Creating a simple webserver with Pottery and Javalin

Javalin is a lightweight and fast Java and Kotlin framework which is having a big adoption rate due to its simplicity and performance. If you are used to work with other frameworks like ktor for Kotlin and express.js for NodeJS, you are not going to be surprised by its API design.

This post summarises how to create a simple HTTP REST API that prints the current date. We will be bundling and testing the application using Pottery and jUnit 5.

Initialising a new pottery project

To initialise a new Pottery project, you will need the Pottery wrapper. You can download it by issuing the following command in your shell:

curl -s -L https://github.com/kmruiz/pottery/releases/latest/download/pottery.sh > pottery.sh && chmod +x pottery.sh

This will download the latest pottery wrapper (pottery.sh) and add executable permissions. Now, create a new project by running the following command.

./pottery.sh init javalin-app "cat.pottery" "javalin_example" "0.0.1"
cp pottery.sh javalin-app/

It will take a few seconds and create a new directory called javalin-app with a sample main class. Open the generated pottery.yaml file and write the following contents:

parameters:
  junit.version: "5.9.1" ## latest junit5 version, for testing
  javalin.version: "5.3.0" ## latest javalin version, the web server

artifact:
  group:    "cat.pottery"
  id:       "javalin_example"
  version:  "0.0.1"

  platform:
    version: "17" ## we will need the JDK 17
    produces:
      - "fatjar" ## we will bundle our app as a fatJar

  manifest:
    main-class: "Main"

  dependencies:
    - production: "io.javalin:javalin:${javalin.version}"
    - test: "org.junit.jupiter:junit-jupiter-api:${junit.version}"

Open the main class. It should be located in src/main/java and it’s a file named Main.java. Write it’s contents with:

import io.javalin.Javalin;
import io.javalin.http.HttpStatus;

import java.time.LocalDateTime;

public class Main {
    public static void main(String[] args) {
        Javalin.create()
                .get("/time", ctx -> {
                    ctx.result(LocalDateTime.now().toString()).status(HttpStatus.OK);
                }).start(9080);
    }
}

Now we can bundle the application and run it. Issue the package command to download all dependencies and create a fatJar:

./pottery.sh package 

Pottery will download all required dependencies for running your application and bundle the fatJar. The command is finished when it shows an output similar to:

[INFO]  Built fatJar target/javalin_example-0.0.1-fat.jar in 0.88 seconds.
[INFO]  All packages built in 8.06 seconds.

Now you can run your application as a normal Java fatJar:

java -jar target/javalin_example-0.0.1-fat.jar

You can call the endpoint by using cURL:

curl http://localhost:9080/time