simple app breaks when opening second stream with openStream

From:

jmail@hursttechnical.com

Newsgroups:

comp.lang.java.programmer

Date:

14 May 2007 12:29:23 -0700

Message-ID:

<1179170963.364392.312990@h2g2000hsg.googlegroups.com>

I have written a simple java app using the two classes at the end of
this post. This app works fine on several machines, but not on the Red
Hat linux server that I really need it to run on. On the Red Hat
machine, I get the following program output and stack traces.

//BEGIN PROGRAM OUTPUT
Starting TestURL
Starting the threads...
Thread 1: Starting
Thread 1: URL is http://www.visnat.com/entry/vnimages/workplace1.jpg
End of TestURL after starting threads...
Thread 2: Starting
Thread 2: URL is http://www.visnat.com/entry/vnimages/justthetv.gif
Thread 2: the url openstream call
failed:java.lang.NullPointerException
java.lang.NullPointerException
   at
gnu.java.net.LineInputStream.LineInputStream(java.io.InputStream,
java.lang.String) (/usr/lib/libgcj.so.6.0.0)
   at
gnu.java.net.LineInputStream.LineInputStream(java.io.InputStream) (/
usr/lib/libgcj.so.6.0.0)
   at gnu.java.net.protocol.http.Request.dispatch() (/usr/lib/
libgcj.so.6.0.0)
   at gnu.java.net.protocol.http.HTTPURLConnection.connect() (/usr/lib/
libgcj.so.6.0.0)
   at gnu.java.net.protocol.http.HTTPURLConnection.getInputStream() (/
usr/lib/libgcj.so.6.0.0)
   at java.net.URL.openStream() (/usr/lib/libgcj.so.6.0.0)
   at ImageDownloader.run() (Unknown Source)
   at .GC_start_routine (/usr/lib/libgcj.so.6.0.0)
   at .__clone (/lib/libc-2.3.6.so)
Thread 2: Ending
Thread 2: the input stream close call
failed:java.lang.NullPointerException
java.lang.NullPointerException
   at ImageDownloader.run() (Unknown Source)
   at .GC_start_routine (/usr/lib/libgcj.so.6.0.0)
   at .__clone (/lib/libc-2.3.6.so)
Thread 1: Ending
//END PROGRAM OUTPUT

If I just run one thread/stream, then even the Red Hat machine is
happy. The threads seem to start and end ok and behave correctly. I
just can't get a second call to openStream to work.

Is there some configuration of linux/java that doesn't permit two
streams to be opened at the same time? At first, I thought it might
be a complete lack of ephemeral ports above 1024, but that doesn't
appear to be the problem after all. I haven't been able to find anyone
else that has ever experienced this problem.

gdhurst

// BEGIN TESTURL CLASS
import java.io.*;

public class TestURL {
static boolean listening = true;

public static void main(String[] args) throws IOException {
  System.out.println("Starting TestURL");
  ImageDownloader id1 = null;
  ImageDownloader id2 = null;

  id1 = new ImageDownloader("http://www.visnat.com/entry/vnimages/
workplace1.jpg","1");
  id2 = new ImageDownloader("http://www.visnat.com/entry/vnimages/
justthetv.gif","2");
  System.out.println("Starting the threads...");
  id1.start();
  id2.start();
  System.out.println("End of TestURL after starting threads...");
}

}
// END TESTURL CLASS

// BEGIN IMAGEDOWNLOADER CLASS
import java.io.*;
import java.net.*;

public class ImageDownloader extends Thread {
private String strUrl;
private String TID;

public ImageDownloader(String theurl,String threadID) {
  strUrl = theurl;
  TID = threadID;
}

public void run() {
  URL url;
  InputStream is = null;
    System.out.println("Thread " + TID + ": Starting");
  System.out.println("Thread " + TID + ": URL is " + strUrl);

  try {
    url = new URL(strUrl);
    is = url.openStream(); //throws an IOException
  } catch (Exception e) {
    System.out.println("Thread " + TID + ": the url openstream call
failed:" + e);
    e.printStackTrace();
  }

  System.out.println("Thread " + TID + ": Ending");
  try {
    is.close();
  } catch (Exception e) {
    System.out.println("Thread " + TID + ": the input stream close
call failed:" + e);
    e.printStackTrace();
  }

} //END RUN()

}
// END IMAGEDOWNLOADER CLASS