Improve getMultipleRecipientServiceAddress

and MultipleRecipient (XEP-33) related code in general (e.g. use
constants where possible).

For getMultipleRecipientServiceAddress() this means that
- the "synchronized (services)" block is removed
- ServiceDiscoveryManager is only retrieved once

smack-extensions/src/main/java/org/jivesoftware/smackx/address/MultipleRecipientManager.java

@@ -22,7 +22,6 @@ import org.jivesoftware.smack.SmackException.NoResponseException;
 import org.jivesoftware.smack.SmackException.FeatureNotSupportedException;
 import org.jivesoftware.smack.SmackException.NotConnectedException;
 import org.jivesoftware.smack.XMPPConnection;
-import org.jivesoftware.smack.XMPPException;
 import org.jivesoftware.smack.XMPPException.XMPPErrorException;
 import org.jivesoftware.smack.packet.Message;
 import org.jivesoftware.smack.packet.Packet;
@@ -36,6 +35,8 @@ import org.jivesoftware.smackx.disco.packet.DiscoverItems;
 import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.List;
+import java.util.logging.Level;
+import java.util.logging.Logger;
 
 /**
  * A MultipleRecipientManager allows to send packets to multiple recipients by making use of
@@ -46,6 +47,8 @@ import java.util.List;
  */
 public class MultipleRecipientManager {
 
+    private static final Logger LOGGER = Logger.getLogger(MultipleRecipientManager.class.getName());
+
     /**
      * Create a cache to hold the 100 most recently accessed elements for a period of
      * 24 hours.
@@ -205,7 +208,7 @@ public class MultipleRecipientManager {
      */
     public static MultipleRecipientInfo getMultipleRecipientInfo(Packet packet) {
         MultipleAddresses extension = (MultipleAddresses) packet
-                .getExtension("addresses", "http://jabber.org/protocol/address");
+                .getExtension(MultipleAddresses.ELEMENT, MultipleAddresses.NAMESPACE);
         return extension == null ? null : new MultipleRecipientInfo(extension);
     }
 
@@ -295,40 +298,37 @@ public class MultipleRecipientManager {
         String serviceName = connection.getServiceName();
         String serviceAddress = (String) services.get(serviceName);
         if (serviceAddress == null) {
-            synchronized (services) {
+            ServiceDiscoveryManager sdm = ServiceDiscoveryManager.getInstanceFor(connection);
-                serviceAddress = (String) services.get(serviceName);
-                if (serviceAddress == null) {
-
             // Send the disco packet to the server itself
-                    DiscoverInfo info = ServiceDiscoveryManager.getInstanceFor(connection).discoverInfo(
+            DiscoverInfo info = sdm.discoverInfo(serviceName);
-                                    serviceName);
+            // Check if the server supports XEP-33
-                    // Check if the server supports JEP-33
+            if (info.containsFeature(MultipleAddresses.NAMESPACE)) {
-                    if (info.containsFeature("http://jabber.org/protocol/address")) {
                 serviceAddress = serviceName;
             }
             else {
                 // Get the disco items and send the disco packet to each server item
-                        DiscoverItems items = ServiceDiscoveryManager.getInstanceFor(connection).discoverItems(
+                DiscoverItems items = sdm.discoverItems(serviceName);
-                                        serviceName);
                 for (DiscoverItems.Item item : items.getItems()) {
                     try {
-                                info = ServiceDiscoveryManager.getInstanceFor(connection).discoverInfo(
+                        info = sdm.discoverInfo(item.getEntityID(), item.getNode());
-                                                item.getEntityID(), item.getNode());
                     }
                     catch (XMPPErrorException|NoResponseException e) {
                         // Don't throw this exceptions if one of the server's items fail
+                        LOGGER.log(Level.WARNING,
+                                        "Exception while discovering info of " + item.getEntityID()
+                                                        + " node: " + item.getNode(), e);
                         continue;
                     }
-                            if (info.containsFeature("http://jabber.org/protocol/address")) {
+                    if (info.containsFeature(MultipleAddresses.NAMESPACE)) {
                         serviceAddress = serviceName;
                         break;
                     }
                 }
             }
+            // Use the empty string to indicate that no service is known for this connection
+            serviceAddress = serviceAddress == null ? "" : serviceAddress;
             // Cache the discovered information
-                    services.put(serviceName, serviceAddress == null ? "" : serviceAddress);
+            services.put(serviceName, serviceAddress);
-                }
-            }
         }
 
         return "".equals(serviceAddress) ? null : serviceAddress;

smack-extensions/src/main/java/org/jivesoftware/smackx/address/packet/MultipleAddresses.java

@@ -30,6 +30,9 @@ import java.util.List;
  */
 public class MultipleAddresses implements PacketExtension {
 
+    public static final String NAMESPACE = "http://jabber.org/protocol/address";
+    public static final String ELEMENT = "addresses";
+
     public static final String BCC = "bcc";
     public static final String CC = "cc";
     public static final String NO_REPLY = "noreply";
@@ -94,17 +97,17 @@ public class MultipleAddresses implements PacketExtension {
     }
 
     public String getElementName() {
-        return "addresses";
+        return ELEMENT;
     }
 
     public String getNamespace() {
-        return "http://jabber.org/protocol/address";
+        return NAMESPACE;
     }
 
     public String toXML() {
         StringBuilder buf = new StringBuilder();
         buf.append("<").append(getElementName());
-        buf.append(" xmlns=\"").append(getNamespace()).append("\">");
+        buf.append(" xmlns=\"").append(NAMESPACE).append("\">");
         // Loop through all the addresses and append them to the string buffer
         for (Iterator<Address> i = addresses.iterator(); i.hasNext();) {
             Address address = (Address) i.next();