ajax+servlet实现轮寻内存中的数据

最近的一个项目需要多个硬件设备发送带参数的url，我们能在web页面实时显示所有参数。

如url：localhost:8080/webtest?id=1&status=2，我们需要把id以及status读取出来实时传递到页面

很明显，url访问servlet，但是服务器不能主动向jsp页面推送数据，所以我们这里用了ajax（当然你对websocket很熟悉也是可以用的，顺便说一句，老哥们真的会的话麻烦给小弟一份demo）

所以简单的做了一个java web项目，数据全部存储在内存中。想法是jsp页面中通过ajax轮寻访问一个servlet a获取静态变量中存放的数据，所有的硬件设备访问servlet b存储数据

目录结构如下

ajax+servlet实现轮寻内存中的数据

AjaxServlet.java

package servlet;

import utils.JavaParamConfig;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.LinkedList;

/**
 * @Version 1.0
 * @Author Martin
 * @Date 2019-04-22 00:36
 */

@WebServlet(name = "AjaxServlet", urlPatterns = "/servlet/AjaxServlet")
public class AjaxServlet extends HttpServlet {

    @Override
    public void init() throws ServletException {
        System.out.println("servlet init");

    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        if (JavaParamConfig.changeflag){
            resp.setContentType("text/plain");
            resp.setCharacterEncoding("UTF-8");
            dealWithInfoList(JavaParamConfig.infoList);
            JavaParamConfig.changeflag = false;
        }
        resp.getWriter().write(JavaParamConfig.allInfoTable.toString());

    }

    private void dealWithInfoList(LinkedList<String> linkedList) {
        int len = linkedList.size();
        for (int i = 0; i < len; i++){
            String[] str = linkedList.peek().split("=");
            JavaParamConfig.allInfoTable.computeIfAbsent(str[0], k -> str[1]);
            JavaParamConfig.allInfoTable.put(str[0], str[1]);
            linkedList.pop();
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("nihao");
    }
}

TestServlet.java

package servlet;

import utils.JavaParamConfig;

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

/**
 * @Version 1.0
 * @Author Martin
 * @Date 2019-04-22 00:36
 */

@WebServlet(name = "TestServelt", urlPatterns = "/servlet/TestServlet")
public class TestServlet extends HttpServlet {

    @Override
    public void init() throws ServletException {
        System.out.println("servlet init");

    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String id = req.getParameter("id");
        String status = req.getParameter("status");
        String info = id + "=" + status;
        JavaParamConfig.infoList.add(info);
        JavaParamConfig.changeflag = true;
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

JavaParamConfig.java

package utils;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.LinkedList;

/**
 * @Version 1.0
 * @Author Martin
 * @Date 2019-04-28 21:43
 */
public class JavaParamConfig {
    //存储所有设备ID以及状态
    public static Hashtable<String, String> allInfoTable = new Hashtable<String, String>();

    //模拟消息队列
    public static LinkedList<String> infoList = new LinkedList<String>();
    //是否有数据变化的标识位
    public static boolean changeflag = false;
    
}

index.jsp

setInterval定时每4s调用一次test方法

这里的ajax是通过jquery实现的，原生js实现的自行百度，至于jquery，其实就是一些js代码的封装包而已

<%--
  Created by IntelliJ IDEA.
  User: matian
  Date: 2019-04-29
  Time: 12:41
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
  <title>没有BUG</title>
  <script src="http://code.jquery.com/jquery-latest.min.js"></script>
  <script>
    function test() { // When HTML DOM "click" event is invoked on element with ID "somebutton", execute the following function...
      $.get("servlet/AjaxServlet", function(responseText) {   // Execute Ajax GET request on URL of "someservlet" and execute the following function with Ajax response text...
        $("#somediv").text(responseText);           // Locate HTML DOM element with ID "somediv" and set its text content with the response text.
      });
    }
  </script>
  <script>
    setInterval(test, 4000);
  </script>
</head>
<body>
欢迎登陆
<div id="somediv"></div>
</body>
</html>

至于MethodUtils.java中的内容本来是想封装一些方法比如输出个时间啥的，但是没有用到

代码到这里就结束了。

测试结果

新开的两个页面只是为了测试传url以及参数，可以看到两个url中的数据都被读取出来了

ajax+servlet实现轮寻内存中的数据

ps：讲道理，这些数据都得存数据库中。等有时间再改进。

ajax+servlet实现轮寻内存中的数据

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