Merge pull request #427 from Flowdalic/elements

Add XmppElementUtil.castOrThrow()

smack-core/src/main/java/org/jivesoftware/smack/packet/StanzaView.java

@@ -90,11 +90,12 @@ public interface StanzaView extends XmlLangElement {
     default <E extends ExtensionElement> E getExtension(Class<E> extensionElementClass) {
         QName qname = XmppElementUtil.getQNameFor(extensionElementClass);
         ExtensionElement extensionElement = getExtension(qname);
-        if (!extensionElementClass.isInstance(extensionElement)) {
+
+        if (extensionElement == null) {
             return null;
         }
 
-        return extensionElementClass.cast(extensionElement);
+        return XmppElementUtil.castOrThrow(extensionElement, extensionElementClass);
     }
 
     /**

smack-core/src/main/java/org/jivesoftware/smack/provider/ProviderManager.java

@@ -243,7 +243,11 @@ public final class ProviderManager {
      */
     public static ExtensionElementProvider<ExtensionElement> getExtensionProvider(String elementName, String namespace) {
         QName key = getQName(elementName, namespace);
-        return extensionProviders.get(key);
+        return getExtensionProvider(key);
+    }
+
+    public static ExtensionElementProvider<ExtensionElement> getExtensionProvider(QName qname) {
+        return extensionProviders.get(qname);
     }
 
     /**

smack-core/src/main/java/org/jivesoftware/smack/util/XmppElementUtil.java

@@ -23,17 +23,31 @@ import java.util.logging.Logger;
 
 import javax.xml.namespace.QName;
 
+import org.jivesoftware.smack.packet.ExtensionElement;
 import org.jivesoftware.smack.packet.FullyQualifiedElement;
+import org.jivesoftware.smack.packet.StandardExtensionElement;
+import org.jivesoftware.smack.provider.ProviderManager;
+
+import org.jxmpp.util.cache.LruCache;
 
 public class XmppElementUtil {
 
+    private static final LruCache<Class<? extends FullyQualifiedElement>, QName> CLASS_TO_QNAME_CACHE = new LruCache<>(512);
+
     public static final Logger LOGGER = Logger.getLogger(XmppElementUtil.class.getName());
 
     public static QName getQNameFor(Class<? extends FullyQualifiedElement> fullyQualifiedElement) {
+        QName qname = CLASS_TO_QNAME_CACHE.get(fullyQualifiedElement);
+        if (qname != null) {
+            return qname;
+        }
+
         try {
             Object qnameObject = fullyQualifiedElement.getField("QNAME").get(null);
             if (QName.class.isAssignableFrom(qnameObject.getClass())) {
-                return (QName) qnameObject;
+                qname = (QName) qnameObject;
+                CLASS_TO_QNAME_CACHE.put(fullyQualifiedElement, qname);
+                return qname;
             }
             LOGGER.warning("The QNAME field of " + fullyQualifiedElement + " is not of type QNAME.");
         } catch (NoSuchFieldException e) {
@@ -52,24 +66,52 @@ public class XmppElementUtil {
             throw new IllegalArgumentException("The " + fullyQualifiedElement + " has no ELEMENT, NAMESPACE or QNAME member. Consider adding QNAME", e);
         }
 
-        return new QName(namespace, element);
+        qname = new QName(namespace, element);
+        CLASS_TO_QNAME_CACHE.put(fullyQualifiedElement, qname);
+        return qname;
     }
 
-    public static <E extends FullyQualifiedElement, R extends FullyQualifiedElement> List<R> getElementsFrom(
-                    MultiMap<QName, E> elementMap, Class<R> extensionElementClass) {
+    public static <E extends ExtensionElement> List<E> getElementsFrom(
+                    MultiMap<QName, ExtensionElement> elementMap, Class<E> extensionElementClass) {
         QName qname = XmppElementUtil.getQNameFor(extensionElementClass);
 
-        List<E> extensionElements = elementMap.getAll(qname);
+        List<ExtensionElement> extensionElements = elementMap.getAll(qname);
 
         if (extensionElements.isEmpty()) {
             return Collections.emptyList();
         }
 
-        List<R> res = new ArrayList<>(extensionElements.size());
-        for (E extensionElement : extensionElements) {
-            R e = extensionElementClass.cast(extensionElement);
+        List<E> res = new ArrayList<>(extensionElements.size());
+        for (ExtensionElement extensionElement : extensionElements) {
+            E e = castOrThrow(extensionElement, extensionElementClass);
             res.add(e);
         }
         return res;
     }
+
+    public static <E extends ExtensionElement> E castOrThrow(ExtensionElement extensionElement, Class<E> extensionElementClass) {
+        if (!extensionElementClass.isInstance(extensionElement)) {
+            final QName qname = getQNameFor(extensionElementClass);
+
+            final String detailMessage;
+            if (extensionElement instanceof StandardExtensionElement) {
+                detailMessage = "because there is no according extension element provider registered with ProviderManager for "
+                                + qname
+                                + ". WARNING: This indicates a serious problem with your Smack setup, probably causing Smack not being able to properly initialize itself.";
+            } else {
+                Object provider = ProviderManager.getExtensionProvider(qname);
+                detailMessage = "because there is an inconsistency with the provider registered with ProviderManager: the active provider for "
+                                + qname + " '" + provider.getClass()
+                                + "' does not return instances of type " + extensionElementClass
+                                + ", but instead returns instances of type " + extensionElement.getClass() + ".";
+            }
+
+            String message = "Extension element is not of expected class '" + extensionElementClass.getName() + "', "
+                            + detailMessage;
+            throw new IllegalStateException(message);
+        }
+
+        return extensionElementClass.cast(extensionElement);
+    }
+
 }

smack-experimental/src/main/java/org/jivesoftware/smackx/mam/element/MamElements.java

@@ -18,9 +18,11 @@ package org.jivesoftware.smackx.mam.element;
 
 import java.util.List;
 
+import javax.xml.namespace.QName;
+
 import org.jivesoftware.smack.packet.Element;
 import org.jivesoftware.smack.packet.ExtensionElement;
-import org.jivesoftware.smack.packet.Message;
+import org.jivesoftware.smack.packet.MessageView;
 import org.jivesoftware.smack.util.StringUtils;
 import org.jivesoftware.smack.util.XmlStringBuilder;
 
@@ -54,6 +56,11 @@ public class MamElements {
          */
         public static final String ELEMENT = "result";
 
+        /**
+         * The qualified name of the MAM result extension element.
+         */
+        public static final QName QNAME = new QName(NAMESPACE, ELEMENT);
+
         /**
          * id of the result.
          */
@@ -139,8 +146,8 @@ public class MamElements {
             return xml;
         }
 
-        public static MamResultExtension from(Message message) {
-            return (MamResultExtension) message.getExtensionElement(ELEMENT, NAMESPACE);
+        public static MamResultExtension from(MessageView message) {
+            return message.getExtension(MamResultExtension.class);
         }
 
     }