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Servlet 中的后台进程

发布于 2024-09-06 21:30:25 字数 158 浏览 4 评论 0原文

是否可以在 servlet 中实现后台进程！？

让我解释一下。我有一个 servlet，可以显示一些数据并生成一些报告。报告的生成意味着数据已经存在，而且是这样的：其他人上传了这些数据。

除了生成报告之外，我还应该实现一种在新数据（已上传）到达时发送电子邮件的方法。

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鹿港巷口少年归 2024-09-13 21:30:25

功能需求尚不清楚，但要回答实际问题：是的，可以在 servletcontainer 中运行后台进程。

如果您想要应用程序范围的后台线程，请使用 ServletContextListener来挂钩 webapp 的启动和关闭并使用 ExecutorService 来运行它。

@WebListener
public class Config implements ServletContextListener {

    private ExecutorService executor;

    public void contextInitialized(ServletContextEvent event) {
        executor = Executors.newSingleThreadExecutor();
        executor.submit(new Task()); // Task should implement Runnable.
    }

    public void contextDestroyed(ServletContextEvent event) {
        executor.shutdown();
    }

}

如果您尚未使用 Servlet 3.0，因此无法使用 @WebListener，请在 web.xml 中按如下方式注册：

<listener>
    <listener-class>com.example.Config</listener-class>
</listener>

如果您想要一个会话范围的后台线程，使用 HttpSessionBindingListener启动和停止它。

public class Task extends Thread implements HttpSessionBindingListener {

    public void run() {
        while (true) {
            someHeavyStuff();
            if (isInterrupted()) return;
        }
    }

    public void valueBound(HttpSessionBindingEvent event) {
        start(); // Will instantly be started when doing session.setAttribute("task", new Task());
    }

    public void valueUnbound(HttpSessionBindingEvent event) {
        interrupt(); // Will signal interrupt when session expires.
    }

}

在第一次创建和启动时，只需执行

request.getSession().setAttribute("task", new Task());

The functional requirement is unclear, but to answer the actual question: yes, it's possible to run a background process in servletcontainer.

If you want an applicationwide background thread, use ServletContextListener to hook on webapp's startup and shutdown and use ExecutorService to run it.

@WebListener
public class Config implements ServletContextListener {

    private ExecutorService executor;

    public void contextInitialized(ServletContextEvent event) {
        executor = Executors.newSingleThreadExecutor();
        executor.submit(new Task()); // Task should implement Runnable.
    }

    public void contextDestroyed(ServletContextEvent event) {
        executor.shutdown();
    }

}

If you're not on Servlet 3.0 yet and thus can't use @WebListener, register it as follows in web.xml instead:

<listener>
    <listener-class>com.example.Config</listener-class>
</listener>

If you want a sessionwide background thread, use HttpSessionBindingListener to start and stop it.

public class Task extends Thread implements HttpSessionBindingListener {

    public void run() {
        while (true) {
            someHeavyStuff();
            if (isInterrupted()) return;
        }
    }

    public void valueBound(HttpSessionBindingEvent event) {
        start(); // Will instantly be started when doing session.setAttribute("task", new Task());
    }

    public void valueUnbound(HttpSessionBindingEvent event) {
        interrupt(); // Will signal interrupt when session expires.
    }

}

On first creation and start, just do

request.getSession().setAttribute("task", new Task());

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离去的眼神 2024-09-13 21:30:25

谢谢你！我想知道这是否应该在请求范围内更好地完成，例如：

public class StartServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {                   
        request.getSession().setAttribute("task", new Task());     
    }
}

这样，当用户离开页面时，进程就会停止。

Thank you! I was wondering whether this should be better done inside of an request scope like:

public class StartServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {                   
        request.getSession().setAttribute("task", new Task());     
    }
}

This way, the process is stopped when the user leaves the page.

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