Libra in Indigo

Eclipse Libra: WTP and PDE Working Together


Kaloyan Raev looks at integrating two separate toolsets.

Enterprise Java vendors have relied on the Java EE technology
for many years. The Java EE specification provides a rich set of
techniques for building large modular applications. Dozens of
middleware vendors implement the specification in their application
servers. This gives application providers the freedom to run their
enterprise Java applications on the platform of their choice. The
ability to build portable applications laid the foundation of the
huge Java community that we know today.

Over the years, the requirements of the modularity aspect of
enterprise applications has increased significantly. Application
vendors wanted better control over modules’ lifecycle and
dependencies. The Java EE specification binds dependency resolution
to deploy time and does not define how modular applications can
change during runtime. Several vendors tried responding to the new
requirements with their own proprietary solutions, but the price
for using them was the loss of portability. There was a clear
demand for a standardized approach.

The solution has been found in OSGi – a specification as old as
Java EE. The OSGi technology has been used for years for building
modular embedded Java applications. OSGi was the solution that Java
EE vendors were looking for. The challenge was how to bring Java EE
and OSGi together. As a first step, Java middleware vendors tried
using OSGi in application servers. Today, most Java applications
servers use OSGi. It was only natural to try bringing the same
experience to the application programming model. The OSGi Expert
Group released the OSGi Enterprise 4.2 specification in March 2010,
which defines how enterprise Java applications can be developed,
deployed and run in an OSGi framework.

The Eclipse Libra project

The change in the application programming model also requires
the development tools to meet the new requirements.

The Eclipse technology is perhaps the most famous platform for
building an IDE. It provides the best tooling for Java application
development and has tools for many other programming languages and
frameworks. Two of the most successful projects in Eclipse are the
Web Tools Platform (WTP) – for developing Web and Java EE
applications, and the Plug-in Development Environment (PDE) – for
developing OSGi bundles and Eclipse Plug-ins (a special type of
OSGi bundles for the Eclipse platform).

Can we use these two Eclipse projects: WTP and PDE, for
developing OSGi Enterprise applications? These are two different
tool sets built independently for two different purposes. Can we
integrate them, so that they can work together? These questions
excited several vendors like SAP, EclipseSource, Eteration, IBM,
VMWare and RedHat, who at the end of 2010 came together with a new
proposal – the Eclipse Libra project.

On June 22, 2011 Eclipse Libra released version 0.1 together
with the Indigo Simultaneous Release. Being part of the Eclipse
release train guarantees that Libra works successfully with the
rest of the Eclipse tooling. This first incubating version of Libra
introduces the first basic features: OSGi Bundle Facet and WAR

The OSGi Bundle facet is the glue between WTP and PDE. It’s
based on the Faceted Project Framework that facilitates treating
projects as though they’re composed of units of capabilities
(called facets) that can be easily added or removed. Facets are
widely used for WTP projects. For example, a Dynamic Web project is
typically composed of two facets: a Java facet that gives the Java
nature to the project and the Java classpath, and the Web facet
that adds the web.xml descriptor and customizes the project’s
structure to represent a WAR file. Adding more facet to the Dynamic
Web project can bring additional capabilities, like the JSF facet
that adds the JSF libraries to the classpath and generates the
faces-config.xml descriptor. In a similar fashion, the OSGi Bundle
facet adds the Plug-in nature to a project, so PDE recognizes it as
an OSGi bundle. This way, adding the OSGi Bundle facet to a Dynamic
Web project makes it effectively a Web Application Bundle – it is
still a Web project from the WTP point of view, but it is also an
OSGi bundle from the PDE point of view. Both WTP and PDE tools can
be used when working with Web Application Bundle projects. Using
the same approach, adding the OSGi Bundle facet to a JPA project
turns it to a Persistent Bundle.

The other feature of version 0.1, WAR Products, addresses a
different need – it enables Server-Side Equinox applications to be
easily exported in a WAR file. Server-Side Equinox is a technology for building Web
applications for the Equinox OSGi framework. It is not the standard
way of building OSGi Enterprise applications, but it has its field
of use – like for building RAP applications. The WAR Products are a
light-weight and customized variant of the Eclipse Products used in
PDE. It enables developers to configure how to export their
applications to WAR files and execute the actual export process as




If you want to give Libra a try then the first step is to
install it in your Eclipse IDE. As part of the Eclipse Simultaneous
Release, the Libra plug-ins are available on the Indigo Discovery
Site, which makes the installation process quite easy. If you don’t
have an Eclipse IDE installed yet, then it is recommended using the
Eclipse IDE for Java EE Developers package that is available for
free download on the Eclipse Foundation website.

With your Eclipse IDE started, go to the main menu and choose
Help > Install New Software… This will call the install
manager. Then select the Indigo repository and, after it is
resolved, browse the Web, XML, Java EE and OSGi Enterprise
Development category. Select the OSGi Bundle Facet and the WAR
Products features and click the Next button. Then follow the
instructions of the install manager to complete the

Web Application Bundles

A simple task for getting started with the Libra tools is
creating and running a Web Application Bundle. To create a new Web
Application Bundle project, switch to the Java EE perspective and
call the New > Dynamic Web Project wizard. If you are familiar
with WTP this will bring up the wizard for creating new Web
projects. Now, you should create your Web project like before with
one exception – adding the OSGi Bundle facet. You can do this by
clicking the Modify… button in the Configuration group, or by
simply selecting OSGi Web Application Bundle from the drop-down

As we mentioned before, the OSGi Bundle facet adds the Plug-in
nature to your Dynamic Web project. Plug-ins and OSGi bundles are
interchangeable terms in the PDE tooling.



