Reactivate protection against the issues similar with #97

demo/app/src/main/java/ro/fortsoft/pf4j/demo/Boot.java

@@ -21,6 +21,7 @@ import java.util.Set;
 import org.apache.commons.lang.StringUtils;
 
 import ro.fortsoft.pf4j.DefaultPluginManager;
+import ro.fortsoft.pf4j.JarPluginManager;
 import ro.fortsoft.pf4j.PluginManager;
 import ro.fortsoft.pf4j.PluginWrapper;
 import ro.fortsoft.pf4j.demo.api.Greeting;
@@ -37,7 +38,8 @@ public class Boot {
         printLogo();
 
         // create the plugin manager
-        final PluginManager pluginManager = new DefaultPluginManager();
+//        final PluginManager pluginManager = new DefaultPluginManager();
+        final PluginManager pluginManager = new JarPluginManager();
 
         // load the plugins
         pluginManager.loadPlugins();

demo/app/src/main/resources/log4j.properties

@@ -5,7 +5,7 @@ log4j.rootLogger=DEBUG, Console
 #
 log4j.logger.ro.fortsoft.pf4j=DEBUG, Console
 # !!! Put the bellow classes on level TRACE when you are in trouble
-log4j.logger.ro.fortsoft.pf4j.PluginClassLoader=WARN, Console
+log4j.logger.ro.fortsoft.pf4j.PluginClassLoader=DEBUG, Console
 log4j.logger.ro.fortsoft.pf4j.AbstractExtensionFinder=DEBUG, Console
 log4j.additivity.ro.fortsoft.pf4j=false
 log4j.additivity.ro.fortsoft.pf4j.PluginClassLoader=false

pf4j/src/main/java/ro/fortsoft/pf4j/AbstractExtensionFinder.java

@@ -17,6 +17,7 @@ package ro.fortsoft.pf4j;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
+import ro.fortsoft.pf4j.util.ClassUtils;
 
 import java.util.ArrayList;
 import java.util.Collections;
@@ -106,6 +107,9 @@ public abstract class AbstractExtensionFinder implements ExtensionFinder, Plugin
                     log.debug("Added extension '{}' with ordinal {}", className, extensionWrapper.getOrdinal());
                 } else {
                     log.trace("'{}' is not an extension for extension point '{}'", className, type.getName());
+                    if (RuntimeMode.DEVELOPMENT.equals(pluginManager.getRuntimeMode())) {
+                        checkDifferentClassLoaders(type, extensionClass);
+                    }
                 }
             } catch (ClassNotFoundException e) {
                 log.error(e.getMessage(), e);
@@ -229,4 +233,15 @@ public abstract class AbstractExtensionFinder implements ExtensionFinder, Plugin
         return extensionWrapper;
     }
 
+    private void checkDifferentClassLoaders(Class<?> type, Class<?> extensionClass) {
+        ClassLoader typeClassLoader = type.getClassLoader(); // class loader of extension point
+        ClassLoader extensionClassLoader = extensionClass.getClassLoader();
+        boolean match = ClassUtils.getAllInterfacesNames(extensionClass).contains(type.getSimpleName());
+        if (match && !extensionClassLoader.equals(typeClassLoader)) {
+            // in this scenario the method 'isAssignableFrom' returns only FALSE
+            // see http://www.coderanch.com/t/557846/java/java/FWIW-FYI-isAssignableFrom-isInstance-differing
+            log.error("Different class loaders: '{}' (E) and '{}' (EP)", extensionClassLoader, typeClassLoader);
+        }
+    }
+
 }

pf4j/src/main/java/ro/fortsoft/pf4j/util/ClassUtils.java

@@ -0,0 +1,91 @@
+/*
+ * Copyright 2016 Decebal Suiu
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package ro.fortsoft.pf4j.util;
+
+import java.lang.reflect.Modifier;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * @author Decebal Suiu
+ */
+public class ClassUtils {
+
+    public static List<String> getAllInterfacesNames(Class<?> aClass) {
+        return toString(getAllInterfaces(aClass));
+    }
+
+    public static List<Class<?>> getAllInterfaces(Class<?> aClass) {
+        List<Class<?>> list = new ArrayList<>();
+
+        while (aClass != null) {
+            Class<?>[] interfaces = aClass.getInterfaces();
+            for (Class<?> anInterface : interfaces) {
+                if (!list.contains(anInterface)) {
+                    list.add(anInterface);
+                }
+
+                List<Class<?>> superInterfaces = getAllInterfaces(anInterface);
+                for (Class<?> superInterface : superInterfaces) {
+                    if (!list.contains(superInterface)) {
+                        list.add(superInterface);
+                    }
+                }
+            }
+
+            aClass = aClass.getSuperclass();
+        }
+
+        return list;
+    }
+
+    /*
+    public static List<String> getAllAbstractClassesNames(Class<?> aClass) {
+        return toString(getAllInterfaces(aClass));
+    }
+
+    public static List getAllAbstractClasses(Class aClass) {
+        List<Class<?>> list = new ArrayList<>();
+
+        Class<?> superclass = aClass.getSuperclass();
+        while (superclass != null) {
+            if (Modifier.isAbstract(superclass.getModifiers())) {
+                list.add(superclass);
+            }
+            superclass = superclass.getSuperclass();
+        }
+
+        return list;
+    }
+    */
+
+    /**
+     * Uses {@link Class#getSimpleName()} to convert from {@link Class} to {@link String}.
+     *
+     * @param classes
+     * @return
+     */
+    private static List<String> toString(List<Class<?>> classes) {
+        List<String> list = new ArrayList<>();
+
+        for (Class<?> aClass : classes) {
+            list.add(aClass.getSimpleName());
+        }
+
+        return list;
+    }
+
+}