We are developing a system on Java. It must call another system and at some point the other system calls our system back via web service. Therefore I can not test this interaction in a stand-alone test, our code must be executed in an HTTP container (we use Tomcat).
In case if the code does not work as desired, I need to stop Tomcat, fix and rebuild Java sources and try again. And what is worse, before the code I am working on can be tested, it performs initialization that takes about a minute. These stumbles are little bit annoying for those who are used to fully dynamic development environments as Lisp.
I decided to embed Clojure into the system during development and connect to it with SLIME to create interactive testing/development environment.
First, I followed Bill Clementson's instructions for usual (not embedded) Clojure/SLIME setup.
After it worked, I started to look for a way to embed Clojure/swank into existing Java system, but didn't find any conventional way to do this. Therefore I torn out a piece of code from the clojure.lang.Repl class and instead of standard input, feed it with commands to start swank (which I found in the *inferior-lisp* buffer when Clojure/SLIME is started "normally", from Emacs).
All this is packed into simple clojure.jsp page in my web application directory. And clojure.jar is placed into WEB-INF/lib.
When the JSP is opened in browser it displays: "swank has been stared".
After that, I use M-X slime-connect from Emacs. The port number, as you can see from the code, is 7777.
What is the result?
I can inspect and control the running system, for example invoke functions I need to test or change object states.
But I must admit that the level of flexibility is lower than I hoped for. The point is that I can not interactively change Java code (which constitutes all the system). To be more flexible, the system must be written on Lisp entirely.
Links
- Bill Clementson's instructions for Clojure/SLIME setup: http://bc.tech.coop/blog/081023.html
- My JSP page to start Clojure/swank: http://paste.lisp.org/display/71209
Mmm i imagine if you could use a dynamic class loader for the java core of the app it would be possible. I dont know if is possible but i remember a blog post about dynamic in memory compilation which mabe could be used for that:
ReplyDeletehttp://www.javablogging.com/dynamic-in-memory-compilation/
I am afraid my knowledge is not enough to offer a more accurated proposal :-/
Thanks, the blog post is interesting.
ReplyDeleteUsual problem with java class is not to compile and load it first time, but to reload it.
It's impossible if you added/removed methods to class, changed it's inheritance, etc.
For example, when you are debugging application with IntelliJ, added/removed method, recompiled class and trying to reload it into the application, Intellij shows error: "schema change is not implemented". You need to stop the application, and start it again.