Wednesday, April 30, 2008

SpringSource Application Platform ships

Today the SpringSource Application Platform shipped its first beta release. Version 1.0 is essentially a combination of Spring, OSGi and Tomcat engineered into a stand-alone runtime.

The programming model is Spring with OSGi and the option of a new packaging format: the platform archive or PAR file. A PAR file comprises multiple OSGi bundles. This brings OSGi modularity and versioning to enterprise applications.

The diagram below gives a high level view of the structure of the platform.

So what does the platform deliver over and above a standard OSGi container? Well, apart from the servlet function, integrated Spring support, the modular kernel-based runtime, and the full support for diagnostics and first failure data capture, there are quite a few features that are of interest to an OSGi audience:

  • The platform has a repository which automatically provisions dependencies as bundles are installed into OSGi. This repository stores the platform's own bundles as well as application and third party bundles.
  • In addition to the PAR mentioned above, there is a new concept of a library which is a named, versioned collection of OSGi bundles installed in the repository typically for use by applications. This is accessed via a new manifest header, import-library, which imports all the packages exported by the bundles of a library.
  • Another new manifest header, import-bundle, imports all the packages exported by a single bundle. This avoids the need to wrap components consisting of a single bundle in a library.
  • There is also some novel diagnostic help when a bundle cannot be resolved. The platform's resolution failure detective attempts to extract a concise summary of the problem and the most likely root causes.
  • Associated with the platform is a carefully constructed repository of commonly used bundles: the SpringSource Enterprise Bundle Repository known informally as the "bundle repository in the sky", or "BRITS". The bundles have validated OSGi manifests and the whole repository has been checked to make sure that its bundles can be used together.
Finally, I can't resist saying a bit about the architecture of the platform. In the past, I've been involved in restructuring projects - adding in modularity after the fact. The platform was built in a modular fashion from day 1.

The whole platform consists of subsystems which are similar in concept to libraries but which are managed specially by the kernel. Each subsystem is a named, versioned collection of bundles. The kernel manages the installation and starting of subsystems as the platform initialises. The kernel manages the lifecycle of each subsystem and its bundles, even reacting to unsolicited lifecycle events of the bundles of a subsystem to keep the state of the subsystem consistent.

Subsystems are used to control the function of the platform. Some subsystems are always present, but others are optional and are configured in a profile. This mechanism allows the precise function of the platform to be configured without rebuilding. For instance, the shipped profile.config file (in the config directory) looks like this:

* SpringSource Application Platform profile manager default
* configuration file.
"profile": {
"version" : 1.0,
"name" : "web",
"subsystems" : ["com.springsource.platform.servlet",
which shows the servlet container and web personality subsystems.

My colleague Rob Harrop just blogged about the platform if you want to know more. Why not register, download the binary, have a play, and tell us what you think.

Tuesday, April 15, 2008

OSGi could be great for JSR 277

Bryan Atsatt describes a plausible way forward for JSR 277. I agree with his reasoning, although OSGi is not only the de facto standard for Java modularity, it's a proper standard too.

Bryan was one of the key movers in the Expert Group when I was involved. In fact, he proposed a solution to JSR 294 ages ago which is close, if not identical, to the approach Alex Buckley is now considering.

Welcome to the blogosphere, Bryan!


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