Improve #292

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

@@ -521,6 +521,7 @@ public abstract class AbstractPluginManager implements PluginManager {
             Class<?> c = extensionWrapper.getDescriptor().extensionClass;
             extensionClasses.add(c);
         }
+
         return extensionClasses;
     }
 
@@ -555,7 +556,11 @@ public abstract class AbstractPluginManager implements PluginManager {
         List<ExtensionWrapper<T>> extensionsWrapper = extensionFinder.find(type);
         List<T> extensions = new ArrayList<>(extensionsWrapper.size());
         for (ExtensionWrapper<T> extensionWrapper : extensionsWrapper) {
-            extensions.add(extensionWrapper.getExtension());
+            try {
+                extensions.add(extensionWrapper.getExtension());
+            } catch (PluginException e) {
+                log.error("Cannot retrieve extension", e);
+            }
         }
 
         return extensions;
@@ -566,7 +571,11 @@ public abstract class AbstractPluginManager implements PluginManager {
         List<ExtensionWrapper<T>> extensionsWrapper = extensionFinder.find(type, pluginId);
         List<T> extensions = new ArrayList<>(extensionsWrapper.size());
         for (ExtensionWrapper<T> extensionWrapper : extensionsWrapper) {
-            extensions.add(extensionWrapper.getExtension());
+            try {
+                extensions.add(extensionWrapper.getExtension());
+            } catch (PluginException e) {
+                log.error("Cannot retrieve extension", e);
+            }
         }
 
         return extensions;
@@ -578,7 +587,11 @@ public abstract class AbstractPluginManager implements PluginManager {
         List<ExtensionWrapper> extensionsWrapper = extensionFinder.find(pluginId);
         List extensions = new ArrayList<>(extensionsWrapper.size());
         for (ExtensionWrapper extensionWrapper : extensionsWrapper) {
-            extensions.add(extensionWrapper.getExtension());
+            try {
+                extensions.add(extensionWrapper.getExtension());
+            } catch (PluginException e) {
+                log.error("Cannot retrieve extension", e);
+            }
         }
 
         return extensions;

pf4j/src/main/java/org/pf4j/DefaultExtensionFactory.java

@@ -29,20 +29,16 @@ public class DefaultExtensionFactory implements ExtensionFactory {
     private static final Logger log = LoggerFactory.getLogger(DefaultExtensionFactory.class);
 
     /**
-     * Creates an extension instance. If an error occurs than that error is logged and the method returns {@code null}.
-     * @param extensionClass
-     * @return
+     * Creates an extension instance.
      */
     @Override
-    public Object create(Class<?> extensionClass) {
+    public <T> T create(Class<T> extensionClass) throws PluginException {
         log.debug("Create instance for extension '{}'", extensionClass.getName());
         try {
             return extensionClass.newInstance();
         } catch (Exception e) {
-            log.error(e.getMessage(), e);
+            throw new PluginException(e);
         }
-
-        return null;
     }
 
 }

pf4j/src/main/java/org/pf4j/ExtensionFactory.java

@@ -20,6 +20,6 @@ package org.pf4j;
  */
 public interface ExtensionFactory {
 
-    Object create(Class<?> extensionClass);
+    <T> T create(Class<T> extensionClass) throws PluginException;
 
 }

pf4j/src/main/java/org/pf4j/ExtensionWrapper.java

@@ -32,7 +32,7 @@ public class ExtensionWrapper<T> implements Comparable<ExtensionWrapper<T>> {
     }
 
     @SuppressWarnings("unchecked")
-    public T getExtension() {
+    public T getExtension() throws PluginException {
         if (extension == null) {
             extension = (T) extensionFactory.create(descriptor.extensionClass);
         }

pf4j/src/main/java/org/pf4j/SingletonExtensionFactory.java

@@ -39,13 +39,14 @@ public class SingletonExtensionFactory extends DefaultExtensionFactory {
     }
 
     @Override
-    public Object create(Class<?> extensionClass) {
+    @SuppressWarnings("unchecked")
+    public <T> T create(Class<T> extensionClass) throws PluginException {
         String extensionClassName = extensionClass.getName();
         if (cache.containsKey(extensionClassName)) {
-            return cache.get(extensionClassName);
+            return (T) cache.get(extensionClassName);
         }
 
-        Object extension = super.create(extensionClass);
+        T extension = super.create(extensionClass);
         if (extensionClassNames.isEmpty() || extensionClassNames.contains(extensionClassName)) {
             cache.put(extensionClassName, extension);
         }

pf4j/src/test/java/org/pf4j/DefaultExtensionFactoryTest.java

@@ -15,27 +15,38 @@
  */
 package org.pf4j;
 
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.pf4j.plugin.FailTestExtension;
 import org.pf4j.plugin.TestExtension;
 
 import static org.junit.jupiter.api.Assertions.assertNotNull;
-import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 /**
- *
  * @author Mario Franco
  */
 public class DefaultExtensionFactoryTest {
 
+    private ExtensionFactory extensionFactory;
+
+    @BeforeEach
+    public void setUp() {
+        extensionFactory = new DefaultExtensionFactory();
+    }
+
+    @AfterEach
+    public void tearDown() {
+        extensionFactory = null;
+    }
+
     /**
      * Test of create method, of class DefaultExtensionFactory.
      */
     @Test
-    public void testCreate() {
-        DefaultExtensionFactory instance = new DefaultExtensionFactory();
-        Object result = instance.create(TestExtension.class);
-        assertNotNull(result);
+    public void testCreate() throws PluginException {
+        assertNotNull(extensionFactory.create(TestExtension.class));
     }
 
     /**
@@ -43,9 +54,7 @@ public class DefaultExtensionFactoryTest {
      */
     @Test
     public void testCreateFailConstructor() {
-        DefaultExtensionFactory instance = new DefaultExtensionFactory();
-        Object result = instance.create(FailTestExtension.class);
-        assertNull(result);
+        assertThrows(PluginException.class, () -> extensionFactory.create(FailTestExtension.class));
     }
 
 }

pf4j/src/test/java/org/pf4j/SingletonExtensionFactoryTest.java

@@ -28,7 +28,7 @@ import static org.junit.jupiter.api.Assertions.assertSame;
 public class SingletonExtensionFactoryTest {
 
     @Test
-    public void create() {
+    public void create() throws PluginException {
         ExtensionFactory extensionFactory = new SingletonExtensionFactory();
         Object extensionOne = extensionFactory.create(TestExtension.class);
         Object extensionTwo = extensionFactory.create(TestExtension.class);
@@ -36,7 +36,7 @@ public class SingletonExtensionFactoryTest {
     }
 
     @Test
-    public void createNewEachTime() {
+    public void createNewEachTime() throws PluginException {
         ExtensionFactory extensionFactory = new SingletonExtensionFactory(FailTestExtension.class.getName());
         Object extensionOne = extensionFactory.create(TestExtension.class);
         Object extensionTwo = extensionFactory.create(TestExtension.class);