一、使用ApplicationContextInitializer，让SpringApplication启动时进行回调，然后获取ApplicationContext

1.创建一个SpringContextHolder对象用来保存ApplicationContext对象

import org.springframework.context.ApplicationContext;

public class SpringContextHolder {

    /**
     * 保存ApplicationContext,可在项目中任意位置中取出ApplicationContext
     */
    private static ApplicationContext applicationContext;

    public static ApplicationContext getApplicationContext() {
        return applicationContext;
    }

    public static void setApplicationContext(ApplicationContext applicationContext) {
        SpringContextHolder.applicationContext = applicationContext;
    }

    /**
     * 通过name获取 Bean.
     * @param name
     * @return
     */
    public static Object getBean(String name){
        return applicationContext.getBean(name);
    }

    /**
     * 通过class获取class下的全部Bean.
     * @param clazz
     * @param <T>
     * @return
     */
    public static <T> Map<String, T> getBeans(Class<T> clazz){
        return applicationContext.getBeansOfType(clazz);
    }

    /**
     * 通过class获取Bean.
     * @param clazz
     * @param <T>
     * @return
     */
    public static <T> T getBean(Class<T> clazz){
        return applicationContext.getBean(clazz);
    }

}

2.在启动类中注册ApplicationContextInitializer接口的匿名对象

import com.yxs.demo.utils.SpringContextHolder;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication springApplication = new SpringApplication(DemoApplication.class);
        //注册ApplicationContextInitializer接口
        //让SpringApplication启动时进行回调
        //调用SpringContextHolder静态方法设置上下文对象
        //org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext
        springApplication.addInitializers(SpringContextHolder::setApplicationContext);
        springApplication.run(args);
    }
}

二、SpringApplication的run方法的返回值就是ApplicationContext实例对象

import com.yxs.demo.utils.SpringContextHolder;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

@SpringBootApplication
public class DemoApplication {
    public static void main(String[] args) {
        //org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext
        ConfigurableApplicationContext applicationContext = SpringApplication.run(DemoApplication.class, args);
        SpringContextHolder.setApplicationContext(applicationContext);
    }
}

三、实现ApplicationContextAware接口，利用Spring Bean的生命周期，在Bean初始化时获取ApplicationContext

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

import java.util.Map;

@Component
public class SpringContextHolder implements ApplicationContextAware {

    /**
     * 保存ApplicationContext,可在项目中任意位置取出ApplicationContext
     */
    private ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        //org.springframework.web.context.support.GenericWebApplicationContext
        this.applicationContext = applicationContext;
    }

    public ApplicationContext getApplicationContext() {
        return applicationContext;
    }

    /**
     * 通过name获取 Bean.
     * @param name
     * @return
     */
    public Object getBean(String name){
        return applicationContext.getBean(name);
    }

    /**
     * 通过class获取class下的全部Bean.
     * @param clazz
     * @param <T>
     * @return
     */
    public <T> Map<String, T> getBeans(Class<T> clazz){
        return applicationContext.getBeansOfType(clazz);
    }

    /**
     * 通过class获取Bean.
     * @param clazz
     * @param <T>
     * @return
     */
    public <T> T getBean(Class<T> clazz){
        return applicationContext.getBean(clazz);
    }
}

四、实现ApplicationListener接口，在SpringApplication启动时，监听ApplicationContextEvent事件触发回调，获取ApplicationContext

import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ApplicationContextEvent;
import org.springframework.stereotype.Component;

import java.util.Map;

@Component
public class SpringContextHolder implements ApplicationListener<ApplicationContextEvent> {

    /**
     * 保存ApplicationContext,可在项目中任意位置取出ApplicationContext
     */
    private ApplicationContext applicationContext;

    @Override
    public void onApplicationEvent(ApplicationContextEvent applicationContextEvent) {
        //org.springframework.web.context.support.GenericWebApplicationContext
        this.applicationContext = applicationContextEvent.getApplicationContext();
    }

    public ApplicationContext getApplicationContext() {
        return applicationContext;
    }

    /**
     * 通过name获取 Bean.
     * @param name
     * @return
     */
    public Object getBean(String name){
        return applicationContext.getBean(name);
    }

    /**
     * 通过class获取class下的全部Bean.
     * @param clazz
     * @param <T>
     * @return
     */
    public <T> Map<String, T> getBeans(Class<T> clazz){
        return applicationContext.getBeansOfType(clazz);
    }

    /**
     * 通过class获取Bean.
     * @param clazz
     * @param <T>
     * @return
     */
    public <T> T getBean(Class<T> clazz){
        return applicationContext.getBean(clazz);
    }
}