Java client: ByteBuffer.clear supports higher JDK versions

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

@@ -3,6 +3,7 @@ package seaweedfs.client;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.nio.Buffer;
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.List;
@@ -34,7 +35,7 @@ public class ByteBufferPool {
     }
 
     public static synchronized void release(ByteBuffer obj) {
-        obj.clear();
+        ((Buffer)obj).clear();
         bufferList.add(0, obj);
     }