目中获取某一个spring bean时，可以定义一个类，实现ApplicationContextAware  该接口，该接口可以加载获取到所有的 spring bean。

package com.lf.mp.test;

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

@Component
public class ApplicationContextUtil implements ApplicationContextAware {

    private static ApplicationContext applicationContext;

    /**
     * 实现ApplicationContextAware接口的回调方法，设置上下文环境
     *
     * @param applicationContext spring上下文对象
     * @throws BeansException 抛出spring异常
     */
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        ApplicationContextUtil.applicationContext = applicationContext;
    }

    /**
     * @return ApplicationContext
     */
    public static ApplicationContext getApplicationContext() {
        return applicationContext;
    }

    /**
     * 获取对象
     *
     * @param name spring配置文件中配置的bean名或注解的名称
     * @return 一个以所给名字注册的bean的实例
     * @throws BeansException 抛出spring异常
     */
    @SuppressWarnings("unchecked")
    public static <T> T getBean(String name) throws BeansException {
        return (T) applicationContext.getBean(name);
    }

    /**
     * 获取类型为requiredType的对象
     *
     * @param clazz 需要获取的bean的类型
     * @return 该类型的一个在ioc容器中的bean
     * @throws BeansException 抛出spring异常
     */
    public static <T> T getBean(Class<T> clazz) throws BeansException {
        return applicationContext.getBean(clazz);
    }

    /**
     * 如果ioc容器中包含一个与所给名称匹配的bean定义，则返回true否则返回false
     *
     * @param name ioc容器中注册的bean名称
     * @return 存在返回true否则返回false
     */
    public static boolean containsBean(String name) {
        return applicationContext.containsBean(name);
    }
}

ApplicationContextAware 接口的定义如下：

package org.springframework.context;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.Aware;

public interface ApplicationContextAware extends Aware {
    void setApplicationContext(ApplicationContext var1) throws BeansException;
}

通过实现 ApplicationContextAware 接口可以获取所有的spring bean，是因为spring会自动执行setApplicationAware .

示例在类中获取静态bean的实例：

import com.alibaba.fastjson.JSONObject;
import com.lf.mp.entity.User;
import com.lf.mp.service.UserService;

public class SpringBeanTest {
    private static UserService userService;
    static {
        userService = ApplicationContextUtil.getBean(UserService.class);
    }
    public static void test(){
        User user = userService.getById(222L);
        System.out.println(JSONObject.toJSON(user));
    }
}