It is possible to finish the wizard directly from the first
wizard page, but if you advance to the following pages, then you
can customize the metadata of the generated OSGi bundle. The OSGi
Bundle facet itself contributes an additional wizard page to the
wizard, where you can specify some generic metadata like Bundle Id,
Bundle Name, etc. But the facet also integrates with the
configuration of other facets, e.g. it reads the Context Root
property that can be specified on the Web facet’s wizard page and
sets its value to the Web-ContextRoot header in the MANIFEST.MF of
the generated Web Application Bundle project.

When finished, the wizard generates a project that looks quite
similar to a regular Dynamic Web project, but it has also some
additional metadata – the Plug-in nature and the
META-INF/MANIFEST.MF descriptor. The bundle root is set to the
WebContent folder.

You will probably notice that the Web Application Bundle project
has some compilation error markers. This is because there is no
appropriate target platform activated in the workspace. The PDE
target platform consists of all the bundles that define the build
and the runtime environment of your target OSGi framework. If you
use Libra for developing on a vendor’s OSGi middleware, then you
would most probably have the target platform already defined. In
the contrary case, you need to define it yourself. There are
comprehensive guidelines on the wiki page
of the Eclipse Gemini Web project on how to setup the Gemini web
container as a target platform. On the same wiki page you can also
follow the instructions on how to setup the launch configuration
that will execute the OSGi framework in an appropriate way.

Before launching your Web Application Bundle you will most
probably want to add some web content. You can use all familiar WTP
tools to do this – remember, you project is still a valid Dynamic
Web project. When ready you can run the OSGi launch configuration
you have defined in the previous step. Once the OSGi framework
starts you can request you application in the browser using URL


All the steps described in this section can be followed in a
YouTube video accessible from the Libra project

Persistent Bundles

Creating OSGi Persistent Bundles is a task as simple as creating
Web Application Bundles. It is a completely analogical routine
where the OSGi Bundle facet plays the same role. Again, you use
familiar WTP wizard – New > JPA Project, where you need to
select the OSGi Bundle facet in the project’s configuration.

The result is a valid WTP JPA project, but with the Plug-in
nature added. There is also a META-INF/MANIFEST.MF descriptor that
contains the bundle metadata, including the Meta-Persistence header
specific to Persistent Bundles.

As you may have noticed, OSGi Bundle facet is quite powerful and
can be added to different types of projects, and its behavior can
be adjusted to the context. You can add all three facets – Web, JPA
and OSGi Bundle into a single project and the result would be as
expected – a Web project that is both a Web Application Bundle and
a Persistent Bundle. This is completely valid according to the OSGi
Enterprise specification, but may not be supported by all OSGi
platforms. You can even add the OSGi Bundle facet to a plain Java
project, which will convert it to a plain core OSGi Bundle.

Launching the Persistent Bundle requires an appropriate target
platform and launch configuration. This can be set up in a similar
way to the ones for the Web Application Bundle. The Gemini JPA
project provides an OSGi JPA container that can be configured to
work together with the web container from the Gemini Web



What’s next?

You have seen an overview of the first basic features that Libra
introduces with the Eclipse Indigo release. So, what to expect
next? As being part of the Eclipse Simultaneous Release, the Libra
project will have two maintenance releases with Indigo SR1 (end of
September 2011) and Indigo SR2 (end of February 2012). So, if you
find any bugs, please let us know and report them in Eclipse
. More interesting features are coming with the next
Eclipse Simultaneous Release – Juno, that is scheduled for the end
of June 2012. We have significant contributions from Eteration and

Integrated support for different open source OSGi frameworks
like Apache Felix, Eclipse Equinox and Knopflerfish. This
contribution provides server adapters, and UI components such as
editors for server adapters, views to manage target platforms and
launch configurations.

The generic parts from the OSGi tooling for Apache Aries – a
full set of wizards to support working with OSGi bundles and
wizards for working with Blueprint files.



Both contributions have already passed the IP review
successfully and are in the process of being integrated in the
master branch. VMWare also plans to move some generic parts of the
Virgo tooling that they have recently contributed to Eclipse, to
the Libra project. So, watch closely for the Juno milestones –
coming soon.




You have seen how the Eclipse Libra project integrates two
independent toolsets – WTP and PDE, so they can be used for
developing OSGi Enterprise applications. Libra assumes that users
have more experience with the WTP tooling and tries to hide the
complexity of PDE behind familiar WTP concepts. This makes the
experience of developing OSGi Enterprise applications similar to
the Java EE application development. The first basic features of
the Libra project have just been delivered with the Indigo
Simultaneous Release. This is just the beginning and there are much
more contributions to come in the next year, with the Juno

Kaloyan is the project lead of the Eclipse Libra project. He is one of the pioneers at SAP that turned the company into a dedicated player in the Open Source world. His first involvement with the Eclipse community dates back to 2006. A year later he became a committer in the Eclipse WTP project
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