Java套接字：读取不返回

Question

It was supposed to be a 5-minutes test just to see whether it works as suggested. I wanted to create a stupidly simple HTTP "server" that does nothing but printing out what it gets (namely the HTTP requests).

public static void main(String args[]) throws IOException {
    ServerSocket server = new ServerSocket(port); 
    try (Socket socket = server.accept()) {
        DataInputStream input = new DataInputStream(socket.getInputStream());
        String received = input.readUTF();
        System.out.println("Received: \n" + received);
    }
}

But I came up with the following problem: When I start his program and then try http://localhost/ in Firefox, the stream gets stuck in the readUTF() method. It simply does not return.

I tried the same with socket channels and a buffer size of 128. There, it gets stuck after the third read (so anywhere between the 384th and 511th byte). This is the following code:

public static void main(String args[]) throws IOException {
    CharsetDecoder decoder = Charset.forName("UTF8").newDecoder();
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.bind(new InetSocketAddress(port)); 
        ByteBuffer buffer = ByteBuffer.allocate(bufferSize);
        buffer.clear();
        SocketChannel socketChannel = serverSocketChannel.accept(); 
        StringBuilder received = new StringBuilder();
        while (socketChannel.read(buffer) > 0) {
            buffer.position(0);
            received.append(decoder.decode(buffer).toString()); 
            buffer.clear();
        }
        System.out.println("Received: \n" + received.toString());
    }

They both show the same behaviour that the read method does not terminate. Do you have any idea, how to solve this and especially, what is the reason for this behaviour?

Answer 1

DataInputStream is used to read binary data. In this particular case it means that readUTF() method reads first the string length as two bytes and then reads as many bytes as the length received.

This stream is not usable for your needs, just simply read from getInputStream() or wrap it with BufferedReader .