The synchronization mechanism that provides reader/writer capabilities for
disconnected RowSet objects.
A SyncProvider implementation is a class that extends the
SyncProvider abstract class.
A SyncProvider implementation is
identified by a unique ID, which is its fully qualified class name.
This name must be registered with the
SyncFactory SPI, thus making the implementation available to
all RowSet implementations.
The factory mechanism in the reference implementation uses this name to instantiate
the implementation, which can then provide a RowSet object with its
reader (a javax.sql.RowSetReader object) and its writer (a
javax.sql.RowSetWriter object).
The Jdbc RowSet Implementations specification provides two
reference implementations of the SyncProvider abstract class:
RIOptimisticProvider and RIXMLProvider.
The RIOptimisticProvider can set any RowSet
implementation with a RowSetReader object and a
RowSetWriter object. However, only the RIXMLProvider
implementation can set an XmlReader object and an
XmlWriter object. A WebRowSet object uses the
XmlReader object to read data in XML format to populate itself with that
data. It uses the XmlWriter object to write itself to a stream or
java.io.Writer object in XML format.
1.0 Naming Convention for Implementations
As a guide to naming SyncProvider
implementations, the following should be noted:
- The name for a
SyncProvider implementation
is its fully qualified class name.
- It is recommended that vendors supply a
SyncProvider implementation in a package named providers.
For instance, if a vendor named Fred, Inc. offered a
SyncProvider implementation, you could have the following:
Vendor name: Fred, Inc.
Domain name of vendor: com.fred
Package name: com.fred.providers
SyncProvider implementation class name: HighAvailabilityProvider
Fully qualified class name of SyncProvider implementation:
com.fred.providers.HighAvailabilityProvider
The following line of code uses the fully qualified name to register
this implementation with the SyncFactory static instance.
SyncFactory.registerProvider(
"com.fred.providers.HighAvailabilityProvider");
The default SyncProvider object provided with the reference
implementation uses the following name:
com.sun.rowset.providers.RIOptimisticProvider
A vendor can register a SyncProvider implementation class name
with Sun Microsystems, Inc. by sending email to jdbc@sun.com.
Sun will maintain a database listing the
available SyncProvider implementations for use with compliant
RowSet implementations. This database will be similar to the
one already maintained to list available JDBC drivers.
Vendors should refer to the reference implementation synchronization
providers for additional guidance on how to implement a new
SyncProvider implementation.
2.0 How a RowSet Object Gets Its Provider
A disconnected Rowset object may get access to a
SyncProvider object in one of the following two ways:
By default, the reference implementations of the RowSet synchronization
providers are always available to the Java platform.
If no other pluggable synchronization providers have been correctly
registered, the SyncFactory will automatically generate
an instance of the default SyncProvider reference implementation.
Thus, in the preceding code fragment, if no implementation named
com.fred.providers.HighAvailabilitySyncProvider has been
registered with the SyncFactory instance, crs will be
assigned the default provider in the reference implementation, which is
com.sun.rowset.providers.RIOptimisticProvider.
3.0 Violations and Synchronization Issues
If an update between a disconnected RowSet object
and a data source violates
the original query or the underlying data source constraints, this will
result in undefined behavior for all disconnected RowSet implementations
and their designated SyncProvider implementations.
Not defining the behavior when such violations occur offers greater flexibility
for a SyncProvider
implementation to determine its own best course of action.
A SyncProvider implementation
may choose to implement a specific handler to
handle a subset of query violations.
However if an original query violation or a more general data source constraint
violation is not handled by the SyncProvider implementation,
all SyncProvider
objects must throw a SyncProviderException.
4.0 Updatable SQL VIEWs
It is possible for any disconnected or connected RowSet object to be populated
from an SQL query that is formulated originally from an SQL VIEW.
While in many cases it is possible for an update to be performed to an
underlying view, such an update requires additional metadata, which may vary.
The SyncProvider class provides two constants to indicate whether
an implementation supports updating an SQL VIEW.
NONUPDATABLE_VIEW_SYNC - Indicates that a SyncProvider
implementation does not support synchronization with an SQL VIEW as the
underlying source of data for the RowSet object.
UPDATABLE_VIEW_SYNC - Indicates that a
SyncProvider implementation
supports synchronization with an SQL VIEW as the underlying source
of data.
The default is for a RowSet object not to be updatable if it was
populated with data from an SQL VIEW.
5.0 SyncProvider Constants
The SyncProvider class provides three sets of constants that
are used as return values or parameters for SyncProvider methods.
SyncProvider objects may be implemented to perform synchronization
between a RowSet object and its underlying data source with varying
degrees of of care. The first group of constants indicate how synchronization
is handled. For example, GRADE_NONE indicates that a
SyncProvider object will not take any care to see what data is
valid and will simply write the RowSet data to the data source.
GRADE_MODIFIED_AT_COMMIT indicates that the provider will check
only modified data for validity. Other grades check all data for validity
or set locks when data is modified or loaded.
- Constants to indicate the synchronization grade of a
SyncProvider object
- SyncProvider.GRADE_NONE
- SyncProvider.GRADE_MODIFIED_AT_COMMIT
- SyncProvider.GRADE_CHECK_ALL_AT_COMMIT
- SyncProvider.GRADE_LOCK_WHEN_MODIFIED
- SyncProvider.GRADE_LOCK_WHEN_LOADED
- Constants to indicate what locks are set on the data source
- SyncProvider.DATASOURCE_NO_LOCK
- SyncProvider.DATASOURCE_ROW_LOCK
- SyncProvider.DATASOURCE_TABLE_LOCK
- SyncProvider.DATASOURCE_DB_LOCK
- Constants to indicate whether a
SyncProvider object can
perform updates to an SQL VIEW
These constants are explained in the preceding section (4.0).
- SyncProvider.UPDATABLE_VIEW_SYNC
- SyncProvider.NONUPDATABLE_VIEW_SYNC
author:
Jonathan Bruce
See Also: javax.sql.rowset.spi.SyncFactory
See Also: javax.sql.rowset.spi.SyncFactoryException | 