Difference between revisions of "Jetty/Feature/Jetty OSGi"

Revision as of 18:29, 1 December 2009

Introduction

Jetty on OSGi consists of bootstrapping a standard jetty server from OSGi. It supports the deployment of traditional J2EE web-applications as well as web-applications contained inside an OSGi bundle (RFC66).

The goal of Jetty on OSGi is to offer a migration path for traditional J2EE applications to run inside an OSGi container. It favors J2EE applications currently deployed on jetty: developers and IT administrators familiar with a jetty deployment will found the same folder structure and configuration files.

Jetty-on-OSGi also provides an SDK for Eclipse-PDE that supports the development and debugging of a mix of traditional web-applications and web-applications contained in an OSGi bundle: Jetty on OSGi SDK for Eclipse PDE.

Feature

Jetty bootstrapping in OSGi

A single bundle 'org.eclipse.jetty.osgi.boot' acts as an alternative to Jetty's Start.jar. It wires up all the jetty jars that can be located. It locates the ${jetty.home} folder where the configuration files are located. It starts a jetty server according to these configuration files:

It locates a ${jetty.home} folder (or generate one by default) and starts a jetty server according to the jetty.xml file.

The classloader inside which the jetty server is executing is a mix of the OSGi classloader provided by the 'org.eclipse.jetty.osgi.boot' bundle and also the jars and folders found inside ${jetty.home}/lib/ext and ${jetty.home}/resources.

The jetty.xml provided by default in jetty will deploy all web-applications found inside the ${jetty.home}/webapps and will read the jetty context files found inside ${jetty.home/contexts}.

Deployment of web-applications via OSGi

Support for RFC66

RFC66 standardize the format of a bundle that contains a web-application and its lifecycle. Jetty-OSGi takes advantage of jetty's native web-app deployer and context deployers and exposes those as extensions to RFC66.

Manifest headers and access to OSGI in the servlet context

The mandatory manifest header of RFC66 is supported:

Web-ContextPath: /theContextPath

The default behavior when it is missing is also supported: the default context path is the symbolic name of the bundle that contains WEB-INF/web.xml.

The optional header "Jsp-ExtractLocation" is not supported currently.

A web-application loaded by OSGi will contain a pointer to the org.osgi.BundleContext object as the attribute 'osgi-bundlecontext' of the servlet context.

Jetty-OSGi does not currently enforce that the WEB-INF/classes folder and the WEB-INF/lib/*.jar must be part of the Manifest entry "Bundle-Classpath". If they are not present, jetty-osgi will still load them in the classloader of the web-application.

"war" URL scheme

The "war" URL scheme specified by RFC66 support the installation of J2EE web archives, "war" files. ON the OSGi shell, it is possible to install a war file with a command like this one:

>install war:file://path/to/pet.war

The corresponding war file is transformed into a suitable OSGi bundle and installed on to the OSGi container.

This protocol is supported.

Internals and extensions to RFC66

Manifest headers specific to jetty

Jetty-WarFolderPath: /path/to/a/webapp

This entry let's the user define a comma separated list of folder pathes relative to the base folder of the bundle. Each folder will be deployed as a web-application. It is required that each folder contains WEB-INF/web.xml Each of those web-application will use its own classloader which is a child of the bundle's classloader that contains them. Hence each webapp can eventually contain WEB-INF/lib and WEB-INF/classes for libraries specific to that web-app.

Jetty-ContextFilePath: /path/to/a/context/file.xml

The OSGi service 'org.eclipse.jetty.server.handler.ContextHandler'

Architecture

Detailed classloader tree

Injecting new server-wide features into jetty-osgi

A common situation for framework developers is to make a set of library installed in the server's classloader and to have a hook in the life-cycle of the server.

This is supported in 2 ways:

• The traditional J2EE way: locate the ${jetty.home} folder and add the libs to lib/ext then configure jetty.xml
• The OSGi way consists of installing a bundle-fragment hosted by 'org.eclipse.jetty.osgi.boot'

This will make the dependencies of the fragment available in the classloader of the server. In order to hook into the lifecycle of server it is possible to define an implementation of BundleActivator that will be invoked by the bundle 'org.eclipse.jetty.osgi.boot'. In order for this BundleActivator to be invoked it must be named following this convention: ${bundle.id.of.this.fragment}+".FragmentActivator"

Jetty-osgi is distributed with a number of optional bundles that are illustrate this technique: Support for jsp with the bundle "org.eclipse.jetty.osgi.boot.jsp" Support for centralized logging on logback; "org.eclipse.jetty.osgi.boot.logback"

Additional Resources

(optional) - links, additional references