Attempting to implement a plugin system for my application, the code of which extends my Plugin class to define custom functionality.
This code to load a class from within a jar, in the same directory as the .jar of the application, works fine:
if(pluginName.endsWith(".jar"))
{
JarFile jarFile = new JarFile(pluginName);
Enumeration jarComponents = jarFile.entries();
while (jarComponents.hasMoreElements())
{
JarEntry entry = (JarEntry) jarComponents.nextElement();
if(entry.getName().endsWith(".class"))
{
className = entry.getName();
}
}
File file = new File(System.getProperty("user.dir")+"/"+pluginName);
URLClassLoader loader = new URLClassLoader(new URL[]{file.toURI().toURL()});
Class newClass = Class.forName(className.replace(".class", ""), true, loader);
newPlugin = (Plugin) newClass.newInstance();
}
Which results in the correct response of:
benpalmer$ java -jar assignment.jar test_subproject.jar
- INFO: Add new plugin: source.com
The issue is I also want to provide the user the option to specify a .class file instead, as that is realistically all that is packed into a .jar for the purposes of my plugin system.
else if(pluginName.endsWith(".class"))
{
File file = new File(System.getProperty("user.dir")+"/"+pluginName);
URLClassLoader loader = new URLClassLoader(new URL[]{file.toURI().toURL()});
Class newClass = Class.forName(className.replace(".class", ""), true, loader);
newPlugin = (Plugin) newClass.newInstance();
}
... exception handling
Which results in the following:
benpalmer$ java -jar assignment.jar TestPlugin.class
SEVERE: Error: Plugin class not found. Class name:
java.lang.ClassNotFoundException:
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at newsfeed.model.Plugin.loadClassFromJarFile(Plugin.java:144)
at newsfeed.controller.NFWindowController.initPlugins(NFWindowController.java:81)
at newsfeed.controller.NewsFeed$1.run(NewsFeed.java:20)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:80)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
I've tried the code above and many variations of path names/other options, but get ClassNotFoundException every time. Originally had trouble loading the jars but using the fully qualified path fixed that, now I can't load the Classes.
Any ideas? :)
Saw my question again and realised I'd forgotten to post a solution I found to my problem. I hope this helps someone in the future, as it's the only working example I ever found for my situation - a university assignment problem. I can't believe it was this simple:
byte[] classData = Files.readAllBytes(Paths.get(fileName));
Class<?> cls = defineClass(null, classData, 0, classData.length);
return (PluginClassName)cls.newInstance();
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