Migration of SCR annotations to OSGi R6 annotations in AEM 6.3

I have recently gone through a migration project from an older version of AEM to AEM 6.3 and the major challenge while migrating java classes is that sometimes the API become deprecated in the newer version.

From AEM 6.2, One of our favorite Apache Felix Maven SCR Plugin has been deprecated and in place of this, Maven Bundle Plugin (version 6.2 or greater) has been introduced.

It always take a small effort to adapt new things, But change is the nature’s law. So here we will discuss how OSGi plugin has replaced all SCR annotations in AEM.

Packages:

Now the package  “org.apache.felix.scr.annotations.*” will be replaced with “org.osgi.service.component.annotations.*”  and “org,osgi.service.metatype.annotations.*”

While using Maven SCR plugin, we can find the Declarative Service(DS) output under /target/classes/OSGi-INF but using OSGi Bundle Plugin our DS output are found in /OSGI-INF, packaged under the compiled JAR File.

Note:The Apache Felix SCR annotations are replaced in AEM 6.3 projects with OSGi R6 annotations

How To start with OSGi Annotations?

1.Add a plugin in Parent Pom.xml

<plugin>  <groupId>org.apache.felix</groupId>  <artifactId>maven-bundle-plugin</artifactId>  <version>3.2.0</version>  <inherited>true</inherited> </plugin>

2.Add the following maven dependencies.

<dependency>  <groupId>org.osgi</groupId>  <artifactId>org.osgi.service.component.annotations</artifactId>  <version>1.3.0</version> </dependency> <dependency>  <groupId>org.osgi</groupId>  <artifactId>org.osgi.annotation</artifactId>  <version>6.0.0</version> </dependency> <dependency>  <groupId>org.osgi</groupId>  <artifactId>org.osgi.service.metatype.annotations</artifactId>  <version>1.3.0</version> </dependency> <dependency>  <groupId>org.osgi</groupId>  <artifactId>org.osgi.compendium</artifactId>  <version>4.2.0</version> <scope>provided</scope> </dependency>

Note: Make sure that while building the code,plugin is working fine.

Migration of OSGi Components and Service

Before : In SCR Annotations:

@Component(name=”Test Service”,immediate=true,description="this is description") @Service(TestService.class) public class TestService {                      public String getName() { return "testService"; } }

After:In OSGi Annotations

@Component(name=”Test Service” service=TestService.class,immediate=true) public class TestService {                      public String getName() { return "testService"; } }

Migration of Servlet

OSGi annotations has reduced our effort to remember a lot of Annotations.

In the Sling Servlets:

We used to use @Component, @Service @SlingServlet @Properties in SCR Annotations.

OSGi annotation just have @Component with the collaboration of all these annotations.

Before : In SCR Annotations:

@SlingServlet(paths="/bin/servlet",selectors = {"test","test1"},extensions = "html") public class Test extends SlingSafeMethodsServlet{   @Override   protected void doGet(SlingHttpServletRequest request, SlingHttpServletResponse response)throws IOException   {       response.getWriter().print(" I am in doGet Method");   } }

After:In OSGi Annotations

@Component(service=Servlet.class,           property={                   Constants.SERVICE_DESCRIPTION + "=Simple Demo Servlet",                   "sling.servlet.methods=" + HttpConstants.METHOD_GET,                   "sling.servlet.resourceTypes="+ "com.poc.osgiannotation/components/structure/page",                  "sling.servlet.paths="+ "/bin/servlet",                   "sling.servlet.extensions=" + "txt"           }) public class SimpleServlet extends SlingSafeMethodsServlet { { @Override   protected void doGet(SlingHttpServletRequest request, SlingHttpServletResponse response)throws IOException   {       response.getWriter().print(" I am in doGet Method");   } }

Custom OSGi Configuration in AEM

OSGi annotations provided a flexibility to create configuration in a separate interface and we can use it in any place.

The OSGi Configurations generates metatype specification that provides a way to describe configuration of the component.Such a metatype information can be used at runtime to generate forms to edit/create the configuration of a component. For example the Apache Felix web console does exactly that.

Let’s understand how to make OSGi configurations in AEM using OSGi Bundle Plugin.

Fig- OSGi COnfiguration in felix Console

Migration of Custom Workflow Process Step

Before:In SCR Annotations

@Component(immediate = true, enabled = true, metatype = true) @Service(value = WorkflowProcess.class) @Property(name = "process.label", value = "Activate Page", propertyPrivate = true) public class RejectionMailProcess implements WorkflowProcess { public void execute(WorkItem workitem, WorkflowSession wfsession,MetaDataMap metaDataMap) { System,.out.println(“ I am in execute method”); } }

After: In OSGi Annotations

@Component(service = WorkflowProcess.class, property = {"process.label=Activate Page" }) public class TestWorkflow implements WorkflowProcess { public void execute(WorkItem workitem, WorkflowSession wfsession,MetaDataMap metaDataMap) { System,.out.println(“ I am in execute method”); } }

How to use @Reference Annotations in OSGi Annotations?

There are multiple ways to use @Reference annotations in OSGi annotations:

1.

@Reference TestService testService;

2.

private TestService testService; @Reference public void bindTestService(TestService testService) {      this.testService = testService; } public void unbindTestService(TestService testService) {      this.testService = testService; }

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Hope it will help you guys !!
Thanks and Happy Learning