java如何使用Tomcat管理后端进程？

# 2 楼答案

您可以创建一个java.lan.Runnable开关，读取文件内容并将其保存到缓冲区中。Runnable使用while循环读取文件内容，因为中断条件可以从外部设置，执行Runnable的线程将在Runnable的run方法终止时终止

在JSP中，您可以创建一个java.lang.Thread，并将Runnable的实例传递给它。将runable的安装保存在ServletContext中，以便您可以跨请求访问它。如果您想终止轮询，而不仅仅是从JSP设置Runnable的中断条件，rum方法将终止，因此线程也将终止

您可以使用javascript setInterval()函数和XMLHttpRequest刷新页面

下面是一个基本实现示例（我希望它能满足您的要求）：

轮询可运行

package com.web;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;

public class FilePollingThread implements Runnable {

    private String filepath = null;
    private boolean polling = false;
    private StringBuffer dataWritenAfterLastPoll = null;
    private String error = null;

    public FilePollingThread(String filepath) {
        this.filepath = filepath;
    }

    @Override
    public void run() {
        BufferedReader br = null;
        try {
            br = new BufferedReader(new InputStreamReader(new FileInputStream(filepath)));
            dataWritenAfterLastPoll = new StringBuffer();
            polling = true;

            String line = null;

            while(polling) {
                try {
                    line = br.readLine();
                    while(line == null) {
                        try {
                            Thread.sleep(500L);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                            error = e.toString();
                        }
                        line = br.readLine();
                    }
                    dataWritenAfterLastPoll.append(markUp(line));
                } catch (IOException e) {
                    e.printStackTrace();
                    error = e.toString();
                }
            }

        } catch (FileNotFoundException e) {
            e.printStackTrace();
            error = e.toString();
        } finally {
            if(br != null) {
                try {
                    br.close();
                } catch (IOException e) {
                    e.printStackTrace();
                    error = e.toString();
                }
            }
        }
    }

    private String markUp(String line) {
        String markup = "";
        if(line != null) {
            markup = "<div style=\"height: 6px\"><span style=\"line-height: 1.1;\">" + line + "</span></div>\n";
        }
        return markup;
    }

    public synchronized void stopPolling() {
        polling = false;
    }

    public synchronized String poll() {
        String tmp = markUp(error == null ? "Not ready" : error);
        if(dataWritenAfterLastPoll != null) {
            tmp = dataWritenAfterLastPoll.toString();
            dataWritenAfterLastPoll = new StringBuffer();
        }
        return tmp;
    }
}

JSP开关启动轮询并继续检索数据

<?xml version="1.0" encoding="ISO-8859-1" ?>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<%@ page import="com.web.FilePollingThread" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Poll file</title>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
<link rel="stylesheet" type="text/css" href="style/default.css"></link>
<script type="text/javascript">
    var c = 1;
    var ih;
    var polling = false;
    var filepath = null;
    function startPolling(interval) {
        ih = setInterval(function () {
            try {
                var xmlHttp = new XMLHttpRequest();
                xmlHttp.onreadystatechange = function () {
                    if(xmlHttp.readyState == 4) {
                        if(xmlHttp.status == 200) {
                            var w = getElementById('ajax_content');
                            w.innerHTML = w.innerHTML + xmlHttp.responseText;
                            getElementById('page_refresh').innerHTML = c++;
                            polling = true;
                            window.scrollTo(0, document.body.scrollHeight);
                        } else {
                            polling = false;
                            throw 'HTTP ' + xmlHttp.status;
                        }
                    }
                };
                xmlHttp.open('GET', 'pollfile.jsp?filepath=' + filepath + '&c=' + c, true);
                xmlHttp.send();
            } catch(e) {
                alert('Error at startPolling: ' + e);
                clearInterval(ih);
            }
        }, interval);
    }

    function startStopPolling() {
        var orgPolling = polling;
        try {
            if(polling) {
                polling = false;
                clearInterval(ih);
                doPolling();
            } else {
                polling = true;
                doPolling();
                startPolling(1000);
            }
            flipStartStopButtonsLabel();
        } catch(e) {
            polling = orgPolling;
            flipStartStopButtonsLabel();
            alert('Error at startStopPolling: ' + e);
        }
    }

