How to create a macOS installer for a Java application (.jar)

1) Launch Unix terminal

Using Finder, go into "Applications" and then open the "Utilities" folder.

Now open Terminal and you'll be at the Unix prompt.

2) Install Homebrew and Java (openjdk)

Homebrew is a widely used open-source software package management system for Apple macOS that makes is easy to install Java (openjdk).

Enter the following commands to install Homebrew and Java (openjdk):

         url=https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh
         /bin/bash -c "$(curl -fsSL $url)"
         brew install openjdk
         java --version
      

Verify you are running openjdk 17.0.0 or later.

If your Mac has a prior version of Java already installed, consulte the openjdk formula documentation for instructions on creating a symlink to point macOS to the new openjdk instalation.

3) Make project folder

Enter these two commands:

         mkdir showtime
         cd showtime
      

The first command creates a folder called "showtime", and the second command moves you into the new folder.

4) Write some Java code

Get the sample Java code and take a look at the Swing commands that create a simple window for displaying the current time:

         curl --remote-name https://centerkey.com/mac/java/ShowTime.java
         cat ShowTime.java
      

You'll see the code:

            import java.util.Date;
            import javax.swing.*;

            public class ShowTime {

               public static void main(String[] args) {
                  JFrame frame = new JFrame();
                  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                  frame.setTitle("It's Showtime!");
                  frame.getContentPane().add(new JLabel(new Date().toString()));
                  frame.pack();
                  frame.setVisible(true);
                  }

            }
         

5) Compile Java program

Back at the Unix prompt, compile the Java program into a class file:

         javac --version
         javac ShowTime.java
         ls -o
      

It is possible to run the class file directly, but that results in a poor user experience.  Instead we will create a more convenient executable JAR file.

6) Make executable JAR

Before we make an executable JAR file, we need a manifest file to indicate which class contains the "main" function.  Create the file:

         echo "Main-Class: ShowTime" > MainClass.txt
         cat MainClass.txt
      

The resulting manifest file contains a single line:

            Main-Class: ShowTime
         

Now use the following jar command to create the "ShowTime.jar" file:

         jar --version
         jar cmfv MainClass.txt ShowTime.jar *.class
         ls -o
      

Test your executable JAR with the following command:

         java -jar ShowTime.jar
      

The "It's Showtime!" window with the current time should display in the upper left corner of your screen.

Click the red button (marble) to exit the program.

While the manual commands above for steps #5 and #6 work fine, you could automate them using Ant with a build.xml file.

7) Create installer background and application icon

The default icon for an executable JAR is a coffee cup.  To add a custom icon, we need to create an .icns file.

Use the following commands to download a sample PNG image, resize the image to appropriate dimensions for an icon, and convert it into the .icns format:

         curl --remote-name https://centerkey.com/mac/java/ShowTime.png
         sips --version
         sips --resampleHeightWidth 120 120 --padToHeightWidth 175 175 \
            ShowTime.png --out ShowTime-background.png
         cp -v ShowTime-background.png ShowTime-background-darkAqua.png
         mkdir ShowTime.iconset
         sips --resampleHeightWidth 128 128 \
            ShowTime.png --out ShowTime.iconset/icon_128x128.png
         iconutil --convert icns ShowTime.iconset
         ls -o
      

8) Create package resource folder

Use the following commands to copy the graphic files into a folder for package resources:

         mkdir -p package/macos
         cp -v *.png *.icns package/macos
      

9) Build macOS application and installer

Run the jpackage tool to build the ShowTime.app appplication and wrap it in into an installer:

         jpackage --version
         jpackage --name ShowTime --input . --main-jar ShowTime.jar \
            --resource-dir package/macos --type pkg
         ls -o *.pkg
      

The executable JAR file ShowTime.jar checks in at a mere 0.001 MB, but the installer file ShowTime-1.0.pkg almost hits a whopping 50 MB.  The reason is that the installer bundles the JRE (an Apple requirement for publishing Java programs to the Mac App Store).

When you are ready to distribute to the public, you'll want to obtain a Developer ID certificate and then sign your installer with it.

10) Try it out

Run the installer:

         open ShowTime-1.0.pkg
      

After completing the installation, go into the "Applications" folder and open the "ShowTime" application.

Wrap-Up

If you run into any problems, compare your terminal commands and output to:

For an example of how you might distribute your installer, take a look at:

That's it.