rewrote discovery and registration code to be composable and higher level

src/main/java/me/clip/placeholderapi/commands/impl/cloud/CommandECloudUpdate.java

@@ -5,16 +5,16 @@ import me.clip.placeholderapi.PlaceholderAPIPlugin;
 import me.clip.placeholderapi.commands.PlaceholderCommand;
 import me.clip.placeholderapi.expansion.PlaceholderExpansion;
 import me.clip.placeholderapi.expansion.cloud.CloudExpansion;
+import me.clip.placeholderapi.util.Futures;
 import me.clip.placeholderapi.util.Msg;
-import org.bukkit.Bukkit;
 import org.bukkit.command.CommandSender;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 import org.jetbrains.annotations.Unmodifiable;
 
-import java.io.File;
 import java.util.ArrayList;
-import java.util.Collection;
 import java.util.List;
+import java.util.Objects;
 import java.util.Optional;
 import java.util.concurrent.CompletableFuture;
 import java.util.stream.Collectors;
@@ -67,9 +67,8 @@ public final class CommandECloudUpdate extends PlaceholderCommand
 		Msg.msg(sender,
 				"&aUpdating expansions: " + expansions.stream().map(CloudExpansion::getName).collect(Collectors.joining("&7, &6", "&8[&6", "&8]&r")));
 
-		downloadExpansions(plugin, expansions)
-				.thenCompose(files -> discoverExpansions(plugin, files))
-				.whenComplete((classes, exception) -> {
+
+		Futures.onMainThread(plugin, downloadAndDiscover(expansions, plugin), (classes, exception) -> {
 			if (exception != null)
 			{
 				Msg.msg(sender,
@@ -80,17 +79,18 @@ public final class CommandECloudUpdate extends PlaceholderCommand
 			Msg.msg(sender,
 					"&aSuccessfully downloaded updates, registering new versions.");
 
-					Bukkit.getScheduler().runTask(plugin, () -> {
+
 			final String message = classes.stream()
+										  .filter(Objects::nonNull)
 										  .map(plugin.getLocalExpansionManager()::register)
 										  .filter(Optional::isPresent)
 										  .map(Optional::get)
 										  .map(expansion -> "  &a" + expansion.getName() + " &f" + expansion.getVersion())
 										  .collect(Collectors.joining("\n"));
+
 			Msg.msg(sender,
-								"&7Registered expansions:",
-								message);
-					});
+					"&7Registered expansions:", message);
+
 		});
 	}
 
@@ -114,22 +114,12 @@ public final class CommandECloudUpdate extends PlaceholderCommand
 	}
 
 
-	public static CompletableFuture<List<File>> downloadExpansions(@NotNull final PlaceholderAPIPlugin plugin, @NotNull final List<CloudExpansion> expansions)
+	private static CompletableFuture<List<@Nullable Class<? extends PlaceholderExpansion>>> downloadAndDiscover(@NotNull final List<CloudExpansion> expansions, @NotNull final PlaceholderAPIPlugin plugin)
 	{
-		final List<CompletableFuture<File>> futures = expansions.stream()
+		return expansions.stream()
 						 .map(expansion -> plugin.getCloudExpansionManager().downloadExpansion(expansion, expansion.getVersion()))
-																.collect(Collectors.toList());
-
-		return CompletableFuture.allOf(futures.toArray(new CompletableFuture[0])).thenApplyAsync(v -> futures.stream().map(CompletableFuture::join).collect(Collectors.toList()));
-	}
-
-	public static CompletableFuture<List<Class<? extends PlaceholderExpansion>>> discoverExpansions(@NotNull final PlaceholderAPIPlugin plugin, @NotNull final List<File> files)
-	{
-		final List<CompletableFuture<List<Class<? extends PlaceholderExpansion>>>> futures = files.stream()
-																								  .map(file -> plugin.getLocalExpansionManager().findExpansionsInFile(file))
-																								  .collect(Collectors.toList());
-
-		return CompletableFuture.allOf(futures.toArray(new CompletableFuture[0])).thenApplyAsync(v -> futures.stream().map(CompletableFuture::join).flatMap(Collection::stream).collect(Collectors.toList()));
+						 .map(future -> future.thenCompose(plugin.getLocalExpansionManager()::findExpansionInFile))
+						 .collect(Futures.collector());
 	}
 
 }

src/main/java/me/clip/placeholderapi/commands/impl/local/CommandExpansionRegister.java

@@ -4,8 +4,8 @@ import me.clip.placeholderapi.PlaceholderAPIPlugin;
 import me.clip.placeholderapi.commands.PlaceholderCommand;
 import me.clip.placeholderapi.expansion.PlaceholderExpansion;
 import me.clip.placeholderapi.expansion.manager.LocalExpansionManager;
+import me.clip.placeholderapi.util.Futures;
 import me.clip.placeholderapi.util.Msg;
-import org.bukkit.Bukkit;
 import org.bukkit.command.CommandSender;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Unmodifiable;
@@ -45,7 +45,7 @@ public final class CommandExpansionRegister extends PlaceholderCommand
 			return;
 		}
 
