RowSetobject with the ability to synchronize the data in the underlying data source with its data. These implementations are provided as the default SyncProvider implementations and are accessible via the SyncProvider SPI managed by the SyncFactory.
A reader, a
object, does the work necessary to populate a
RowSet object with data.
A writer, a
javax.sql.RowSetWriter object, does the work necessary for
RowSet object's data with the data in the originating
source of data. Put another way, a writer writes a
object's data back to the data source.
Generally speaking, the course of events is this. The reader makes a connection to
the data source and reads the data from a
ResultSet object into its
RowSet object. Then it closes the connection. While
RowSet object is disconnected, an application makes some modifications
to the data and calls the method
acceptChanges. At this point, the
writer is called to write the changes back to the database table or view
from which the original data came. This is called synchronization.
If the data in the originating data source has not changed, there is no problem
with just writing the
RowSet object's new data to the data source.
If it has changed, however, there is a conflict that needs to be resolved. One
way to solve the problem is not to let the data in the data source be changed in
the 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 be
very 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 avoid
SyncProvider implementations may handle synchronization in
any of these ways, varying from doing no checking for
conflicts, to doing various levels of checking, to guaranteeing that there are no
SyncProvider class offers methods to help a
object discover and manage how a provider handles synchronization.
getProviderGrade returns the
grade of synchronization a provider offers. An application can
direct the provider to use a particular level of locking by calling
setDataSourceLock and specifying the level of locking desired.
RowSet object's data came from an SQL
application may call the method
find out whether the
VIEW can be updated.
Synchronization is done completely behind the scenes, so it is third party vendors of synchronization provider implementations who have to take care of this complex task. Application programmers can decide which provider to use and the level of locking to be done, but they are free from having to worry about the implementation details.
RowSet Implementations reference implementation provides two
implementations of the
SyncFactorywill supply to a
RowSetwill 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 be changed to something completely new to get a new result set.
Once a rowset contains the rows from a ResultSet 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 as
a 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
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 acceptChanges, and the data source backing the rowset will be updated to match the current values in the rowset.
A disconnected rowset, such as a CachedRowSet or WebRowSet
object, establishes a connection to populate itself with data from a database
and then closes the connection. The
RowSet 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.
RowSetobject 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 (http://www.syncml.org/)
|RIOptimisticProvider||The reference implementation of a JDBC Rowset synchronization provider providing optimistic synchronization with a relational datastore using any JDBC technology-enabled driver.|
|RIXMLProvider||A reference implementation of a JDBC RowSet synchronization provider with the ability to read and write rowsets in well formed XML using the standard WebRowSet schema.|