SpringBoot如何使用ApplicationContext获取bean对象

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public class ApplicationContextFactory{
 private static ApplicationContext applicationContext = null;
 public static void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
  applicationContext = applicationContext;
 }
 public static ApplicationContext getApplicationContext(){
  return applicationContext;
 }
}

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public class Application {
 public static void main(String[] args) {
  ConfigurableApplicationContext app = SpringApplication.run(Application.class, args);
  ApplicationContextFactory.setApplicationContext(app);
 }
}

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ApplicationContext applicationContext=ApplicationContextFactory.getApplicationContext();
Clazz clazz = applicationContext.getBean(Clazz.class);

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@Service
public class DemoService {
    public void save(){
        System.out.println("DemoService save");
    }
}

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@Component
public class CommonClass {
    @Resource
    private DemoService demoService;
    public void fun(){
        System.out.println("fun");
        demoService.save();
    }
}

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@Resource
private CommonClass commonClass;
@ResponseBody
@GetMapping("/fun")
public void fun(){
    commonClass.fun();
}

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@Service
public class DemoService {
    public void save(){
        System.out.println("DemoService save");
    }
}

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public class CommonClass {
    @Resource
    private DemoService demoService;
    public void fun(){
        System.out.println("fun");
        demoService.save();
    }
}

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@ResponseBody
@GetMapping("/fun")
public void fun(){
    CommonClass commonClass = new CommonClass();
    commonClass.fun();
}

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@Component
public class ApplicationContextUtil implements ApplicationContextAware {
    private static  ApplicationContext act;
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        act = applicationContext;
    }
    /**
     * 根据bean的名字获取工厂中对应的bean对象
     * @param beanName
     * @return
     */
    public static Object getBean(String beanName){
        return act.getBean(beanName);
    }
}

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@Service
public class DemoService {
    public void save(){
        System.out.println("DemoService save");
    }
}

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public class CommonClass {
    @Resource
    private DemoService demoService;
    public void fun(){
    DemoService demoService = (DemoService) ApplicationContextUtil.getBean("demoService");
        System.out.println("fun");
        demoService.save();
    }
}

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@ResponseBody
@GetMapping("/fun")
public void fun(){
    CommonClass commonClass = new CommonClass();
    commonClass.fun();
}