Explain how to use the Extension Point and Extensions. Refer1 Refer2 Refer3

1. Introduction

  • Extensions are the central mechanism for contribute behavior to the platform. We used it to contribute functionality to a certain type of API.
  • Extension points define new functions points for the platform that other plug-ins can plug into.
  • E.g. When you want to create modular that can be added or removed at runtime, you can use the OSGi service.
  • These extensions and extension points are defined via the plugin.xml file.

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2. Using Extension points/ Extensions

2.1. Create an EXTENSION POINT

  • A plugin which declares an extension point must declare the extension point in its plugin.xml.
  • It will contain code to evaluate the extensions.
<?xml version="1.0" encoding="UTF-8"?>
<?eclipse version="3.4"?>
<plugin>
    <extension-point id="com.extensionpoint.greeters"
        name="Greeters" 
        schema="schema/com.extensionpoint.greeters.exsd" />
</plugin>

  • It has three attributes:

    • id: a required attr, simple name id
    • name: a required attr, sime name string
    • schema: optional attr, describe

  • Examples: Create a plugin named com.extensionpoint.definition contained the a extension point.

//MANIFEST
Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: A Plugin for the Extension Point Definition
Bundle-SymbolicName: com.extensionpoint.definition;singleton:=true
Bundle-Version: 1.0.0.qualifier
Export-Package: com.extensionpoint.definition
Bundle-Vendor: Phong
Automatic-Module-Name: com.extensionpoint.definition
Bundle-RequiredExecutionEnvironment: JavaSE-21
Import-Package: org.eclipse.core.runtime;version="[3.7.0,4.0.0)",
 org.eclipse.e4.core.di.annotations;version="[1.6.0,2.0.0)"

// plugin.xml
<?xml version="1.0" encoding="UTF-8"?>
<?eclipse version="3.4"?>
<plugin>
   <extension-point id="com.vogella.extensionpoint.definition.greeter" name="Greeter (Extension Point Name)" schema="schema/com.vogella.extensionpoint.definition.greeter.exsd"/>

</plugin>

// exsd

[Enter description of this extension point.] 
           </documentation>
        </annotation>
     </attribute>
     <attribute name="id" type="string">
        <annotation>
           <documentation>
              
           </documentation>
        </annotation>
     </attribute>
     <attribute name="name" type="string">
        <annotation>
           <documentation>
              
           </documentation>
           <appinfo>
              <meta.attribute translatable="true"/>
           </appinfo>
        </annotation>
     </attribute>
  </complexType>

           </documentation>
           <appinfo>
              <meta.attribute kind="java"/>
           </appinfo>
        </annotation>
     </attribute>
  </complexType>
[Enter the first release in which this extension point appears.] [Enter extension point usage example here.] [Enter API information here.] [Enter information about supplied implementation of this extension point.] 
// Evaluation class
package com.extensionpoint.definition;

import org.eclipse.core.runtime.CoreException;
import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.core.runtime.IExtensionRegistry;
import org.eclipse.core.runtime.ISafeRunnable;
import org.eclipse.core.runtime.SafeRunner;
import org.eclipse.e4.core.di.annotations.Execute;

public class EvaluateContributionsHandler {
    private static final String IGREETER_ID = 
            "com.extensionpoint.definition.greeter";
    
    @Execute
    public void execute(IExtensionRegistry registry) {
        IConfigurationElement[] config =
                registry.getConfigurationElementsFor(IGREETER_ID);
        try {
            for (IConfigurationElement e : config) {
                System.out.println("Evaluating extension");
                final Object o =
                        e.createExecutableExtension("class");
                if (o instanceof IGreeter) {
                    executeExtension(o);
                }
            }
        } catch (CoreException ex) {
            System.out.println(ex.getMessage());
        }
    }

    private void executeExtension(final Object o) {
        ISafeRunnable runnable = new ISafeRunnable() {
            @Override
            public void handleException(Throwable e) {
                System.out.println("Exception in client");
            }

            @Override
            public void run() throws Exception {
                ((IGreeter) o).greet();
            }
        };
        SafeRunner.run(runnable);
    }
}

// Attribute class
package com.vogella.extensionpoint.definition;

public interface IGreeter {
    void greet();
}

2.2. Create/adding EXTENSIONS to EXTENSION POINTS

  • Examples: Create a plugin named com.extension.contribution contained the a extension.
// MANIFEST
Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: Contribution
Bundle-SymbolicName: com.vogella.extensionpoint.contribution;singleton:=true
Bundle-Version: 1.0.0.qualifier
Require-Bundle: org.eclipse.core.runtime;bundle-version="3.32.0",
 com.vogella.extensionpoint.definition;bundle-version="1.0.0"
Bundle-Vendor: VOGELLA
Automatic-Module-Name: com.vogella.extensionpoint.contribution
Bundle-RequiredExecutionEnvironment: JavaSE-21

// plugin.xml

// The client class that implemented attribute class

package com.vogella.extensionpoint.contribution;

import com.vogella.extensionpoint.definition.IGreeter;

public class GreeterExensionContribution implements IGreeter {

	@Override
	public void greet() {
		System.err.println("This call from GreeterExensionContribution");
	}

}

2.3. Accessing EXTENSIONS

  • The information about the available extensions point and the provided extensions are stored in a class of type IExtensionRegistry .
  • We can use the dependency injection mechanism to get the IExtensionRegistry class that injected.
  • IExtensionRegistry contains all extensions of all extensions point.
// The following will read all existing extensions 
// for the defined ID of the extension point
Platform.getExtensionRegistry().
    getConfigurationElementsFor("yourextensionpointid");

		IConfigurationElement[] elements = Platform.getExtensionRegistry()
				.getConfigurationElementsFor("com.renesas.cdt.devicesupport.api.builderDeviceSupport");
		for (IConfigurationElement ele : elements) {

        }