ensure changing buffer size requirements

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

@@ -1,22 +1,39 @@
 package seaweedfs.client;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.List;
 
 public class ByteBufferPool {
 
-    static List<ByteBuffer> bufferList = new ArrayList<>();
+    private static final int MIN_BUFFER_SIZE = 8 * 1024 * 1024;
+    private static final Logger LOG = LoggerFactory.getLogger(ByteBufferPool.class);
+
+    private static final List<ByteBuffer> bufferList = new ArrayList<>();
 
     public static synchronized ByteBuffer request(int bufferSize) {
+        if (bufferSize < MIN_BUFFER_SIZE) {
+            bufferSize = MIN_BUFFER_SIZE;
+        }
         if (bufferList.isEmpty()) {
             return ByteBuffer.allocate(bufferSize);
         }
-        return bufferList.remove(bufferList.size()-1);
+        ByteBuffer buffer = bufferList.remove(bufferList.size() - 1);
+        if (buffer.capacity() >= bufferSize) {
+            return buffer;
+        }
+
+        LOG.info("add new buffer from {} to {}", buffer.capacity(), bufferSize);
+        bufferList.add(0, buffer);
+        return ByteBuffer.allocate(bufferSize);
+
     }
 
     public static synchronized void release(ByteBuffer obj) {
-        bufferList.add(obj);
+        bufferList.add(0, obj);
     }
 
 }