TCP 套接字上的多个图像文件

Question

我正在尝试在 TCP 套接字上发送多个图像。

以下代码运行良好，没有问题：客户端和服务器交换问候语。然后客户端正在发送 服务器接收的单个图像文件。

客户端：

...        
try      {
    Socket clientSocket = new Socket(serverName, port);
    DataInputStream in=new DataInputStream(clientSocket.getInputStream());
    System.out.println("Heard from server: "+in.readUTF());

    DataOutputStream out = new DataOutputStream(clientSocket.getOutputStream());
    out.writeUTF("Hello from " + clientSocket.getLocalSocketAddress());

    BufferedImage bimg;

//    for (int i=0; i<3; i++)  {
    bimg = ImageIO.read(new File("flowers.jpg"));  
    ImageIO.write(bimg,"jpg",clientSocket.getOutputStream());   
    out.flush(); 
    System.out.println("Image sent");
//    }
    clientSocket.close();
  } catch(Exception e) { ... }

服务器端：

...
Socket socket=null;
DataInputStream din=null;
DataOutputStream dout=null;
...
socket = serverSocket.accept();  
din=new DataInputStream(socket.getInputStream());
dout=new DataOutputStream(socket.getOutputStream());

for (;;)  {  
    try  {

        dout.writeUTF("ImageReceiver here at your service: ");

        System.out.println("from the client: "+din.readUTF());
        BufferedImage img;

//for (int i=0; i<3; i++) {
        img=ImageIO.read(socket.getInputStream());   
        ImageIO.write(img, "png", new File(timeStamp+"img.png"));
        System.out.println("Image received...");
//} 
        socket.close();
        break;
   }
  catch(Exception e) {  .... }
 }

当我取消注释上面的 2*2 行并因此循环发送和接收图像时，我收到图像为空的异常：

服务器正在接收第一张图片，没有错误。然而，在那之后，它不是 将输入流视为图像。

处对 ImageIO.read() 的调用

img=ImageIO.read(socket.getInputStream());    

正在返回 null 并且

        ImageIO.write(img, "png", new File(timeStamp+"img.png"));

正在引发异常。

客户端进程运行良好，没有任何错误。

这是管理 I/O 缓冲区的问题吗？

去哪里修复它？

TIA。

//========================================

我在发送 2 张图片时遇到了同样的错误：第一张图片可以正常传输和接收。

客户端正在发送第二张图片作为关闭前的最后一件事。但是，服务器没有将第二个视为图像。在传输第一张图像后，服务器套接字的输入缓冲区中除了第二张图像之外什么都没有。

Answer 1

ImageIO 读取图像后关闭输入流。需要通过 ImageIO.createImageInputStream() 反复创建读取多个图像。 可以看这里-https://docs.oracle.com/javase/8/docs/api/javax/imageio/ImageIO.html#read-javax.imageio.stream.ImageInputStream-

Answer 2

你可以试试这个代码。此代码以字节为单位发送数据。

客户（发件人）：

try {
        int port = 8989; // Your Server port number
        Socket sender = new Socket("Server IP", port);
        int count,i=0;

        byte[] data = new byte[1024]; // Here provide size of your file
        FileInputStream fileStream = null;
        BufferedInputStream fileBuffer = null;
        OutputStream out = sender.getOutputStream();
        InputStream in = sender.getInputStream();

        while (i < 10) {

            fileStream = new FileInputStream("fileURL");
            fileBuffer = new BufferedInputStream(fileStream);

            // Sending file data in bytes
            while ((count = fileBuffer.read(data)) > 0) {
                System.out.println("Data Sent : " + count);
                out.write(data, 0, count);
                out.flush();
            }

            // Waiting for response
            while (in.available() <= 0) {
            }
            if (in.read() == 0) {
                System.out.println("File Sent Successfully");
                i++;
            } else {
                System.out.println("File Not Sent Successfully");
            }
        }
    } catch (Exception e) {
    }

服务器（接收方）：

try {
        ServerSocket server = new ServerSocket(port);

        // Waiting for client
        Socket receiveSocket = server.accept();
        InputStream in = receiveSocket.getInputStream();
        OutputStream out = receiveSocket.getOutputStream();
        int count, cnt = 10, i = 0;

        // cnt will be total number of files
        while (i < cnt) {
            byte data[] = new byte[1024]; // Provide file size here
            FileOutputStream fileOut = new FileOutputStream("fileURL");
            BufferedOutputStream fileBuffer = new BufferedOutputStream(fileOut);

            // Waiting till client is sending the file
            while (in.available() <= 0) {
            }
            // Receiving byte data and storing it in the file
            while ((count = in.read(data)) > 0) {
                fileBuffer.write(data, 0, count);
                System.out.println("Data Received : " + count);
                fileBuffer.flush();
            }
            // Notify client that you received that file successfully
            out.write(0);

            // Close all streams
            in.close();
            out.close();
            fileBuffer.close();
            fileOut.close();
            i++;
        }
    } catch (Exception e) {
    }

希望对你有所帮助。