Introduction to CRaSH

eXo Platform Blog

I’ve just written a new tutorial that gives a technical introduction to CRaSH, an open source project I lead that makes interacting with Java Content Repository (JCR) technology easier. The complete tutorial can be found on the eXo Resource Center – but here’s a sneak peak:

It’s been a year now since I started the CRaSH project. We use Java Content Repository (JCR) technology a lot at eXo, and I realized we all spent too much time and effort trying to interact with content repositories. We needed a tool to make this easier – so I decided to write a shell for JCR. While this new project, CRaSH, started as an interactive shell for browsing, querying and modifying JCR repositories, it has evolved into more than that.

The architecture of CRaSH is founded on two ideas:

  • The capability to serve multiple protocols: telnet and SSH are must-have’s
  • Extending the shell should be easy, and possible at runtime

CRaSH started very simply, so the first usable version took me only a few days to write. In this first version, I remember I used the Netty library to provide connectivity, as it had basic support for the telnet protocol (I didn’t need anything more at the time). I also selected Groovy language for writing shell commands, thinking it was the perfect match for two reasons. First, Groovy is dynamic and easy to compile, and second, you only need a little knowledge of Groovy to begin using it.

Since then, CRaSH has evolved to become richer and offer more capabilities. Netty was dropped because its telnet support was too basic; instead, Wimpi Telnetd and Apache SSHD were adopted to provide a real shell experience. CRaSH benefited from a couple of contributions as well (it’s always nice to have people in the open source community helping you), so it is pretty mature as of the recent 1.0.0-beta18 release (the only missing feature I would like is command line completion).

CRaSH is now a valuable tool to interact with a JVM runtime. The latest release provides two bundles. The first one, the core bundle, can be deployed in any servlet container. The second one is the GateIn bundle, which is built specifically for the GateIn portal server to add a powerful set of JCR features.

In this tutorial, we will focus on explaining basic CRaSH development, and demonstrate this by coding a command that will display a nice list of the JVM system properties.

Continue reading the “Introduction to CRaSH” tutorial on the eXo Resource Center…

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