StreamGobbler

The StreamGobbler class constantly consumes the input from an InputStream, and distribute the input lines to a listener. This is often useful when using ProcessBuilder and listen to the InputStream coming from the external process, but you can use it with any InputStream.

Contrary to many implementations seen on the Web, this class defer the actual work to a listener.

Listener interface

The StreamGobbler.Listener interface has two methods:

• The StreamGobbler.Listener.close() method is called when the StreamGobbler is closed
• The StreamGobbler.Listener.readLine(String) method is called when a line from the InputStream is read

Usage

After the creation of the StreamGobbler:

• You set the listener with the StreamGobbler.setListener(Listener) method
• You can configure the behavior (see handling the listener in another thread for more information
• Then you start the reading of the stream with the StreamGobbler.start() method

Stopping the reading

You can force top the reading of the stream with the StreamGobbler.stop() method. However the reading will stop as soon as the stream return a null String. In that case the StreamGobbler.Listener.close() method will be called.

Handling the listener in another thread

By default the listener is called in the same Thread as the reading of the InputStream, which means that if the stream receives a lot of inputs in a short time, some of them could be discarded by the listener, leading to problems.

The following methods allow to handle the StreamGobbler.Listener.readLine(String) method in another Thread using a Queue, which ensures that no event in the InputStream readings will be discarded:

• The StreamGobbler.setQueued(boolean, int, int) will queue the InputStream reading events and use them in the listener in another Thread. Between each even, there will be a delay of x ms, and a polling of y ms
• The StreamGobbler.setQueued(boolean, int) will queue the InputStream reading events and use them in the listener in another Thread. Between each even, there will be a delay of x ms
• The StreamGobbler.setQueued(boolean) will queue the InputStream reading events and use them in the listener in another Thread, with no delay

Example

The following code will redirect the output of an executable (normally on the console) to a List of Strings:

   ProcessBuilder pb = new ProcessBuilder("my_executable.exe");
   Process process = pb.start();
      
   StreamGobbler outgobbler = new StreamGobbler(process.getInputStream());
   List<String> lines = new ArrayList<>
   outgobbler.setListener(new StreamGobbler.Listener() {
      @Override
      public void readLine(String line) {
        lines.add(line);
      }

      @Override
      public void close() {
      }
   });
   errorgobbler.start();
   outgobbler.start();