Use WeakReference to store alternative commands

Essentials/src/main/java/com/earth2me/essentials/AlternativeCommandsHandler.java

@@ -4,6 +4,7 @@
 import org.bukkit.command.PluginIdentifiableCommand;
 import org.bukkit.plugin.Plugin;
 
+import java.lang.ref.WeakReference;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.Iterator;
@@ -13,7 +14,7 @@
 import java.util.logging.Level;
 
 public class AlternativeCommandsHandler {
-    private final transient Map<String, List<Command>> altcommands = new HashMap<>();
+    private final transient Map<String, List<WeakReference<Command>>> altCommands = new HashMap<>();
     private final transient Map<String, String> disabledList = new HashMap<>();
     private final transient IEssentials ess;
 
@@ -35,17 +36,30 @@ public final void addPlugin(final Plugin plugin) {
             final String commandName = commandSplit.length > 1 ? commandSplit[1] : entry.getKey();
             final Command command = entry.getValue();
 
-            final List<Command> pluginCommands = altcommands.computeIfAbsent(commandName.toLowerCase(Locale.ENGLISH), k -> new ArrayList<>());
+            final List<WeakReference<Command>> pluginCommands = altCommands.computeIfAbsent(commandName.toLowerCase(Locale.ENGLISH), k -> new ArrayList<>());
             boolean found = false;
-            for (final Command pc2 : pluginCommands) {
+
+            final Iterator<WeakReference<Command>> pluginCmdIterator = pluginCommands.iterator();
+            while (pluginCmdIterator.hasNext()) {
+                final Command cmd = pluginCmdIterator.next().get();
+                if (cmd == null) {
+                    if (ess.getSettings().isDebug()) {
+                        ess.getLogger().log(Level.INFO, "Essentials: Alternative command for " + commandName + " removed due to garbage collection");
+                    }
+
+                    pluginCmdIterator.remove();
+                    continue;
+                }
+
                 // Safe cast, everything that's added comes from getPluginCommands which already performs the cast check.
-                if (((PluginIdentifiableCommand) pc2).getPlugin().equals(plugin)) {
+                if (((PluginIdentifiableCommand) cmd).getPlugin().equals(plugin)) {
                     found = true;
                     break;
                 }
             }
+
             if (!found) {
-                pluginCommands.add(command);
+                pluginCommands.add(new WeakReference<>(command));
             }
         }
     }
@@ -61,32 +75,51 @@ private Map<String, Command> getPluginCommands(Plugin plugin) {
     }
 
     public void removePlugin(final Plugin plugin) {
-        final Iterator<Map.Entry<String, List<Command>>> iterator = altcommands.entrySet().iterator();
+        final Iterator<Map.Entry<String, List<WeakReference<Command>>>> iterator = altCommands.entrySet().iterator();
         while (iterator.hasNext()) {
-            final Map.Entry<String, List<Command>> entry = iterator.next();
-            entry.getValue().removeIf(pc -> !(pc instanceof PluginIdentifiableCommand) || ((PluginIdentifiableCommand) pc).getPlugin().equals(plugin));
+            final Map.Entry<String, List<WeakReference<Command>>> entry = iterator.next();
+
+            final Iterator<WeakReference<Command>> commands = entry.getValue().iterator();
+            while (commands.hasNext()) {
+                final Command pc = commands.next().get();
+                if (pc instanceof PluginIdentifiableCommand && !((PluginIdentifiableCommand) pc).getPlugin().equals(plugin)) {
+                    continue;
+                }
+                commands.remove();
+            }
+
             if (entry.getValue().isEmpty()) {
                 iterator.remove();
             }
         }
     }
 
     public Command getAlternative(final String label) {
-        final List<Command> commands = altcommands.get(label);
+        final List<WeakReference<Command>> commands = altCommands.get(label);
         if (commands == null || commands.isEmpty()) {
             return null;
         }
+
         if (commands.size() == 1) {
-            return commands.get(0);
+            return commands.get(0).get();
         }
+
         // return the first command that is not an alias
-        for (final Command command : commands) {
-            if (command.getName().equalsIgnoreCase(label)) {
-                return command;
+        final Iterator<WeakReference<Command>> iterator = commands.iterator();
+        while (iterator.hasNext()) {
+            final Command cmd = iterator.next().get();
+            if (cmd == null) {
+                iterator.remove();
+                continue;
+            }
+
+            if (cmd.getName().equalsIgnoreCase(label)) {
+                return cmd;
             }
         }
+
         // return the first alias
-        return commands.get(0);
+        return commands.get(0).get();
     }
 
     public void executed(final String label, final Command pc) {