option to disable chunk cache

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

@@ -10,6 +10,9 @@ public class ChunkCache {
     private final Cache<String, byte[]> cache;
 
     public ChunkCache(int maxEntries) {
+        if (maxEntries == 0) {
+            return;
+        }
         this.cache = CacheBuilder.newBuilder()
                 .maximumSize(maxEntries)
                 .expireAfterAccess(1, TimeUnit.HOURS)
@@ -17,10 +20,16 @@ public class ChunkCache {
     }
 
     public byte[] getChunk(String fileId) {
+        if (this.cache == null) {
+            return;
+        }
         return this.cache.getIfPresent(fileId);
     }
 
     public void setChunk(String fileId, byte[] data) {
+        if (this.cache == null) {
+            return;
+        }
         this.cache.put(fileId, data);
     }