Question

我最近一直在研究这个“更新程序”，它会自动将URL中的文件下载到目录中，尽管它没有按计划运行。每当我运行这个程序时，我总是会收到错误消息（当文件无法访问时）弹出给我，因此告诉我文件没有下载。这个脚本可能有什么问题？

感谢您的帮助。

@SuppressWarnings("serial")
public class GameLauncher extends JFrame {

/**
 * Directory of the Download Client.
 * <p>
 * This is the location the Jar filed will be stored and executed at.
 */
static String directory = System.getProperty("user.home") + "/LRLauncher/LostRedemption.jar";

/**
 * Download link of the Download Client.
 */
static String downloadLink = "http://lostredemption.com/LostRedemption.jar";

/**
 * Creates the main frame of the application being initiated.
 * @throws IOException 
 */


  /**
 * Download the client.
 */
static void downloadFile() {
        try {
                URL url2 = new URL("http://lostredemption.com/LostRedemption.jar");
                InputStream in = new BufferedInputStream(url2.openStream());
                ByteArrayOutputStream out = new ByteArrayOutputStream();
                byte[] buf = new byte[1024];
                int n = 0;
                while (-1 != (n = in .read(buf))) {
                        out.write(buf, 0, n);
                }
                out.close(); 
                in .close();
                byte[] response = out.toByteArray();
                FileOutputStream fos = new FileOutputStream(directory);
                fos.write(response);
                fos.close();
                //openDownloadClient();
        }
        catch (IOException e) {
                JOptionPane.showMessageDialog(null, "Unable to download latest client. Please check your internet connection and try again.", "Error", JOptionPane.ERROR_MESSAGE);
                closeProgram();
        }
}

/**
 * Open the Download Client.
 */
static void openDownloadClient() {
        File execute = new File(directory);
        try {
                Desktop.getDesktop().open(execute);
        }
        catch (IOException e) {
                e.printStackTrace();
        }
        closeProgram();
}

/**
 * Close the program.
 */
static void closeProgram() {
        System.exit(0);
     }
}

Answer 1

对代码进行布局我看到了方法

/**
 * Download the client.
 */
static void downloadFile() {
    try {
            URL url2 = new URL("http://lostredemption.com/LostRedemption.jar");
            InputStream in = new BufferedInputStream(url2.openStream());
            ByteArrayOutputStream out = new ByteArrayOutputStream();
            byte[] buf = new byte[1024];
            int n = 0;
            while (-1 != (n = in .read(buf))) {
                    out.write(buf, 0, n);
            }
            out.close(); 
            in .close();
            byte[] response = out.toByteArray();
            FileOutputStream fos = new FileOutputStream(directory);
            fos.write(response);
            fos.close();
            //openDownloadClient();
    }
    catch (IOException e) {
            JOptionPane.showMessageDialog(null, "Unable to download latest client. Please check your internet connection and try again.", "Error", JOptionPane.ERROR_MESSAGE);
            closeProgram();
    }
}

很好的工作捕获异常并向用户显示，但你从未告诉自己错误是什么。这就是大多数程序都有错误日志的原因！

只需输入System.out.println(e);即可看到此错误消息：

java.io.IOException: Server returned HTTP response code: 403 for URL: http://lostredemption.com/LostRedemption.jar

现在很棒，我在谷歌搜索Java URL open Stream 403，谷歌的最终结果将是最终结果：Server returning 403 for url openStream() SO问题的第一个答案将使您的计划正常运作

URL url2 = new URL("http://lostredemption.com/LostRedemption.jar");
HttpURLConnection httpcon = (HttpURLConnection) url2.openConnection();
httpcon.addRequestProperty("User-Agent", "Mozilla/4.0");
ReadableByteChannel rbc = Channels.newChannel(httpcon.getInputStream());
FileOutputStream fos = new FileOutputStream(directory);
fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);

请记住，在进行任何研究之前，请始终查看错误消息。

从URL下载到目录

1 个答案: