部署 Java EE 应用程序后执行任务
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Executing task after deployment of Java EE application
提问by Oliver
I have a Java EE application which should start a synchronization process with an external system once after its deployment.
我有一个 Java EE 应用程序，它应该在部署后启动一次与外部系统的同步过程。
How could I implement this requirement?
我怎样才能实现这个要求？
采纳答案by Oliver
I tested the suggested solution which uses the @Startupand @PostConstructannotations. It turned out that Glassfish does not complete the deployment of an application until all methods annotated with @PostConstructhave finished. So in my case the deployment would take from several minutes up to an hour.
我测试了使用@Startup和@PostConstruct注释的建议解决方案。事实证明，Glassfish 不会完成应用程序的部署，直到所有注释的方法@PostConstruct都完成。所以在我的情况下，部署需要几分钟到一个小时。
But I figured out a different way to achive what I want. The best solution seems to be a timer callback method which cancels its timer after its execution.
但我想出了一种不同的方法来实现我想要的。最好的解决方案似乎是一个计时器回调方法，它在执行后取消其计时器。
@Stateless
public class SynchronisationService {
@Schedule(hour = "*", minute = "*", persistent = false)
protected void init(Timer timer)
{
doTheSync();
timer.cancel();
}
}
Using a non-persistent timer allows the timer to be re-created if the application server is restarted.
如果应用程序服务器重新启动，则使用非持久性计时器允许重新创建计时器。
回答by Dev
Below are listed a couple of popular methods for getting lifecycle callbacks in JavaEE apps.
下面列出了一些在 JavaEE 应用程序中获取生命周期回调的流行方法。
Create a javax.servlet.ServletContextListener implementation
创建一个 javax.servlet.ServletContextListener 实现
If you have a web component to your .ear file (embedded .war) or your deployment is a .war by itself you can add a ServletContextListenerto your web.xmland get a callback when the server starts or is shutting down.
如果您的 .ear 文件（嵌入的 .war）中有一个 Web 组件，或者您的部署本身就是一个 .war，您可以在服务器启动或关闭时ServletContextListener向您添加一个web.xml并获得回调。
Example:
例子：
package com.stackoverflow.question
import javax.servlet.ServletContextListener;
import javax.servlet.ServletContextEvent;
public class MyServletContextListener implements ServletContextListener{
@Override
public void contextInitialized(ServletContextEvent contextEvent) {
/* Do Startup stuff. */
}
@Override
public void contextDestroyed(ServletContextEvent contextEvent) {
/* Do Shutdown stuff. */
}
}
and then add this configuration to your web.xmldeployment descriptor.$WAR_ROOT/WEB-INF/web.xml.
然后将此配置添加到您的web.xml部署描述符中。$WAR_ROOT/WEB-INF/web.xml.
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee">
<listener>
<listener-class>com.stackoverflow.question.MyServletContextListener</listener-class>
</listener>
</web-app>
Create an EJB 3.1 @Startup Bean
创建 EJB 3.1 @Startup Bean
This method uses an EJB 3.1 singleton to get a startup and shutdown callback from the server.
此方法使用 EJB 3.1 单例从服务器获取启动和关闭回调。
import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
import javax.ejb.Startup;
import javax.ejb.Singleton;
@Singleton
@Startup
public class LifecycleBean {
@PostConstruct
public void init() {
/* Startup stuff here. */
}
@PreDestroy
public void destroy() {
/* Shutdown stuff here */
}
}
回答by JB Nizet
Using a ServletContextListener, or a servlet that is initialized at startup, for example. Of course, this becomes much harder if you have multiple deployments of the application in a cluster, and only want this process to be run once.
例如，使用ServletContextListener, 或在启动时初始化的 servlet。当然，如果您在一个集群中有多个应用程序部署，并且只希望此进程运行一次，这将变得更加困难。
回答by Kayaman
You can use the @Startupand @PostConstructannotations to perform tasks on application startup.
您可以使用@Startup和@PostConstruct注释在应用程序启动时执行任务。
