/**
*
* 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.Closeable;
import java.io.IOException;
import java.nio.ByteBuffer;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.regionserver.Shipper;
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.
*
* <p>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(Cell)} 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 extends Shipper, Closeable {
/**
* SeekTo or just before the passed <code>cell</code>. Examine the return
* code to figure whether we found the cell or not.
* Consider the cell stream of all the cells in the file,
* <code>c[0] .. c[n]</code>, where there are n cells in the file.
* @param cell
* @return -1, if cell < c[0], no position;
* 0, such that c[i] = cell and scanner is left in position i; and
* 1, such that c[i] < cell, and scanner is left in position i.
* The scanner will position itself between c[i] and c[i+1] where
* c[i] < cell <= c[i+1].
* If there is no cell c[i+1] greater than or equal to the input cell, then the
* scanner will position itself at the end of the file and next() will return
* false when it is called.
* @throws IOException
*/
int seekTo(Cell cell) throws IOException;
/**
* Reseek to or just before the passed <code>cell</code>. 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 cells which come after the current position
* of the scanner.
* Consider the cell stream of all the cells in the file,
* <code>c[0] .. c[n]</code>, where there are n cellc in the file after
* current position of HFileScanner.
* The scanner will position itself between c[i] and c[i+1] where
* c[i] < cell <= c[i+1].
* If there is no cell c[i+1] greater than or equal to the input cell, then the
* scanner will position itself at the end of the file and next() will return
* false when it is called.
* @param cell Cell to find (should be non-null)
* @return -1, if cell < c[0], no position;
* 0, such that c[i] = cell and scanner is left in position i; and
* 1, such that c[i] < cell, and scanner is left in position i.
* @throws IOException
*/
int reseekTo(Cell cell) throws IOException;
/**
* Consider the cell stream of all the cells in the file,
* <code>c[0] .. c[n]</code>, where there are n cells in the file.
* @param cell Cell to find
* @return false if cell <= c[0] or true with scanner in position 'i' such
* that: c[i] < cell. Furthermore: there may be a c[i+1], such that
* c[i] < cell <= c[i+1] but there may also NOT be a c[i+1], and next() will
* return false (EOF).
* @throws IOException
*/
boolean seekBefore(Cell cell) 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 the current key in the form of a cell. You must call
* {@link #seekTo(Cell)} before this method.
* @return gets the current key as a Cell.
*/
Cell getKey();
/**
* Gets a buffer view to the current value. You must call
* {@link #seekTo(Cell)} 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.Cell}.
*/
Cell getCell();
/**
* Convenience method to get a copy of the key as a string - interpreting the
* bytes as UTF8. You must call {@link #seekTo(Cell)} before this method.
* @return key as a string
* @deprecated Since hbase-2.0.0
*/
@Deprecated
String getKeyString();
/**
* Convenience method to get a copy of the value as a string - interpreting
* the bytes as UTF8. You must call {@link #seekTo(Cell)} before this method.
* @return value as a string
* @deprecated Since hbase-2.0.0
*/
@Deprecated
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(Cell)} or {@link #seekTo()} or {@link #seekTo(Cell)}.
* Otherwise returns false.
*/
boolean isSeeked();
/**
* @return the next key in the index (the key to seek to the next block)
*/
Cell getNextIndexedKey();
/**
* Close this HFile scanner and do necessary cleanup.
*/
void close();
}