Official Blog of Michael Liao

Be careful when using Timer

Michael Liao — Thu, 05 Nov 2009 09:29:17 +0000

Timer is used to schedule tasks that run at a fixed rate in Java. However, the thread of Timer itself may stop unexpected when your TimerTask throws an uncaught exception. See following code:

public class TimerTest {

    public static void main(String[] args) {
        Timer timer = new Timer();
        timer.scheduleAtFixedRate(
                new TimerTask() {
                    int n = 0;
                    @Override
                    public void run() {
                        if (n==10)
                            throw new RuntimeException("task failed.");
                        System.out.print('.');
                        n++;
                    }
                },
                1000L,
                1000L
        );
    }
}

When the TimerTask runs 10 times it throws a RuntimeException, which cause the thread of Timer stopped. You will get the following output:

..........Exception in thread "Timer-0" java.lang.RuntimeException: task failed.
	at sync.test.TimerTest$1.run(TimerTest.java:16)
	at java.util.TimerThread.mainLoop(Timer.java:512)
	at java.util.TimerThread.run(Timer.java:462)

It is necessary to catch all exceptions in TimerTask. But the best way to schedule tasks is using Executor if you are working with JDK 5 or later. It is fast, with pooled thread, and more simple API to schedule tasks.

JexiEditor: a WYSIWYG Editor

Michael Liao — Fri, 16 Oct 2009 07:49:32 +0000

JexiEditor is a WYSIWYG (what you see is what you get) editor written by Java. It is a very good example of learning the famous "GoF: Design Patterns".

The source code can be downloaded or checked out from SVN. Please visit the project home page:

http://code.google.com/p/jexieditor/

The word "Jexi" is a combination of "Java" and "Lexi". See snapshot:

JOpenID: OpenID 2.0 Client Library for Java

Michael Liao — Fri, 16 Oct 2009 07:36:58 +0000

JOpenID is a lightweight Java client library of OpenID 2.0.

JOpenID supports sign on by OpenID 2.0 protocol, which enables user to sign on with their OpenID account without registration on your website. The well-known OpenID providers are Google account, Yahoo account, etc.

JOpenID is simple, fast and very small, about 50 KB including both binary and source code. You can download from:

http://code.google.com/p/jopenid/downloads/list

For more information about JOpenID, please visit the project home page:

http://code.google.com/p/jopenid/

JOpenID is now on the list of recommended libraries on OpenID official website:

How to use OpenID to sign on with Google account

Michael Liao — Wed, 14 Oct 2009 05:40:46 +0000

Recently Google announced its support for OpenID, called "Federated Login", to let any site enable their users to sign on by their Google accounts, without registrations.

This is really a good news, and for Java developers they can write some code to make the 3rd-part site to connect to Google. There are already lots of libaries that can be used in J2EE. However, after I do some evaluation of these libaries, I do not find a suitable libary. The well-known "OpenID4Java", is too large (46MB!), with dependencies on many other libaries. So I decided to write a small, but very lightweight libary to support OpenID 2.0 spec, called "JOpenID".

It is very small, about 50KB including both source & binary. You can download from:

http://code.google.com/p/jopenid/downloads/list.

It only depends commons-logging!

Sample code is provided:

http://code.google.com/p/jopenid/source/browse/trunk/JOpenId/src/com/javaeedev/openid/Main.java

It has been fully tested based on Google accounts. However, I think it also can support Yahoo! OpenID, but with little information provided by Yahoo! I do not test yet.

About Michael Liao

Michael Liao — Wed, 14 Oct 2009 03:26:32 +0000

Hi, I'm Michael Liao, a software engineer in China.

I have 5 years experiences in software development, especially Java and Python.