Question

对于常规Servlet，我想你可以声明一个context listener，但对于Spring MVC，Spring会让这更容易吗？

此外，如果我定义了一个上下文侦听器，然后需要访问我的servlet.xml或applicationContext.xml中定义的bean，我将如何访问它们？

Answer 1

Spring has some standard events which you can handle.

为此，您必须创建并注册实现ApplicationListener接口的bean，如下所示：

package test.pack.age;

import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;

public class ApplicationListenerBean implements ApplicationListener {

    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        if (event instanceof ContextRefreshedEvent) {
            ApplicationContext applicationContext = ((ContextRefreshedEvent) event).getApplicationContext();
            // now you can do applicationContext.getBean(...)
            // ...
        }
    }
}

然后，您可以在servlet.xml或applicationContext.xml文件中注册此bean：

<bean id="eventListenerBean" class="test.pack.age.ApplicationListenerBean" />

并且Spring将在初始化应用程序上下文时通知它。

在Spring 3中（如果您使用的是此版本），ApplicationListener class is generic并且您可以声明您感兴趣的事件类型，并相应地过滤事件。您可以像这样简化bean代码：

public class ApplicationListenerBean implements ApplicationListener<ContextRefreshedEvent> {

    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        ApplicationContext applicationContext = event.getApplicationContext();
        // now you can do applicationContext.getBean(...)
        // ...
    }
}

Answer 2

从Spring 4.2开始，您可以使用@EventListener（documentation）

@Component
class MyClassWithEventListeners {

    @EventListener({ContextRefreshedEvent.class})
    void contextRefreshedEvent() {
        System.out.println("a context refreshed event happened");
    }
}

Answer 3

创建注释

  @Retention(RetentionPolicy.RUNTIME)
    public @interface AfterSpringLoadComplete {
    }

创建课程

    public class PostProxyInvokerContextListener implements ApplicationListener<ContextRefreshedEvent> {

    @Autowired
    ConfigurableListableBeanFactory factory;

    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        ApplicationContext context = event.getApplicationContext();
        String[] names = context.getBeanDefinitionNames();
        for (String name : names) {
            try {
                BeanDefinition definition = factory.getBeanDefinition(name);
                String originalClassName = definition.getBeanClassName();
                Class<?> originalClass = Class.forName(originalClassName);
                Method[] methods = originalClass.getMethods();
                for (Method method : methods) {
                    if (method.isAnnotationPresent(AfterSpringLoadComplete.class)){
                        Object bean = context.getBean(name);
                        Method currentMethod = bean.getClass().getMethod(method.getName(), method.getParameterTypes());
                        currentMethod.invoke(bean);
                    }
                }
            } catch (Exception ignored) {
            }
        }
    }
}

通过@Component注释或xml

注册此类

<bean class="ua.adeptius.PostProxyInvokerContextListener"/>

并使用注释来处理在上下文初始化后要运行的任何方法，例如：

   @AfterSpringLoadComplete
    public void init() {}

Answer 4

我有一个单页应用程序在输入URL时创建了一个HashMap（由我的网页使用），其中包含来自多个数据库的数据。我在服务器启动时加载了所有内容 -

1- Created ContextListenerClass

public class MyAppContextListener implements ServletContextListener
    @Autowired

    private  MyDataProviderBean myDataProviderBean; 

    public MyDataProviderBean getMyDataProviderBean() {

        return MyDataProviderBean;

    }

    public void setMyDataProviderBean(MyDataProviderBean MyDataProviderBean) {

        this.myDataProviderBean = MyDataProviderBean;

    }

    @Override
    public void contextDestroyed(ServletContextEvent arg0) {

        System.out.println("ServletContextListener destroyed");

    }


    @Override

    public void contextInitialized(ServletContextEvent context) {

        System.out.println("ServletContextListener started");

        ServletContext sc = context.getServletContext();

        WebApplicationContext springContext = WebApplicationContextUtils.getWebApplicationContext(sc);

        MyDataProviderBean MyDataProviderBean = (MyDataProviderBean)springContext.getBean("myDataProviderBean");

        Map<String, Object> myDataMap = MyDataProviderBean.getDataMap();

        sc.setAttribute("myMap", myDataMap);

    }

2-在web.xml中添加以下条目

<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener> 
<listener>
    <listener-class>com.context.listener.MyAppContextListener</listener-class>
</listener>

3-在我的Controller类更新代码中首先检查servletContext中的Map

    @RequestMapping(value = "/index", method = RequestMethod.GET)
        public String index(@ModelAttribute("model") ModelMap model) {

            Map<String, Object> myDataMap = new HashMap<String, Object>();
            if (context != null && context.getAttribute("myMap")!=null)
            {

                myDataMap=(Map<String, Object>)context.getAttribute("myMap");
            }

            else
            {

                myDataMap = myDataProviderBean.getDataMap();
            }

            for (String key : myDataMap.keySet())
            {
                model.addAttribute(key, myDataMap.get(key));
            }
            return "myWebPage";

        }

当我启动tomcat时会发生这么大的变化，它会在startTime期间加载dataMap并将所有内容放在servletContext中，然后Controller Class使用它来获取已填充的servletContext的结果。

Answer 5

请在应用上下文被加载（即应用已准备好服务）之后，按照以下步骤进行一些处理。

在下方创建注释，即

@Retention（RetentionPolicy.RUNTIME） @Target（值= {ElementType.METHOD，ElementType.TYPE}）公共@interface AfterApplicationReady {}

2.Create Under Class是一个侦听器，可在应用就绪状态下进行调用。

    @Component
    public class PostApplicationReadyListener implements ApplicationListener<ApplicationReadyEvent> {

    public static final Logger LOGGER = LoggerFactory.getLogger(PostApplicationReadyListener.class);
    public static final String MODULE = PostApplicationReadyListener.class.getSimpleName();

    @Override
    public void onApplicationEvent(ApplicationReadyEvent event) {
        try {
            ApplicationContext context = event.getApplicationContext();
            String[] beans = context.getBeanNamesForAnnotation(AfterAppStarted.class);

            LOGGER.info("bean found with AfterAppStarted annotation are : {}", Arrays.toString(beans));

            for (String beanName : beans) {
                Object bean = context.getBean(beanName);
                Class<?> targetClass = AopUtils.getTargetClass(bean);
                Method[] methods = targetClass.getMethods();
                for (Method method : methods) {
                    if (method.isAnnotationPresent(AfterAppStartedComplete.class)) {

                        LOGGER.info("Method:[{} of Bean:{}] found with AfterAppStartedComplete Annotation.", method.getName(), beanName);

                        Method currentMethod = bean.getClass().getMethod(method.getName(), method.getParameterTypes());

                        LOGGER.info("Going to invoke method:{} of bean:{}", method.getName(), beanName);

                        currentMethod.invoke(bean);

                        LOGGER.info("Invocation compeleted method:{} of bean:{}", method.getName(), beanName);
                    }
                }
            }
        } catch (Exception e) {
            LOGGER.warn("Exception occured : ", e);
        }
    }
}

最后，当您在启动日志说明应用程序之前启动Spring应用程序时，将调用监听器。

如何将钩子添加到应用程序上下文初始化事件？

5 个答案: