Move JNDI provider to inner class to avoid CNE on Android

src/main/java/org/xbill/DNS/config/JndiContextResolverConfigProvider.java

@@ -5,12 +5,14 @@
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.util.Hashtable;
+import java.util.List;
 import java.util.StringTokenizer;
 import javax.naming.Context;
 import javax.naming.NamingException;
 import javax.naming.directory.DirContext;
 import javax.naming.directory.InitialDirContext;
 import lombok.extern.slf4j.Slf4j;
+import org.xbill.DNS.Name;
 import org.xbill.DNS.SimpleResolver;
 
 /**
@@ -19,49 +21,78 @@
  * Provider</a>.
  */
 @Slf4j
-public class JndiContextResolverConfigProvider extends BaseResolverConfigProvider {
-  public void initialize() {
-    Hashtable<String, String> env = new Hashtable<>();
-    env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.dns.DnsContextFactory");
-    // http://mail.openjdk.java.net/pipermail/net-dev/2017-March/010695.html
-    env.put("java.naming.provider.url", "dns://");
+public class JndiContextResolverConfigProvider implements ResolverConfigProvider {
+  private InnerJndiContextResolverConfigProvider inner;
 
-    String servers = null;
-    try {
-      DirContext ctx = new InitialDirContext(env);
-      servers = (String) ctx.getEnvironment().get("java.naming.provider.url");
-      ctx.close();
-    } catch (NamingException e) {
-      // ignore
+  public JndiContextResolverConfigProvider() {
+    if (!System.getProperty("java.vendor").contains("Android")) {
+      try {
+        inner = new InnerJndiContextResolverConfigProvider();
+      } catch (NoClassDefFoundError e) {
+        log.debug("JNDI DNS not available");
+      }
     }
+  }
 
-    if (servers != null) {
-      StringTokenizer st = new StringTokenizer(servers, " ");
-      while (st.hasMoreTokens()) {
-        String server = st.nextToken();
-        try {
-          URI serverUri = new URI(server);
-          String host = serverUri.getHost();
-          if (host == null || host.isEmpty()) {
-            // skip the fallback server to localhost
-            continue;
-          }
+  private static class InnerJndiContextResolverConfigProvider extends BaseResolverConfigProvider {
+    public void initialize() {
+      Hashtable<String, String> env = new Hashtable<>();
+      env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.dns.DnsContextFactory");
+      // http://mail.openjdk.java.net/pipermail/net-dev/2017-March/010695.html
+      env.put("java.naming.provider.url", "dns://");
 
-          int port = serverUri.getPort();
-          if (port == -1) {
-            port = SimpleResolver.DEFAULT_PORT;
-          }
+      String servers = null;
+      try {
+        DirContext ctx = new InitialDirContext(env);
+        servers = (String) ctx.getEnvironment().get("java.naming.provider.url");
+        ctx.close();
+      } catch (NamingException e) {
+        // ignore
+      }
+
+      if (servers != null) {
+        StringTokenizer st = new StringTokenizer(servers, " ");
+        while (st.hasMoreTokens()) {
+          String server = st.nextToken();
+          try {
+            URI serverUri = new URI(server);
+            String host = serverUri.getHost();
+            if (host == null || host.isEmpty()) {
+              // skip the fallback server to localhost
+              continue;
+            }
+
+            int port = serverUri.getPort();
+            if (port == -1) {
+              port = SimpleResolver.DEFAULT_PORT;
+            }
 
-          addNameserver(new InetSocketAddress(host, port));
-        } catch (URISyntaxException e) {
-          log.debug("Could not parse {} as a dns server, ignoring", server, e);
+            addNameserver(new InetSocketAddress(host, port));
+          } catch (URISyntaxException e) {
+            log.debug("Could not parse {} as a dns server, ignoring", server, e);
+          }
         }
       }
     }
   }
 
+  @Override
+  public void initialize() {
+    inner.initialize();
+  }
+
+  @Override
+  public List<InetSocketAddress> servers() {
+    return inner.servers();
+  }
+
+  @Override
+  public List<Name> searchPaths() {
+    return inner.searchPaths();
+  }
+
   @Override
   public boolean isEnabled() {
-    return !System.getProperty("java.vendor").contains("Android");
+    return inner != null;
   }
 }