incorporating review comments

solr/core/src/java/org/apache/solr/core/PluginBag.java

@@ -29,6 +29,7 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 import java.util.zip.ZipEntry;
 import java.util.zip.ZipInputStream;
@@ -141,7 +142,10 @@ public PluginHolder<T> createPlugin(PluginInfo info) {
       return new LazyPluginHolder<T>(meta, info, core, core.getResourceLoader(), false);
     } else {
       if (info.pkgName != null) {
-        return getPackagePluginHolder(info);
+        PackagePluginHolder<T> holder = new PackagePluginHolder<>(info, core, meta);
+        return meta.clazz == UpdateRequestProcessorFactory.class ?
+            new PluginHolder(info, new LazyUpdateProcessorFactoryHolder(holder)) :
+            holder;
       } else {
         T inst = core.createInstance(info.className, (Class<T>) meta.clazz, meta.getCleanTag(), null, core.getResourceLoader(info.pkgName));
         initInstance(inst, info);
@@ -150,13 +154,6 @@ public PluginHolder<T> createPlugin(PluginInfo info) {
     }
   }
 
-  private PluginHolder<T> getPackagePluginHolder(PluginInfo info) {
-    PackagePluginHolder<T> holder = new PackagePluginHolder<>(info, core, meta);
-    return meta.clazz == UpdateRequestProcessorFactory.class ?
-        new PluginHolder(info, new LazyUpdateProcessorFactoryHolder(holder)) :
-        holder;
-  }
-
   /**
    * make a plugin available in an alternate name. This is an internal API and not for public use
    *
@@ -355,7 +352,7 @@ public static void closeQuietly(Object inst)  {
    * An indirect reference to a plugin. It just wraps a plugin instance.
    * subclasses may choose to lazily load the plugin
    */
-  public static class PluginHolder<T> implements AutoCloseable {
+  public static class PluginHolder<T> implements Supplier<T>,  AutoCloseable {
     protected T inst;
     protected final PluginInfo pluginInfo;
     boolean registerAPI = false;

solr/core/src/java/org/apache/solr/core/PluginInfo.java

@@ -60,6 +60,11 @@ public PluginInfo(String type, Map<String, String> attrs, NamedList initArgs, Li
     this.children = children == null ? Collections.<PluginInfo>emptyList(): unmodifiableList(children);
     isFromSolrConfig = false;
   }
+
+  /** class names can be prefixed with package name e.g: my_package:my.pkg.Class
+   * This checks if it is a package name prefixed classname.
+   * the return value has first = package name & second = class name
+   */
   static Pair<String,String > parseClassName(String name) {
     String pkgName = null;
     String className = name;

solr/core/src/java/org/apache/solr/core/SolrCore.java

@@ -283,6 +283,9 @@ public SolrResourceLoader getResourceLoader() {
     return resourceLoader;
   }
 
+  /** Gets the SolrResourceLoader for a given package
+   * @param pkg The package name
+   */
   public SolrResourceLoader getResourceLoader(String pkg) {
     if (pkg == null) {
       return resourceLoader;

solr/core/src/java/org/apache/solr/handler/SolrConfigHandler.java

@@ -249,6 +249,8 @@ private void handleGET() {
                 Object o = map.get(componentName);
                 val.put(parts.get(1), makeMap(componentName, o));
                 if (req.getParams().getBool("meta", false)) {
+                  // meta=true is asking for the package info of the plugin
+                  // We go through all the listeners and see if there is one registered for this plugin
                   List<PackageListeners.Listener> listeners = req.getCore().getPackageListeners().getListeners();
                   for (PackageListeners.Listener listener :
                       listeners) {

solr/solrj/src/java/org/apache/solr/client/solrj/request/beans/Package.java

@@ -22,6 +22,9 @@
 import com.fasterxml.jackson.annotation.JsonProperty;
 import org.apache.solr.common.util.ReflectMapWriter;
 
+/**Just a container class for POJOs used in Package APIs
+ *
+ */
 public class Package {
   public static class AddVersion implements ReflectMapWriter {
     @JsonProperty(value = "package", required = true)