Question

While executing the following under Java 7, the program hangs. However, it doesn’t hang under Java 6.

package pkg;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;

final public class Main
{
    public static void main(String[] args)
    {
        try
        {
            URL url = new URL("http://en.wikipedia.org/wiki/Cancer");
            BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
            String line;
            while((line = in.readLine())!= null)
            {
                System.out.println(line);
            }
            in.close();
        }
        catch (IOException ex)
        {
            ex.printStackTrace();
        }
    }
}

What might be the reason?

Answer 1

The code is not guaranteed to work under any version of Java. YOu might have gotten luck with a particular Java runtime. The issue is that you’re trying to buffer input coming from the network, and this can hang. You must set the buffer size to 1 (effectively turning off buffering) before using BufferedReader with a network connection or with System.in; otherwise read() calls can hang trying to buffer input that’s not available, and may never become available. See the (new) second argument to the BufferedReader constructor:

BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()), 1);