Java在线程中解析和更新xml值

Question

我写了一个多线程程序，每个线程都需要解析一个xml文件并更新新值。问题:假设我有 ABC 的 xml 内容，现在线程 A 解析 xml 并将其更新为 ABCA，同时线程 B 也解析 xml(内容为 ABC)并将其更新为 ABCB。线程 B 在线程 A 更新后更新 xml，所以 xml 的结果是 ABCB，我想要的是 xml 结果应该是 ABCAB。有什么想法可以控制线程中解析和更新的方式吗？这是我的代码:

WSthread.java

public class WSthread extends Thread {
    public String WSname;
    Process proc= null;
    WebServicesXML xml;
    WSthread(String name){
        WSname=name;
    }

    public void run() {
try {
    //my code
    // Run a java app in a separate system process
    String cmd = (WSname);
    proc = Runtime.getRuntime().exec("java -jar "+cmd);
    xml = new WebServicesXML();
    //Process proc = Runtime.getRuntime().exec("java -jar .jar");
    // Then retreive the process output
    //InputStream in = proc.getInputStream();
    //InputStream err = proc.getErrorStream();

    BufferedReader is = new BufferedReader(new InputStreamReader(proc.getInputStream()));
    String line;
    String regex = "\\bhttp\\b";
    Pattern pattern = Pattern.compile(regex);
    String WSaddress = "";
    while ((line = is.readLine()) != null){
        Matcher matcher = pattern.matcher(line);
        if(matcher.find()){
            WSaddress = line;
            System.out.println("Updating WS address..."+WSaddress);
            xml.create(WSname, WSaddress);
        }
        System.out.println(line);
    }

    }catch(Exception e){
        System.out.println(e.getMessage());
    }
}
    public void close(){
        proc.destroy();
    }

WebServicesXML.java

public class WebServicesXML{
public int totalWebServices;
public String WSnamelist[];
public synchronized void create(String WSname, String WSaddress) throws OException,     TransformerConfigurationException, TransformerException, ParserConfigurationException{
    try {

    DocumentBuilderFactory dbfac = DocumentBuilderFactory.newInstance();
    DocumentBuilder docBuilder = dbfac.newDocumentBuilder();

    Document readdoc = docBuilder.parse("webservices.xml");
//      normalize text representation
    readdoc.getDocumentElement ().normalize ();
    Node rootList = readdoc.getDocumentElement();
    Element rootElement = (Element)rootList;

    Element webservice = readdoc.createElement("WebService");

    Element name = readdoc.createElement("name");
    Element address = readdoc.createElement("address");

    name.setTextContent(WSname);
    address.setTextContent(WSaddress);

    webservice.appendChild(name);
    webservice.appendChild(address);

    rootElement.appendChild(webservice);
    /////////////////
    //Output the XML

    //set up a transformer
    TransformerFactory transfac = TransformerFactory.newInstance();
    Transformer trans = transfac.newTransformer();
    trans.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
    trans.setOutputProperty(OutputKeys.INDENT, "yes");

    //create string from xml tree
    File file = new File("webservices.xml");
    StringWriter sw = new StringWriter();
    StreamResult result = new StreamResult(file);
    DOMSource source = new DOMSource(readdoc);
    trans.transform(source, result);

}
    catch (ParserConfigurationException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (SAXException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (TransformerConfigurationException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (TransformerException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

Answer 1

基本问题是在每个线程中构建一个单独的 DOM 以应用单个转换。这意味着最后一个运行的线程在将其内容写回 XML 文件方面“获胜”。

一方面您正在使用线程，我假设是为了性能，但另一方面您多次解析和序列化 XML。而且线程实现是不安全的。

我的建议是删除线程并在循环中进行更改。当它工作时，您可以衡量性能，然后选择查看使用线程的实现。

请记住，过早的优化是万恶之源。