Reuse the IResource instance.

The IResource is stateless so it is OK to reuse it.

Optimize imports

wicket/src/main/java/hellowicket/HelloDbReference.java

@@ -1,11 +1,14 @@
 package hellowicket;
 
-import org.apache.wicket.request.resource.*;
+import org.apache.wicket.request.resource.IResource;
+import org.apache.wicket.request.resource.ResourceReference;
 
 public class HelloDbReference extends ResourceReference
 {
   private static final long serialVersionUID = 1L;
 
+  private final HelloDbResponse resource = new HelloDbResponse();
+
   public HelloDbReference()
   {
     super(HelloDbReference.class, "hello_json");
@@ -14,6 +17,6 @@ public class HelloDbReference extends ResourceReference
   @Override
   public IResource getResource()
   {
-    return new HelloDbResponse();
+    return resource;
   }
 }

wicket/src/main/java/hellowicket/HelloDbResponse.java

@@ -1,13 +1,12 @@
 package hellowicket;
 
 import java.io.IOException;
-import java.util.*;
-import java.util.concurrent.*;
+import java.util.concurrent.ThreadLocalRandom;
 
 import org.apache.wicket.request.resource.AbstractResource;
-import com.fasterxml.jackson.databind.*;
 import org.hibernate.Session;
-import org.hibernate.Transaction;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
 
 public class HelloDbResponse extends AbstractResource
 {
@@ -21,7 +20,7 @@ public class HelloDbResponse extends AbstractResource
   {
     final int queries = attributes.getRequest().getQueryParameters().getParameterValue("queries").toInt(1);
     final World[] worlds = new World[queries];
-    final Random random = ThreadLocalRandom.current();
+    final ThreadLocalRandom random = ThreadLocalRandom.current();
 
     final ResourceResponse response = new ResourceResponse();
     response.setContentType("application/json");