Revert "chore: refactor code a bit"

This reverts commit 60ad75a.

pulsar-common/src/main/java/org/apache/pulsar/common/util/netty/DnsResolverUtil.java

@@ -21,11 +21,9 @@
 import io.netty.resolver.dns.DnsNameResolverBuilder;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
-import lombok.experimental.UtilityClass;
 import lombok.extern.slf4j.Slf4j;
 
 @Slf4j
-@UtilityClass
 public class DnsResolverUtil {
     private static final int MIN_TTL = 0;
     private static final int TTL;
@@ -56,6 +54,10 @@ public class DnsResolverUtil {
         NEGATIVE_TTL = negativeTtl < 0 ? DEFAULT_NEGATIVE_TTL : negativeTtl;
     }
 
+    private DnsResolverUtil() {
+        // utility class with static methods, prevent instantiation
+    }
+
     /**
      * Configure Netty's {@link DnsNameResolverBuilder}'s ttl and negativeTtl to match the JDK's DNS caching settings.
      * If the JDK setting for TTL is forever (-1), the TTL will be set to 60 seconds.

pulsar-common/src/test/java/org/apache/pulsar/common/util/netty/DnsResolverTest.java

@@ -18,29 +18,24 @@
  */
 package org.apache.pulsar.common.util.netty;
 
-import static org.assertj.core.api.Assertions.assertThat;
 import io.netty.channel.EventLoop;
-import io.netty.resolver.dns.DnsNameResolver;
 import io.netty.resolver.dns.DnsNameResolverBuilder;
-import java.util.concurrent.CountDownLatch;
-import java.util.concurrent.TimeUnit;
-import org.mockito.MockedConstruction;
 import org.mockito.Mockito;
+import org.testng.Assert;
 import org.testng.annotations.Test;
 
 public class DnsResolverTest {
 
     @Test
-    public void testMaxTtl() throws Exception {
-        DnsNameResolverBuilder dnsNameResolverBuilder = new DnsNameResolverBuilder(Mockito.mock(EventLoop.class));
-        assertThat(dnsNameResolverBuilder).isNotNull();
+    public void testMaxTtl() {
+        EventLoop eventLoop = Mockito.mock(EventLoop.class);
+        DnsNameResolverBuilder dnsNameResolverBuilder = new DnsNameResolverBuilder(eventLoop);
         DnsResolverUtil.applyJdkDnsCacheSettings(dnsNameResolverBuilder);
-
-        CountDownLatch latch = new CountDownLatch(1);
-        try (MockedConstruction<?> ignore = Mockito.mockConstruction(
-                DnsNameResolver.class, (a, b) -> latch.countDown())) {
+        // If the maxTtl is <=0, it will throw IllegalArgumentException.
+        try {
             dnsNameResolverBuilder.build();
-            assertThat(latch.await(5, TimeUnit.SECONDS)).isTrue();
+        } catch (Exception ex) {
+            Assert.assertFalse(ex instanceof IllegalArgumentException);
         }
     }
 }