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2.4. API Bundle

Overview
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This section explains how to set up a Maven project for a typical API bundle.
The hello-paris bundle exemplifies an API bundle, which contains only public Java interfaces. Hence, the API bundle should export all of its own packages and associate a version number with the exported packages.

Directory structure
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The hello-paris bundle has the following directory structure: 
hello-paris/
  |
  \--src/
     |
     \--main/
     |  |
     |  \--java/
     |     |
     |     \--org/fusesource/example/hello/paris/
     |        |
     |        \-HelloParis.java
     |   
     \--test/
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The Java source code is located under the src/main/java sub-directory. The org.fusesource.example.hello.paris package is public and all of its classes and interfaces can be exported from the bundle.
There are no blueprint resources associated with this bundle.

Sample API
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The hello-paris bundle is a pure API, which means it contains only Java interfaces. In this example, there is a single interface, HelloParis, which returns a localized greeting and a Clock object that tells the local time. The HelloParis interface is defined as follows: 
// Java
package org.fusesource.example.hello.paris;

import org.fusesource.example.time.Clock;

public interface HelloParis {
    public String getGreeting();
    
    public Clock getLocalTime();
}
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Maven dependencies
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In the Maven POM file, the hello-paris bundle defines dependencies on the following Maven artifact:
  • time-util

Import and export rules
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The following import and export rules apply to the hello-paris bundle:
  • Exporting own packages—the org.fusesource.example.hello.paris package is public, and must be exported.
  • Importing own packages—none of the bundle's own packages should be imported.
  • Importing dependent packages—any external package dependencies must be imported.

Maven bundle plug-in settings
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The Maven bundle plug-in is configured to export the API package, org.fusesource.example.hello.paris (coded as ${project.groupId}.hello.paris*). The Export-Package instruction also contains entries to block the export of any packages containing .impl or .internal. In this case, the bundle plug-in instructions are as follows: 
<instructions>
  <Bundle-SymbolicName>${project.groupId}.${project.artifactId}</Bundle-SymbolicName>
  <Import-Package>*</Import-Package>
  <Export-Package>
    !${project.groupId}*.impl*,
    !${project.groupId}*.internal*,
	${project.groupId}.hello.paris*;version=${project.version}
  </Export-Package>
</instructions>
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Generated MANIFEST.MF file
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When you build the bundle using Maven, the Maven bundle plug-in automatically generates the following MANIFEST.MF file: 
Manifest-Version: 1.0
Bundle-Name: hello-paris
Built-By: JBLOGGS
Build-Jdk: 1.5.0_08
Created-By: Apache Maven Bundle Plugin
Import-Package: org.fusesource.example.time;version="[1.0,2)"
Bundle-ManifestVersion: 2
Bundle-SymbolicName: org.fusesource.example.hello-paris
Tool: Bnd-1.15.0
Bnd-LastModified: 1296826928285
Export-Package: org.fusesource.example.hello.paris;uses:="org.fusesour
 ce.example.time";version="1.0"
Bundle-Version: 1.0.0
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The Import-Package header lists one external package dependency, org.fusesource.example.time. None of the bundle's own packages are imported.
The Export-Package header is used to export the API package, org.fusesource.example.hello.paris, while the uses clause declares a transitive dependency on the org.fusesource.example.time package.
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