Question

我正在尝试使用Java创建一个程序，该程序截取用户屏幕的截图，压缩图像，并通过套接字将其发送到服务器。由于某种原因，图像最终被破坏（它是不可读的）。你能帮我找一下问题吗？

客户端:(屏幕截图以BufferedImage形式输入，然后返回的字节数组返回到第二个函数，将其发送到服务器）

    public static byte[] compressImage(BufferedImage image) throws IOException {
    System.out.println("starting compression");

    ByteArrayOutputStream os = new ByteArrayOutputStream(37628);

    float quality = 0.16f;

    // create a BufferedImage as the result of decoding the supplied InputStream

    // get all image writers for JPG format
    Iterator<ImageWriter> writers = ImageIO.getImageWritersByFormatName("jpg");
    //Iterator iter = ImageIO.getImageWritersByFormatName("jpeg");

    if (!writers.hasNext())
        throw new IllegalStateException("No writers found");

    ImageWriter writer = (ImageWriter) writers.next();
    ImageOutputStream ios = ImageIO.createImageOutputStream(os);
    writer.setOutput(ios);

    ImageWriteParam param = writer.getDefaultWriteParam();

    // compress to a given quality
    param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
    param.setCompressionQuality(quality);

    // appends a complete image stream containing a single image and
    //associated stream and image metadata and thumbnails to the output
    writer.write(null, new IIOImage(image, null, null), param);
    os.flush();

    return os.toByteArray();
}

    public void uploadShot(byte[] imgData, String nickname) {

    try {
        /* Try to connect to the server on localhost, port 5555 */

        Socket sk = new Socket("localhost", 23232);
        OutputStream output = sk.getOutputStream();

        /* Send filename to server */

        OutputStreamWriter outputStream = new OutputStreamWriter(sk.getOutputStream());
        outputStream.write(nickname + "\n");
        outputStream.flush();

        /* Get response from server */

        BufferedReader inReader = new BufferedReader(new InputStreamReader(sk.getInputStream()));

        String serverStatus = inReader.readLine(); // Read the first line

        /* If server is ready, send the file */

        if (serverStatus.equals("READY")){
            int len = imgData.length;
            int start = 0;

            if (len < 0)
                throw new IllegalArgumentException("Negative length not allowed");
            if (start < 0 || start >= imgData.length)
                throw new IndexOutOfBoundsException("Out of bounds: " + start);
            // Other checks if needed.

            // May be better to save the streams in the support class;
            // just like the socket variable.
            OutputStream out = sk.getOutputStream(); 
            DataOutputStream dos = new DataOutputStream(out);

            dos.writeInt(len);
            if (len > 0) {
                dos.write(imgData, start, len);
            }
            dos.close();
            output.close();
            sk.close();

            System.out.println("Transfer complete.");
        }
    } catch (Exception ex){
        /* Catch any errors */
        System.out.println(ex.getMessage());
    }
}

SERVER :(收到的图像保存到带有时间戳的文件夹中）

public static void main(String args[]) throws Exception{
    System.out.println("Server running...");

    /* Listen on port 5555 */

    ServerSocket server = new ServerSocket(23232);

    /* Accept the sk */

    Socket sk = server.accept();

    System.out.println("Server accepted client");
    InputStream input = sk.getInputStream();
    BufferedReader inReader = new BufferedReader(new InputStreamReader(sk.getInputStream()));
    BufferedWriter outReader = new BufferedWriter(new OutputStreamWriter(sk.getOutputStream()));

    /* Read the filename */
    String nickname = inReader.readLine();

    if ( !nickname.equals("") ){

        /* Reply back to client with READY status */

        outReader.write("READY\n");
        outReader.flush();
    }


    String current = "/home/kasgel/screenshots";

    DateFormat dateFormat = new SimpleDateFormat("dd-MM-yyyy__HH:mm:ss");
    Date timestamp = new Date();
    File filename = new File(current + "/" + nickname + "-" + dateFormat.format(timestamp) + ".jpg");
    if (!filename.exists()) {
        filename.createNewFile();
    }
    FileOutputStream wr = new FileOutputStream(filename);

    byte[] buffer = new byte[sk.getReceiveBufferSize()];

    int bytesReceived = 0;

    while((bytesReceived = input.read(buffer))>0) {
        wr.write(buffer,0,bytesReceived);
    }
    wr.close();
}

打开保存的屏幕截图时收到的错误消息如下： display.im6：不是JPEG文件：以0x00 0x03开头`MyNick-30-03-2015__19：27：58.jpg'@ error / jpeg.c / JPEGErrorHandler / 316。

Answer 1

当您编写图像时，首先要编写一个包含图像长度的32位有符号整数：

        dos.writeInt(len);
        if (len > 0) {
            dos.write(imgData, start, len);
        }

但是当你重读图像时，你不会先读取长度;您正在阅读所有数据（包括长度），就好像它们是图像的一部分一样。

你有第二个问题，这本身也会导致这个问题。当您创建BufferedReader并在其上调用readLine时，它将读取超出换行符 - 它将一直读取，直到其缓冲区已满。如果你继续读取它不是问题，但是在读取该行之后，你继续从底层的InputStream中读取，在换行之后通常会有更多的字节消耗。

解决方案是：只使用一个抽象来读/写数据。在这种情况下，最简单的方法是使用DataOutputStream和DataInputStream。使用writeUTF编写文件名，然后使用readUTF将其读回。使用writeInt写下文件的长度，并使用readInt将其读回。使用write写入数据并使用read读取数据 - 并确保只读取从readInt调用中收到的字节数。最重要的是，继续使用相同的DataOutputStream和DataInputStream个实例;不要在同一个底层InputStream

上构建缓冲读者和输入流

在套接字上发送压缩的JPG图像

1 个答案: