java-config

Java configuration option command line tool. This does for java what similar tools for packages such as freetype (freetype-config) provide. I wrote this so that I could find what I needed quickly to build JNI libraries for all unixish platforms.

Using

Copy the java-config.jar file into your project. Run it as "java -jar java-config.jar" with the correct java executable and it will report vital statistics about your installation including cflags and ldflags for jni linking.

Syntax

Syntax: java -jar java-config.jar [FLAGS]

Flags:
    --home              Java Home
    --jdkhome           JDK home (discovered by heuristic)
    --arch              JRE architecture (ie. amd64)
    --version           Java version
    --vmversion         Virtual machine version
    --specversion           Java specification version (ie. 1.6)
    --runtimeversion        Runtime version
    --osversion         Operating System version
    --osname            Operating System name (ie. Linux)
    --datamodel         JRE data model (ie. 32 or 64)
    --endian            System endian-ness (ie. little or big)
    --cflags            CFLAGS to use when compiling a JNI library
    --ldflags           LDFLAGS to use when linking to the jvm

Example Usage

I wrote this tool primarily to aid in building JNI libraries. All of the other options are present because they are easy to get at and I was forever writing little one liner java programs to pull them out of the system properties.

Here is an example Linux makefile for building a shared library:

JAVA_CMD ?= java
CFLAGS ?= -O3
FREETYPE_CFLAGS ?= $(shell freetype-config --cflags)
JAVA_CFLAGS ?= $(shell $(JAVA_CMD) -jar java-config.jar --cflags)


libmapnik-jni.so: mapnikjni.cpp mapnikjni.h
    g++ -o libmapnik-jni.so \
        -fPIC -shared \
        $(CFLAGS) \
        $(FREETYPE_CFLAGS) \
        $(JAVA_CFLAGS) \
        mapnikjni.cpp \
        $(LDFLAGS) \
        -lmapnik2

And here is an example OSX makefile for building a jnilib:

JAVA_CMD ?= java
CFLAGS ?= -O3
FREETYPE_CFLAGS ?= $(shell freetype-config --cflags)
JAVA_CFLAGS ?= $(shell $(JAVA_CMD) -jar java-config.jar --cflags)


libmapnik-jni.jnilib: mapnikjni.cpp mapnikjni.h
    g++ -dynamiclib -o libmapnik-jni.jnilib \
        $(CFLAGS) \
        $(FREETYPE_CFLAGS) \
        $(JAVA_CFLAGS) \
        mapnikjni.cpp \
        $(LDFLAGS) \
        -lmapnik2 -framework JavaVM

I used to use autoconf or other such craziness for this stuff, but JNI libraries are usually simple enough to require just quick incantations like the above. Bundling the java-config.jar with your source and using it to discover compilation options on the fly makes it all self-configuring.