ApplicationContext背景關系

ApplicationContext

ApplicationContext是什么？

• ApplicationContext是一個大哥，手下有很多小弟，自己基本上不實作功能，干活的都是小弟，
• 具體從下面的代碼可以看出ApplicationContext繼承了Environment、MessageSource、Resource…也就擁有了他們的功能

public interface ApplicationContext extends EnvironmentCapable, ListableBeanFactory, HierarchicalBeanFactory,
		MessageSource, ApplicationEventPublisher, ResourcePatternResolver

• 那么如何來獲取ApplicationContext呢？

方式一 ApplicationContextInitializer

• 通過實作ApplicationContextInitializer介面來引入ApplicationContext
• 直接上代碼

public class SpringBeanUtil1 implements ApplicationContextInitializer {

    private static ApplicationContext applicationContext;

    @Override
    public void initialize(ConfigurableApplicationContext configurableApplicationContext) {
        if (null == applicationContext) {
            applicationContext = configurableApplicationContext;
        }
    }

    /**
     * @param clazz
     * @param <T>
     * @return 獲取bean
     */
    public static <T> T getBean(Class<T> clazz) {
        return applicationContext.getBean(clazz);
    }
}

// 在Application類中啟動方式如下
@SpringBootApplication
public class SpringUtilApplication {

    public static void main(String[] args) {
        // 方式1，通過ApplicationContextInitializer
        // 也可以通過spring.factories來加載 org.springframework.context.ApplicationContextInitializer=xxx 初始化的
        SpringApplication springApplication = new SpringApplication(SpringUtilApplication.class);
        springApplication.addInitializers(new SpringBeanUtil1());
        springApplication.run(args);
        ServiceDemo bean = SpringBeanUtil1.getBean(ServiceDemo.class);
        System.out.println(bean.toString());
    }
}

方式二 ApplicationListener

• 通過背景關系初始化的時候會處理監聽介面
• 直接上代碼

@Component
public class SpringBeanUtil2 implements ApplicationListener<ApplicationContextEvent> {

    private static ApplicationContext applicationContext;

    /**
     * @param clazz
     * @param <T>
     * @return 獲取bean
     */
    public static <T> T getBean(Class<T> clazz) {
        return applicationContext.getBean(clazz);
    }


    /**
     * 監聽重繪事件
     * @param event
     */
    @Override
    public void onApplicationEvent(ApplicationContextEvent event) {
        if (null == applicationContext) {
            applicationContext = event.getApplicationContext();
        }
    }
}
// 啟動類
@SpringBootApplication
public class SpringUtilApplication {
    public static void main(String[] args) {
      // 方式2，通過ApplicationListener
      SpringApplication.run(SpringUtilApplication.class);
        ServiceDemo bean = SpringBeanUtil2.getBean(ServiceDemo.class);
        System.out.println(bean.toString()); 
    }
}

方式三 ApplicationContextAware

• 通過Spring的通知介面來注入背景關系配置
• 直接上代碼

@Component
public class SpringBeanUtil3 implements ApplicationContextAware {

    private static ApplicationContext context;

    /**
     * @param clazz
     * @param <T>
     * @return 獲取bean
     */
    public static <T> T getBean(Class<T> clazz) {
        return context.getBean(clazz);
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        if (null == context) {
            context = applicationContext;
        }
    }
}

// 啟動類配置
@SpringBootApplication
public class SpringUtilApplication {

    public static void main(String[] args) {
      // 方式3，通過ApplicationContextAware來獲取
      SpringApplication.run(SpringUtilApplication.class);
        ServiceDemo bean = SpringBeanUtil3.getBean(ServiceDemo.class);
        System.out.println(bean.toString());
    }
}

方式四 SpringApplication

• SpringBoot啟動Application的時候可以獲取到ApplicationContext，這個時候可以把ApplicationContext注入到SpringBeanUtil中去
• 直接上代碼

@Component
public class SpringBeanUtil4 {

    private static ApplicationContext context;

    /**
     * @param clazz
     * @param <T>
     * @return 獲取bean
     */
    public static <T> T getBean(Class<T> clazz) {
        return context.getBean(clazz);
    }


    public static void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        if (null == context) {
            context = applicationContext;
        }
    }
}

// main方法
@SpringBootApplication
public class SpringUtilApplication {

    public static void main(String[] args) {
        // 直接通過main方法設定值
        ConfigurableApplicationContext applicationContext = SpringApplication.run(SpringUtilApplication.class);
        SpringBeanUtil4.setApplicationContext(applicationContext);
        ServiceDemo bean = SpringBeanUtil4.getBean(ServiceDemo.class);
        System.out.println(bean.toString());

    }
}

總結

• 以上就是獲取ApplicationContext的四種方式，可以通過上面的任意一種方式來實作自己的SpringBeanUtil類，方便獲取Bean實體，同時也可以在自己的類中通過@Autowired的方式直接引入ApplicationContext，

大家也可以關注spring-cloud系列
1-openfeign
2-hystrix
你們的點贊和關注是我創作的最大動力，有什么不足和錯誤的地方歡迎留言！可以微信搜索關注【小二說碼】