Java tutorial
/** * 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 com.facebook.infrastructure.db; import java.util.concurrent.atomic.AtomicInteger; import java.io.ByteArrayInputStream; import java.io.DataOutputStream; import java.io.DataInputStream; import java.io.IOException; import com.facebook.infrastructure.io.ICompactSerializer; import org.apache.commons.lang.ArrayUtils; /* * An instance of this class represents an update to a table. * This is written to the CommitLog to be replayed on recovery. It * contains enough information to be written to a SSTable to * capture events that happened before some catastrophe. * * Author : Avinash Lakshman ( alakshman@facebook.com) & Prashant Malik ( pmalik@facebook.com ) */ class CommitLogEntry { private static AtomicInteger lsnGenerator_ = new AtomicInteger(0); private static ICompactSerializer<CommitLogEntry> serializer_; static { serializer_ = new CommitLogEntrySerializer(); } static ICompactSerializer<CommitLogEntry> serializer() { return serializer_; } private int length_; private byte[] value_ = ArrayUtils.EMPTY_BYTE_ARRAY; CommitLogEntry() { } CommitLogEntry(byte[] value) { this(value, 0); } CommitLogEntry(byte[] value, int length) { value_ = value; length_ = length; } void value(byte[] bytes) { value_ = bytes; } byte[] value() { return value_; } void length(int size) { length_ = size; } int length() { return length_; } } class CommitLogEntrySerializer implements ICompactSerializer<CommitLogEntry> { public void serialize(CommitLogEntry logEntry, DataOutputStream dos) throws IOException { int length = logEntry.length(); dos.writeInt(length); dos.write(logEntry.value(), 0, length); } public CommitLogEntry deserialize(DataInputStream dis) throws IOException { byte[] value = new byte[dis.readInt()]; dis.readFully(value); return new CommitLogEntry(value); } }