The Service Provider Interface (SPI) mechanism that generates SyncProvider instances to be used by disconnected RowSet objects.

  The Service Provider Interface (SPI) mechanism that generates SyncProvider instances to be used by disconnected RowSet objects. The SyncProvider instances in turn provide the javax.sql.RowSetReader object the RowSet object needs to populate itself with data and the javax.sql.RowSetWriter object it needs to propagate changes to its data back to the underlying data source.

Because the methods in the SyncFactory class are all static, there is only one SyncFactory object per Java VM at any one time. This ensures that there is a single source from which a RowSet implementation can obtain its SyncProvider implementation.

1.0 Overview

The SyncFactory class provides an internal registry of available synchronization provider implementations (SyncProvider objects). This registry may be queried to determine which synchronization providers are available. The following line of code gets an enumeration of the providers currently registered.

     java.util.Enumeration e = SyncFactory.getRegisteredProviders();
 

All standard RowSet implementations must provide at least two providers:

• an optimistic provider for use with a CachedRowSet implementation or an implementation derived from it
• an XML provider, which is used for reading and writing XML, such as with WebRowSet objects

Note that the JDBC RowSet Implementations include the SyncProvider implemtations RIOptimisticProvider and RIXmlProvider, which satisfy this requirement.

The SyncFactory class provides accessor methods to assist applications in determining which synchronization providers are currently registered with the SyncFactory.

Other methods let RowSet persistence providers be registered or de-registered with the factory mechanism. This allows additional synchronization provider implementations to be made available to RowSet objects at run time.

Applications can apply a degree of filtering to determine the level of synchronization that a SyncProvider implementation offers. The following criteria determine whether a provider is made available to a RowSet object:

1. If a particular provider is specified by a RowSet object, and the SyncFactory does not contain a reference to this provider, a SyncFactoryException is thrown stating that the synchronization provider could not be found.

2. If a RowSet implementation is instantiated with a specified provider and the specified provider has been properly registered, the requested provider is supplied. Otherwise a SyncFactoryException is thrown.

3. If a RowSet object does not specify a SyncProvider implementation and no additional SyncProvider implementations are available, the reference implementation providers are supplied.

2.0 Registering SyncProvider Implementations

Both vendors and developers can register SyncProvider implementations using one of the following mechanisms.

• Using the command line
  The name of the provider is supplied on the command line, which will add the provider to the system properties. For example:

   
      -Drowset.provider.classname=com.fred.providers.HighAvailabilityProvider
   

• Using the Standard Properties File
  The reference implementation is targeted to ship with J2SE 1.5, which will include an additional resource file that may be edited by hand. Here is an example of the properties file included in the reference implementation:

     #Default JDBC RowSet sync providers listing
     #
  
     # Optimistic synchronization provider
     rowset.provider.classname.0=com.sun.rowset.providers.RIOptimisticProvider
     rowset.provider.vendor.0=Sun Microsystems Inc
     rowset.provider.version.0=1.0
     
     # XML Provider using standard XML schema
     rowset.provider.classname.1=com.sun.rowset.providers.RIXMLProvider
     rowset.provider.vendor.1=Sun Microsystems Inc.
     rowset.provider.version.1=1.0
   

  The SyncFactory checks this file and registers the SyncProvider implementations that it contains. A developer or vendor can add other implementations to this file. For example, here is a possible addition:

       rowset.provider.classname.2=com.fred.providers.HighAvailabilityProvider
       rowset.provider.vendor.2=Fred, Inc.
       rowset.provider.version.2=1.0
   

• Using a JNDI Context
  Available providers can be registered on a JNDI context, and the SyncFactory will attempt to load SyncProvider implementations from that JNDI context. For example, the following code fragment registers a provider implementation on a JNDI context. This is something a deployer would normally do. In this example, MyProvider is being registered on a CosNaming namespace, which is the namespace used by J2EE resources.

      import javax.naming.*;
      
      Hashtable svrEnv = new  Hashtable();
      srvEnv.put(Context.INITIAL_CONTEXT_FACTORY, "CosNaming");
  
      Context ctx = new InitialContext(svrEnv);
      com.fred.providers.MyProvider = new MyProvider();
      ctx.rebind("providers/MyProvider", syncProvider);
   

Next, an application will register the JNDI context with the SyncFactory instance. This allows the SyncFactory to browse within the JNDI context looking for SyncProvider implementations.

    Hashtable appEnv = new Hashtable();
    appEnv.put(Context.INITIAL_CONTEXT_FACTORY, "CosNaming");
    appEnv.put(Context.PROVIDER_URL, "iiop://hostname/providers");
    Context ctx = new InitialContext(appEnv);

    SyncFactory.registerJNDIContext(ctx);
 

If a RowSet object attempts to obtain a MyProvider object, the SyncFactory will try to locate it. First it searches for it in the system properties, then it looks in the resource files, and finally it checks the JNDI context that has been set. The SyncFactory instance verifies that the requested provider is a valid extension of the SyncProvider abstract class and then gives it to the RowSet object. In the following code fragment, a new CachedRowSet object is created and initialized with env, which contains the binding to MyProvider.

    Hashtable env = new Hashtable();
    env.put(SyncFactory.ROWSET_SYNC_PROVIDER, "com.fred.providers.MyProvider");
    CachedRowSet crs = new com.sun.rowset.CachedRowSetImpl(env); 
 

Further details on these mechanisms are available in the javax.sql.rowset.spi package specification.