001 /** 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 package org.apache.kahadb.page; 018 019 import java.io.DataInput; 020 import java.io.DataOutput; 021 import java.io.IOException; 022 023 /** 024 * A Page within a file. 025 */ 026 public class Page<T> { 027 028 public static final int PAGE_HEADER_SIZE = 21; 029 030 public static final byte PAGE_FREE_TYPE = 0; 031 public static final byte PAGE_PART_TYPE = 1; 032 public static final byte PAGE_END_TYPE = 2; 033 034 long pageId; 035 036 // The following fields are persisted 037 byte type = PAGE_FREE_TYPE; 038 long txId; 039 // A field reserved to hold checksums.. Not in use (yet) 040 int checksum; 041 042 // Points to the next page in the chunk stream 043 long next; 044 T data; 045 046 public Page() { 047 } 048 049 public Page(long pageId) { 050 this.pageId=pageId; 051 } 052 053 public Page<T> copy(Page<T> other) { 054 this.pageId = other.pageId; 055 this.txId = other.txId; 056 this.type = other.type; 057 this.next = other.next; 058 this.data = other.data; 059 return this; 060 } 061 062 Page<T> copy() { 063 return new Page<T>().copy(this); 064 } 065 066 void makeFree(long txId) { 067 this.type = Page.PAGE_FREE_TYPE; 068 this.txId = txId; 069 this.data = null; 070 this.next = 0; 071 } 072 073 public void makePagePart(long next, long txId) { 074 this.type = Page.PAGE_PART_TYPE; 075 this.next = next; 076 this.txId = txId; 077 } 078 079 public void makePageEnd(long size, long txId) { 080 this.type = Page.PAGE_END_TYPE; 081 this.next = size; 082 this.txId = txId; 083 } 084 085 void write(DataOutput os) throws IOException { 086 os.writeByte(type); 087 os.writeLong(txId); 088 os.writeLong(next); 089 os.writeInt(checksum); 090 } 091 092 void read(DataInput is) throws IOException { 093 type = is.readByte(); 094 txId = is.readLong(); 095 next = is.readLong(); 096 checksum = is.readInt(); 097 } 098 099 public long getPageId() { 100 return pageId; 101 } 102 103 public long getTxId() { 104 return txId; 105 } 106 107 public T get() { 108 return data; 109 } 110 111 public void set(T data) { 112 this.data = data; 113 } 114 115 public short getType() { 116 return type; 117 } 118 119 public long getNext() { 120 return next; 121 } 122 123 public String toString() { 124 return "[Page:" + getPageId()+", type: "+type+"]"; 125 } 126 127 public int getChecksum() { 128 return checksum; 129 } 130 131 public void setChecksum(int checksum) { 132 this.checksum = checksum; 133 } 134 }