我开发了一个桌面应用程序，它有一个读取 XML 文件(使用 DOM)的类，然后对数据执行一些操作，并将数据保存回 XML(替换以前的文件)。此类被实例化并且该方法每 30 秒调用一次。我遇到的问题是，如果运行应用程序的计算机关闭(突然按电源按钮，不正常)。然后，当 pc 再次启动时，XML 文件为空。留下一个空白文件。并非每次计算机关闭时都会发生这种情况，但经常发生。如果计算机正确关闭，则不会发生这种情况。 这是代码:

private org.w3c.dom.Document dom;
private javax.xml.parsers.DocumentBuilder db;

public PlayerConfigHandler() {
    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
    try {
        db = dbf.newDocumentBuilder();
        dom = db.newDocument();
    } catch (Exception e) {  }
}

public void updateConfig(List<File> playlists) {
    String playerPath = Preferences.getInstance().readStringProperty("PlayerDirectory");
    File configuration = new File(playerPath + "\\playerconfiguration.sdpp"); // replace with configuration path
    if(!configuration.exists()) {
        Logger.getLogger(PlayerConfigHandler.class).info("File " + configuration 
                + " does not exist! Unable to update it.");
        return;
    }
    dom = db.newDocument();
    InputStream is = null;
    Reader reader = null;
    try {
        is = new FileInputStream(configuration);
        reader = new InputStreamReader(is);
        InputSource source = new InputSource(reader);
        dom = db.parse(source);
    } catch (SAXException ex) {
        Logger.getLogger(PlayerConfigHandler.class).error("updateConfig(). SAXException reading XML file: " + ex);
        return;
    } catch (IOException ex) {
        Logger.getLogger(PlayerConfigHandler.class).error("updateConfig(). IOException reading XML file: " + ex);
        return;
    } catch(Exception ex) {
        Logger.getLogger(PlayerConfigHandler.class).error("updateConfig(). Exception reading XML file: " + ex);
        return;
    } finally {
        try {
            reader.close();
            is.close();
        } catch (Exception e) { 
            Logger.getLogger(PlayerConfigHandler.class).error("Exception closing FileInputStream/Reader after reading XML file: " + e);
        }
    }
    Element element = dom.getDocumentElement();

    //perform some operations to the data read...

    FileOutputStream outputStream = null;
    try {
        TransformerFactory transformerFactory = TransformerFactory.newInstance();
        transformerFactory.setAttribute("indent-number", 4);
        Transformer transformer = transformerFactory.newTransformer();
        transformer.setOutputProperty("encoding","ISO-8859-1");
        Source source = new DOMSource(dom);
        outputStream = new FileOutputStream(configuration);
        Result result = new StreamResult(new OutputStreamWriter(outputStream));
        transformer.setOutputProperty(OutputKeys.METHOD, "xml");
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
        transformer.transform(source, result);
    } catch (TransformerConfigurationException tce) {
        Logger.getLogger(PlayerConfigHandler.class).error("Exception saving XML file: " + tce);
    } catch (TransformerException te) {
        Logger.getLogger(PlayerConfigHandler.class).error("Exception saving XML file: " + te);
    } catch (FileNotFoundException fe) {
        Logger.getLogger(PlayerConfigHandler.class).error("Exception saving XML file: " + fe);
    } catch(Exception e) {
        Logger.getLogger(PlayerConfigHandler.class).error("Exception saving XML file: " + e);
    }
    finally {
        try {
            outputStream.close();
        } catch (Exception e) { 
            Logger.getLogger(PlayerConfigHandler.class).error("Exception closing FileOutputStream after writing XML file: " + e);
        }
    }
    dom = db.newDocument();
}

知道为什么会这样吗？代码有什么问题吗？有什么办法可以防止这种情况发生吗？ 谢谢，达米安

最佳答案

new FileOutputStream 正在截断文件，并且在写入和关闭任何新数据之前关闭计算机。这个简单的例子演示了这个问题。如果您运行一次，编辑 foo.txt 然后再次运行，内容将被截断。

import java.io.*;

public class FileCreate {
    public static void main(String[] args) throws Exception {
        File f = new File("C:\\temp\\foo.txt");
        FileOutputStream outputStream = new FileOutputStream(f);
        outputStream.close();
    }
}

解决此问题的一种方法是将新配置写入不同的文件，然后执行“删除”和“重命名”。

关于java - 如果计算机关闭，由 java 应用程序创建的 XML 文件的内容会消失，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/6611503/