001/* 002 * Licensed to the Apache Software Foundation (ASF) under one 003 * or more contributor license agreements. See the NOTICE file 004 * distributed with this work for additional information 005 * regarding copyright ownership. The ASF licenses this file 006 * to you under the Apache License, Version 2.0 (the 007 * "License"); you may not use this file except in compliance 008 * with the License. You may obtain a copy of the License at 009 * 010 * http://www.apache.org/licenses/LICENSE-2.0 011 * 012 * Unless required by applicable law or agreed to in writing, software 013 * distributed under the License is distributed on an "AS IS" BASIS, 014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 015 * See the License for the specific language governing permissions and 016 * limitations under the License. 017 */ 018package org.apache.hadoop.hbase.wal; 019 020import java.io.Closeable; 021import java.io.IOException; 022import org.apache.yetus.audience.InterfaceAudience; 023 024/** 025 * A one way WAL reader, without reset and seek support. 026 * <p/> 027 * In most cases you should use this interface to read WAL file, as the implementation is simple and 028 * robust. For replication, where we want to tail the WAL file which is currently being written, you 029 * should use {@link WALTailingReader} instead. 030 * @see WALTailingReader 031 */ 032@InterfaceAudience.Private 033public interface WALStreamReader extends Closeable { 034 035 /** 036 * Read the next entry in WAL. 037 * <p/> 038 * In most cases you should just use this method, especially when reading a closed wal file for 039 * splitting or printing. 040 */ 041 default WAL.Entry next() throws IOException { 042 return next(null); 043 } 044 045 /** 046 * Read the next entry in WAL, use the given {@link WAL.Entry} if not {@code null} to hold the 047 * data. 048 * <p/> 049 * Mainly used in MR. 050 * @param reuse the entry to be used for reading, can be {@code null} 051 */ 052 WAL.Entry next(WAL.Entry reuse) throws IOException; 053 054 /** 055 * Get the current reading position. 056 */ 057 long getPosition() throws IOException; 058 059 /** 060 * Override to remove the 'throws IOException' as we are just a reader. 061 */ 062 @Override 063 void close(); 064}