Question

Following is a part of the code snippet that I will be using for my project.

public String fetchFromStream()
{
    try
    {
        int charVal;
        StringBuffer sb = new StringBuffer();

        while((charVal = inputStream.read()) > 0) {
            sb.append((char)charVal);
        }
        return sb.toString();
    } catch (Exception e)
    {
        m_log.error("readUntil(..) : " + e.getMessage());
        return null;
    } finally {
        System.out.println("<<<<<<<<<<<<<<<<<<<<<< Called >>>>>>>>>>>>>>>>>>>>>>>>>>>");
    }
}

Initially the while loop start working pretty fine. But after the probable last character is read from the stream I was expecting to get -1 return value. But this is where my problem starts. The code gets hanged, even the finally block is not executed.

I was debugging this code in Eclipse to see what is actually happening during the run-time. I set a pointer (debug) inside the while loop and was constantly monitoring the StringBuffer getting populated with char values one by one. But suddenly while checking the condition inside the while loop, the debugging control is getting lost and this is the point where the code goes to hangup state !! No exception is thrown as well !!

What is happening here ?

Edit::

This is how I’m getting my InputStream. Basically I’m using Apache Commons Net for Telnet.

private TelnetClient getTelnetSession(String hostname, int port)
{
    TelnetClient tc = new TelnetClient();
    try
    {
        tc.connect(hostname, port != 0 ? port : 23);

                    //These are instance variables
        inputStream = tc.getInputStream();
        outputStream = new PrintStream(tc.getOutputStream());

        //More codes...

        return tc;
    } catch (SocketException se)
    {
        m_log.error("getTelnetSession(..) : " + se.getMessage());
        return null;
    } catch (IOException ioe)
    {
        m_log.error("getTelnetSession(..) : " + ioe.getMessage());
        return null;
    } catch (Exception e)
    {
        m_log.error("getTelnetSession(..) : " + e.getMessage());
        return null;
    }
}

Answer 1

Look at the JavaDocs:

Reads the next byte of data from the input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.

In simple turns: if your stream ended (e.g. end of file), read() returns -1 immediately. However if the stream is still open but JVM is waiting for data (slow disk, socket connection), read() will block (not really hung).

Where are you getting the stream from? Check out the available() – but please do not call it in a loop exhausting CPU.

Finally: casting int/byte to char will only work for ASCII characters, consider using Reader on top of InputStream.