cl-log4j is an experiment in bringing Java libraries to Common Lisp
using OpenLDK. The real Apache
Log4J code is
executed in-process without any external JVM. This is possible
because OpenLDK transpiles Java bytecode into Common Lisp code in
memory, ready for compilation and execution by your Lisp runtime
environment.
Check out log4cl if you want a proper logging system for Common Lisp. The purpose of this project is exercise OpenLDK.
Log4J is an interesting library for exercising OpenLDK thanks to extensive use of reflection, dynamic code generation, unsafe methods, stack walking, and more.
The OpenLDK APIs are under very active development and are sure to change. Any feedback would really be appreciated!
You will need to set your JAVA_HOME environment variable, as well as
LDK_CLASSPATH. JAVA_HOME should point at your JDK 1.8
installation. On my Fedora Linux box, I have it set like so:
export LDK_HOME=/usr/lib/jvm/java-1.8.0/jre
LDK_CLASSPATH should point at the log4j jar files. I run sbcl like so:
$ LDK_CLASSPATH=log4j-api-2.3.2.jar:log4j-core-2.3.2.jar sbcl
OpenLDK is available in the ocicl
repo. Just run ocicl install openldk to download OpenLDK.
Before using cl-log4j, you must first initialize it like so:
(log4j:initialize)
This transpiles the necessary java bytecode to common lisp in memory. This initial step is currently very slow. I expect great improvements over time.
To log an error message, use:
(log4j:log-error "Hello World!")
The first message logged will trigger more classes to be loaded and methods to be compiled (OpenLDK is a JIT compiler). Subsequent logging should be fast.
The output may look unusual. There's work to be done. I expect things to improve fairly rapidly.
Happy Hacking,
Anthony Green