KAFKA-19178 Replace Vector by ArrayList for PluginClassLoader#getResources (#19529)

The vector is a synchronized collection, and in the case we don't need
to sync. Also, we can use `Collections.enumeration` to convert
collection to enumeration easily.

Reviewers: PoAn Yang <[email protected]>, Ken Huang
 <[email protected]>, Chia-Ping Tsai <[email protected]>

Author: Rancho-7

connect/runtime/src/main/java/org/apache/kafka/connect/runtime/isolation/PluginClassLoader.java

@@ -22,9 +22,11 @@
 import java.io.IOException;
 import java.net.URL;
 import java.net.URLClassLoader;
+import java.util.ArrayList;
+import java.util.Collections;
 import java.util.Enumeration;
+import java.util.List;
 import java.util.Objects;
-import java.util.Vector;
 
 /**
  * A custom classloader dedicated to loading Connect plugin classes in classloading isolation.
@@ -87,7 +89,7 @@ public URL getResource(String name) {
     @Override
     public Enumeration<URL> getResources(String name) throws IOException {
         Objects.requireNonNull(name);
-        Vector<URL> resources = new Vector<>();
+        List<URL> resources = new ArrayList<>();
         for (Enumeration<URL> foundLocally = findResources(name); foundLocally.hasMoreElements();) {
             URL url = foundLocally.nextElement();
             if (url != null)
@@ -99,7 +101,7 @@ public Enumeration<URL> getResources(String name) throws IOException {
             if (url != null)
                 resources.add(url);
         }
-        return resources.elements();
+        return Collections.enumeration(resources);
     }
 
     // This method needs to be thread-safe because it is supposed to be called by multiple