项目____web项目中实现：一直运行某个后台小程序+定时+多任务

如何在web项目启动后就运行某个java程序段？

把xx类写成一个servlet，然后配置到web.xml中。设置这个servlet在应用启动之后就运行。项目中web.xml配置代码如下：

<!-- maple服务器 定时服务 --><servlet><servlet-name>mapleServlet</servlet-name><servlet-class>com.csValue.Servlet.mapleServlet</servlet-class><load-on-startup>1</load-on-startup></servlet><servlet-mapping><servlet-name>mapleServlet</servlet-name><url-pattern>/mapleServlet.view</url-pattern></servlet-mapping>

servlet启动后如何定时调用某个功能？

servlet随着项目的启动而启动，至于servlet中如何实现定时可以参考 实现定时功能 中的三种方法实现。

本项目中的mapleServlet代码如下：

package com.csValue.Servlet;import java.io.IOException;import java.io.PrintStream;import java.util.Timer;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class mapleServlet extends HttpServlet{  private static final long serialVersionUID = 1L;  public void init()    throws ServletException  {    System.out.println("监控启动");    Timer timer = new Timer();    timer.schedule(new Task(), 6000L, 30000L);  }  protected void doGet(HttpServletRequest request, HttpServletResponse response)    throws ServletException, IOException  {    doPost(request, response);  }  protected void doPost(HttpServletRequest request, HttpServletResponse response)    throws ServletException, IOException  {  }}

默认执行init方法 实例化Timer，并调用timer的schedule方法。延迟多少毫秒后。每隔多少毫秒执行一次Task。

利用Timer实现定时功能的总体步骤，用代码表示如下：

package scheduleTest;import java.util.Timer;import java.util.TimerTask;public class scheduleTimerTest {  public static void main(String[] args) {    TimerTask task = new TimerTask() {      @Override      public void run() {        // task to run goes here        System.out.println("Hello !!!");      }    };    Timer timer = new Timer();    long delay = 5000;    long intevalPeriod = 1 * 1000;    // schedules the task to be run in an interval    timer.scheduleAtFixedRate(task, delay,                                intevalPeriod);  } // end of main}

实例化Timer，调用scheduleAtFixedRate方法。其中传入的task参数在之前实例化，run方法中是具体实现：输出hello

至于Timer的源码研究请参照timer研究。其中给出了关于Timer源码的具体实现，通过queue实现队列中各任务的notify。

而task是具体任务内容，代码如下：

public class Task extends TimerTask{  public void run()  {Map changedLines=compareMapleBean(selectLocalMapleList(), selectMapleList());    if (changedLines != null)    {      Object[] lines=changedLines.keySet().toArray();      Map<String, String> usageLine=new HashMap<String, String>();      usageLine.put("UVA 1", "");      usageLine.put("UVA 2", "");      usageLine.put("UVA 3", "");      usageLine.put("UVA 4", "");      usageLine.put("UVA 5", "");      usageLine.put("UVA 6", "");      usageLine.put("UVA 7", "");      usageLine.put("UVA 8", "");      usageLine.put("JINYI 9", "");      usageLine.put("JINYI 10", "");      usageLine.put("JINYI 11", "");      usageLine.put("JINYI 12", "");      usageLine.put("JINYI 13", "");      usageLine.put("JINYI 14", "");      usageLine.put("JINYI 15", "");      usageLine.put("JINYI 16", "");      usageLine.put("JINYI 17", "");      usageLine.put("JINYI 18", "");      usageLine.put("JINYI 19", "");                 for (Object object : lines) {      if(usageLine.containsKey(object.toString())){      updateMaple(object.toString(),changedLines.get(object.toString()).toString().split("::"));      }      }        System.out.println("推送完成");      }  }}

定时功能的具体实现？

返回来接着看servlet中的代码：

timer.schedule(new Task(), 6000L, 30000L);

实现源代码如下：

/**     * Schedules the specified task for repeated <i>fixed-delay execution</i>,     * beginning after the specified delay.  Subsequent executions take place     * at approximately regular intervals separated by the specified period.     *     * <p>In fixed-delay execution, each execution is scheduled relative to     * the actual execution time of the previous execution.  If an execution     * is delayed for any reason (such as garbage collection or other     * background activity), subsequent executions will be delayed as well.     * In the long run, the frequency of execution will generally be slightly     * lower than the reciprocal of the specified period (assuming the system     * clock underlying <tt>Object.wait(long)</tt> is accurate).     *     * <p>Fixed-delay execution is appropriate for recurring activities     * that require "smoothness."  In other words, it is appropriate for     * activities where it is more important to keep the frequency accurate     * in the short run than in the long run.  This includes most animation     * tasks, such as blinking a cursor at regular intervals.  It also includes     * tasks wherein regular activity is performed in response to human     * input, such as automatically repeating a character as long as a key     * is held down.     *     * @param task   task to be scheduled.     * @param delay  delay in milliseconds before task is to be executed.     * @param period time in milliseconds between successive task executions.     * @throws IllegalArgumentException if <tt>delay</tt> is negative, or     *         <tt>delay + System.currentTimeMillis()</tt> is negative.     * @throws IllegalStateException if task was already scheduled or     *         cancelled, timer was cancelled, or timer thread terminated.     */    public void schedule(TimerTask task, long delay, long period) {        if (delay < 0)            throw new IllegalArgumentException("Negative delay.");        if (period <= 0)            throw new IllegalArgumentException("Non-positive period.");        sched(task, System.currentTimeMillis()+delay, -period);    }

sched实现源代码如下：

 /**     * Schedule the specified timer task for execution at the specified     * time with the specified period, in milliseconds.  If period is     * positive, the task is scheduled for repeated execution; if period is     * zero, the task is scheduled for one-time execution. Time is specified     * in Date.getTime() format.  This method checks timer state, task state,     * and initial execution time, but not period.     *     * @throws IllegalArgumentException if <tt>time()</tt> is negative.     * @throws IllegalStateException if task was already scheduled or     *         cancelled, timer was cancelled, or timer thread terminated.     */    private void sched(TimerTask task, long time, long period) {        if (time < 0)            throw new IllegalArgumentException("Illegal execution time.");        synchronized(queue) {            if (!thread.newTasksMayBeScheduled)                throw new IllegalStateException("Timer already cancelled.");            synchronized(task.lock) {                if (task.state != TimerTask.VIRGIN)                    throw new IllegalStateException(                        "Task already scheduled or cancelled");                task.nextExecutionTime = time;                task.period = period;                task.state = TimerTask.SCHEDULED;            }            queue.add(task);            if (queue.getMin() == task)                queue.notify();        }    }