Java DataInputStream挂起没有错误

Question

I'm writing a client and server app for file transfer. In the download functionality the client seems to be getting hung at a call to the readUTF function call. I've attached the code snippet below. I get no errors or any other warnings. If anyone has any insight I'd be greatly appreciative.

Client:

os = new PrintStream(socket.getOutputStream());
os.println(fileName);
System.out.println("sending file name to server");

// wait for server to confirm file exists on server
String codeTest = input.readLine();
int code = Integer.parseInt(codeTest);

System.out.println("Code received from server: " + code);

while (code == 0) {
    System.out.println("File: " + fileName + " does not exist on server!");
    System.out.print("Please enter the file name you would like to download: ");
    fileName = sc.next();
    os.println(fileName);
    codeTest = input.readLine();
    code = Integer.parseInt(codeTest);
}

if (code == 1) {

    InputStream inputStream = socket.getInputStream();
    DataInputStream dataInStream = new DataInputStream(inputStream);
    // download
    System.out.println("File exists on the server!");

    String fileToSave = "";

    // get OS downloads directory
    String home = System.getProperty("user.home");
    String operatingSystem = System.getProperty("os.name");

    if ( operatingSystem.startsWith("Windows") ) {
        fileToSave = home + "\\" + "Downloads\\";
    } else {
        System.out.println(home);
        fileToSave = home + "/" + "Downloads/";
    }

    System.out.println(fileToSave + fileName);

    fileToSave += fileName;
    System.out.println("file to download: " + fileToSave);
    int bytesRead;

    System.out.println("got streams");

    fileName = dataInStream.readUTF();
    System.out.println("fileName from server: " + fileName);
    fileToSave += fileName;
    System.out.println("File to save: " + fileToSave);
    OutputStream output = new FileOutputStream((fileToSave));
    long size = dataInStream.readLong();
    byte[] buffer = new byte[1024];
    while (size > 0 && (bytesRead = dataInStream.read(buffer, 0, (int) Math.min(buffer.length, size))) != -1) {
        output.write(buffer, 0, bytesRead);
        size -= bytesRead;
    }
    System.out.println("file downloaded successfully");

    continue;
}

Server

System.out.println("user selected upload");

DataInputStream clientData = new DataInputStream(socket.getInputStream());

//String fileName = input.readLine();
String fileName = clientData.readUTF();

if ( fileName.equals("q")) {
    System.out.println("continue");
    continue;
}

//System.out.println("fileName received: " + fileName);
String fileNameToStore = DIRECTORY + fileName;

System.out.println("Saving file to: " + fileNameToStore);
OutputStream output = new FileOutputStream(fileNameToStore);

int bytesRead;
long size = clientData.readLong();
byte[] buffer = new byte[1024];

while( size>0 && (bytesRead = clientData.read(buffer, 0, (int) Math.min(buffer.length, size))) != -1) {
    output.write(buffer, 0, bytesRead);
    size -= bytesRead;
}

output.close();
//clientData.close();

System.out.println("done");

break;
case "d":
System.out.println("user selected download");

//handle file download

String requestedFile = input.readLine();
String fileToDownload = DIRECTORY + requestedFile;

System.out.println("User requested: " + fileToDownload);

// check if file exists and tell client 
File file = new File(fileToDownload);

int code;
while ( !file.exists() ) {
    code = 0;

    textOut.println(code);

    System.out.println("Code sent to client: " + code);

    // wait for file name
    requestedFile = input.readLine();
    System.out.println("user resent filename: " + fileToDownload);

    file = new File(fileToDownload);
} 

// file exists - send to client
code = 1;
textOut.println(code);

byte[] mybytearray = new byte[(int)file.length()];
FileInputStream fis = new FileInputStream(file);
BufferedInputStream bis = new BufferedInputStream(fis);
DataInputStream dis = new DataInputStream(bis);

OutputStream os = socket.getOutputStream();

DataOutputStream dos = new DataOutputStream(os);
dos.writeUTF(file.getName());
System.out.println("dos writeUTF: " + file.getName());
dos.writeLong(mybytearray.length);
System.out.println(mybytearray.length + " sent to client.");
dos.write(mybytearray, 0, mybytearray.length);
dos.flush();
System.out.println("File "+fileToDownload+" sent to client.");


break;  

Answer 1

I was able to get it working. I simply added an output from client to server letting the server know that the client was ready for the file to be sent. I did this right before the fileName = dataInStream.readUTF();

I'm not sure why that fixed it, but it did. Thanks for the help.