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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.Cell;
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    @Deprecated
58    int seekTo(byte[] key) throws IOException;
59    @Deprecated
60    int seekTo(byte[] key, int offset, int length) throws IOException;
61  
62    int seekTo(Cell c) throws IOException;
63    /**
64     * Reseek to or just before the passed <code>key</code>. Similar to seekTo
65     * except that this can be called even if the scanner is not at the beginning
66     * of a file.
67     * This can be used to seek only to keys which come after the current position
68     * of the scanner.
69     * Consider the key stream of all the keys in the file,
70     * <code>k[0] .. k[n]</code>, where there are n keys in the file after
71     * current position of HFileScanner.
72     * The scanner will position itself between k[i] and k[i+1] where
73     * k[i] < key <= k[i+1].
74     * If there is no key k[i+1] greater than or equal to the input key, then the
75     * scanner will position itself at the end of the file and next() will return
76     * false when it is called.
77     * @param key Key to find (should be non-null)
78     * @return -1, if key < k[0], no position;
79     * 0, such that k[i] = key and scanner is left in position i; and
80     * 1, such that k[i] < key, and scanner is left in position i.
81     * @throws IOException
82     */
83    @Deprecated
84    int reseekTo(byte[] key) throws IOException;
85    @Deprecated
86    int reseekTo(byte[] key, int offset, int length) throws IOException;
87  
88    int reseekTo(Cell c) throws IOException;
89    /**
90     * Consider the key stream of all the keys in the file,
91     * <code>k[0] .. k[n]</code>, where there are n keys in the file.
92     * @param key Key to find
93     * @return false if key <= k[0] or true with scanner in position 'i' such
94     * that: k[i] < key.  Furthermore: there may be a k[i+1], such that
95     * k[i] < key <= k[i+1] but there may also NOT be a k[i+1], and next() will
96     * return false (EOF).
97     * @throws IOException
98     */
99    @Deprecated
100   boolean seekBefore(byte[] key) throws IOException;
101   @Deprecated
102   boolean seekBefore(byte[] key, int offset, int length) throws IOException;
103 
104   boolean seekBefore(Cell kv) throws IOException;
105   /**
106    * Positions this scanner at the start of the file.
107    * @return False if empty file; i.e. a call to next would return false and
108    * the current key and value are undefined.
109    * @throws IOException
110    */
111   boolean seekTo() throws IOException;
112   /**
113    * Scans to the next entry in the file.
114    * @return Returns false if you are at the end otherwise true if more in file.
115    * @throws IOException
116    */
117   boolean next() throws IOException;
118   /**
119    * Gets a buffer view to the current key. You must call
120    * {@link #seekTo(byte[])} before this method.
121    * @return byte buffer for the key. The limit is set to the key size, and the
122    * position is 0, the start of the buffer view.
123    */
124   ByteBuffer getKey();
125   /**
126    * Gets a buffer view to the current value.  You must call
127    * {@link #seekTo(byte[])} before this method.
128    *
129    * @return byte buffer for the value. The limit is set to the value size, and
130    * the position is 0, the start of the buffer view.
131    */
132   ByteBuffer getValue();
133   /**
134    * @return Instance of {@link org.apache.hadoop.hbase.KeyValue}.
135    */
136   Cell getKeyValue();
137   /**
138    * Convenience method to get a copy of the key as a string - interpreting the
139    * bytes as UTF8. You must call {@link #seekTo(byte[])} before this method.
140    * @return key as a string
141    */
142   String getKeyString();
143   /**
144    * Convenience method to get a copy of the value as a string - interpreting
145    * the bytes as UTF8. You must call {@link #seekTo(byte[])} before this method.
146    * @return value as a string
147    */
148   String getValueString();
149   /**
150    * @return Reader that underlies this Scanner instance.
151    */
152   HFile.Reader getReader();
153   /**
154    * @return True is scanner has had one of the seek calls invoked; i.e.
155    * {@link #seekBefore(byte[])} or {@link #seekTo()} or {@link #seekTo(byte[])}.
156    * Otherwise returns false.
157    */
158   boolean isSeeked();
159 }