Usually writing a Java application requires using Maven or Gradle. While both are great tools for large projects, they are too complicated for small scripts. jbang is a new tool that lets you create scripts or simple applications with Java. I will create a geospatial command line tool using jbang and the Java Topology Suite (JTS).

There are a few different ways to install jbang, but I used sdk man.

skd install jbang

You can use jbang to create a script.

jbang init buffer.java

Use your favorite editor to fill in the details. Our script will use the Java Topology Suite to read a WKT geometry from the command line, buffer that geometry using a distance from the command line, and then write the geometry as WKT.

First, add JTS as a dependency in our script:

//DEPS org.locationtech.jts:jts-core:1.18.2

Then replace the main method with the following:

WKTReader reader = new WKTReader();
Geometry geometry = reader.read(args[0]);
WKTWriter writer = new WKTWriter();
System.out.println(writer.write(geometry.buffer(Double.parseDouble(args[1]))));

and then add some imports:

import org.locationtech.jts.io.WKTReader;
import org.locationtech.jts.io.WKTWriter;
import org.locationtech.jts.geom.Geometry;

The final result should look like this:

///usr/bin/env jbang "$0" "$@" ; exit $?
//DEPS org.locationtech.jts:jts-core:1.18.2

import org.locationtech.jts.io.WKTReader;
import org.locationtech.jts.io.WKTWriter;
import org.locationtech.jts.geom.Geometry;

public class buffer {

    public static void main(String... args) throws Exception {
        WKTReader reader = new WKTReader();
        Geometry geometry = reader.read(args[0]);
        WKTWriter writer = new WKTWriter();
        System.out.println(writer.write(geometry.buffer(Double.parseDouble(args[1]))));
    }
    
}

We can use jbang to run our script (no pre-complication required).

jbang buffer.java "POINT(1 1)" 2

If we want to distribute our script, we can use the jbang export portable command to create a jar and lib directory (which contains the jars our script depends on).

jbang export portable buffer.java

We can try out the jar from the command line.

java -jar buffer.jar "POINT(1 1)" 2

We can also use GraalVM to create a native executable. I used sdk man to install GraalVM version 21.3.0.

sdk install 21.3.0.r17-grl
sdk use java 21.3.0.r17-grl

To make sure things work correctly, try running your script again but this time with the –native flag.

jbang --native buffer.java "POINT(1 1)" 2

Now we can build the native executable with the jbang export portable command with the –native flag.

jbang export portable --native --output geom-buffer buffer.java

Try it out!

./geom-buffer "POINT(1 1)" 2

The combination of jbang and GraalVM make writing scripts with Java really easy.

• java
• jts
• jbang
• geospatial