套接字未在Java 7中接收输入

Question

I have run into an interesting issue trying to upgrade one of my applications from the Java 6 to Java 7. It is a simple Java socket program. It sends a command to a COM socket and receives a response. It works perfectly in a Java 6 environment, but when I try to run the same code in a Java 7 environment, the socket appears to receive nothing in the InputStream.

I can confirm that the COM socket it's connecting to does receive the command and sends the response. This is run on the exact same machine in both cases with the firewall disabled, and it's the exact same code ran both times.

Has something changed in Java 7, do I have some deeper flaw, or is this simply a Java bug?

Here is a slightly stripped version of the code.

public static void main(String[] arguments) throws Exception {
  InetAddress server = InetAddress.getByName(serverAddress);
  Socket sock = SSLSocketFactory.getDefault().createSocket(server.getHostAddress(), port);
  InputStream in = sock.getInputStream();
  OutputStream out = sock.getOutputStream();
  out.write(command.getBytes()); //Is valid command
  String token = "";
  responseReader: while (true) {
    try {
      Thread.sleep(1);
    }
    catch (InterruptedException exception) {}
    byte[] d = new byte[in.available()];
    int avail = in.read(d);
    for (int i = 0; i < avail; i++) {
      if (d[i] == fieldSeperator) {
        token = "";
      }
      else if (d[i] == commandSeperator) {
        break responseReader;
      }
      else {
        token += (char) d[i];
      }
    }
  }
}

I've tried as much as I can think of, most of the time knowing it shouldn't matter. Using different methods of reading the stream, casting to SSLSocket and making different calls, adding some sleeps.

Answer 1

The code is wrong. You shouldn't use available() like that. If there is no data available you will allocate a zero length buffer and execute a zero length read, which will retun zero without blocking. Use a constant like 8192 for the buffer size, and allocate the buffer outside the loop. And get rid of the sleep() too.

There are few if any correct uses of available(), and this isn't one of them.

And note that available() always returns zero for an SSLSocket, and has always done so right back to Java 1.3 and the separate JSSE download. So I am unable to accept that the same code worked in Java 6.