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/**
 *
 * 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.hadoop.hbase.io.hfile;

import java.io.IOException;
import java.nio.ByteBuffer;

import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.Cell;

/**
 * A scanner allows you to position yourself within a HFile and
 * scan through it.  It allows you to reposition yourself as well.
 *
 * 

A scanner doesn't always have a key/value that it is pointing to * when it is first created and before * {@link #seekTo()}/{@link #seekTo(byte[])} are called. * In this case, {@link #getKey()}/{@link #getValue()} returns null. At most * other times, a key and value will be available. The general pattern is that * you position the Scanner using the seekTo variants and then getKey and * getValue. */ @InterfaceAudience.Private public interface HFileScanner { /** * SeekTo or just before the passed key. Examine the return * code to figure whether we found the key or not. * Consider the key stream of all the keys in the file, * k[0] .. k[n], where there are n keys in the file. * @param key Key to find. * @return -1, if key < k[0], no position; * 0, such that k[i] = key and scanner is left in position i; and * 1, such that k[i] < key, and scanner is left in position i. * The scanner will position itself between k[i] and k[i+1] where * k[i] < key <= k[i+1]. * If there is no key k[i+1] greater than or equal to the input key, then the * scanner will position itself at the end of the file and next() will return * false when it is called. * @throws IOException */ @Deprecated int seekTo(byte[] key) throws IOException; @Deprecated int seekTo(byte[] key, int offset, int length) throws IOException; int seekTo(Cell c) throws IOException; /** * Reseek to or just before the passed key. Similar to seekTo * except that this can be called even if the scanner is not at the beginning * of a file. * This can be used to seek only to keys which come after the current position * of the scanner. * Consider the key stream of all the keys in the file, * k[0] .. k[n], where there are n keys in the file after * current position of HFileScanner. * The scanner will position itself between k[i] and k[i+1] where * k[i] < key <= k[i+1]. * If there is no key k[i+1] greater than or equal to the input key, then the * scanner will position itself at the end of the file and next() will return * false when it is called. * @param key Key to find (should be non-null) * @return -1, if key < k[0], no position; * 0, such that k[i] = key and scanner is left in position i; and * 1, such that k[i] < key, and scanner is left in position i. * @throws IOException */ @Deprecated int reseekTo(byte[] key) throws IOException; @Deprecated int reseekTo(byte[] key, int offset, int length) throws IOException; int reseekTo(Cell c) throws IOException; /** * Consider the key stream of all the keys in the file, * k[0] .. k[n], where there are n keys in the file. * @param key Key to find * @return false if key <= k[0] or true with scanner in position 'i' such * that: k[i] < key. Furthermore: there may be a k[i+1], such that * k[i] < key <= k[i+1] but there may also NOT be a k[i+1], and next() will * return false (EOF). * @throws IOException */ @Deprecated boolean seekBefore(byte[] key) throws IOException; @Deprecated boolean seekBefore(byte[] key, int offset, int length) throws IOException; boolean seekBefore(Cell kv) throws IOException; /** * Positions this scanner at the start of the file. * @return False if empty file; i.e. a call to next would return false and * the current key and value are undefined. * @throws IOException */ boolean seekTo() throws IOException; /** * Scans to the next entry in the file. * @return Returns false if you are at the end otherwise true if more in file. * @throws IOException */ boolean next() throws IOException; /** * Gets a buffer view to the current key. You must call * {@link #seekTo(byte[])} before this method. * @return byte buffer for the key. The limit is set to the key size, and the * position is 0, the start of the buffer view. */ ByteBuffer getKey(); /** * Gets a buffer view to the current value. You must call * {@link #seekTo(byte[])} before this method. * * @return byte buffer for the value. The limit is set to the value size, and * the position is 0, the start of the buffer view. */ ByteBuffer getValue(); /** * @return Instance of {@link org.apache.hadoop.hbase.KeyValue}. */ Cell getKeyValue(); /** * Convenience method to get a copy of the key as a string - interpreting the * bytes as UTF8. You must call {@link #seekTo(byte[])} before this method. * @return key as a string */ String getKeyString(); /** * Convenience method to get a copy of the value as a string - interpreting * the bytes as UTF8. You must call {@link #seekTo(byte[])} before this method. * @return value as a string */ String getValueString(); /** * @return Reader that underlies this Scanner instance. */ HFile.Reader getReader(); /** * @return True is scanner has had one of the seek calls invoked; i.e. * {@link #seekBefore(byte[])} or {@link #seekTo()} or {@link #seekTo(byte[])}. * Otherwise returns false. */ boolean isSeeked(); /** * @return the next key in the index (the key to seek to the next block) */ Cell getNextIndexedKey(); /** * Close the stream socket to handle RS CLOSE_WAIT. HBASE-9393 */ void close(); }





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