dockerlog.java

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.HttpURLConnection;

// This is a very basic implementation of the Docker API v. 1.12 for attaching to a containers StdOut and StdErr stream using HTTP
// It is not perfect (see official Docker API documentation for details and how to handle the bytestream) but up to this date its
// the most compleate, working example for this to get an idea what's going on there. Happy about any improvement ideas.

public class Readin
{
  // Docker hostname or IP
	private final static String hostname = "";
	// Port that the docker deamon is listening on (API port)
	private final static String port = "4243";
	// The container name or id that we want to attach to
	private final static String container = "";
	
	private final static Boolean showStdOut = true;
	private final static Boolean showStdErr = false;
	
	public static void main(String[] args) throws IOException
	{		
	  // Remember that we will only see output if there is output in the specified container stream (Stdout and/or Stderr)
		URL url = new URL("http://"+hostname+":"+port+"/containers/"+container+"/attach?logs=1&stream=1&stdout="+showStdOut.toString()+"&stderr="+showStdErr.toString()+"&tty=false");
		HttpURLConnection con = (HttpURLConnection) url.openConnection();
		
		con.setRequestMethod("POST");   // we have to use post as specified in API v 1.12
		con.setConnectTimeout(0);       // since we listen to a stream we want to timeout
		con.setReadTimeout(0);          // since we listen to a stream we want to timeout
		con.setUseCaches(false);

    // Quick error checking. See Docker API and the Java HttpURLConnection documentationfor the meaning of the return codes.
		int status = con.getResponseCode();
		System.out.println("Returncode: " + status);

		InputStream stream = null;
		stream = con.getInputStream();

		int b = -1;
		do {
			b = stream.read();
			// We use simple int to char conversion (quick and dirty)
			// Yet it is not perfect, but good enough to get the idea of how to fetch the hijacked HTTP stream of a Docker containers StdOut and StdErr
			System.out.print((char) b);
			
		} while (b != -1); 
		
		stream.close();
	}
}