View Providers

Author: Victor Roldan Betancort

A view provider allows clients to inject custom logic into the resource factory mechansim, capable of handling the whole session and view instantiation process. This permits to obtain resources through the resource set API transparently, without any prior CDO client API code. The view provider automatically kicks in the middle of the ResourceSet.getResource() call, forgetting about the whole openning session / openning transaction process, which happens behind the scenes.

This is quite useful when integrating CDO with EMF-based frameworks and tools that are not prepared for a CDO scenario themselves.

Table of Contents

1  Implementing a View Provider

Clients should implement the CDOViewProvider interface, or sub class the AbstractCDOViewProvider class, which provides common functionality.

The example below shows a simple implementation that opens a new session to a local server and a new transaction on that session.

	ExampleViewProvider.java
new AbstractCDOViewProvider("cdo\\.local:.*", 100) {   private IManagedContainer container;    @Override   public CDOView getView(URI uri, ResourceSet resourceSet)   {     if (container == null)     {       container = new ManagedContainer();       Net4jUtil.prepareContainer(container);       TCPUtil.prepareContainer(container);       container.activate();     }     int startIndex = uri.toString().indexOf(':');     String repoName = uri.toString().substring(startIndex);     IConnector connector = (IConnector)container.getElement("org.eclipse.net4j.connectors", "tcp", "localhost");     CDONet4jSessionConfiguration config = CDONet4jUtil.createNet4jSessionConfiguration();     config.setConnector(connector);     config.setRepositoryName(repoName);     CDOSession session = config.openNet4jSession();     return session.openTransaction();   } };

 The example provider catches all URIs with shape "cdo.local:".

 Register the provider with CDOViewProviderRegistry.

2  Contributing View Providers Programmatically

A client's view provider implementation can be contributed programmatically to the CDOViewProviderRegistry, as the following example suggests:

	ProviderContribution.java
// Instantiate your view provider CDOViewProvider viewProvider =  org.eclipse.emf.internal.cdo.view.PluginContainerViewProvider.INSTANCE; // Add the instance to the registry  CDOViewProviderRegistry.INSTANCE.addViewProvider(viewProvider);

 Get the target CDOViewProvider implementation.

 Add the provider instance to CDOViewProviderRegistry.

3  Contributing View Providers Using Extension Points

A specific CDOViewProvider implementation can also be contributed using the org.eclipse.emf.cdo.viewProviders extension point. Clients specify:

• A mandatory class implementing the CDOViewProvider interface.
• A mandatory regular expression string indicating the shape of URIs that should match with the contributed provider.
• An optional priority integer value, to indicate preference over other implementations matching the same regular expression. A higher value indicates a higher priority, Integer#MAX_VALUE being the maximum priority value and Integer#MIN_VALUE the minimum.