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Copyright (c) 2003, 2006, Oracle and/or its affiliates. All rights reserved.
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DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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This code is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License version 2 only, as
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published by the Free Software Foundation. Oracle designates this
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particular file as subject to the "Classpath" exception as provided
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by Oracle in the LICENSE file that accompanied this code.
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This code is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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version 2 for more details (a copy is included in the LICENSE file that
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accompanied this code).
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You should have received a copy of the GNU General Public License version
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2 along with this work; if not, write to the Free Software Foundation,
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Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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CA 95054 USA or visit www.sun.com if you need additional information or
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have any questions.
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-->
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<title>javax.sql.rowset.providers Package</title>
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</head>
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<body bgcolor="#ffffff">
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Repository for the <tt>RowSet</tt> reference implementations of the
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<tt>SyncProvider</tt> abstract class. These implementations provide a
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disconnected <code>RowSet</code>
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object with the ability to synchronize the data in the underlying data
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source with its data. These implementations are provided as
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the default <tt>SyncProvider</tt> implementations and are accessible via the
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<tt>SyncProvider</tt> SPI managed by the <tt>SyncFactory</tt>.
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<h3>1.0 <code>SyncProvider</code> Reference Implementations</h3>
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The main job of a <tt>SyncProvider</tt> implementation is to manage
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the reader and writer mechanisms.
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The <tt>SyncProvider</tt> SPI, as specified in the <tt>javax.sql.rowset.spi</tt>
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package, provides a pluggable mechanism by which <tt>javax.sql.RowSetReader</tt>
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and <tt>javax.sql.RowSetWriter</tt> implementations can be supplied to a disconnected
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<tt>RowSet</tt> object.
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<P>
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A reader, a <code>javax.sql.RowSetReader</code>
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object, does the work necessary to populate a <code>RowSet</code> object with data.
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A writer, a <code>javax.sql.RowSetWriter</code> object, does the work necessary for
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synchronizing a <code>RowSet</code> object's data with the data in the originating
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source of data. Put another way, a writer writes a <code>RowSet</code>
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object's data back to the data source.
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<P>
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Generally speaking, the course of events is this. The reader makes a connection to
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the data source and reads the data from a <code>ResultSet</code> object into its
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<code>RowSet</code> object. Then it closes the connection. While
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the <code>RowSet</code> object is disconnected, an application makes some modifications
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to the data and calls the method <code>acceptChanges</code>. At this point, the
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writer is called to write the changes back to the database table or view
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from which the original data came. This is called <i>synchronization</i>.
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<P>
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If the data in the originating data source has not changed, there is no problem
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with just writing the <code>RowSet</code> object's new data to the data source.
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If it has changed, however, there is a conflict that needs to be resolved. One
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way to solve the problem is not to let the data in the data source be changed in
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the first place, which can be done by setting locks on a row, a table, or the
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whole data source. Setting locks is a way to avoid conflicts, but it can be
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very expensive. Another approach, which is at the other end of the spectrum,
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is simply to assume that no conflicts will occur and thus do nothing to avoid
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conflicts.
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Different <code>SyncProvider</code> implementations may handle synchronization in
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any of these ways, varying from doing no checking for
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conflicts, to doing various levels of checking, to guaranteeing that there are no
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conflicts.
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<P>
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The <code>SyncProvider</code> class offers methods to help a <code>RowSet</code>
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object discover and manage how a provider handles synchronization.
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The method <code>getProviderGrade</code> returns the
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grade of synchronization a provider offers. An application can
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direct the provider to use a particular level of locking by calling
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the method <code>setDataSourceLock</code> and specifying the level of locking desired.
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If a <code>RowSet</code> object's data came from an SQL <code>VIEW</code>, an
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application may call the method <code>supportsUpdatableView</code> to
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find out whether the <code>VIEW</code> can be updated.