-		manager.findExpansionsInFile(file).whenComplete((classes, exception) -> {
+		Futures.onMainThread(plugin, manager.findExpansionInFile(file), (clazz, exception) -> {
 			if (exception != null)
 			{
 				Msg.msg(sender,
@@ -55,15 +55,15 @@ public final class CommandExpansionRegister extends PlaceholderCommand
 				return;
 			}
 
-			if (classes.isEmpty())
+			if (clazz == null)
 			{
 				Msg.msg(sender,
 						"&cNo expansion class found in file: &f" + file);
 				return;
 			}
 
-			Bukkit.getScheduler().runTask(plugin, () -> {
-				final Optional<PlaceholderExpansion> expansion = manager.register(classes.get(0));
+
+			final Optional<PlaceholderExpansion> expansion = manager.register(clazz);
 			if (!expansion.isPresent())
 			{
 				Msg.msg(sender,
@@ -73,7 +73,7 @@ public final class CommandExpansionRegister extends PlaceholderCommand
 
 			Msg.msg(sender,
 					"&aSuccessfully registered expansion: &f" + expansion.get().getName());
-			});
+
 		});
 	}
 

src/main/java/me/clip/placeholderapi/expansion/manager/LocalExpansionManager.java

@@ -13,6 +13,7 @@ import me.clip.placeholderapi.expansion.Taskable;
 import me.clip.placeholderapi.expansion.VersionSpecific;
 import me.clip.placeholderapi.expansion.cloud.CloudExpansion;
 import me.clip.placeholderapi.util.FileUtil;
+import me.clip.placeholderapi.util.Futures;
 import me.clip.placeholderapi.util.Msg;
 import org.bukkit.Bukkit;
 import org.bukkit.command.CommandSender;
@@ -28,7 +29,7 @@ import org.jetbrains.annotations.Nullable;
 import org.jetbrains.annotations.Unmodifiable;
 
 import java.io.File;
-import java.io.IOException;
+import java.util.Arrays;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.List;
@@ -290,19 +291,18 @@ public final class LocalExpansionManager implements Listener
 	{
 		plugin.getLogger().info("Placeholder expansion registration initializing...");
 
-		findExpansionsOnDisk().whenCompleteAsync((classes, exception) -> {
+		Futures.onMainThread(plugin, findExpansionsOnDisk(), (classes, exception) -> {
 			if (exception != null)
 			{
 				plugin.getLogger().log(Level.SEVERE, "failed to load class files of expansions", exception);
 				return;
 			}
 
-			Bukkit.getScheduler().runTask(plugin, () -> {
 			final long registered = classes.stream().map(this::register).filter(Optional::isPresent).count();
+
 			Msg.msg(sender,
 					registered == 0 ? "&6No expansions were registered!" : registered + "&a placeholder hooks successfully registered!");
 		});
-		});
 	}
 
 	private void unregisterAll()
@@ -320,33 +320,26 @@ public final class LocalExpansionManager implements Listener
 
 
 	@NotNull
-	public CompletableFuture<List<Class<? extends PlaceholderExpansion>>> findExpansionsOnDisk()
+	public CompletableFuture<@NotNull List<@NotNull Class<? extends PlaceholderExpansion>>> findExpansionsOnDisk()
 	{
-		return CompletableFuture.supplyAsync(() -> {
-			try
-			{
-				return FileUtil.getClasses(getExpansionsFolder(), PlaceholderExpansion.class);
-			}
-			catch (final IOException | ClassNotFoundException ex)
-			{
-				throw new CompletionException(ex);
-			}
-		});
+		return Arrays.stream(folder.listFiles((dir, name) -> name.endsWith(".jar")))
+					 .map(this::findExpansionInFile)
+					 .collect(Futures.collector());
 	}
 
 	@NotNull
-	public CompletableFuture<List<Class<? extends PlaceholderExpansion>>> findExpansionsInFile(@NotNull final File file)
+	public CompletableFuture<@Nullable Class<? extends PlaceholderExpansion>> findExpansionInFile(@NotNull final File file)
 	{
 		return CompletableFuture.supplyAsync(() -> {
 			try
 			{
-				final List<@NotNull Class<? extends PlaceholderExpansion>> classes = FileUtil.getClasses(getExpansionsFolder(), PlaceholderExpansion.class, file.getName());
-				if (classes.size() > 1)
-				{
-					throw new IllegalStateException("multiple expansion classes in one file!");
+				return FileUtil.findClass(file, PlaceholderExpansion.class);
 			}
-
-				return classes;
+			catch (final VerifyError ex)
+			{
+				plugin.getLogger().severe("expansion file " + file.getName() + " is outdated: \n" +
+										  "Failed to load due to a [" + ex.getClass().getSimpleName() + "], attempted to use" + ex.getMessage().substring(ex.getMessage().lastIndexOf(' ')));
+				return null;
 			}
 			catch (final Exception ex)
 			{
@@ -365,6 +358,11 @@ public final class LocalExpansionManager implements Listener
 		}
 		catch (final Exception ex)
 		{
+			if (ex.getCause() instanceof LinkageError)
+			{
+				throw ((LinkageError) ex.getCause());
+			}
+
 			plugin.getLogger().log(Level.SEVERE, "Failed to load placeholder expansion from class: " + clazz.getName(), ex);
 			return null;
 		}

