Add PluginClassLoader#isClosed method

pf4j/src/main/java/org/pf4j/PluginClassLoader.java

@@ -49,6 +49,7 @@ public class PluginClassLoader extends URLClassLoader {
     private final PluginManager pluginManager;
     private final PluginDescriptor pluginDescriptor;
     private final ClassLoadingStrategy classLoadingStrategy;
+    private boolean closed;
 
     public PluginClassLoader(PluginManager pluginManager, PluginDescriptor pluginDescriptor, ClassLoader parent) {
         this(pluginManager, pluginDescriptor, parent, ClassLoadingStrategy.PDA);
@@ -206,7 +207,6 @@ public class PluginClassLoader extends URLClassLoader {
         return null;
     }
 
-
     @Override
     public Enumeration<URL> getResources(String name) throws IOException {
         List<URL> resources = new ArrayList<>();
@@ -231,6 +231,27 @@ public class PluginClassLoader extends URLClassLoader {
         return Collections.enumeration(resources);
     }
 
+    /**
+     * Closes this class loader.
+     * <p>
+     * This method should be called when the class loader is no longer needed.
+     */
+    @Override
+    public void close() throws IOException {
+        super.close();
+
+        closed = true;
+    }
+
+    /**
+     * Returns whether this class loader has been closed.
+     *
+     * @return {@code true} if this class loader has been closed, {@code false} otherwise
+     */
+    public boolean isClosed() {
+        return closed;
+    }
+
     /**
      * Loads the class with the specified name from the dependencies of the plugin.
      *

pf4j/src/test/java/org/pf4j/PluginClassLoaderTest.java

@@ -35,12 +35,16 @@ import java.util.Collections;
 import java.util.Enumeration;
 import java.util.List;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 /**
  * @author Sebastian Lövdahl
  */
-public class PluginClassLoaderTest {
+class PluginClassLoaderTest {
 
     private TestPluginManager pluginManager;
     private TestPluginManager pluginManagerParentFirst;
@@ -321,6 +325,12 @@ public class PluginClassLoaderTest {
         assertNumberOfResourcesAndFirstLineOfFirstElement(3, "parent", resources);
     }
 
+    @Test
+    void isClosed() throws IOException {
+        parentLastPluginClassLoader.close();
+        assertTrue(parentLastPluginClassLoader.isClosed());
+    }
+
     private static void assertFirstLine(String expected, URL resource) throws URISyntaxException, IOException {
         assertNotNull(resource);
         assertEquals(expected, Files.readAllLines(Paths.get(resource.toURI())).get(0));
@@ -334,7 +344,7 @@ public class PluginClassLoaderTest {
         assertEquals(expectedFirstLine, Files.readAllLines(Paths.get(firstResource.toURI())).get(0));
     }
 
-    class TestPluginManager extends DefaultPluginManager {
+    static class TestPluginManager extends DefaultPluginManager {
 
         public TestPluginManager(Path pluginsPath) {
             super(pluginsPath);
@@ -343,5 +353,7 @@ public class PluginClassLoaderTest {
         void addClassLoader(String pluginId, PluginClassLoader classLoader) {
             getPluginClassLoaders().put(pluginId, classLoader);
         }
+
     }
+
 }