How can I create Log4j 2 appender connected with jTextPane?

Question

I'm currently trying to make Log4j 2 log into a JTextPane. It should act like a STDERR or STDOUT in Netbeans IDE console (incl. text style - color).

I know that I need to create an appender and connect it with JTextPane, however I don't know how do it using Log4j 2.

Do you have any suggestions?

I appreciate your help, marty

Answer 1

I have done this for Logback (with plain text only). The basic things you need to do are:

• Implement your own Appender to receive the log events. Log4j 2 provides AbstractAppender, which will give you the baseline functionality.
• Use an appropriate Layout to format the log event (will depend what type of Document you're using for your JTextPane.
• Append the formatted text to the underlying Document for the JTextPane.

A couple of other points:

• Things will be simpler if you log plain text only, in which case you should use a JTextArea.
• Presumably you will want to cap the amount of text in the Document. You can do this by checking the length on each append and cutting out the first X% using Document.remove when it exceeds the maximum length.
• If you have frequent log operations, you should limit the frequency at which you append to the document, and buffer the changes in between to reduce the swing update/repaint overhead. I typically use 3 Hz. This is also advisable when you have multiple log producer threads because although the Document.insertString method is thread-safe, it obtains a lock on the document before performing the update and can result in quite a bit of contention.

I'd highly recommend referencing the documentation for this. I've never used Log4j 2, but the documentation looks quite straight forward. Similarly, the "Using Text Components" section of the Java Tutorials provides everything you need to know about the Swing side. Unfortunately I can't provide additional links here.