update balanced download provider

FCL/src/main/java/com/tungsten/fcl/setting/DownloadProviders.java

@@ -84,7 +84,7 @@ public final class DownloadProviders {
 
         AdaptedDownloadProvider fileProvider = new AdaptedDownloadProvider();
         fileProvider.setDownloadProviderCandidates(Arrays.asList(MCBBS, BMCLAPI, MOJANG));
-        BalancedDownloadProvider balanced = new BalancedDownloadProvider(Arrays.asList(MCBBS, BMCLAPI, MOJANG));
+        BalancedDownloadProvider balanced = new BalancedDownloadProvider(MOJANG, MCBBS, BMCLAPI);
 
         providersById = mapOf(
                 pair("official", new AutoDownloadProvider(MOJANG, fileProvider)),

FCLCore/src/main/java/com/tungsten/fclcore/download/BalancedDownloadProvider.java

@@ -18,20 +18,17 @@
 package com.tungsten.fclcore.download;
 
 import java.util.HashMap;
-import java.util.List;
 import java.util.Map;
-import java.util.stream.Collectors;
 
 /**
  * Official Download Provider fetches version list from Mojang and
  * download files from mcbbs.
  */
-public class BalancedDownloadProvider implements DownloadProvider {
-    List<DownloadProvider> candidates;
+public final class BalancedDownloadProvider implements DownloadProvider {
+    private final DownloadProvider[] candidates;
+    private final Map<String, VersionList<?>> versionLists = new HashMap<>();
 
-    Map<String, VersionList<?>> versionLists = new HashMap<>();
-
-    public BalancedDownloadProvider(List<DownloadProvider> candidates) {
+    public BalancedDownloadProvider(DownloadProvider... candidates) {
         this.candidates = candidates;
     }
 
@@ -52,13 +49,13 @@ public class BalancedDownloadProvider implements DownloadProvider {
 
     @Override
     public VersionList<?> getVersionListById(String id) {
-        if (!versionLists.containsKey(id)) {
-            versionLists.put(id, new MultipleSourceVersionList(
-                    candidates.stream()
-                            .map(downloadProvider -> downloadProvider.getVersionListById(id))
-                            .collect(Collectors.toList())));
-        }
-        return versionLists.get(id);
+        return versionLists.computeIfAbsent(id, value -> {
+            VersionList<?>[] lists = new VersionList<?>[candidates.length];
+            for (int i = 0; i < candidates.length; i++) {
+                lists[i] = candidates[i].getVersionListById(value);
+            }
+            return new MultipleSourceVersionList(lists);
+        });
     }
 
     @Override

FCLCore/src/main/java/com/tungsten/fclcore/download/MultipleSourceVersionList.java

@@ -17,23 +17,26 @@
  */
 package com.tungsten.fclcore.download;
 
-import java.util.List;
+import static com.tungsten.fclcore.util.Logging.LOG;
+
+import java.util.Arrays;
 import java.util.concurrent.CompletableFuture;
+import java.util.logging.Level;
 
 public class MultipleSourceVersionList extends VersionList<RemoteVersion> {
 
-    private final List<VersionList<?>> backends;
+    private final VersionList<?>[] backends;
 
-    MultipleSourceVersionList(List<VersionList<?>> backends) {
+    MultipleSourceVersionList(VersionList<?>[] backends) {
         this.backends = backends;
 
-        assert (backends.size() >= 1);
+        assert (backends.length >= 1);
     }
 
     @Override
     public boolean hasType() {
-        boolean hasType = backends.get(0).hasType();
-        assert (backends.stream().allMatch(versionList -> versionList.hasType() == hasType));
+        boolean hasType = backends[0].hasType();
+        assert (Arrays.stream(backends).allMatch(versionList -> versionList.hasType() == hasType));
         return hasType;
     }
 
@@ -47,11 +50,9 @@ public class MultipleSourceVersionList extends VersionList<RemoteVersion> {
         throw new UnsupportedOperationException("MultipleSourceVersionList does not support loading the entire remote version list.");
     }
 
-    @Override
-    public CompletableFuture<?> refreshAsync(String gameVersion) {
-        versions.clear(gameVersion);
-        return CompletableFuture.anyOf(backends.stream()
-                .map(versionList -> versionList.refreshAsync(gameVersion)
+    private CompletableFuture<?> refreshAsync(String gameVersion, int sourceIndex) {
+        VersionList<?> versionList = backends[sourceIndex];
+        CompletableFuture<Void> future = versionList.refreshAsync(gameVersion)
                 .thenRunAsync(() -> {
                     lock.writeLock().lock();
 
@@ -60,7 +61,25 @@ public class MultipleSourceVersionList extends VersionList<RemoteVersion> {
                     } finally {
                         lock.writeLock().unlock();
                     }
-                }))
-                .toArray(CompletableFuture[]::new));
+                });
+
+        if (sourceIndex == backends.length - 1) {
+            return future;
+        } else {
+            return future.<CompletableFuture<?>>handle((ignore, e) -> {
+                if (e == null) {
+                    return future;
+                }
+
+                LOG.log(Level.WARNING, "Failed to fetch versions list and try to fetch from other source", e);
+                return refreshAsync(gameVersion, sourceIndex + 1);
+            }).thenCompose(it -> it);
+        }
+    }
+
+    @Override
+    public CompletableFuture<?> refreshAsync(String gameVersion) {
+        versions.clear(gameVersion);
+        return refreshAsync(gameVersion, 0);
     }
 }