feat: remove and replace JndiDnsResolve with DnsJavaResolver (#2195)

This is a cleanup, to remove and replace JndiDnsResolver with DnsJavaResolver

Author: panavenue

core/src/main/java/com/google/cloud/sql/core/DnsJavaResolver.java

@@ -19,7 +19,6 @@
 import java.net.UnknownHostException;
 import java.util.Arrays;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.stream.Collectors;
 import javax.naming.NameNotFoundException;
 import org.xbill.DNS.Lookup;
@@ -91,7 +90,7 @@ public Collection<String> resolveTxt(String domainName) throws NameNotFoundExcep
       // 5. Process the records, sort them, and return.
       Record[] records = lookup.getAnswers();
       if (records == null || records.length == 0) {
-        return Collections.emptyList();
+        throw new NameNotFoundException("DNS record type TXT not found for " + domainName);
       }
 
       // A single TXT record can contain multiple strings, so we use flatMap.

core/src/main/java/com/google/cloud/sql/core/InternalConnectorRegistry.java

@@ -338,7 +338,7 @@ private Connector createConnector(ConnectorConfig config) {
         MIN_REFRESH_DELAY_MS,
         connectTimeoutMs,
         serverProxyPort,
-        new DnsInstanceConnectionNameResolver(new JndiDnsResolver()),
+        new DnsInstanceConnectionNameResolver(new DnsJavaResolver()),
         this.mdxProtocolHandler);
   }