Getting Started on Heroku with Java

Introduction

Complete this tutorial to deploy a sample Java app to Cedar, the legacy generation of the Heroku platform. To deploy the app to the Fir generation, only available to Heroku Private Spaces, follow this guide instead.

The tutorial assumes that you have:

• A verified Heroku Account
• OpenJDK 17 (or newer) installed locally
• Postgres installed locally
• An Eco dynos plan subscription (recommended)

If you prefer to use Gradle instead of Maven, see the Getting Started with Gradle on Heroku guide.

Set Up

Install the Heroku Command Line Interface (CLI). You can use the CLI to manage and scale your applications, provision add-ons, view your logs, and run your application locally.

Download and run the installer for your platform:

After installation completes, you can use the heroku command from your terminal.

To log in to the Heroku CLI, use the heroku login command:

$ heroku login
heroku: Press any key to open up the browser to login or q to exit
 ›   Warning: If browser does not open, visit
 ›   https://cli-auth.heroku.com/auth/browser/***
heroku: Waiting for login...
Logging in... done
Logged in as me@example.com

This command opens your web browser to the Heroku login page. If your browser is already logged in to Heroku, simply click the Log in button displayed on the page.

Both the heroku and git commands require this authentication to work correctly.

Prepare the App

Create a local copy of the sample app by executing the following commands in your local command shell or terminal:

$ git clone https://github.com/heroku/java-getting-started
$ cd java-getting-started

This functioning Git repository contains a sample Java application. It includes a pom.xml file, which is used by Maven, a Java build tool.

Create Your App

 

To prepare Heroku to receive your source code, create an app:

$ heroku create
Creating app... done, ⬢ peaceful-inlet-84135
http://peaceful-inlet-84135.herokuapp.com/ | https://git.heroku.com/peaceful-inlet-84135.git

When you create an app, a git remote called heroku is also created and associated with your local git repository. Git remotes are versions of your repository that live on other servers. You deploy your app by pushing its code to that special Heroku-hosted remote associated with your app.

Heroku generates a random name for your app, in this case, peaceful-inlet-84135. You can specify your own app name.

Define a Procfile

Use a Procfile, a text file in the root directory of your application, to explicitly declare what command to execute to start your app.

The Procfile in the example app looks like this:

web: java -jar target/java-getting-started-1.0.0-SNAPSHOT.jar

This Procfile declares a single process type, web, and the command needed to run it. The name web is important here. It declares that this process type is attached to Heroku’s HTTP routing stack and receives web traffic when deployed.

A Procfile can contain additional process types. For example, you can declare a background worker process that processes items off a queue.

Provision a Database

The sample app requires a database. Provision a Heroku Postgres database, one of the add-ons available through the Elements Marketplace. Add-ons are cloud services that provide out-of-the-box additional services for your application, such as logging, monitoring, databases, and more.

$ heroku addons:create heroku-postgresql:essential-0
Creating heroku-postgresql:essential-0 on ⬢ peaceful-inlet-84135... ~$0.007/hour (max $5/month)
Database should be available soon
postgresql-fitted-70383 is being created in the background. The app will restart when complete...
Use heroku addons:info postgresql-fitted-70383 to check creation progress
Use heroku addons:docs heroku-postgresql to view documentation

Your Heroku app now has access to a Postgres database. The DATABASE_URL environment variable stores the credentials. Heroku also automatically makes a JDBC_DATABASE_URL environment variable available for Java applications. It contains a JDBC-compatible version of DATABASE_URL.

You can see all the add-ons provisioned with the addons command:

$ heroku addons
Add-on                                       Plan         Price     State
───────────────────────────────────────────  ───────────  ────────  ───────
heroku-postgresql (postgresql-fitted-70383)  essential-0  $5/month  created
 └─ as DATABASE

The table above shows add-ons and the attachments to the current app (peaceful-inlet-84135) or other apps.

Deploy the App

Deploy your code. This command pushes the main branch of the sample repo to your heroku remote, which then deploys to Heroku:

$ git push heroku main
remote: Compressing source files... done.
remote: Building source:
remote:
remote: -----> Building on the Heroku-22 stack
remote: -----> Determining which buildpack to use for this app
remote: -----> Java app detected
remote: -----> Installing OpenJDK 17... done
remote: -----> Executing Maven
remote:        $ ./mvnw -DskipTests clean dependency:list install
...
remote:        [INFO] ------------------------------------------------------------------------
remote:        [INFO] BUILD SUCCESS
remote:        [INFO] ------------------------------------------------------------------------
remote:        [INFO] Total time:  10.733 s
remote:        [INFO] Finished at: 2023-03-09T16:00:12Z
remote:        [INFO] ------------------------------------------------------------------------
remote: -----> Discovering process types
remote:        Procfile declares types -> web
remote:
remote: -----> Compressing...
remote:        Done: 86.4M
remote: -----> Launching...
remote:        Released v5
remote:        https://peaceful-inlet-84135.herokuapp.com/ deployed to Heroku
remote:
remote: Verifying deploy... done.
To https://git.heroku.com/peaceful-inlet-84135.git
 * [new branch]      main -> main

By default, apps use Eco dynos if you’re subscribed to Eco. A dyno is a lightweight Linux container that runs the command specified in your Procfile. After deployment, ensure that you have one web dyno running the app. You can check how many dynos are running using the heroku ps command:

