When class loading fails, chain the reason

Several places in SciJava Common call the ClassUtils.loadClass routine.
Previously, that routine simply returned null without explanation when
the class could not be loaded for any reason. Now, by setting the
'quietly' flag to false, we can do proper exception handling so that the
reason for failure is known and can be passed along to the caller.

So this commit does that in all the places where it makes sense.

This commit is dedicated to Eike Heinz!

Author: ctrueden

src/main/java/org/scijava/Context.java

@@ -320,10 +320,7 @@ public <S extends Service> S service(final Class<S> c) {
 	 *           service.
 	 */
 	public Service service(final String className) {
-		final Class<?> c = ClassUtils.loadClass(className);
-		if (c == null) {
-			throw new IllegalArgumentException("No such class: " + className);
-		}
+		final Class<?> c = ClassUtils.loadClass(className, false);
 		if (!Service.class.isAssignableFrom(c)) {
 			throw new IllegalArgumentException("Not a service class: " + c.getName());
 		}

src/main/java/org/scijava/main/DefaultMainService.java

@@ -101,10 +101,13 @@ public String[] args() {
 		@Override
 		public void exec() {
 			try {
-				final Class<?> mainClass = ClassUtils.loadClass(className);
+				final Class<?> mainClass = ClassUtils.loadClass(className, false);
 				final Method main = mainClass.getMethod("main", String[].class);
 				main.invoke(null, new Object[] { args });
 			}
+			catch (final IllegalArgumentException exc) {
+				if (log != null) log.error(exc);
+			}
 			catch (final NoSuchMethodException exc) {
 				if (log != null) {
 					log.error("No main method for class: " + className, exc);

src/main/java/org/scijava/menu/ShadowMenu.java

@@ -231,13 +231,20 @@ public URL getIconURL() {
 			else return null;
 		}
 		final String className = moduleInfo.getDelegateClassName();
-		final Class<?> c = ClassUtils.loadClass(className);
-		if (c == null) return null;
-		final URL iconURL = c.getResource(iconPath);
-		if (iconURL == null) {
-			if (log != null) log.error("Could not load icon: " + iconPath);
+		try {
+			final Class<?> c = ClassUtils.loadClass(className, false);
+			final URL iconURL = c.getResource(iconPath);
+			if (iconURL == null) {
+				if (log != null) log.error("Could not load icon: " + iconPath);
+			}
+			return iconURL;
+		}
+		catch (final IllegalArgumentException exc) {
+			final String message = "Could not load icon for class: " + className;
+			if (log.isDebug()) log.debug(message, exc);
+			else log.error(message);
+			return null;
 		}
-		return iconURL;
 	}
 
 	/**

src/main/java/org/scijava/plugin/PluginInfo.java

@@ -280,13 +280,15 @@ public String getClassName() {
 	@Override
 	public Class<? extends PT> loadClass() throws InstantiableException {
 		if (pluginClass == null) {
-			final Class<?> c = ClassUtils.loadClass(className, classLoader);
-			if (c == null) {
-				throw new InstantiableException("Class not found: " + className);
+			try {
+				final Class<?> c = ClassUtils.loadClass(className, classLoader, false);
+				@SuppressWarnings("unchecked")
+				final Class<? extends PT> typedClass = (Class<? extends PT>) c;
+				pluginClass = typedClass;
+			}
+			catch (final IllegalArgumentException exc) {
+				throw new InstantiableException("Class not found: " + className, exc);
 			}
-			@SuppressWarnings("unchecked")
-			final Class<? extends PT> typedClass = (Class<? extends PT>) c;
-			pluginClass = typedClass;
 		}
 
 		return pluginClass;

src/main/java/org/scijava/script/DefaultScriptService.java

@@ -255,13 +255,16 @@ public synchronized Class<?> lookupClass(final String alias)
 		final Class<?> type = aliasMap().get(alias);
 		if (type != null) return type;
 
-		final Class<?> c = ClassUtils.loadClass(alias);
-		if (c != null) {
+		try {
+			final Class<?> c = ClassUtils.loadClass(alias, false);
 			aliasMap().put(alias, c);
 			return c;
 		}
-
-		throw new ScriptException("Unknown type: " + alias);
+		catch (final IllegalArgumentException exc) {
+			final ScriptException se = new ScriptException("Unknown type: " + alias);
+			se.initCause(exc);
+			throw se;
+		}
 	}
 
 	// -- PTService methods --