Being new to reflection, I am trying to implement a simple plugin architecture that loads plugins (fat jars) using Reflection.
I have two JavaFx applications (simple demo from org.codehaus.mojo.archetypes:javafx) named myPlugin and myHost. For simplicity, I haven't used any plugin interfaces.
Getting to the code:
>> myPlugin project
com.plugin.MainApp.java
package com.plugin;
import javafx.application.Application;
import static javafx.application.Application.launch;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;
public class MainApp extends Application {
@Override
public void start(Stage stage) throws Exception {
Parent root = FXMLLoader.load(getClass().getResource("/fxml/Scene.fxml"));
Scene scene = new Scene(root);
scene.getStylesheets().add("/styles/Styles.css");
stage.setTitle("JavaFX and Maven");
stage.setScene(scene);
stage.show();
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
printArgs(args);
launch(args);
}
public static void printArgs(String[] args){
for (int i = 0; i < args.length; i++){
System.out.println("PLUGIN: " + args[i]);
}
}
}
The output of myPlugin project is packaged in myPlugin.jar which resides in C:// directory (I used Intellij IDEA Artifacts builder). The jar file runs simply by following command without any problems around identifying main class or etc: java -jar myPlugin.jar
>> myHost project
com.host.MainApp.java
package com.host;
import javafx.application.Application;
import static javafx.application.Application.launch;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;
public class MainApp extends Application {
@Override
public void start(Stage stage) throws Exception {
Parent root = FXMLLoader.load(getClass().getResource("/fxml/Scene.fxml"));
Scene scene = new Scene(root);
scene.getStylesheets().add("/styles/Styles.css");
stage.setTitle("JavaFX and Maven");
stage.setScene(scene);
stage.show();
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
launch(args);
}
}
I want to run myPlugin when button clicked in host. so, the runPlugin method is responsible for reflecting:
com.host.FXMLController.java
package com.host;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ResourceBundle;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Label;
public class FXMLController implements Initializable {
@FXML
private Label label;
@FXML
private void handleButtonAction(ActionEvent event) {
System.out.println("HOST: You clicked me!");
this.runPlugin();
System.out.println("HOST: After running plugin!");
}
@Override
public void initialize(URL url, ResourceBundle rb) {
// TODO
}
public void runPlugin(){
try {
URLClassLoader child = new URLClassLoader (
new URL[] {new URL("file:///C:/myPlugin.jar")}, ClassLoader.getSystemClassLoader());
Method method = URLClassLoader.class.getDeclaredMethod("addURL", URL.class);
method.setAccessible(true);
method.invoke(child, child.getURLs()[0]);
Class<?> mainClass = Class.forName("com.plugin.MainApp", true, child);
Object instance = mainClass.newInstance();
Method mainMethod = mainClass.getDeclaredMethod("main", String[].class);
mainMethod.setAccessible(true);
String[] args = new String[]{"message", "from", "host"};
mainMethod.invoke(null, new Object[] {args});
}
catch (InvocationTargetException e){
e.printStackTrace(); }
catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (MalformedURLException e) {
e.printStackTrace();
}
}
}
By clicking button in myHost app, the main method of myPlugin is executed and args sent from host are printed, which means that MainApp class and its main method are loaded successfully by class loader. But when launching the view in myPlugin (launch(args)), I get java.lang.ClassNotFoundException: com.plugin.MainApp exception, which doesn't make any sense to me.
The exact output from stack trace is as follow:
HOST: You clicked me!
PLUGIN: message
PLUGIN: from
PLUGIN: host
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.host.FXMLController.runPlugin(FXMLController.java:49)
at com.host.FXMLController.handleButtonAction(FXMLController.java:22)
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.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Node.fireEvent(Node.java:8413)
at javafx.scene.control.Button.fire(Button.java:185)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
HOST: After running plugin!
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:381)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:417)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.RuntimeException: java.lang.ClassNotFoundException: com.plugin.MainApp
at javafx.application.Application.launch(Application.java:260)
at com.plugin.MainApp.main(MainApp.java:30)
... 64 more
Caused by: java.lang.ClassNotFoundException: com.plugin.MainApp
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at javafx.application.Application.launch(Application.java:248)
... 65 more
If the problem is from Reflection, the main method in myPlugin would not be executed. Referencing static method and passing parameters is also correct. Packaging myPlugin into fat jar file seems also correct because extracting it gives me the resources/styles files and folders too, which means all dependencies are resolved.
I mentioned these, because most of similar questions are about reflection problems and packaging .
What am I doing wrong?
Since reflecting a simple console-based plugin works like a charm (I have tested), are there any important differences that should be considered when dealing with gui-based plugins?
I would appreciate any helps.
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