The most recent version of OSGeo/proj.4 may work better, but last time I tried to build it I couldn't get JNI to work properly with my Docker files.

Pull the docker image with the tag appropriate to your Java environment. In this case I'm pulling the JDK Alpine image

docker pull echoparklabs/proj.4:8-jdk-alpine

After cloning the repo locally, you'll need to install some build tools. These can be installed with homebrew (I can't remember if mozjpeg is necessary, someone please try building without it and let me know):

brew reinstall libtool
brew reinstall mozjpeg
brew reinstall autoconf
brew reinstall automake
brew install ant

Change directories into the proj.4 directory and execute the following to build proj.4 and copy the proj.4 jar into /usr/local/lib:

export PROJ_DIR=/usr/local/Cellar/proj/5.2.0
export JAVA_HOME="$(/usr/libexec/java_home)"
autoreconf -i
CFLAGS=-I$JAVA_HOME/include/darwin ./configure --with-jni=$JAVA_HOME/include --prefix=$PROJ_DIR
make -j 8
make install
cd jniwrap
ant -v
cp ./out/proj.jar $PROJ_DIR/lib/proj.jar
brew link proj

The Docker images are based off of the openjdk images. You can build a jdk image or a jre image, you can use Java 8 or 10 (maybe 11, haven't tested), and you can use debian or alpine.

To build the latest debian 11 jdk image:

docker build -t us.gcr.io/echoparklabs/proj.4:11-jdk-slim .

The latest debian 11 jre image

docker build --build-arg JRE_TAG=11-jre-slim -t echoparklabs/proj.4:11-jre-slim .

At this time, the resulting Alpine docker image is about 50% smaller than the slim debian images. The default Alpine image uses the 12-jdk-apline image

To build the latest Alpine JDK 12 image:

docker build -t echoparklabs/proj.4:12-jdk-alpine -f Dockerfile.alpine .