3

我在将 XML 文件加载到网页并显示其中包含的信息时遇到了一个小问题。对于这个程序，我正在尝试使用加载到 XML 文件的恒定数据流来更新一个非常简单的网页。当我的程序找到新数据时（通常每隔几秒一次），它会修改 XML 文件并保存它。另一个 Web 客户端（在 Netbeans 中）运行显示此信息的网页。截至目前，我的问题是当我刷新页面时，没有出现新数据（相同的值仍然存在，即使我知道它们不应该存在）。然后我检查 XML 文件，新数据存在，因此它成功写入。奇怪的是，一旦我打开xml文件查看信息，一旦我刷新页面，网页就会自动更新。这似乎是更新网页的唯一方法是我自己打开 xml 文件。我的问题是有谁知道发生了什么，你能提供解决这个问题的方法吗？

我提供了我的 ModifyXML.java 代码和 index.jsp 页面以供参考

修改 XML

import java.io... //all import statements not shown
public class ModifyXML {

    //provide the byte array and the number of the sensor that needs to be 
    //updated in the XML file
    public ModifyXML(byte[] array, int signal) {

        try {
            //create a new Document Builder to modify the XML file 
            String filepath = "C:\\user\\projects\\onlineClient\\web\\HTTP.xml";
            DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
            Document doc = docBuilder.parse(filepath);


            // Get the root element
            Node Sensor = doc.getFirstChild();

            // Get the staff elements by tag name directly
            Node data = doc.getElementsByTagName("Data").item(0);
            Node data2 = doc.getElementsByTagName("Data2").item(0);

         /* Methods to update the information are not shown as they work fine (it saves space)*/



            // write the content into xml file
            TransformerFactory transformerFactory = TransformerFactory.newInstance();
            Transformer transformer = transformerFactory.newTransformer();
            DOMSource source = new DOMSource(doc);
            StreamResult result = new StreamResult(new File(filepath));
            transformer.transform(source, result);

            System.out.println("Done");

        } catch (ParserConfigurationException pce) {
            pce.printStackTrace();
        } catch (TransformerException tfe) {
            tfe.printStackTrace();
        } catch (IOException ioe) {
            ioe.printStackTrace();
        } catch (SAXException sae) {
            sae.printStackTrace();
        }
    }
}

索引.jsp

<html>
<title>Home Monitor Web Client</title>
<body>
    <h1>Home Monitor</h1>
    <p id="demo">Paragraph.</p>

    <p id="demo2">Paragraph.</p>

    <br>

    <p id="demo3">Paragraph.</p>

    <p id="demo4">Paragraph.</p>

    <script type="text/javascript">
    if (window.XMLHttpRequest)
    {// code for IE7+, Firefox, Chrome, Opera, Safari
        xmlhttp=new XMLHttpRequest();
    }
    else
    {// code for IE6, IE5
        xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
    }
    xmlhttp.open("GET","HTTP.xml",false);
    xmlhttp.send();
    xmlDoc=xmlhttp.responseXML;

    //document.write("<table border='1'>");
    var data=xmlDoc.getElementsByTagName("data");
    var data2=xmlDoc.getElementsByTagName("data2");
    for (i=0;i<temperature.length;i++)
    {
        document.getElementById("demo").innerHTML="ID Number: "+data[i].getElementsByTagName("ID")[0].childNodes[0].nodeValue;
        document.getElementById("demo2").innerHTML="Reading: "+data[i].getElementsByTagName("Value")[0].childNodes[0].nodeValue;
        document.getElementById("demo3").innerHTML="ID Number: "+data2[i].getElementsByTagName("ID")[0].childNodes[0].nodeValue;
        document.getElementById("demo4").innerHTML="Reading: "+data2[i].getElementsByTagName("Value")[0].childNodes[0].nodeValue;
    }
    </script>
</body>
</html>
4

1 回答 1

0

You can use the html5 Event Sources with Server Side Events. There is a good article on it at

They show this example (written in PHP and js, but you should be able to convert it to java)

Server Code (PHP)

<?php
header('Content-Type: text/event-stream');
header('Cache-Control: no-cache'); // recommended to prevent caching of event data.

/**
 * Constructs the SSE data format and flushes that data to the client.
 *
 * @param string $id Timestamp/id of this connection.
 * @param string $msg Line of text that should be transmitted.
 */
function sendMsg($id, $msg) {
  echo "id: $id" . PHP_EOL;
  echo "data: $msg" . PHP_EOL;
  echo PHP_EOL;
  ob_flush();
  flush();
}

$serverTime = time();

sendMsg($serverTime, 'server time: ' . date("h:i:s", time()));

Client Code (js)

if (!!window.EventSource) {
var source = new EventSource('stream.php');
source.onmessage = function(e) {
      document.body.innerHTML += e.data + '<br>';
    };    
} else {
  // Result to xhr polling :(
}

check out the tutorial here. http://www.html5rocks.com/en/tutorials/eventsource/basics/

于 2012-08-23T15:34:50.853 回答