How do I write logs and display them real-time in a Java Swing application?

Question

I have created a GUI program that uses a class to perform some tasks.

I would like to add logging in both the JFrame and the class. Logs should be kept in a file and displayed in a JTextArea concurrently.

What is a convient solution for this?

with regard to logging, try [log4j](http://logging.apache.org/log4j/1.2/) — mre, May 31 '11 at 15:50
What have you done so far? It sounds like you need to pick your favorite Logging framework (either java.util.logging or log4j) and wrap it with some class/instance that simply writes to your `JTextArea`. — pickypg, May 31 '11 at 15:51

dertkw · Accepted Answer · 2011-05-31T16:00:03.110

7

Create a wrapper that

updates your JTextArea
logs via log4j, SLF4J or Apache Commons Logging or another logging framework

public void log(String msg) {
      appendToJTextArea(msg);
      LOG.info(msg);
 }

edited May 31 '11 at 16:00

answered May 31 '11 at 15:49

dertkw

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And why not simply "write to a file using a printstream"? – Martijn Courteaux May 31 '11 at 16:37
Because a logging framework is doing nothing else. PLUS you can customize it, turn it on/off easily, create customer appenders/loggers, have different loglevels, ... So why reinvent the wheel? – dertkw May 31 '11 at 16:43

score 4 · Answer 2 · answered May 31 '11 at 15:51

4

I suggest using a simple System.out.println() call and then running your application like this:

java -cp path/to/my/class/or/jar/MyClass.class MyClass -debug > myLog.log

Which will create a text pane for you (-debug parameter), as well as put them in a log file for you.

answered May 31 '11 at 15:51

Richard J. Ross III

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Come on, this is ridiculous! Logging frameworks are easy to use and if you one don't know about them it's investment for the future to learn this. `System.out.println()` is ok for a HelloWorld or debugging problems with you logging framework, but not for real applications. Please look at timbooo's answer describing a wrapper class. – Thor May 31 '11 at 16:21
@Thor: Indeed, real applications should not work this way. But I gave a +1 because of a simple alternative, using something that already exists. I didn't know this option. And yes, I gave timbooo also a +1. – Martijn Courteaux May 31 '11 at 16:39
@Thor, I fully understand logging, I have made my own framework for that in objective-c. However, I meant this to be a simple way that the OP can log data, without any extra writing of code. – Richard J. Ross III Jun 09 '11 at 14:41

score 0 · Answer 3 · answered May 31 '11 at 15:52

One of the ways you can log to a file easily is to use a FileWriter:
http://download.oracle.com/javase/1.4.2/docs/api/java/io/FileWriter.html

Additionally, as you log data you can always update the text of a JTextArea with JTextArea.append():
http://download.oracle.com/javase/1.4.2/docs/api/javax/swing/JTextArea.html

If you're logging to a file, might I suggest logging to multiple timestamped files? This ensures that you're saving the data and that you won't lose too much in the event of a program crash.

Hope this helped!

Those links are to an old version of Java. – jzd May 31 '11 at 16:10 — jzd, May 31 '11 at 16:10

How do I write logs and display them real-time in a Java Swing application?

3 Answers3