1 <!DOCTYPE doctype PUBLIC "-//w3c//dtd html 4.0 transitional//en"> 2 <html> 3 <head> 4 5 <meta http-equiv="Content-Type" 6 content="text/html; charset=iso-8859-1"> 7 8 <meta name="GENERATOR" 9 content="Mozilla/4.79 [en] (Windows NT 5.0; U) [Netscape]"> 10 <!-- 11 12 Copyright (c) 2003, 2006, Oracle and/or its affiliates. All rights reserved. 13 DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 14 15 This code is free software; you can redistribute it and/or modify it 16 under the terms of the GNU General Public License version 2 only, as 17 published by the Free Software Foundation. Oracle designates this 18 particular file as subject to the "Classpath" exception as provided 19 by Oracle in the LICENSE file that accompanied this code. 20 21 This code is distributed in the hope that it will be useful, but WITHOUT 22 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 23 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 24 version 2 for more details (a copy is included in the LICENSE file that 25 accompanied this code). 26 27 You should have received a copy of the GNU General Public License version 28 2 along with this work; if not, write to the Free Software Foundation, 29 Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 30 31 Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 32 or visit www.oracle.com if you need additional information or have any 33 questions. 34 --> 35 <title>javax.sql.rowset.providers Package</title> 36 </head> 37 <body bgcolor="#ffffff"> 38 Repository for the <code>RowSet</code> reference implementations of the 39 <code>SyncProvider</code> abstract class. These implementations provide a 40 disconnected <code>RowSet</code> 41 object with the ability to synchronize the data in the underlying data 42 source with its data. These implementations are provided as 43 the default <code>SyncProvider</code> implementations and are accessible via the 44 <code>SyncProvider</code> SPI managed by the <code>SyncFactory</code>. 45 46 <h3>1.0 <code>SyncProvider</code> Reference Implementations</h3> 47 The main job of a <code>SyncProvider</code> implementation is to manage 48 the reader and writer mechanisms. 49 The <code>SyncProvider</code> SPI, as specified in the <code>javax.sql.rowset.spi</code> 50 package, provides a pluggable mechanism by which <code>javax.sql.RowSetReader</code> 51 and <code>javax.sql.RowSetWriter</code> implementations can be supplied to a disconnected 52 <code>RowSet</code> object. 53 <P> 54 A reader, a <code>javax.sql.RowSetReader</code> 55 object, does the work necessary to populate a <code>RowSet</code> object with data. 56 A writer, a <code>javax.sql.RowSetWriter</code> object, does the work necessary for 57 synchronizing a <code>RowSet</code> object's data with the data in the originating 58 source of data. Put another way, a writer writes a <code>RowSet</code> 59 object's data back to the data source. 60 <P> 61 Generally speaking, the course of events is this. The reader makes a connection to 62 the data source and reads the data from a <code>ResultSet</code> object into its 63 <code>RowSet</code> object. Then it closes the connection. While 64 the <code>RowSet</code> object is disconnected, an application makes some modifications 65 to the data and calls the method <code>acceptChanges</code>. At this point, the 66 writer is called to write the changes back to the database table or view 67 from which the original data came. This is called <i>synchronization</i>. 68 <P> 69 If the data in the originating data source has not changed, there is no problem 70 with just writing the <code>RowSet</code> object's new data to the data source. 71 If it has changed, however, there is a conflict that needs to be resolved. One 72 way to solve the problem is not to let the data in the data source be changed in 73 the first place, which can be done by setting locks on a row, a table, or the 74 whole data source. Setting locks is a way to avoid conflicts, but it can be 75 very expensive. Another approach, which is at the other end of the spectrum, 76 is simply to assume that no conflicts will occur and thus do nothing to avoid 77 conflicts. 78 Different <code>SyncProvider</code> implementations may handle synchronization in 79 any of these ways, varying from doing no checking for 80 conflicts, to doing various levels of checking, to guaranteeing that there are no 81 conflicts. 82 <P> 83 The <code>SyncProvider</code> class offers methods to help a <code>RowSet</code> 84 object discover and manage how a provider handles synchronization. 85 The method <code>getProviderGrade</code> returns the 86 grade of synchronization a provider offers. An application can 87 direct the provider to use a particular level of locking by calling 88 the method <code>setDataSourceLock</code> and specifying the level of locking desired. 