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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.