Fixed EDT Classloading issues after EDT shutdown.

core/src/main/java/net/sourceforge/jnlp/Launcher.java

@@ -27,13 +27,14 @@
 import net.adoptopenjdk.icedteaweb.resources.UpdatePolicy;
 import net.adoptopenjdk.icedteaweb.ui.swing.SwingUtils;
 import net.sourceforge.jnlp.config.DeploymentConfiguration;
+import net.sourceforge.jnlp.runtime.AppContextFactory;
 import net.sourceforge.jnlp.runtime.AppletInstance;
 import net.sourceforge.jnlp.runtime.ApplicationInstance;
-import net.sourceforge.jnlp.runtime.classloader.JNLPClassLoader;
 import net.sourceforge.jnlp.runtime.JNLPRuntime;
+import net.sourceforge.jnlp.runtime.classloader.DelegatingClassLoader;
+import net.sourceforge.jnlp.runtime.classloader.JNLPClassLoader;
 import net.sourceforge.jnlp.services.InstanceExistsException;
 import net.sourceforge.jnlp.services.ServiceUtil;
-import sun.awt.SunToolkit;
 
 import javax.swing.text.html.parser.ParserDelegator;
 import java.applet.Applet;
@@ -436,6 +437,9 @@ private void setContextClassLoaderForAllThreads(ThreadGroup tg, ClassLoader clas
             }
         }
 
+        //inject classloader into edt delegating classloader
+        DelegatingClassLoader.getInstance().setClassLoader(classLoader);
+
     }
 
     /**
@@ -643,8 +647,7 @@ public void run() {
             try {
                 // Do not create new AppContext if we're using NetX and icedteaplugin.
                 // The plugin needs an AppContext too, but it has to be created earlier.
-                SunToolkit.createNewAppContext();
-
+                AppContextFactory.createNewAppContext();
                 doPerApplicationAppContextHacks();
 
                 if (file.isApplication()) {

core/src/main/java/net/sourceforge/jnlp/runtime/AppContextFactory.java

@@ -0,0 +1,22 @@
+package net.sourceforge.jnlp.runtime;
+
+import net.sourceforge.jnlp.runtime.classloader.DelegatingClassLoader;
+import sun.awt.SunToolkit;
+
+public class AppContextFactory {
+    public static void createNewAppContext() {
+        //set temporary classloader for EventQueue initialization
+        //already a call to AppContext.getAppContext(...) initializes the EventQueue.class
+        ClassLoader originalLoader = Thread.currentThread().getContextClassLoader();
+        try {
+            DelegatingClassLoader delegatingLoader = DelegatingClassLoader.getInstance();
+            delegatingLoader.setClassLoader(originalLoader);
+
+            Thread.currentThread().setContextClassLoader(delegatingLoader);
+            SunToolkit.createNewAppContext();
+        }finally {
+            //restore original classloader
+            Thread.currentThread().setContextClassLoader(originalLoader);
+        }
+    }
+}

core/src/main/java/net/sourceforge/jnlp/runtime/classloader/DelegatingClassLoader.java

@@ -0,0 +1,62 @@
+package net.sourceforge.jnlp.runtime.classloader;
+
+import net.adoptopenjdk.icedteaweb.Assert;
+
+import java.net.URL;
+import java.util.Objects;
+
+public class DelegatingClassLoader extends ClassLoader {
+    public static final DelegatingClassLoader instance = new DelegatingClassLoader(Thread.currentThread().getContextClassLoader());
+    private ClassLoader classLoader;
+
+    public static DelegatingClassLoader getInstance() {
+        return instance;
+    }
+
+    private DelegatingClassLoader(ClassLoader loader) {
+        super(Assert.requireNonNull(loader, "loader"));
+        this.classLoader = loader;
+    }
+
+    public void setClassLoader(ClassLoader loader) {
+        Assert.requireNonNull(loader, "loader");
+        this.classLoader = loader;
+    }
+
+    protected Class findClass(String name) throws ClassNotFoundException {
+        return this.classLoader.loadClass(name);
+    }
+
+    protected URL findResource(String name) {
+        return this.classLoader.getResource(name);
+    }
+
+    public int hashCode() {
+        int result = 1;
+        result = 31 * result + (this.classLoader == null ? 0 : this.classLoader.hashCode());
+        result = 31 * result + (this.getParent() == null ? 0 : this.getParent().hashCode());
+        return result;
+    }
+
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        else if (obj == null) {
+            return false;
+        }
+        else if (this.getClass() != obj.getClass()) {
+            return false;
+        }
+        else {
+            DelegatingClassLoader other = (DelegatingClassLoader) obj;
+            if(!Objects.equals(this.classLoader,other.classLoader)) {
+                return false;
+            }
+            if(!Objects.equals(this.getParent(),other.getParent())) {
+                return false;
+            }
+            return true;
+        }
+    }
+}