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<P>
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Synchronization is done completely behind the scenes, so it is third party vendors of
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synchronization provider implementations who have to take care of this complex task.
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Application programmers can decide which provider to use and the level of locking to
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be done, but they are free from having to worry about the implementation details.
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<P>
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The JDBC <code>RowSet</code> Implementations reference implementation provides two
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implementations of the <code>SyncProvider</code> class:
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<UL>
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<LI>
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<b><tt>RIOptimisticProvider </tt></b>- provides the <tt>javax.sql.RowSetReader</tt>
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and <tt>javax.sql.RowSetWriter</tt> interface implementations and provides
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an optimistic concurrency model for synchronization. This model assumes that there
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will be few conflicts and therefore uses a relatively low grade of synchronization.
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If no other provider is available, this is the default provider that the
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<code>SyncFactory</code> will supply to a <code>RowSet</code> object.
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<br>
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<LI>
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<b><tt>RIXMLProvider </tt></b>- provides the <tt>XmlReader</tt> (an extension
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of the <tt>javax.sql.RowSetReader</tt> interface) and the <tt>XmlWriter</tt>
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(an extension of the <tt>javax.sql.RowSetWriter</tt> interface) to enable
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<tt>WebRowSet</tt> objects to write their state to a
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well formed XML document according to the <tt>WebRowSet</tt> XML schema
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definition.<br>
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</UL>
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<h3>2.0 Basics in RowSet Population & Synchronization</h3>
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A rowset's first task is to populate itself with rows of column values.
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Generally, these rows will come from a relational database, so a rowset
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has properties that supply what is necessary for making a connection to
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a database and executing a query. A rowset that does not need to establish
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a connection and execute a command, such as one that gets its data from
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a tabular file instead of a relational database, does not need to have these
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properties set. The vast majority of RowSets, however, do need to set these
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properties. The general rule is that a RowSet is required to set only the
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properties that it uses.<br>
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<br>
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The <tt>command</tt> property contains the query that determines what
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data a <code>RowSet</code> will contain. Rowsets have methods for setting a query's
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parameter(s), which means that a query can be executed multiple times with
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different parameters to produce different result sets. Or the query can be
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changed to something completely new to get a new result set.
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<p>Once a rowset contains the rows from a <tt>ResultSet</tt> object or some
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other data source, its column values can be updated, and its rows can be
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inserted or deleted. Any method that causes a change in the rowset's values
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or cursor position also notifies any object that has been registered as
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a listener with the rowset. So, for example, a table that displays the rowset's
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data in an applet can can be notified of changes and make updates as they
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occur.<br>
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<br>
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The changes made to a rowset can be propagated back to the original data
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source to keep the rowset and its data source synchronized. Although this
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involves many operations behind the scenes, it is completely transparent
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to the application programmer and remains the concern of the RowSet provider
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developer. All an application has to do is invoke the method <tt>acceptChanges</tt>,
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and the data source backing the rowset will be updated to match the current
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values in the rowset. </p>
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<p>A disconnected rowset, such as a <tt>CachedRowSet</tt> or <tt>WebRowSet</tt>
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object, establishes a connection to populate itself with data from a database
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and then closes the connection. The <code>RowSet</code> object will remain
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disconnected until it wants to propagate changes back to its database table,
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which is optional. To write its changes back to the database (synchronize with
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the database), the rowset establishes a connection, write the changes, and then
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once again disconnects itself.<br>
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</p>
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<h3> 3.0 Other Possible Implementations</h3>
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There are many other possible implementations of the <tt>SyncProvider</tt> abstract
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class. One possibility is to employ a more robust synchronization model, which
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would give a <code>RowSet</code> object increased trust in the provider's
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ability to get any updates back to the original data source. Another possibility
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is a more formal synchronization mechanism such as SyncML
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(<a href="http://www.syncml.org/">http://www.syncml.org/</a>) <br>
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<br>
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<br>
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</body>
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</html>
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