Make smack-resolver-javax an OSGi ServiceComponent

Fixes SMACK-576

build.gradle

@@ -200,7 +200,7 @@ subprojects {
 	}
 }
 
-['smack-extensions', 'smack-experimental', 'smack-legacy'].each { name ->
+['smack-resolver-javax', 'smack-extensions', 'smack-experimental', 'smack-legacy'].each { name ->
 	project(":$name") {
 		jar {
 			manifest {

smack-core/build.gradle

@@ -29,6 +29,7 @@ task dnsJar(type: Jar) {
 	from sourceSets.main.output
 	include('org/jivesoftware/smack/util/dns/**')
 	include('org/jivesoftware/smack/util/DNSUtil.class')
+	include('org/jivesoftware/smack/initializer/**')
 }
 
 artifacts {

smack-resolver-javax/src/main/java/org/jivesoftware/smack/util/dns/javax/JavaxResolver.java

@@ -17,6 +17,7 @@
 package org.jivesoftware.smack.util.dns.javax;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.Hashtable;
 import java.util.List;
 
@@ -27,6 +28,7 @@ import javax.naming.directory.Attributes;
 import javax.naming.directory.DirContext;
 import javax.naming.directory.InitialDirContext;
 
+import org.jivesoftware.smack.initializer.SmackInitializer;
 import org.jivesoftware.smack.util.DNSUtil;
 import org.jivesoftware.smack.util.dns.DNSResolver;
 import org.jivesoftware.smack.util.dns.SRVRecord;
@@ -37,7 +39,7 @@ import org.jivesoftware.smack.util.dns.SRVRecord;
  * @author Florian Schmaus
  *
  */
-public class JavaxResolver implements DNSResolver {
+public class JavaxResolver implements DNSResolver, SmackInitializer {
     
     private static JavaxResolver instance;
     private static DirContext dirContext;
@@ -52,24 +54,28 @@ public class JavaxResolver implements DNSResolver {
         }
 
         // Try to set this DNS resolver as primary one
-        DNSUtil.setDNSResolver(getInstance());
+        setup();
     }
     
-    private JavaxResolver() {
+    public JavaxResolver() {
         
     }
-    
-    public static DNSResolver getInstance() {
+
+    public static synchronized DNSResolver getInstance() {
         if (instance == null && isSupported()) {
             instance = new JavaxResolver();
         }
         return instance;
     }
-    
+
     public static boolean isSupported() {
         return dirContext != null;
     }
 
+    public static void setup() {
+        DNSUtil.setDNSResolver(getInstance());
+    }
+
     @Override
     public List<SRVRecord> lookupSRVRecords(String name) throws NamingException {
         List<SRVRecord> res = new ArrayList<SRVRecord>();
@@ -93,4 +99,15 @@ public class JavaxResolver implements DNSResolver {
         }
         return res;
     }
+
+    @Override
+    public List<Exception> initialize() {
+        return initialize(null);
+    }
+
+    @Override
+    public List<Exception> initialize(ClassLoader classLoader) {
+        setup();
+        return Collections.emptyList();
+    }
 }

smack-resolver-javax/src/main/resources/org.jivesoftware.smack/smack-resolver-javax-components.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<scr:component xmlns:scr="http://www.osgi.org/xmlns/scr/v1.2.0"
+	enabled="true" immediate="true" name="Smack Resolver JavaX API">
+	<implementation
+		class="org.jivesoftware.smack.util.dns.javax.JavaxResolver" />
+</scr:component>