| author | ohair |
| Wed, 26 May 2010 20:28:04 -0700 | |
| changeset 5551 | 327690766109 |
| parent 5506 | 202f599c92aa |
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Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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6956202: Fix a few missed rebranding issues, please contact lines etc.
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or visit www.oracle.com if you need additional information or have any |
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questions. |
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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> |