org.apache.hadoop.hbase.io.hfile.HFileScanner Maven / Gradle / Ivy
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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();
}