How do I recognize EOF in Java Sockets?

问题:

I want to recognize end of data stream in Java Sockets. When I run the code below, it just stuck and keeps running (it stucks at value 10).

I also want the program to download binary files, but the last byte is always distinct, so I don't know how to stop the while (pragmatically).

String host = "example.com";
String path = "/";
Socket connection = new Socket(host, 80);

PrintWriter out = new PrintWriter(connection.getOutputStream());
  out.write("GET "+ path +" HTTP/1.1\r\nHost: "+ host +"\r\n\r\n");
out.flush();

int dataBuffer;
while ((dataBuffer = connection.getInputStream().read()) != -1)
  System.out.println(dataBuffer);

out.close();

Thanks for any hints.

回答1:

1. You should use existing libraries for HTTP. See here.
2. Your code works as expected. The server doesn't close the connection, and dataBuffer never becomes -1. This happens because connections are kept alive in HTTP 1.1 by default. Use HTTP 1.0, or put Connection: close header in your request.

For example:

out.write("GET "+ path +" HTTP/1.1\r\nHost: "+ host +"\r\nConnection: close\r\n\r\n");
out.flush();

int dataBuffer;
while ((dataBuffer = connection.getInputStream().read()) != -1) 
   System.out.print((char)dataBuffer);

out.close();

回答2:

Actually your code is not correct.

In HTTP 1.0 each connection is closed and as a result the client could detect when an input has ended.

In HTTP 1.1 with persistent connections, the underlying TCP connection remains open, so a client can detect when an input ends with 1 of the following 2 ways:

1) The HTTP Server puts a Content-Length header indicating the size of the response. This can be used by the client to understand when the reponse has been fully read.

2)The response is send in Chunked-Encoding meaning that it comes in chunks prefixed with the size of each chunk. The client using this information can construct the response from the chunks received by the server.

You should be using an HTTP Client library since implementing a generic HTTP client is not trivial (at all I may say).

To be specific in your code posted you should have followed one of the above approaches.

Additionally you should read in lines, since HTTP is a line terminated protocol.

I.e. something like:

BufferedReader in =new BufferedReader(new InputStreamReader( Connection.getInputStream() ) );
String s=null;
while ( (s=in.readLine()) != null)  {
//Read HTTP header
     if (s.isEmpty()) break;//No more headers
   }
}

By sending a Connection: close as suggested by khachik, gets the job done (since the closing of the connection helps detect the end of input) but the performance gets worse because for each request you start a new connection.

It depends of course on what you are trying to do (if you care or not)