Bundle Plugin for Maven

This plugin for Maven 2 is based on the BND tool from Peter Kriens. The way BND works is by treating your project as a big collection of classes (e.g., project code, dependencies, and the class path). The way you create a bundle with BND is to tell it the content of the bundle's JAR file as a subset of the available classes. This plugin wraps BND to make it work specifically with the Maven 2 project structure and to provide it with reasonable default behavior for Maven 2 projects.

Simple Example

Rather than going straight to a detailed list of plugin features, we will first look at a simple example of how to use the plugin to give an immediate flavor. A detailed "how to" will follow.

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The <Export-Package> and <Private-Package> instructions tell the plugin about the contents of the resulting bundle JAR file. The <Export-Package> instruction tells the plugin which of the available packages to copy into the bundle and to export, while the <Private-Package> instruction indicates which of the available packages to copy into the bundle but not export. If the two sets overlap, as they do in the case, then the export takes precedence. Since we did not specify any values for any other bundle manifest headers, they will assume default values which are described below. One specific behavior to highlight is that the plugin generates the Import-Package bundle manifest header based on the contents of the bundle, which means that you generally do not ever need to explicitly specify it yourself. That's it.

Features

The BND library underlying the plugin defines instructions to direct its behavior. For this Maven plugin, these instructions are issued in the plugin configuration section of the POM file, as was illustrated above. BND recognizes three types of instructions:

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Instructions

<Export-Package>

The <Export-Package> instruction is a list of packages for the bundle to export. These packages are copied into the resulting bundle JAR file from the available classes (i.e., project classes, dependencies, and class path); thus, it is possible to include classes into your bundle that are not associated with source files in your project. <Export-Package> can be specified with package patterns using the '*' wildcard. Also, it is possible to exclude packages using negation by starting the package pattern with '!'. Thus, non-negated patterns indicate which of the available packages to include in the bundle, whereas negated patterns indicate which should not be included in the bundle.

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Following standard OSGi R4 syntax, package patterns can include both directives and attributes, which will be copied appropriately into the generated Export-Package manifest header. Besides explicitly listing package version attributes, BND will also determine package versions by examining the source JAR file or from packageinfo files in the package directory.

<Private-Package>

The <Private-Package> instruction is similar in every way to the <Export-Package> instruction, except for the fact that these packages will not be exported by the bundle. If a package is selected by both the export and private package headers, then the export takes precedence.

<Include-Resource>

The <Include-Resource> instruction is a list of arbitrary resources that should be copied into the bundle JAR file. The specified resources are declared as clauses that can have the following forms:

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If a resource clause is specified inside of "{ ... }" brackets, then variable substitution will be performed on the resource, where variables in the resources are denoted with "${ ... }" syntax.

<Import-Package>

The <Import-Package> instruction is a list of packages that are required by the bundle's contained packages. The default for this header is "*", resulting in importing all referred packages. This header rarely has to be explicitly specified. However, in certain cases when there is an unwanted import, such an import can be removed by using a negation package pattern. The package patterns work in the same way as for <Export-Package>, which means they are ordered. For example, if you wanted to import all packages except org.foo.impl you would specify "!org.foo.impl,*"

Default Behavior

To use this plugin, very little information is required by BND. As part of the Maven integration, the plugin tries to set reasonable defaults for various instructions. For example:

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Since the plugin creates bundles for OSGi R4, it hard codes Bundle-ManifestVersion to be '2'. Additionally, it generates imports for every export to ensure package substitutability, which is very important when working with collaborating services. It is possible to override any of these values (except Bundle-ManifestVersion) just by specifying the desired value in the plugin configuration section of the POM file.

Detailed "How To"

Get Maven2

The first step in the process of using the plugin is downloading and installing the latest version of the Maven2 runtime. The latest Maven2 release and instuctions for getting started with Maven2 can be found at the Maven website.

Using the Plugin

To use the maven-bundle-plugin, you first need to add the plugin and some appropriate plugin configuration to your bundle project's POM. Below is an example of a simple OSGi bundle POM for Maven2:

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There are four main things to note: (1) the <packaging> specifier must be "bundle", (2) the plugin and configuration must be specified (the configuration section is where you will issue instructions to the plugin), and the snapshot repository to resolve dependencies (3) and plugins (4).

Real-World Example

Consider this more real-world example using Felix' Log Service implementation. The Log Service project is comprised of a single package: org.apache.felix.log.impl. It has a dependency on the core OSGi interfaces as well as a dependency on the compendium OSGi interfaces for the specific log service interfaces. The following is its POM file:

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META-INF/MANIFEST.MF
LICENSE
META-INF/
META-INF/maven/
META-INF/maven/org.apache.felix/
META-INF/maven/org.apache.felix/org.apache.felix.log/
META-INF/maven/org.apache.felix/org.apache.felix.log/pom.properties
META-INF/maven/org.apache.felix/org.apache.felix.log/pom.xml
NOTICE
org/
org/apache/
org/apache/felix/
org/apache/felix/log/
org/apache/felix/log/impl/
org/apache/felix/log/impl/Activator.class
org/apache/felix/log/impl/Log.class
org/apache/felix/log/impl/LogEntryImpl.class
org/apache/felix/log/impl/LogException.class
org/apache/felix/log/impl/LogListenerThread.class
org/apache/felix/log/impl/LogNode.class
org/apache/felix/log/impl/LogNodeEnumeration.class
org/apache/felix/log/impl/LogReaderServiceFactory.class
org/apache/felix/log/impl/LogReaderServiceImpl.class
org/apache/felix/log/impl/LogServiceFactory.class
org/apache/felix/log/impl/LogServiceImpl.class
org/osgi/
org/osgi/service/
org/osgi/service/log/
org/osgi/service/log/LogEntry.class
org/osgi/service/log/LogListener.class
org/osgi/service/log/LogReaderService.class
org/osgi/service/log/LogService.class
org/osgi/service/log/package.html
org/osgi/service/log/packageinfo

Building the Plugin

The plugin is hosted at the Apache Felix incubator project. The following steps describe how to build and install the plugin into your local Maven2 repository.

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