content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you under the Apache License, Version 2.0 (the
   * "License"); you may not use this file except in compliance
   * with the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.bookkeeper.metastore;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.util.Iterator;
  
  /**
   * A Metastore Cursor.
   */
  public interface MetastoreCursor extends Closeable {
  
      MetastoreCursor EMPTY_CURSOR = new MetastoreCursor() {
          @Override
          public boolean hasMoreEntries() {
              return false;
          }
  
          @Override
          public Iterator<MetastoreTableItem> readEntries(int numEntries)
          throws MSException {
              throw new MSException.NoEntriesException("No entries left in the cursor.");
          }
  
          @Override
          public void asyncReadEntries(int numEntries, ReadEntriesCallback callback, Object ctx) {
              callback.complete(MSException.Code.NoEntries.getCode(), null, ctx);
          }
  
          @Override
          public void close() throws IOException {
              // do nothing
          }
      };
  
      /**
       * A callback for reading entries.
       */
      interface ReadEntriesCallback extends
          MetastoreCallback<Iterator<MetastoreTableItem>> {
      }
  
      /**
       * Is there any entries left in the cursor to read.
       *
       * @return true if there is entries left, false otherwise.
       */
      boolean hasMoreEntries();
  
      /**
       * Read entries from the cursor, up to the specified <code>numEntries</code>.
       * The returned list can be smaller.
       *
       * @param numEntries
       *            maximum number of entries to read
       * @return the iterator of returned entries.
       * @throws MSException when failed to read entries from the cursor.
       */
      Iterator<MetastoreTableItem> readEntries(int numEntries) throws MSException;
  
      /**
       * Asynchronously read entries from the cursor, up to the specified <code>numEntries</code>.
       *
       * @see #readEntries(int)
       * @param numEntries
       *            maximum number of entries to read
       * @param callback
       *            callback object
       * @param ctx
       *            opaque context
       */
      void asyncReadEntries(int numEntries, ReadEntriesCallback callback, Object ctx);
  }
  