1 /** 2 * Copyright 2010 The Apache Software Foundation 3 * 4 * Licensed to the Apache Software Foundation (ASF) under one 5 * or more contributor license agreements. See the NOTICE file 6 * distributed with this work for additional information 7 * regarding copyright ownership. The ASF licenses this file 8 * to you under the Apache License, Version 2.0 (the 9 * "License"); you may not use this file except in compliance 10 * with the License. You may obtain a copy of the License at 11 * 12 * http://www.apache.org/licenses/LICENSE-2.0 13 * 14 * Unless required by applicable law or agreed to in writing, software 15 * distributed under the License is distributed on an "AS IS" BASIS, 16 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 17 * See the License for the specific language governing permissions and 18 * limitations under the License. 19 */ 20 package org.apache.hadoop.hbase.regionserver; 21 22 import java.io.IOException; 23 24 import org.apache.hadoop.hbase.KeyValue; 25 26 /** 27 * Scanner that returns the next KeyValue. 28 */ 29 public interface KeyValueScanner { 30 /** 31 * Look at the next KeyValue in this scanner, but do not iterate scanner. 32 * @return the next KeyValue 33 */ 34 public KeyValue peek(); 35 36 /** 37 * Return the next KeyValue in this scanner, iterating the scanner 38 * @return the next KeyValue 39 */ 40 public KeyValue next() throws IOException; 41 42 /** 43 * Seek the scanner at or after the specified KeyValue. 44 * @param key seek value 45 * @return true if scanner has values left, false if end of scanner 46 */ 47 public boolean seek(KeyValue key) throws IOException; 48 49 /** 50 * Reseek the scanner at or after the specified KeyValue. 51 * This method is guaranteed to seek to or before the required key only if the 52 * key comes after the current position of the scanner. Should not be used 53 * to seek to a key which may come before the current position. 54 * @param key seek value (should be non-null) 55 * @return true if scanner has values left, false if end of scanner 56 */ 57 public boolean reseek(KeyValue key) throws IOException; 58 59 /** 60 * Get the sequence id associated with this KeyValueScanner. This is required 61 * for comparing multiple files to find out which one has the latest data. 62 * The default implementation for this would be to return 0. A file having 63 * lower sequence id will be considered to be the older one. 64 */ 65 public long getSequenceID(); 66 67 /** 68 * Close the KeyValue scanner. 69 */ 70 public void close(); 71 }