1 /** 2 * 3 * Licensed to the Apache Software Foundation (ASF) under one 4 * or more contributor license agreements. See the NOTICE file 5 * distributed with this work for additional information 6 * regarding copyright ownership. The ASF licenses this file 7 * to you under the Apache License, Version 2.0 (the 8 * "License"); you may not use this file except in compliance 9 * with the License. You may obtain a copy of the License at 10 * 11 * http://www.apache.org/licenses/LICENSE-2.0 12 * 13 * Unless required by applicable law or agreed to in writing, software 14 * distributed under the License is distributed on an "AS IS" BASIS, 15 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 * See the License for the specific language governing permissions and 17 * limitations under the License. 18 */ 19 package org.apache.hadoop.hbase.io.hfile; 20 21 import java.io.IOException; 22 import java.nio.ByteBuffer; 23 24 import org.apache.hadoop.hbase.classification.InterfaceAudience; 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 @InterfaceAudience.Private 40 public interface HFileScanner { 41 /** 42 * SeekTo or just before the passed <code>key</code>. Examine the return 43 * code to figure whether we found the key or not. 44 * Consider the key stream of all the keys in the file, 45 * <code>k[0] .. k[n]</code>, where there are n keys in the file. 46 * @param key Key to find. 47 * @return -1, if key < k[0], no position; 48 * 0, such that k[i] = key and scanner is left in position i; and 49 * 1, such that k[i] < key, and scanner is left in position i. 50 * The scanner will position itself between k[i] and k[i+1] where 51 * k[i] < key <= k[i+1]. 52 * If there is no key k[i+1] greater than or equal to the input key, then the 53 * scanner will position itself at the end of the file and next() will return 54 * false when it is called. 55 * @throws IOException 56 */ 57 int seekTo(byte[] key) throws IOException; 58 int seekTo(byte[] key, int offset, int length) throws IOException; 59 /** 60 * Reseek to or just before the passed <code>key</code>. Similar to seekTo 61 * except that this can be called even if the scanner is not at the beginning 62 * of a file. 63 * This can be used to seek only to keys which come after the current position 64 * of the scanner. 65 * Consider the key stream of all the keys in the file, 66 * <code>k[0] .. k[n]</code>, where there are n keys in the file after 67 * current position of HFileScanner. 68 * The scanner will position itself between k[i] and k[i+1] where 69 * k[i] < key <= k[i+1]. 70 * If there is no key k[i+1] greater than or equal to the input key, then the 71 * scanner will position itself at the end of the file and next() will return 72 * false when it is called. 73 * @param key Key to find (should be non-null) 74 * @return -1, if key < k[0], no position; 75 * 0, such that k[i] = key and scanner is left in position i; and 76 * 1, such that k[i] < key, and scanner is left in position i. 77 * @throws IOException 78 */ 79 int reseekTo(byte[] key) throws IOException; 80 int reseekTo(byte[] key, int offset, int length) throws IOException; 81 /** 82 * Consider the key stream of all the keys in the file, 83 * <code>k[0] .. k[n]</code>, where there are n keys in the file. 84 * @param key Key to find 85 * @return false if key <= k[0] or true with scanner in position 'i' such 86 * that: k[i] < key. Furthermore: there may be a k[i+1], such that 87 * k[i] < key <= k[i+1] but there may also NOT be a k[i+1], and next() will 88 * return false (EOF). 89 * @throws IOException 90 */ 91 boolean seekBefore(byte[] key) throws IOException; 92 boolean seekBefore(byte[] key, int offset, int length) throws IOException; 93 /** 94 * Positions this scanner at the start of the file. 95 * @return False if empty file; i.e. a call to next would return false and 96 * the current key and value are undefined. 97 * @throws IOException 98 */ 99 boolean seekTo() throws IOException; 100 /** 101 * Scans to the next entry in the file. 102 * @return Returns false if you are at the end otherwise true if more in file. 103 * @throws IOException 104 */ 105 boolean next() throws IOException; 106 /** 107 * Gets a buffer view to the current key. You must call 108 * {@link #seekTo(byte[])} before this method. 109 * @return byte buffer for the key. The limit is set to the key size, and the 110 * position is 0, the start of the buffer view. 111 */ 112 ByteBuffer getKey(); 113 /** 114 * Gets a buffer view to the current value. You must call 115 * {@link #seekTo(byte[])} before this method. 116 * 117 * @return byte buffer for the value. The limit is set to the value size, and 118 * the position is 0, the start of the buffer view. 119 */ 120 ByteBuffer getValue(); 121 /** 122 * @return Instance of {@link KeyValue}. 123 */ 124 KeyValue getKeyValue(); 125 /** 126 * Convenience method to get a copy of the key as a string - interpreting the 127 * bytes as UTF8. You must call {@link #seekTo(byte[])} before this method. 128 * @return key as a string 129 */ 130 String getKeyString(); 131 /** 132 * Convenience method to get a copy of the value as a string - interpreting 133 * the bytes as UTF8. You must call {@link #seekTo(byte[])} before this method. 134 * @return value as a string 135 */ 136 String getValueString(); 137 /** 138 * @return Reader that underlies this Scanner instance. 139 */ 140 HFile.Reader getReader(); 141 /** 142 * @return True is scanner has had one of the seek calls invoked; i.e. 143 * {@link #seekBefore(byte[])} or {@link #seekTo()} or {@link #seekTo(byte[])}. 144 * Otherwise returns false. 145 */ 146 boolean isSeeked(); 147 148 /** 149 * @return the next key in the index (the key to seek to the next block) 150 */ 151 byte[] getNextIndexedKey(); 152 }