Servlet: Now logs a message on context startup to aid debugging.

+ bonus generic refactorings

servlet/src/main/java/com/twelvemonkeys/servlet/image/IIOProviderContextListener.java

@@ -37,6 +37,7 @@ import java.util.List;
 import javax.imageio.ImageIO;
 import javax.imageio.spi.IIORegistry;
 import javax.imageio.spi.ServiceRegistry;
+import javax.servlet.ServletContext;
 import javax.servlet.ServletContextEvent;
 import javax.servlet.ServletContextListener;
 
@@ -57,31 +58,38 @@ import javax.servlet.ServletContextListener;
 public final class IIOProviderContextListener implements ServletContextListener {
     
     public void contextInitialized(final ServletContextEvent event) {
+        event.getServletContext().log("Scanning for locally installed ImageIO plugin providers");
+
         // Registers all locally available IIO plugins.
         ImageIO.scanForPlugins();
     }
 
     public void contextDestroyed(final ServletContextEvent event) {
-        // De-register any locally registered IIO plugins. Relies on each web app having its own context class loader.
-        final IIORegistry registry = IIORegistry.getDefaultInstance();
-        final LocalFilter localFilter = new LocalFilter(Thread.currentThread().getContextClassLoader()); // scanForPlugins uses context class loader
+        ServletContext servletContext = event.getServletContext();
 
+        // De-register any locally registered IIO plugins. Relies on each web app having its own context class loader.
+        LocalFilter localFilter = new LocalFilter(Thread.currentThread().getContextClassLoader()); // scanForPlugins uses context class loader
+
+        IIORegistry registry = IIORegistry.getDefaultInstance();
         Iterator<Class<?>> categories = registry.getCategories();
 
         while (categories.hasNext()) {
-            Class<?> category = categories.next();
-            Iterator<?> providers = registry.getServiceProviders(category, localFilter, false);
+            deregisterLocalProvidersForCategory(registry, localFilter, categories.next(), servletContext);
+        }
+    }
+
+    private static <T> void deregisterLocalProvidersForCategory(IIORegistry registry, LocalFilter localFilter, Class<T> category, ServletContext context) {
+        Iterator<T> providers = registry.getServiceProviders(category, localFilter, false);
 
         // Copy the providers, as de-registering while iterating over providers will lead to ConcurrentModificationExceptions.
-            List<Object> providersCopy = new ArrayList<>();
+        List<T> providersCopy = new ArrayList<>();
         while (providers.hasNext()) {
             providersCopy.add(providers.next());
         }
 
-            for (Object provider : providersCopy) {
-                registry.deregisterServiceProvider(provider);
-                event.getServletContext().log(String.format("Unregistered locally installed provider class: %s", provider.getClass()));
-            }
+        for (T provider : providersCopy) {
+            registry.deregisterServiceProvider(provider, category);
+            context.log(String.format("Unregistered locally installed provider class: %s", provider.getClass()));
         }
     }
 

servlet/src/test/java/com/twelvemonkeys/servlet/image/IIOProviderContextListenerTest.java

@@ -33,7 +33,6 @@ package com.twelvemonkeys.servlet.image;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.when;
 
 import java.util.Locale;
 
@@ -54,32 +53,29 @@ import org.junit.Test;
  * @version $Id: IIOProviderContextListenerTest.java,v 1.0 02.01.14 12:33 haraldk Exp$
  */
 public class IIOProviderContextListenerTest {
+
+    private final ServletContext context = mock(ServletContext.class);
+    private  final ServletContextEvent initialized = new ServletContextEvent(context);
+    private  final ServletContextEvent destroyed = new ServletContextEvent(context);
+
     @Test
     public void testContextInitialized() {
         ServletContextListener listener = new IIOProviderContextListener();
-        listener.contextInitialized(mock(ServletContextEvent.class));
+        listener.contextInitialized(initialized);
     }
 
     @Test
     public void testContextDestroyed() {
-        ServletContext context = mock(ServletContext.class);
-        ServletContextEvent destroyed = mock(ServletContextEvent.class);
-        when(destroyed.getServletContext()).thenReturn(context);
-
         ServletContextListener listener = new IIOProviderContextListener();
-        listener.contextInitialized(mock(ServletContextEvent.class));
+        listener.contextInitialized(initialized);
         listener.contextDestroyed(destroyed);
     }
 
     // Regression test for issue #29
     @Test
     public void testDestroyConcurrentModRegression() {
-        ServletContext context = mock(ServletContext.class);
-        ServletContextEvent destroyed = mock(ServletContextEvent.class);
-        when(destroyed.getServletContext()).thenReturn(context);
-
         ServletContextListener listener = new IIOProviderContextListener();
-        listener.contextInitialized(mock(ServletContextEvent.class));
+        listener.contextInitialized(initialized);
 
         ImageReaderSpi provider1 = new MockImageReaderSpiOne();
         ImageReaderSpi provider2 = new MockImageReaderSpiToo();