<!DOCTYPE doctype PUBLIC "-//w3c//dtd html 4.0 transitional//en"><html><head>                      <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">                      <meta name="GENERATOR" content="Mozilla/4.79 [en] (Windows NT 5.0; U) [Netscape]">     <!-- Copyright (c) 2003, 2006, Oracle and/or its affiliates. All rights reserved.DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. This code is free software; you can redistribute it and/or modify itunder the terms of the GNU General Public License version 2 only, aspublished by the Free Software Foundation.  Oracle designates thisparticular file as subject to the "Classpath" exception as providedby Oracle in the LICENSE file that accompanied this code. This code is distributed in the hope that it will be useful, but WITHOUTANY WARRANTY; without even the implied warranty of MERCHANTABILITY orFITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public Licenseversion 2 for more details (a copy is included in the LICENSE file thataccompanied this code). You should have received a copy of the GNU General Public License version2 along with this work; if not, write to the Free Software Foundation,Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USAor visit www.oracle.com if you need additional information or have anyquestions.-->  <title>javax.sql.rowset.providers Package</title></head>  <body bgcolor="#ffffff">  Repository for the <tt>RowSet</tt> reference implementations of the  <tt>SyncProvider</tt> abstract class. These implementations provide a  disconnected <code>RowSet</code> object with the ability to synchronize the data in the underlying data  source with its data.  These implementations are provided asthe default <tt>SyncProvider</tt> implementations and are accessible via the<tt>SyncProvider</tt> SPI managed by the <tt>SyncFactory</tt>.   <h3>1.0 <code>SyncProvider</code> Reference Implementations</h3>  The main job of a <tt>SyncProvider</tt> implementation is to managethe reader and writer mechanisms. The <tt>SyncProvider</tt> SPI, as specified in the <tt>javax.sql.rowset.spi</tt>package, provides a pluggable mechanism by which <tt>javax.sql.RowSetReader</tt>and <tt>javax.sql.RowSetWriter</tt> implementations can be supplied to a disconnected<tt>RowSet</tt> object.<P> A reader, a <code>javax.sql.RowSetReader</code>object, does the work necessary to populate a <code>RowSet</code> object with data.A writer, a <code>javax.sql.RowSetWriter</code> object, does the work necessary forsynchronizing a <code>RowSet</code> object's data with the data in the originatingsource of data. Put another way, a writer writes a <code>RowSet</code>object's data back to the data source. <P>Generally speaking, the course of events is this.  The reader makes a connection tothe data source and reads the data from a <code>ResultSet</code> object into its<code>RowSet</code> object.  Then it closes the connection.  While the <code>RowSet</code> object is disconnected, an application makes some modifications to the data and calls the method <code>acceptChanges</code>. At this point, thewriter is called to write the changes back to the database table or viewfrom which the original data came. This is called <i>synchronization</i>.<P>If the data in the originating data source has not changed, there is no problemwith just writing the <code>RowSet</code> object's new data to the data source.If it has changed, however, there is a conflict that needs to be resolved. Oneway to solve the problem is not to let the data in the data source be changed inthe first place, which can be done by setting locks on a row, a table, or the whole data source.  Setting locks is a way to avoid conflicts, but it can bevery expensive. Another approach, which is at the other end of the spectrum, is simply to assume that no conflicts will occur and thus do nothing to avoidconflicts.  Different <code>SyncProvider</code> implementations may handle synchronization inany of these ways, varying from doing no checking forconflicts, to doing various levels of checking, to guaranteeing that there are noconflicts. <P>The <code>SyncProvider</code> class offers methods to help a <code>RowSet</code>object discover and manage how a provider handles synchronization.The method <code>getProviderGrade</code> returns thegrade of synchronization a provider offers. An application can direct the provider to use a particular level of locking by callingthe method <code>setDataSourceLock</code> and specifying the level of locking desired.If a <code>RowSet</code> object's data came from an SQL <code>VIEW</code>, an application may call the method <code>supportsUpdatableView</code> to find out whether the <code>VIEW</code> can be updated.<P>Synchronization is done completely behind the scenes, so it is third party vendors ofsynchronization provider implementations who have to take care of this complex task.Application programmers can decide which provider to use and the level of locking tobe done, but they are free from having to worry about the implementation details.<P>The JDBC <code>RowSet</code> Implementations reference implementation provides twoimplementations of the <code>SyncProvider</code> class:   <UL><LI><b><tt>RIOptimisticProvider </tt></b>- provides the <tt>javax.sql.RowSetReader</tt> and <tt>javax.sql.RowSetWriter</tt> interface implementations and providesan optimistic concurrency model for synchronization. This model assumes that therewill be few conflicts and therefore uses a relatively low grade of synchronization.If no other provider is available, this is the default provider that the <code>SyncFactory</code> will supply to a <code>RowSet</code> object.    <br><LI>    <b><tt>RIXMLProvider </tt></b>- provides the <tt>XmlReader</tt> (an extensionof  the <tt>javax.sql.RowSetReader</tt> interface) and the <tt>XmlWriter</tt>(an extension of the <tt>javax.sql.RowSetWriter</tt> interface) to enable  <tt>WebRowSet</tt> objects to write their state to awell formed XML document according to the <tt>WebRowSet</tt> XML schemadefinition.<br></UL>   <h3>2.0 Basics in RowSet Population &amp; Synchronization</h3>  A rowset's first task is to populate itself with rows of column values.Generally,   these rows will come from a relational database, so a rowsethas properties   that supply what is necessary for making a connection toa database and executing  a query. A rowset that does not need to establisha connection and execute  a command, such as one that gets its data froma tabular file instead of a relational database, does not need to have theseproperties set. The vast  majority of RowSets, however, do need to set theseproperties. The general  rule is that a RowSet is required to set only theproperties that it uses.<br>    <br>    The <tt>command</tt> property contains the query that determines what data  a <code>RowSet</code> will contain. Rowsets have methods for setting a query's parameter(s),  which means that a query can be executed multiple times with different parameters  to produce different result sets. Or the query can bechanged to something  completely new to get a new result set.           <p>Once a rowset contains the rows from a <tt>ResultSet</tt> object or some  other data source, its column values can be updated, and its rows can be inserted or deleted. Any method that causes a change in the rowset's values or cursor position also notifies any object that has been registered asa  listener with the rowset. So, for example, a table that displays the rowset's data in an applet can can be notified of changes and make updates as they occur.<br>    <br>  The changes made to a rowset can be propagated back to the original data  source to keep the rowset and its data source synchronized. Although this  involves many operations behind the scenes, it is completely transparent  to the application programmer and remains the concern of the RowSet provider   developer. All an application has to do is invoke the method <tt>acceptChanges</tt>,   and the data source backing the rowset will be updated to match the current   values in the rowset. </p>       <p>A disconnected rowset, such as a <tt>CachedRowSet</tt> or <tt>WebRowSet</tt> object, establishes a connection to populate itself with data from a database  and then closes the connection. The <code>RowSet</code> object will remain  disconnected until it wants to propagate changes back to its database table,  which is optional. To write its changes back to the database (synchronize with the database), the rowset establishes a connection, write the changes, and then  once again disconnects itself.<br>  </p>      <h3> 3.0 Other Possible Implementations</h3> There are many other possible implementations of the <tt>SyncProvider</tt> abstract class. One possibility is to employ a more robust synchronization model, which would give a <code>RowSet</code> object increased trust in the provider's ability to get any updates back to the original data source. Another possibility  is a more formal synchronization mechanism such as SyncML (<a href="http://www.syncml.org/">http://www.syncml.org/</a>)   <br>    <br> <br></body></html>