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If I have a java.net.HttpURLConnection that's receiving data (or is about to receive data) in a worker thread, is it safe to call disconnect() to stop it at any point of the connection's lifecycle in another thread?

I'm wondering about this because I couldn't find a clearly documented way to abort an ongoing HTTP connection. Interrupting the worker thread by calling Thread.interrupt() won't work because the InputStream you get from HttpURLConnection is not interruptible.

I did some experiments that look like this:

// MyRequest.run() gets an HttpURLConnection by calling someUrl.openConnection()
MyRequest request = new MyRequest(someUrl);

FutureTask<SomeResult> task = new FutureTask<SomeResult>(request);
someExecutor.execute(task);

// The connection opens, data comes in, ...

// Get the HttpURLConnection from the request, call disconnect()
// Should be part of the cancel() of a FutureTask subclass
request.getConnection().disconnect();

It seems to work, and both the connection and the socket object it creates will be eventually cleaned up by gc. Still, I wonder if that's the right way to do it? Will there be any issue with calling disconnect() from another thread?

lukhnos
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2 Answers2

1

That will work, if you handle it correctly in the task. The better way to do that is to check the interruptState of the task while you read from the InputStream.

For example with BufferedReader:

HttpURLConnection conn = null;
try {

      //open Connection

   BufferedReader br = new BufferedReader(new InputStreamReader(inputstream));
   for(String line = br.readLine(); line != null && !Thread.currentThread().isInterrupted(); line = br.readLine()) {
         //do something
   }
} catch(IOException io) {
     //error handling
} finally {
   if(conn != null)
          conn.disconnect();
}
NerdNeo
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  • This only works once the server has started returning data. It doesn't help when the client is still waiting for a response. – Greg Brown Apr 25 '19 at 21:03
0

The doc for HttpURLConnection says, "Instances of this class are not thread safe." Since disconnect is an instance method, then per the documentation, you can't call it while any other method related to the object is being called. Typically, the I/O thread code is almost always calling HttpURLConnection-related methods since these methods block while waiting for the network.

If you make concurrent calls, like threading safety violations in general, you can expect it to work perfectly when you're testing an fail horribly in front of your you most important customer. :-)

Edward Brey
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  • To work around this limitation, wrap the code that uses `HttpURLConnection` inside a `Future`, as described [here](http://stackoverflow.com/a/26489077/145173). – Edward Brey Oct 21 '14 at 14:25