src/main/java/me/clip/placeholderapi/util/FileUtil.java

@@ -24,51 +24,25 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import java.io.File;
-import java.io.FilenameFilter;
 import java.io.IOException;
 import java.net.URL;
 import java.net.URLClassLoader;
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.List;
 import java.util.jar.JarEntry;
 import java.util.jar.JarInputStream;
 
 public class FileUtil
 {
 
-	@NotNull
-	public static <T> List<@NotNull Class<? extends T>> getClasses(@NotNull final File folder, @NotNull final Class<T> clazz) throws IOException, ClassNotFoundException
+	@Nullable
+	public static <T> Class<? extends T> findClass(@NotNull final File file, @NotNull final Class<T> clazz) throws IOException, ClassNotFoundException
 	{
-		return getClasses(folder, clazz, null);
+		if (!file.exists())
+		{
+			return null;
 		}
 
-	@NotNull
-	public static <T> List<@NotNull Class<? extends T>> getClasses(@NotNull final File folder, @NotNull final Class<T> clazz, @Nullable final String target) throws IOException, ClassNotFoundException
-	{
-		if (!folder.exists())
-		{
-			return Collections.emptyList();
-		}
+		final URL jar = file.toURI().toURL();
 
-		final File[] jars = folder.listFiles((dir, name) -> name.endsWith(".jar") && (target == null || name.replace(".jar", "").equalsIgnoreCase(target.replace(".jar", ""))));
-		if (jars == null)
-		{
-			return Collections.emptyList();
-		}
-
-		final List<@NotNull Class<? extends T>> list = new ArrayList<>();
-
-		for (final File file : jars)
-		{
-			gather(file.toURI().toURL(), clazz, list);
-		}
-
-		return list;
-	}
-
-	private static <T> void gather(@NotNull final URL jar, @NotNull final Class<T> clazz, @NotNull final List<@NotNull Class<? extends T>> list) throws IOException, ClassNotFoundException
-	{
 		try (final URLClassLoader loader = new URLClassLoader(new URL[]{jar}, clazz.getClassLoader()); final JarInputStream stream = new JarInputStream(jar.openStream()))
 		{
 			JarEntry entry;
@@ -85,7 +59,7 @@ public class FileUtil
 					final Class<?> loaded = loader.loadClass(name.substring(0, name.lastIndexOf('.')).replace('/', '.'));
 					if (clazz.isAssignableFrom(loaded))
 					{
-						list.add(loaded.asSubclass(clazz));
+						return loaded.asSubclass(clazz);
 					}
 				}
 				catch (final NoClassDefFoundError ignored)
@@ -93,6 +67,8 @@ public class FileUtil
 				}
 			}
 		}
+
+		return null;
 	}
 
 }

src/main/java/me/clip/placeholderapi/util/Futures.java

@@ -0,0 +1,63 @@
+package me.clip.placeholderapi.util;
+
+import org.bukkit.Bukkit;
+import org.bukkit.plugin.Plugin;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Collection;
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+import java.util.function.BiConsumer;
+import java.util.stream.Collector;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public final class Futures
+{
+
+	private Futures()
+	{}
+
+
+	public static <T> void onMainThread(@NotNull final Plugin plugin, @NotNull final CompletableFuture<T> future, @NotNull final BiConsumer<T, Throwable> consumer)
+	{
+		future.whenComplete((value, exception) -> {
+			if (Bukkit.isPrimaryThread())
+			{
+				consumer.accept(value, exception);
+			}
+			else
+			{
+				Bukkit.getScheduler().runTask(plugin, () -> consumer.accept(value, exception));
+			}
+		});
+	}
+
+
+	@NotNull
+	public static <T> Collector<CompletableFuture<T>, ?, CompletableFuture<List<T>>> collector()
+	{
+		return Collectors.collectingAndThen(Collectors.toList(), Futures::of);
+	}
+
+
+	@NotNull
+	public static <T> CompletableFuture<List<T>> of(@NotNull final Stream<CompletableFuture<T>> futures)
+	{
+		return of(futures.collect(Collectors.toList()));
+	}
+
+	@NotNull
+	public static <T> CompletableFuture<List<T>> of(@NotNull final Collection<CompletableFuture<T>> futures)
+	{
+		return CompletableFuture.allOf(futures.toArray(new CompletableFuture[0]))
+								.thenApplyAsync($ -> awaitCompletion(futures));
+	}
+
+	@NotNull
+	private static <T> List<T> awaitCompletion(@NotNull final Collection<CompletableFuture<T>> futures)
+	{
+		return futures.stream().map(CompletableFuture::join).collect(Collectors.toList());
+	}
+
+}