JavaWeb启动时执行初始化操作-优快云博客

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在java web项目中我们通常会有这样的需求：当项目启动时执行一些初始化操作，例如从数据库加载全局配置文件，或者加载必要的配置信息进行初始化等，．

常用的方法有两种，第一种是自定义监听（Listener），第二种是配置随项目启动而启动的Servlet，在初始化方法里面实现自己的功能需求．

下面对这两种方法做一简单的介绍：

1.监听

1.建一个监听类，重写 ServletContextListener的 contextInitialized和contextDestroyed 方法

package com.mindfind.thread;

import javax.servlet.ServletContextListener;
import javax.servlet.ServletContextEvent;
/**
 * Created by Ktao on 9/6/16.
 */
public class MyListenerWay implements ServletContextListener {
    private MyThreadTest myThreadTest;

    public void contextDestroyed(ServletContextEvent e) {
        if (myThreadTest != null && myThreadTest.isInterrupted()) {
            myThreadTest.interrupt();
        }
    }

    public void contextInitialized(ServletContextEvent e) {
        String str = null;
        if (str == null && myThreadTest == null) {
            myThreadTest = new MyThreadTest();
            myThreadTest.start(); // servlet 上下文初始化时启动 socket
        }
    }
}

2.定义一个线程类继承自线程类，重写 run() 方法，用来做数据处理

package com.mindfind.thread;

/**
 * Created by wangtao on 9/6/16.
 */
public class MyThreadTest extends Thread {
    public void run() {
        while (!this.isInterrupted()) {// 线程未中断执行循环
            try {
                Thread.sleep(1000); //每隔1000ms执行一次
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("test begin:" + System.currentTimeMillis());
        }
    }
}

3.在web.xml配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         id="WebApp_ID" version="3.0">

    <listener>
        <listener-class> com.mindfind.thread.MyListenerWay</listener-class>
    </listener>
</web-app>

部署运行结果如下：

2. 继承HttpServlet

　1.首先创建servlet，代码如下：

package com.mindfind.thread;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * Created by wangtao on 9/6/16.
 */
public class MyWayServlet extends HttpServlet {

    private MyThreadTest threadTest;

    public MyWayServlet() {}

    public void init(){
        if(threadTest == null) {
            threadTest = new MyThreadTest();
            threadTest.start();
        }
    }

    public void doGet(HttpServletRequest httpservletrequest, HttpServletResponse httpservletresponse)
            throws ServletException, IOException {
    }

    public void destory(){
        if (threadTest != null && threadTest.isInterrupted()) {
            threadTest.interrupt();
        }
    }
}

2.线程类用刚才现成的

package com.mindfind.thread;

/**
 * Created by wangtao on 9/6/16.
 */
public class MyThreadTest extends Thread {
    public void run() {
        while (!this.isInterrupted()) {
            try {
                Thread.sleep(1000); //每隔1000ms执行一次
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("test begin:" + System.currentTimeMillis());
        }
    }
}

3.在web.xml中配置如下：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         id="WebApp_ID" version="3.0">

    <!--<listener>
        <listener-class> com.mindfind.thread.MyListenerWay</listener-class>
    </listener>-->
    <!-- LISTENNING THREAD -->
    <servlet>
        <servlet-name>MyWayServlet</servlet-name>
        <servlet-class>com.mindfind.thread.MyWayServlet</servlet-class>
        <!--load-on-startup 数字和优先级成反比，都是大于0 -->
        <load-on-startup>9</load-on-startup>
    </servlet>
</web-app>

运行结果如下：