89 If a <code>RowSet</code> object's data came from an SQL <code>VIEW</code>, an 90 application may call the method <code>supportsUpdatableView</code> to 91 find out whether the <code>VIEW</code> can be updated. 92 <P> 93 Synchronization is done completely behind the scenes, so it is third party vendors of 94 synchronization provider implementations who have to take care of this complex task. 95 Application programmers can decide which provider to use and the level of locking to 96 be done, but they are free from having to worry about the implementation details. 97 <P> 98 The JDBC <code>RowSet</code> Implementations reference implementation provides two 99 implementations of the <code>SyncProvider</code> class: 100 101 <UL> 102 <LI> 103 <b><code>RIOptimisticProvider</code></b> - provides the <code>javax.sql.RowSetReader</code> 104 and <code>javax.sql.RowSetWriter</code> interface implementations and provides 105 an optimistic concurrency model for synchronization. This model assumes that there 106 will be few conflicts and therefore uses a relatively low grade of synchronization. 107 If no other provider is available, this is the default provider that the 108 <code>SyncFactory</code> will supply to a <code>RowSet</code> object. 109 <br> 110 <LI> 111 <b><code>RIXMLProvider</code></b> - provides the <code>XmlReader</code> (an extension 112 of the <code>javax.sql.RowSetReader</code> interface) and the <code>XmlWriter</code> 113 (an extension of the <code>javax.sql.RowSetWriter</code> interface) to enable 114 <code>WebRowSet</code> objects to write their state to a 115 well formed XML document according to the <code>WebRowSet</code> XML schema 116 definition.<br> 117 </UL> 118 119 <h3>2.0 Basics in RowSet Population & Synchronization</h3> 120 A rowset's first task is to populate itself with rows of column values. 121 Generally, these rows will come from a relational database, so a rowset 122 has properties that supply what is necessary for making a connection to 123 a database and executing a query. A rowset that does not need to establish 124 a connection and execute a command, such as one that gets its data from 125 a tabular file instead of a relational database, does not need to have these 126 properties set. The vast majority of RowSets, however, do need to set these 127 properties. The general rule is that a RowSet is required to set only the 128 properties that it uses.<br> 129 <br> 130 The <code>command</code> property contains the query that determines what 131 data a <code>RowSet</code> will contain. Rowsets have methods for setting a query's 132 parameter(s), which means that a query can be executed multiple times with 133 different parameters to produce different result sets. Or the query can be 134 changed to something completely new to get a new result set. 135 <p>Once a rowset contains the rows from a <code>ResultSet</code> object or some 136 other data source, its column values can be updated, and its rows can be 137 inserted or deleted. Any method that causes a change in the rowset's values 138 or cursor position also notifies any object that has been registered as 139 a listener with the rowset. So, for example, a table that displays the rowset's 140 data in an applet can be notified of changes and make updates as they 141 occur.<br> 142 <br> 143 The changes made to a rowset can be propagated back to the original data 144 source to keep the rowset and its data source synchronized. Although this 145 involves many operations behind the scenes, it is completely transparent 146 to the application programmer and remains the concern of the RowSet provider 147 developer. All an application has to do is invoke the method <code>acceptChanges</code>, 148 and the data source backing the rowset will be updated to match the current 149 values in the rowset. </p> 150 151 <p>A disconnected rowset, such as a <code>CachedRowSet</code> or <code>WebRowSet</code> 152 object, establishes a connection to populate itself with data from a database 153 and then closes the connection. The <code>RowSet</code> object will remain 154 disconnected until it wants to propagate changes back to its database table, 155 which is optional. To write its changes back to the database (synchronize with 156 the database), the rowset establishes a connection, write the changes, and then 157 once again disconnects itself.<br> 158 </p> 159 160 <h3> 3.0 Other Possible Implementations</h3> 161 There are many other possible implementations of the <code>SyncProvider</code> abstract 162 class. One possibility is to employ a more robust synchronization model, which 163 would give a <code>RowSet</code> object increased trust in the provider's 164 ability to get any updates back to the original data source. Another possibility 165 is a more formal synchronization mechanism such as SyncML 166 (<a href="http://www.syncml.org/">http://www.syncml.org/</a>) <br> 167 <br> 168 <br> 169 </body> 170 </html>