    function flipStartStopButtonsLabel() {
        var label;
        if(polling) {
            c = 1;
            label = 'Stop polling';
            getElementById('page_refresh').innerHTML = '0';
        } else {
            label = 'Sart polling';
            getElementById('page_refresh').innerHTML = 'stoped';
        }
        var buttons = document.getElementsByName('start_stop_polling');
        if(buttons) {
            for(var i = 0; i < buttons.length; i++) {
                buttons[i].value = label;
            }
        }
    } 

    function doPolling() {
        var url = 'pollfile.jsp?polling=';
        if(polling) {
            filepath = getElementById('filepath');
            if(filepath && filepath.value && filepath.value.length > 0) {
                url += 'true&filepath=' + encodeURIComponent(filepath.value);
            } else {
                throw 'No filepath specified.';
            }
        } else {
            url += 'false';
        }
        var xmlHttp = new XMLHttpRequest();
        xmlHttp.onreadystatechange = function () {
            if(xmlHttp.readyState == 4) {
                if(xmlHttp.status != 200) {
                    throw 'HTTP ' + xmlHttp.status;
                }
            }
        };
        xmlHttp.open('POST', url, false);
        xmlHttp.send();
    }

    function clearWindow() {
        var w = getElementById('ajax_content');
        if(w) {
            w.innerHTML = '';
        }
    }

    function getElementById(id) {
        try {
            if(id) {
                elm = document.getElementById(id);
                return elm;
            } 
        } catch(e) {
            alert('Error at getElementById: ' + e);
        }
        return null;
    }
</script>
</head>
<body>


<%
    String polling = request.getParameter("polling");

    if("true".equals(polling)) {
        String filepath = request.getParameter("filepath");
        if(filepath != null && filepath.length() > 0) {
            FilePollingThread pollingThread = new FilePollingThread(filepath);
            new Thread(pollingThread, "polling thread for file '" + filepath + "'").start();
            request.getServletContext().setAttribute("pollingThread", pollingThread);
        }
    } else if("false".equals(polling)) {
        FilePollingThread pollingThread = (FilePollingThread) request.getServletContext().getAttribute("pollingThread");
        if(pollingThread != null) {
            pollingThread.stopPolling();
        }
    } else {
        FilePollingThread pollingThread = (FilePollingThread) request.getServletContext().getAttribute("pollingThread");
        if(pollingThread != null) {
            response.getWriter().println(pollingThread.poll());
            response.getWriter().close();
            return;
        }
    }
%>
<div class="label">
        <span>Page polling:</span>
    </div>
    <div style="float: left;">
        <span id="page_refresh">0</span>
    </div>
<div class="clear_both">&nbsp;</div>
<form id="input_form" action="pollfile.jsp" method="get">
    <div>
        <div style="float: left;">
            <label>Filepath:
                <input style="height: 24px;" id="filepath" type="text" size="120" value=""/>
            </label>
        </div>
        <div style="clear: both;"/>
        <div style="float: left;">
            <input style="height: 24px;" name="start_stop_polling" id="start_stop_polling_button" type="button" onclick="startStopPolling(); return false;" value="Start polling"/>
        </div>
        <div style="float: left;">
            <input style="height: 24px;" name="clear_window" id="clear_window_button" type="button" onclick="clearWindow(); return false;" value="Clear"/>
        </div>
        <div style="clear: both;">&nbsp;</div>
    </div>
</form>
<div id="ajax_content">
</div>
<div>
    <div style="float: left;">
        <input style="height: 24px;" name="start_stop_polling" id="start_stop_polling_button" type="button" onclick="startStopPolling(); return false;" value="Start polling"/>
    </div>
    <div style="float: left;">
        <input style="height: 24px;" name="clear_window" id="clear_window_button" type="button" onclick="clearWindow(); return false;" value="Clear"/>
    </div>
    <div style="clear: both;">&nbsp;</div>
</div>
</body>
</html>

编辑

在FilePollingThread中有一个错误：如果文件中没有可用的数据，线程可能会卡在内部while循环中。应该是的

while(line == null && polling)

此外，JSP将无法在IE上运行（在IE9上测试）。似乎写入行中响应的数据

response.getWriter().println(pollingThread.poll());

包含洞页面的HTML。如果添加到目标分区，IE似乎无法渲染它

我用一个简单的静态HTML文件制作了另一个版本，作为一个servlet，因为它提供了对写入响应的更多控制

如果你对代码感兴趣，请告诉我

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java如何使用Tomcat管理后端进程？

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