How to implement an app in a bridge to grab input stream from the Internet

Question

I set up a pc as a linux-based (Red Hat 9.0) bridge device at first. The pc got two NICs, both of their IPs set as 0.0.0.0. Just now, whole the LAN can uses the pc as a transparent bridge to communicate with external network without change any network setting.
Consider to monitor the data stream between LAN and external network. I try to implement a sniffer-like app in the bridge device now.
Below is a portion of my sniffer app, as I run the app in the bridge device, the outcoming result will be:
print test line 01
not my expected result:
print test line 01
print test line 02
Can anyone help me to clear my idea?
public grabInputStream()
     String t = "";
     int listenPort = 80;
     try
          ServerSocket serverSocket = new ServerSocket(listenPort);
          System.out.println("print test line 01");
          Socket listenSocket = serverSocket.accept();
          System.out.println("print test line 02");
          InputSream listenInputStream = listenSocket.getInputStream();
          while (listenInputStream.available()>0)
               t+=(char)listenInputStream.read();
     catch (Exception e)
          e.printStackTrace();
}

Answer 1

Using available() is a bad way to check if the stream is still open.
Reread the documenation on available to see while.
Just read only byte at a time until the stream ends. See the javadoc on read() to see how.
Note: a byte is not a char and a single char can take up 2 or 3 bytes.
Using a String like this is both inefficient and incorrect.
I suggest you use apache's IOUtils class to convert an InputStream into a String.