1 /* 2 * Copyright (c) 1997, 2001, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package sun.rmi.log; 27 28 import java.io.*; 29 import sun.rmi.server.MarshalOutputStream; 30 import sun.rmi.server.MarshalInputStream; 31 32 /** 33 * A LogHandler represents snapshots and update records as serializable 34 * objects. 35 * 36 * This implementation does not know how to create an initial snaphot or 37 * apply an update to a snapshot. The client must specifiy these methods 38 * via a subclass. 39 * 40 * @see ReliableLog 41 * 42 * @author Ann Wollrath 43 */ 44 public abstract 45 class LogHandler { 46 47 /** 48 * Creates a LogHandler for a ReliableLog. 49 */ LogHandler()50 public LogHandler() {} 51 52 /** 53 * Creates and returns the initial state of data structure that needs 54 * to be stably stored. This method is called when a ReliableLog is 55 * created. 56 * @return the initial state 57 * @exception Exception can raise any exception 58 */ 59 public abstract initialSnapshot()60 Object initialSnapshot() throws Exception; 61 62 /** 63 * Writes the snapshot object to a stream. This callback is 64 * invoked when the client calls the snaphot method of ReliableLog. 65 * @param out the output stream 66 * @param value the snapshot 67 * @exception Exception can raise any exception 68 */ 69 public snapshot(OutputStream out, Object value)70 void snapshot(OutputStream out, Object value) throws Exception { 71 MarshalOutputStream s = new MarshalOutputStream(out); 72 s.writeObject(value); 73 s.flush(); 74 } 75 76 /** 77 * Read the snapshot object from a stream and returns the snapshot. 78 * This callback is invoked when the client calls the recover method 79 * of ReliableLog. 80 * @param in the input stream 81 * @return the state (snapshot) 82 * @exception Exception can raise any exception 83 */ 84 85 public recover(InputStream in)86 Object recover(InputStream in) throws Exception { 87 MarshalInputStream s = new MarshalInputStream(in); 88 return s.readObject(); 89 } 90 91 /** 92 * Writes the representation (a serializable object) of an update 93 * to a stream. This callback is invoked when the client calls the 94 * update method of ReliableLog. 95 * @param out the output stream 96 * @param value the snapshot 97 * @exception Exception can raise any exception 98 */ 99 public writeUpdate(LogOutputStream out, Object value)100 void writeUpdate(LogOutputStream out, Object value) throws Exception { 101 102 MarshalOutputStream s = new MarshalOutputStream(out); 103 s.writeObject(value); 104 s.flush(); 105 } 106 107 /** 108 * Reads a stably logged update (a serializable object) from a 109 * stream. This callback is invoked during recovery, once for 110 * every record in the log. After reading the update, this method 111 * invokes the applyUpdate (abstract) method in order to obtain 112 * the new snapshot value. It then returns the new snapshot. 113 * 114 * @param in the input stream 115 * @param state the current state 116 * @return the new state 117 * @exception Exception can raise any exception 118 */ 119 public readUpdate(LogInputStream in, Object state)120 Object readUpdate(LogInputStream in, Object state) throws Exception { 121 MarshalInputStream s = new MarshalInputStream(in); 122 return applyUpdate(s.readObject(), state); 123 } 124 125 /** 126 * Reads a stably logged update (a serializable object) from a stream. 127 * This callback is invoked during recovery, once for every record in the 128 * log. After reading the update, this method is invoked in order to 129 * obtain the new snapshot value. The method should apply the update 130 * object to the current state <code>state</code> and return the new 131 * state (the new snapshot value). 132 * @param update the update object 133 * @param state the current state 134 * @return the new state 135 * @exception Exception can raise any exception 136 */ 137 public abstract applyUpdate(Object update, Object state)138 Object applyUpdate(Object update, Object state) throws Exception; 139 140 } 141