Heroku Gradle Plugin

To deploy our server application directly to Heroku, we will use the heroku-gradle plugin. Add the following to plugins declaration of your build.gradle:

id "com.heroku.sdk.heroku-gradle" version "2.0.0"

So your plugins declaration must look like this:

plugins {
  id 'java'
  id "com.heroku.sdk.heroku-gradle" version "2.0.0"
}

Moreover, you need to add a configuration for the heroku-gradle plugin; add the following to your build.gradle:¹

heroku {
  jdkVersion = 11
  processTypes(web: "java -jar build/libs/course-search-api-0.0.1.jar")
}

Notice the jdkVersion must be the same as your Java SDK version. Moreover, the command in processTypes is the same command we used to run the API server from the terminal after we had packaged it into a single JAR file.

Port on Heroku

Before we deploy, we need to make an adjustment to our server application; when we run our server locally, by default, Spark runs on port 4567. Heroku assigns your application a new port every time you deploy it, so we have to find this port and tell Spark to use it.

Add the following method to ApiServer class:

private static int getHerokuAssignedPort() {
  // Heroku stores port number as an environment variable
  String herokuPort = System.getenv("PORT");
  if (herokuPort != null) {
    return Integer.parseInt(herokuPort);
  }
  //return default port if heroku-port isn't set (i.e. on localhost)
  return 4567; 
}

Update the main method in ApiServer class:

public class ApiServer {
  public static void main(String[] args) {
+   port(getHerokuAssignedPort());

    // the rest has not changed

Run the API server (from within IntelliJ). Then, go to Postman and send a Get request to http://localhost:4567/api/courses to get the list of sample courses.