Designing an API - troubles with class loading (Groovy) - javafx

Question

It's my first time designing an API. I have a program with folder 'plugins'. I made a test plugin in that folder packaged in JAR. In the program I have a Groovy class 'Configuration', which is supposed to load the plugins.
Configuration.java:
static void processConfiguration()
{
File pluginDirectory=new File(PLUGINDIRECTORY)//it's 'plugins'
if(!pluginDirectory.exists()) pluginDirectory.mkdir()
File[] pluginfiles=pluginDirectory.listFiles()
for(File f:pluginfiles)
{
if(f.name.endsWith('.jar'))
{
JarFile jar=new JarFile(f)
for(JarEntry jarEntry:jar.entries())
{
if(jarEntry.getName().endsWith('.class'))
{
//try loading the class
}
}
}
}
}
So, I tried doing these at the //try loading the class block
Class cl=ClassLoader.getSystemClassLoader().loadClass(jarEntry.name)
Class cl=new GroovyClassLoader().loadClass(jarEntry.name)
Class cl=Configuration.classLoader.loadClass(jarEntry.name)
Class cl=Class.forName(jarEntry.getName())
also tried with replacing - jarEntry.name.replaceAll('/','.').replace('.class',''), but I think it's done automatically.
Getting Class not found exception:
Exception in Application start method
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.RuntimeException: Exception in Application start method
at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$155(LauncherImpl.java:182)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.ClassNotFoundException: jace/plugins/JavaPlugin.class
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at java_lang_ClassLoader$loadClass.call(Unknown Source)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)
at jace.Configuration.processConfiguration(Configuration.groovy:87)
at jace.Jace.start(Jace.java:56)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$162(LauncherImpl.java:863)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$175(PlatformImpl.java:326)
at com.sun.javafx.application.PlatformImpl.lambda$null$173(PlatformImpl.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$174(PlatformImpl.java:294)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
at com.sun.glass.ui.gtk.GtkApplication.lambda$null$49(GtkApplication.java:139)

Answer 1

After some searching and tinkering I finally resolved it.
First, need to create a list of proper URLs;
Second, make a list of classes from the jar;
Third, instantiate GroovyClassLoader and give him all URLs;
Fourth, load classes from list, check whether they implement plugin interfaces, then instantiate them.
static void processConfiguration()
{
File pluginDirectory=new File(PLUGINDIRECTORY)
if(!pluginDirectory.exists()) pluginDirectory.mkdir()
File[] pluginfiles=pluginDirectory.listFiles()
URL[] urls=[]
ArrayList<String> classes=new ArrayList<>()
for(File f:pluginfiles)
{
if(f.name.endsWith('.jar'))
{
JarFile jar=new JarFile(f)
URL url=new URL('jar:file:'+PLUGINDIRECTORY+'/'+f.name+'!/')
urls+=url
jar.entries().each {if(it.name.endsWith('.class'))classes.add(it.name) }
}
}
// println(gcl.loadedClasses)
GroovyClassLoader groovyClassLoader=new GroovyClassLoader()
urls.each {groovyClassLoader.addURL(it)}
// println(classes)
classes.each {
Class cl=groovyClassLoader.loadClass(it.replaceAll('/','.').replace('.class',''))
Class[] interfaces=cl.getInterfaces()
if(interfaces.contains(Plugin.class))
{
Object instance=cl.newInstance()
if(interfaces.contains(SuggestionPlugin.class))
{
SuggestionProcessor.suggestionPlugins.add(instance as SuggestionPlugin)
}
Constructor[] constructors=cl.getConstructors()
println("Loaded a plugin $cl.simpleName")
}
}
}