Resolve #218

pf4j/src/main/java/org/pf4j/AbstractPluginManager.java

@@ -807,8 +807,7 @@ public abstract class AbstractPluginManager implements PluginManager {
         // test for plugin duplication
         String pluginId = idForPath(pluginPath);
         if (pluginId != null) {
-            log.warn("Plugin '{}' already loaded with id '{}'", pluginPath, pluginId);
-            return null;
+            throw new PluginAlreadyLoadedException(pluginId, pluginPath);
         }
 
         // retrieves the plugin descriptor

pf4j/src/main/java/org/pf4j/PluginAlreadyLoadedException.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2012-present the original author or authors.
+ *
+ * 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 org.pf4j;
+
+import java.nio.file.Path;
+
+/**
+ * @author Decebal Suiu
+ */
+public class PluginAlreadyLoadedException extends PluginException {
+
+    private final String pluginId;
+    private final Path pluginPath;
+
+    public PluginAlreadyLoadedException(String pluginId, Path pluginPath) {
+        super("Plugin '{}' already loaded with id '{}'", pluginPath, pluginId);
+
+        this.pluginId = pluginId;
+        this.pluginPath = pluginPath;
+    }
+
+    public String getPluginId() {
+        return pluginId;
+    }
+
+    public Path getPluginPath() {
+        return pluginPath;
+    }
+
+}

pf4j/src/main/java/org/pf4j/PluginException.java

@@ -19,6 +19,7 @@ import org.pf4j.util.StringUtils;
 
 /**
  * An exception used to indicate that a plugin problem occurred.
+ * It's a generic plugin exception class to be thrown when no more specific class is applicable.
  *
  * @author Decebal Suiu
  */