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WORKSHOP-INSTRUCTIONS-PART-1.md

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Part 1 Instructions

Get started. Create a project and a Java interface

  1. Create new project

    1. Open IDE (IntelliJ)
    2. File --> New --> Project
    3. Make sure it is a "maven" project and select Next
    4. Enter a group ID (e.g. com.connexta)
    5. Enter an artifact ID (e.g. karaf-turorial)
    6. Select Next
    7. Change project name and location if desired, or just select Next

  2. Add an module for the service contract (i.e.the interface or API)

    1. Add a new module called api
    2. Open the module and add a Java interface named Greeting
    3. Define one method for the interface. The method should be named hello, accept a String as a parameter and return a String
    4. Do not leave the interface in the default package. OSGi relies heavily on package names. Use the package directive to make the interface part of a real package. For simplicity, use the package name api.

  3. Update the Project Object Model (POM.xml) for the module

    1. Add the maven-bundle-plugin to generate the OSGi manifest headers
    2. For the sake of time, copy and paste this POM up on GitHub.

  4. Execute a mvn install to build the bundle. Look for warnings and errors in the output.

Let's review what we did.

  • Created a Java interface. Big whoop.
  • Added the maven bundle plugin
  • Used maven to create the bundle (e.g. target/api-1.0-SNAPSHOT) WORKSHOP-INSTRUCTIONS-PART-1.md Let's take a quick look at the instructions to the maven bundle plugin:
<Bundle-SymbolicName>${project.artifactId}</Bundle-SymbolicName>
<Bundle-Version>${project.version}</Bundle-Version>
<Bundle-Activator/>
<Export-Package>com.connexta.api;version=${project.version}</Export-Package>
<Import-Package> * </Import-Package>

The symbolic name and bundle version are just the name and version of the bundle. Together, they make a unique key-- no two bundles can have the same symbolic name and version.

Why is there an empty bundle activator element? No idea. Would it would without it? Probably.

Export Export-Package is important. In OGSi land, bundles can only see packages inside of their own JAR file, or packages that have been imported from other bundles. Because this is our API, we want the whole world to have access to it. So we export it. Now is is visible inside the runtime OSGi container.

Import Import-Package can be important. It is great that the Java package for the API was exported. But what about THIS bundle's dependencies? We need to import them. Thanks to the magic of the maven bundle plugin (and, under the covers, BND), we don't have to type out the package names we depend on. The plugin and BND exames the generated byte code and adds the correct manifest headers.

Exercise

  • Unzip the JAR file in the target/ directory.
  • Find the manifest file
  • What instructions from the POM made it into the manifests? Which didn't?
  • which instruction could we remove from the POM file and still get a the same manifest headers?