Comments on: Developing A Simple Pluggable Java Application

By: Xavier

Xavier — Sat, 10 Sep 2011 12:40:26 +0000

Hi, very usefull post. I use it in my java simple executable app, it work so good. But when I want to use it in servlet in Tomcat, ClassCastException is throw by ServiceLoader when getting iterator (getPlugins). Have you heared something that ?
I thought it’s same thing that a tomcat Classloader bord effect… Please help me !

Sorry for my frenlish

Xavier

By: uyalap

uyalap — Fri, 09 Sep 2011 08:06:33 +0000

Thanks James. Very useful post.

By: Adam

Adam — Sun, 04 Sep 2011 07:20:53 +0000

James,
I know this is quite an old post, but I am having the same problem as Sathish. I get “No plugins were found” when I run Main. I have all the files set up the way mentioned in this article, but it would not compile so I moved in dependancies and built the plugin jar, copied it to the plugins folder, I have the META/services file in place (in fact I copied it to the main app project as well to test that as well). I copied all the code and pasted directly from this webpage. Nothing works. Any ideas?

Here is a screenshot of my project files and the Files list:
http://i.imgur.com/4BPFi.jpg

By: James

James — Tue, 21 Dec 2010 03:41:10 +0000

@Suchitto Palit

1> The class StandardPluginService.java is a Singleton, isn’t it ?

– Yes the StandardPluginService is a singleton.

2> In the Main.java line 10 we do not need that line of code
“private static Logger logger = Logger.getLogger(Main.class.getName());”Isn’t it?

– Logging is upto you and is not mandatory but it’s a good practice to log.

3> In ClasspathUtils.java line 59 I changed “Class sysclass = URLClassLoader.class;” to “Class sysclass = URLClassLoader.class;” .

– Sorry, I don’t understand what do you mean here.

By: James

James — Tue, 21 Dec 2010 03:35:54 +0000

@Kevin Thanks for the nice suggestion. Yes, I’m aware of the issues associated with the system class loader.

By: James

James — Tue, 21 Dec 2010 03:32:36 +0000

@Satish Did you create the respective files in “META-INF” folder?

By: Sathish

Sathish — Thu, 16 Dec 2010 07:16:32 +0000

Hi I got the following output. But I placed the plugin-jar files in proper folder. I don’t know where the mistake is..

16 Dec, 2010 12:41:18 PM com.pluggableapp.StandardPluginService initPlugins
INFO: No plugins were found!

Regards,
Sathish

By: Bruce

Bruce — Tue, 16 Nov 2010 21:13:35 +0000

James,

I have followed your example to the T, but get this error when I run it:
Nov 16, 2010 2:03:29 PM pluggableapp.StandardPluginService initPlugins
INFO: No plugins were found!

Any ideas?

TIA,

Bruce

By: Kevin

Kevin — Thu, 08 Jul 2010 10:09:17 +0000

Hi, very useful indead, thanks a lot;
but don’t you prefer this version:
public static ClassLoader addDirToClasspath(File directory) throws IOException { MyURLClassLoader cl = new MyURLClassLoader() ; if (directory.exists()) for (File file : directory.listFiles()) if (file.getName().endsWith(".jar")) cl.addURL(file.toURI().toURL()); return cl ; }

private static class MyURLClassLoader extends URLClassLoader { public MyURLClassLoader() { super(new URL[]{}) ; } @Override public void addURL(URL url) { super.addURL(url); } }
which doesn’t rely on the System classloader to to an URLClassLoader, doesn’t use reflection to access illegaly addURL, and also doesn’t create a class leak when you unload you app? (please let me know if you see any drawback, it’s just an open suggestion)

By: tugalsan

tugalsan — Tue, 15 Jun 2010 07:38:46 +0000

- I takes to much time to configure for every program man;
- I am using javascript to “plug in” some code in my program, it basicly changes whole program into another.
- I know it highly risky, but highly configurable. with one exe(jar) file and directing “target directory” to some other directory with “plugins js files” in it, i solved great deal. I am searching same style plug in framework with java-class files now.