5. HelloWorld


Fantom is distributed as a simple zip file you will need to unzip to your local machine. Make sure the correct binary directory is included in your path:


When you first install Fantom it will automatically try to run using your currently configured Java VM (requires Java 8 or greater). If things are working correctly you should be able to run "fan -version":

C:\dev\fan\bin>fan -version
Fantom Launcher
Copyright (c) 2006-2020, Brian Frank and Andy Frank
Licensed under the Academic Free License version 3.0

Java Runtime:
  java.version:    1.8.0_91
  java.vm.name:    Java HotSpot(TM) 64-Bit Server VM
  java.vm.vendor:  Oracle Corporation
  java.vm.version: 25.91-b14
  java.home:       /Library/Java/JavaVirtualMachines/jdk1.8.0_91.jdk/Contents/Home/jre
  fan.platform:    macosx-x86_64
  fan.version:     1.0.74
  fan.env:         sys::BootEnv
  fan.home:        /work/fan

If that doesn't work then try these options:

  1. Review setup instructions
  2. Install Java 8 or greater and retry
  3. Explicitly configure where your JVM is installed

Fantom Shell

The Fantom shell is a command line tool for evaluating expressions and statements. It is a great way to test things out. To launch the shell run the fansh executable and call the Obj.echo method:

Fantom Shell v1.0.74 ('?' for help)
fansh> echo("hello world #1")
hello world #1
fansh> quit

Checkout Fansh for more details on the Fantom shell.

Fantom Script

You can also execute any file with the ".fan" extension as a script file. The script must contain a full class definition with a method called "main". Create a file called "hello.fan":

class Hello
  static Void main() { echo("hello world #2") }

Pass the script file name to the fan executable:

C:\dev\fan\bin>fan hello.fan
hello world #2

Note that unlike Java or C# the arguments aren't required to be passed as a parameter to main. You can declare a Str[] parameter if you want or you can access them via Env.args.

Checkout Fan for more details running Fantom scripts. Also see unix setup and windows setup to make fan scripts executable without calling the launcher explicitly.

Fantom Pod

For production systems, you typically organize your code into precompiled modules called pods. Pods are built using Fantom's build toolkit. To build a new pod called "hello" use the init tool to create a new project:

C:\projects> fan build init hello

Which will generate a directory that looks like:

├── etc
├── fan.props
├── lib
└── src
    ├── build.fan
    └── hello
        ├── build.fan
        ├── fan
        └── test

Add a file called "Main.fan" under src/hello/fan/:

└── src
    └── hello
        └── fan
            └── Main.fan

Which declares a single class called "Main":

class Main
  static Void main() { echo("hello world #3") }

The build file itself is just a normal Fantom script file which will compile the pod:

C:\projects> cd hello\src
C:\projects\hello\src> fan build.fan
compile [hello]
  Compile [hello]
    FindSourceFiles [1 files]
    WritePod [C:\projects\hello\lib\fan\hello.pod]

If you look in your "lib/fan" directory you should now see a file called "hello.pod". Assuming you called your method "main" in a class called "Main" you can run the main method using the fan executable:

C:\projects\hello> fan hello
hello world #3

C:\projects\hello> fan hello::Main
hello world #3

C:\projects\hello> fan hello::Main.main
hello world #3

Checkout Fan for more details running methods in a pod, and Build for details on the build toolkit.

Fantom WebApp

To create a very simple hello world web application we can create a daemon boot script which launches Fantom's built-in web server with a simple hello WebMod.

Let's look at some example code (this script is available under "examples/web/hello.fan"):

using util
using web
using wisp

class WebHello : AbstractMain
  @Opt { help = "http port" }
  Int port := 8080

  override Int run()
    wisp := WispService
      it.port = this.port
      it.root = HelloMod()
    return runServices([wisp])

const class HelloMod : WebMod
  override Void onGet()
    res.headers["Content-Type"] = "text/plain; charset=utf-8"
    res.out.print("hello world #4")

The boot script contains two classes. The first class WebHello subclasses AbstractMain which provides the standard plumbing for writing main routines. It's primary purpose is to configure the web server to run on port 8080 and to use a simple webmod which defines how to process HTTP requests.

The HelloMod class subclasses WebMod which is Fantom's "servlet" API for servicing web requests. It doesn't do much - sets the content type and writes the response text.

If you run this script:

C:\dev\fan\bin>fan ../examples/web/hello.fan
[09:57:40 11-Apr-08] [info] [fand] booting...
[09:57:40 11-Apr-08] [info] [web] WispService started on port 8080

You should be able to hit http://localhost:8080/ with your browser!