Java套接字: unable to send response to client after sending file to server

Question

这个问题已经有答案了:

Java multiple file transfer over socket (3 个回答)

已关闭 4 年前。

我正在使用 Java Socket 将文件发送到服务器，然后获取响应。问题是每次我尝试从服务器读取响应时，它都会使服务器的文件读取部分挂起。我真的需要你的帮助来了解这里发生的事情吗？

这是服务器代码:

ServerSocket server = new ServerSocket(PORT);
Socket client = server.accept();
BufferedInputStream netInStream = new BufferedInputStream(client.getInputStream());
BufferedOutputStream netOutStream = new BufferedOutputStream(client.getOutputStream());

String outFileName = "output/test";
File outputFile = new File(outFileName);
if (!outputFile.exists()) {
    outputFile.getParentFile().mkdirs();
}
FileOutputStream fileOutStream = new FileOutputStream(outputFile);
BufferedOutputStream bufOutStream = new BufferedOutputStream(fileOutStream);

// read file from client and save
int bytesRead = 0;
byte[] buffer = new byte[1024];
while ((bytesRead = netInStream.read(buffer)) > 0) {
    bufOutStream.write(buffer, 0, bytesRead);
    bufOutStream.flush();
    Log.line("Bytes read: " + bytesRead);
}
// clean up file IO
// ...

// send response to client
netOutStream.write("File received by server".getBytes());
netOutStream.flush();

// clean up network IO
// ...

客户端代码:

Socket client = new Socket(DOMAIN_SERVER, PORT_SERVER);
BufferedOutputStream netOutStream = new BufferedOutputStream(client.getOutputStream());
BufferedInputStream netInStream = new BufferedInputStream(client.getInputStream());

String inFileName = "input/test";
File file = new File(inFileName);
if (!file.exists()) {
    client.close();
    return;
}
FileInputStream fileInSream = new FileInputStream(file);
BufferedInputStream bufInStream = new BufferedInputStream(fileInSream);

// read and send file to server
int bytesRead = 0;
byte[] buffer = new byte[1024];
while ((bytesRead = bufInStream.read(buffer)) > 0) {
    netOutStream.write(buffer, 0, bytesRead);
    netOutStream.flush();
    Log.line("Bytes sent: " + bytesRead);
}
// clean up file IO
// ...

// read response from server
StringBuilder res = new StringBuilder();
byte[] charBuf = new byte[128];
int msgBytesRead = 0;
while ((msgBytesRead = netInStream.read(charBuf)) > 0) {
    res.append(new String(charBuf, 0, msgBytesRead));
}
Log.line(res.toString());

// clean up network IO
// ...

流程是，客户端向服务器发送文件，服务器读取文件并保存到本地存储，然后服务器向客户端发送响应字符串，客户端读取响应并将其打印在屏幕上。

如果代码如上面所示，服务器将不会退出 while 循环并挂起，因此客户端第二个 while 循环也不会读取任何内容并挂起。但是，如果我注释/删除客户端第二个 while 循环，则两个程序都会运行并且不会发生挂起。文件传输也成功。

Answer 1

您的期望是，一旦服务器发送完文件，read 返回时不会有任何数据。这种期望是错误的。如果服务器关闭了 TCP 连接，并且您显示的 flush 不会关闭连接，而只是确保所有缓冲数据都写入，则 read 只会返回没有数据的情况TCP 连接。

这意味着服务器在刷新之后仍然可以发送更多数据，这就是为什么您的客户端卡在读取并等待更多数据的原因。