1 /** 2 * Copyright 2009 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.io.hfile; 21 22 import java.io.IOException; 23 import java.nio.ByteBuffer; 24 25 import org.apache.hadoop.hbase.KeyValue; 26 27 /** 28 * A scanner allows you to position yourself within a HFile and 29 * scan through it. It allows you to reposition yourself as well. 30 * 31 * <p>A scanner doesn't always have a key/value that it is pointing to 32 * when it is first created and before 33 * {@link #seekTo()}/{@link #seekTo(byte[])} are called. 34 * In this case, {@link #getKey()}/{@link #getValue()} returns null. At most 35 * other times, a key and value will be available. The general pattern is that 36 * you position the Scanner using the seekTo variants and then getKey and 37 * getValue. 38 */ 39 public interface HFileScanner { 40 /** 41 * SeekTo or just before the passed <code>key</code>. Examine the return 42 * code to figure whether we found the key or not. 43 * Consider the key stream of all the keys in the file, 44 * <code>k[0] .. k[n]</code>, where there are n keys in the file. 45 * @param key Key to find. 46 * @return -1, if key < k[0], no position; 47 * 0, such that k[i] = key and scanner is left in position i; and 48 * 1, such that k[i] < key, and scanner is left in position i. 49 * The scanner will position itself between k[i] and k[i+1] where 50 * k[i] < key <= k[i+1]. 51 * If there is no key k[i+1] greater than or equal to the input key, then the 52 * scanner will position itself at the end of the file and next() will return 53 * false when it is called. 54 * @throws IOException 55 */ 56 public int seekTo(byte[] key) throws IOException; 57 public int seekTo(byte[] key, int offset, int length) throws IOException; 58 /** 59 * Reseek to or just before the passed <code>key</code>. Similar to seekTo 60 * except that this can be called even if the scanner is not at the beginning 61 * of a file. 62 * This can be used to seek only to keys which come after the current position 63 * of the scanner. 64 * Consider the key stream of all the keys in the file, 65 * <code>k[0] .. k[n]</code>, where there are n keys in the file after 66 * current position of HFileScanner. 67 * The scanner will position itself between k[i] and k[i+1] where 68 * k[i] < key <= k[i+1]. 69 * If there is no key k[i+1] greater than or equal to the input key, then the 70 * scanner will position itself at the end of the file and next() will return 71 * false when it is called. 72 * @param key Key to find (should be non-null) 73 * @return -1, if key < k[0], no position; 74 * 0, such that k[i] = key and scanner is left in position i; and 75 * 1, such that k[i] < key, and scanner is left in position i. 76 * @throws IOException 77 */ 78 public int reseekTo(byte[] key) throws IOException; 79 public int reseekTo(byte[] key, int offset, int length) throws IOException; 80 /** 81 * Consider the key stream of all the keys in the file, 82 * <code>k[0] .. k[n]</code>, where there are n keys in the file. 83 * @param key Key to find 84 * @return false if key <= k[0] or true with scanner in position 'i' such 85 * that: k[i] < key. Furthermore: there may be a k[i+1], such that 86 * k[i] < key <= k[i+1] but there may also NOT be a k[i+1], and next() will 87 * return false (EOF). 88 * @throws IOException 89 */ 90 public boolean seekBefore(byte [] key) throws IOException; 91 public boolean seekBefore(byte []key, int offset, int length) throws IOException; 92 /** 93 * Positions this scanner at the start of the file. 94 * @return False if empty file; i.e. a call to next would return false and 95 * the current key and value are undefined. 96 * @throws IOException 97 */ 98 public boolean seekTo() throws IOException; 99 /** 100 * Scans to the next entry in the file. 101 * @return Returns false if you are at the end otherwise true if more in file. 102 * @throws IOException 103 */ 104 public boolean next() throws IOException; 105 /** 106 * Gets a buffer view to the current key. You must call 107 * {@link #seekTo(byte[])} before this method. 108 * @return byte buffer for the key. The limit is set to the key size, and the 109 * position is 0, the start of the buffer view. 110 */ 111 public ByteBuffer getKey(); 112 /** 113 * Gets a buffer view to the current value. You must call 114 * {@link #seekTo(byte[])} before this method. 115 * 116 * @return byte buffer for the value. The limit is set to the value size, and 117 * the position is 0, the start of the buffer view. 118 */ 119 public ByteBuffer getValue(); 120 /** 121 * @return Instance of {@link KeyValue}. 122 */ 123 public KeyValue getKeyValue(); 124 /** 125 * Convenience method to get a copy of the key as a string - interpreting the 126 * bytes as UTF8. You must call {@link #seekTo(byte[])} before this method. 127 * @return key as a string 128 */ 129 public String getKeyString(); 130 /** 131 * Convenience method to get a copy of the value as a string - interpreting 132 * the bytes as UTF8. You must call {@link #seekTo(byte[])} before this method. 133 * @return value as a string 134 */ 135 public String getValueString(); 136 /** 137 * @return Reader that underlies this Scanner instance. 138 */ 139 public HFile.Reader getReader(); 140 /** 141 * @return True is scanner has had one of the seek calls invoked; i.e. 142 * {@link #seekBefore(byte[])} or {@link #seekTo()} or {@link #seekTo(byte[])}. 143 * Otherwise returns false. 144 */ 145 public boolean isSeeked(); 146 }