protect against edge cases when locations expires

other/java/client/src/main/java/seaweedfs/client/SeaweedRead.java

@@ -28,20 +28,26 @@ public class SeaweedRead {
 
         List<ChunkView> chunkViews = viewFromVisibles(visibleIntervals, position, bufferLength);
 
+        Map<String, FilerProto.Locations> knownLocations = new HashMap<>();
+
         FilerProto.LookupVolumeRequest.Builder lookupRequest = FilerProto.LookupVolumeRequest.newBuilder();
         for (ChunkView chunkView : chunkViews) {
             String vid = parseVolumeId(chunkView.fileId);
-            if (volumeIdCache.getLocations(vid)==null){
+            FilerProto.Locations locations = volumeIdCache.getLocations(vid);
+            if (locations == null) {
                 lookupRequest.addVolumeIds(vid);
+            } else {
+                knownLocations.put(vid, locations);
             }
         }
 
-        if (lookupRequest.getVolumeIdsCount()>0){
+        if (lookupRequest.getVolumeIdsCount() > 0) {
             FilerProto.LookupVolumeResponse lookupResponse = filerGrpcClient
                     .getBlockingStub().lookupVolume(lookupRequest.build());
             Map<String, FilerProto.Locations> vid2Locations = lookupResponse.getLocationsMapMap();
-            for (Map.Entry<String,FilerProto.Locations> entry : vid2Locations.entrySet()) {
+            for (Map.Entry<String, FilerProto.Locations> entry : vid2Locations.entrySet()) {
                 volumeIdCache.setLocations(entry.getKey(), entry.getValue());
+                knownLocations.put(entry.getKey(), entry.getValue());
             }
         }
 
@@ -57,7 +63,7 @@ public class SeaweedRead {
                 startOffset += gap;
             }
 
-            FilerProto.Locations locations = volumeIdCache.getLocations(parseVolumeId(chunkView.fileId));
+            FilerProto.Locations locations = knownLocations.get(parseVolumeId(chunkView.fileId));
             if (locations == null || locations.getLocationsCount() == 0) {
                 LOG.error("failed to locate {}", chunkView.fileId);
                 // log here!