项目中有时需要在Java类中启动一个长时间运行的服务进程(监听进程、监控进程等)，且该进程需要在tomcat启动时启动，在tomcat停止时退出。在项目开发的过程中，我需要在Java类中启动一个监听进程，而在该进程成功启动后，一调用该监听服务进程时，该进程就挂掉(退出)，现将解决方法记录如下。

ServletContextListener接口能够接收到web context初始化和销毁的消息事件，因此我们可以在该接口中事件长时间运行进程的启动和停止。代码如下:

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public class MyContextListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        ClassLoader classLoader = Thread.currentThread()
                .getContextClassLoader();
        String scriptPath = classLoader.getResource("daemon.sh")
                .getPath();
        List<String> commandsList = new ArrayList<String>();
        commandsList.add("sh");
        commandsList.add(scriptPath);
        commandsList.add("start");
        ProcessBuilder processBuilder = new ProcessBuilder(commandsList);
        try {
            Process process = processBuilder.start();
            //以下两行代码是关键
            ServletContext servletContext = sce.getServletContext();
            servletContext.setAttribute("daemon", process);
            int exitValue = process.waitFor();
            if (0 == exitValue) {
                System.out.println("start daemon success.");
            } else {
                System.out.println("start daemon failed, exitValue: " + exitValue);
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        ClassLoader classLoader = Thread.currentThread()
                .getContextClassLoader();
        String scriptPath = classLoader.getResource("daemon.sh")
                .getPath();
        List<String> commandsList = new ArrayList<String>();
        commandsList.add("sh");
        commandsList.add(scriptPath);
        commandsList.add("stop");
        ProcessBuilder processBuilder = new ProcessBuilder(commandsList);
        try {
            Process process = processBuilder.start();
            int exitValue = process.waitFor();
            if (0 == exitValue) {
                System.out.println("stop daemon success.");
            } else {
                System.out.println("stop daemon failed, exitValue: " + exitValue);
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

然后需要在web.xml的所有filters和servlets定义之前定义:

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<listener>
    <listener-class>org.readus.executescript.MyContextListener</listener-class>
</listener>

如果使用Spring，则可使用如下设置代替上面的listener-class:

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

在上述的实现中，最重要的概括为两点:

  • 实现了ServletContextListener的接口
  • 将生成的长时间运行的进程写入ServletContext的属性中

Java中使用ServletContextListener接口来监听web应用的生命周期变化。其中包含的两个接口:

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public void contextInitialized(ServletContextEvent sce);

该接口文档说明如下:

Receives notification that the web application initialization process is starting.All ServletContextListeners are notified of context initialization before any filters or servlets in the web application are initialized. @param sce the ServletContextEvent containing the ServletContext that is being initialized.

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public void contextDestroyed(ServletContextEvent sce);

该接口的文档说明如下:

Receives notification that the ServletContext is about to be shut down. All servlets and filters will have been destroyed before any ServletContextListeners are notified of context destruction. @param sce the ServletContextEvent containing the ServletContext that is being destroyed.

本文所涉及的代码托管在了GitHub上ExecuteScriptDemo.