Cache asset files

HMCLCore/src/main/java/org/jackhuang/hmcl/download/game/GameAssetDownloadTask.java

@@ -28,10 +28,7 @@ import org.jackhuang.hmcl.util.Logging;
 import org.jackhuang.hmcl.util.NetworkUtils;
 
 import java.io.File;
-import java.util.Collection;
-import java.util.LinkedList;
-import java.util.List;
-import java.util.Map;
+import java.util.*;
 import java.util.logging.Level;
 
 /**
@@ -43,7 +40,6 @@ public final class GameAssetDownloadTask extends Task {
     private final AbstractDependencyManager dependencyManager;
     private final Version version;
     private final GameAssetRefreshTask refreshTask;
-    private final List<Task> dependents = new LinkedList<>();
     private final List<Task> dependencies = new LinkedList<>();
 
     /**
@@ -56,16 +52,15 @@ public final class GameAssetDownloadTask extends Task {
         this.dependencyManager = dependencyManager;
         this.version = version;
         this.refreshTask = new GameAssetRefreshTask(dependencyManager, version);
-        this.dependents.add(refreshTask);
     }
 
     @Override
     public Collection<Task> getDependents() {
-        return dependents;
+        return Collections.singleton(refreshTask);
     }
 
     @Override
-    public List<Task> getDependencies() {
+    public Collection<Task> getDependencies() {
         return dependencies;
     }
     

HMCLCore/src/main/java/org/jackhuang/hmcl/download/game/GameAssetIndexDownloadTask.java

@@ -65,6 +65,9 @@ public final class GameAssetIndexDownloadTask extends Task {
         if (!FileUtils.makeDirectory(assetDir))
             throw new IOException("Cannot create directory: " + assetDir);
         File assetIndexFile = dependencyManager.getGameRepository().getIndexFile(version.getId(), assetIndexInfo.getId());
+
+        // We should not check the hash code of asset index file since this file is not consistent
+        // And Mojang will modify this file anytime. So assetIndex.hash might be outdated.
         dependencies.add(new FileDownloadTask(
                 NetworkUtils.toURL(dependencyManager.getDownloadProvider().injectURL(assetIndexInfo.getUrl())),
                 assetIndexFile

HMCLCore/src/main/java/org/jackhuang/hmcl/game/AssetObject.java

@@ -53,7 +53,7 @@ public final class AssetObject implements Validation {
 
     @Override
     public void validate() throws JsonParseException {
-        if (StringUtils.isBlank(hash))
+        if (StringUtils.isBlank(hash) || hash.length() < 2)
             throw new IllegalStateException("AssetObject hash cannot be blank.");
     }
 }