The synchronization mechanism that provides reader/writer capabilities for disconnected RowSet objects.

  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:

• Using a constructor
  

         CachedRowSet crs = new CachedRowSet(
                    "com.fred.providers.HighAvailabilitySyncProvider"); 
        

• Using the setSyncProvider method

         CachedRowSet crs = new CachedRowSet(); 
         crs.setSyncProvider("com.fred.providers.HighAvailabilitySyncProvider"); 
        

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.

1. 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
2. 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
3. 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