Logback+Swing in small tool

Question

I need to hack up a small tool. It should read a couple of files and convert them. Right now that works in my IDE. For the user, I'd like to add a small UI which simply shows the log output.

Do you know of a ready-to-use Swing appender for logback? Or something which redirects System.out to a little UI with nothing more than a text field and a "Close" button?

PS: I'm not looking for Chainsaw or Jigsaw or Lilith. I want the display of the log messages in the application, please.

Answer 1

You need to write a custom appender class like so:

public class MyConsoleAppender extends AppenderBase<ILoggingEvent> {
  private Encoder<ILoggingEvent> encoder = new EchoEncoder<ILoggingEvent>();
  private ByteArrayOutputStream  out     = new ByteArrayOutputStream();

  public MyConsoleAppender() {
     LoggerContext lc = (LoggerContext) LoggerFactory.getILoggerFactory();
     setContext(lc);
     start();
     lc.getLogger("ROOT").addAppender(this);
  }

  @Override
  public void start() {
     try {
        encoder.init(out);
     } catch (IOException e) {}
     super.start();
  }

  @Override
  public void append(ILoggingEvent event) {
     try {
        encoder.doEncode(event);
        out.flush();
        String line = out.toString(); // TODO: append _line_ to your JTextPane
        out.reset();
     } catch (IOException e) {}
  }
}

You can replace the EchoEncoder with a PatternLayoutEncoder (see CountingConsoleAppender example in the logback examples folder).

The encoder will write each event to a byte buffer, which you can then extract a string and write this to your JTextPane or JTextArea, or whatever you want.