$ heroku ps
Eco dyno hours quota remaining this month: 1000h 0m (100%)
Eco dyno usage for this app: 0h 0m (0%)
For more information on Eco dyno hours, see:
https://devcenter.heroku.com/articles/eco-dyno-hours

=== web (Eco): java -jar target/java-getting-started-1.0.0-SNAPSHOT.jar (1)
web.1: up 2023/03/09 17:00:28 +0100 (~ 1m ago)

The running web dyno serves requests. Visit the app at the URL shown in the logs. As a handy shortcut, you can open the website with:

$ heroku open

The Eco dynos plan is shared across all Eco dynos in your account and is recommended if you plan on deploying many small apps to Heroku. Eco dynos sleep if they don’t receive any traffic for half an hour. This sleep behavior causes a few seconds delay for the first request upon waking. Eco dynos consume from a monthly, account-level quota of eco dyno hours. As long as you haven’t exhausted the quota, your apps can continue to run.

To avoid dyno sleeping, upgrade to a Basic or Professional dyno type as described in Dyno Types.

Scale the App

Horizontal scaling an application on Heroku is equivalent to changing the number of running dynos.

Scale the number of web dynos to zero:

$ heroku ps:scale web=0

Access the app again by refreshing your browser or running heroku open. You get an error message because your app no longer has any web dynos available to serve requests.

Scale it up again:

$ heroku ps:scale web=1

View Logs

Heroku treats logs as streams of time-ordered events, aggregated from the output streams of all your app and Heroku components. Heroku provides a single stream for all events.

View information about your running app by using one of the logging commands, heroku logs --tail:

$ heroku logs --tail
2023-03-09T16:03:23.130513+00:00 app[web.1]: 2023-03-09T16:03:23.130Z  INFO 2 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 41040 (http)
2023-03-09T16:03:23.141029+00:00 app[web.1]: 2023-03-09T16:03:23.140Z  INFO 2 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2023-03-09T16:03:23.141265+00:00 app[web.1]: 2023-03-09T16:03:23.141Z  INFO 2 --- [           main] o.apache.catalina.core.StandardEngine    : Starting Servlet engine: [Apache Tomcat/10.1.5]
2023-03-09T16:03:23.218914+00:00 app[web.1]: 2023-03-09T16:03:23.218Z  INFO 2 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2023-03-09T16:03:23.220624+00:00 app[web.1]: 2023-03-09T16:03:23.220Z  INFO 2 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 976 ms
2023-03-09T16:03:23.469655+00:00 app[web.1]: 2023-03-09T16:03:23.469Z  INFO 2 --- [           main] o.s.b.a.w.s.WelcomePageHandlerMapping    : Adding welcome page template: index
2023-03-09T16:03:23.692938+00:00 app[web.1]: 2023-03-09T16:03:23.692Z  INFO 2 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 41040 (http) with context path ''
2023-03-09T16:03:23.707694+00:00 app[web.1]: 2023-03-09T16:03:23.707Z  INFO 2 --- [           main] c.heroku.java.GettingStartedApplication  : Started GettingStartedApplication in 1.927 seconds (process running for 2.33)
2023-03-09T16:03:23.940755+00:00 heroku[web.1]: State changed from starting to up
2023-03-09T16:03:24.673236+00:00 app[web.1]: 2023-03-09T16:03:24.672Z  INFO 2 --- [io-41040-exec-3] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
2023-03-09T16:03:24.673549+00:00 app[web.1]: 2023-03-09T16:03:24.673Z  INFO 2 --- [io-41040-exec-3] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2023-03-09T16:03:24.674938+00:00 app[web.1]: 2023-03-09T16:03:24.674Z  INFO 2 --- [io-41040-exec-3] o.s.web.servlet.DispatcherServlet        : Completed initialization in 1 ms
2023-03-09T16:03:24.948408+00:00 heroku[router]: at=info method=GET path="/" host=peaceful-inlet-84135.herokuapp.com request_id=e010a5e5-f212-4e0b-a624-c96f7421c98f fwd="85.222.134.1" dyno=web.1 connect=0ms service=304ms status=200 bytes=8917 protocol=https
2023-03-09T16:03:25.162539+00:00 heroku[router]: at=info method=GET path="/stylesheets/main.css" host=peaceful-inlet-84135.herokuapp.com request_id=dcbe440f-82c5-4442-80bc-be7be0b5cd61 fwd="85.222.134.1" dyno=web.1 connect=0ms service=10ms status=304 bytes=208 protocol=https
2023-03-09T16:03:25.335819+00:00 heroku[router]: at=info method=GET path="/lang-logo.png" host=peaceful-inlet-84135.herokuapp.com request_id=071b67a6-1e22-4cfe-b57b-c49db6b5af19 fwd="85.222.134.1" dyno=web.1 connect=0ms service=3ms status=304 bytes=208 protocol=https
2023-03-09T16:03:25.534061+00:00 heroku[router]: at=info method=GET path="/favicon.ico" host=peaceful-inlet-84135.herokuapp.com request_id=cc651ead-23ce-4c43-a3ce-4edc93450b14 fwd="85.222.134.1" dyno=web.1 connect=0ms service=82ms status=404 bytes=333 protocol=https

To see more log messages generate, visit your application in the browser first.

To stop streaming the logs, press Control+C.

Provision a Logging Add-on

Add-ons are third-party cloud services that provide out-of-the-box additional services for your application, from persistence through logging to monitoring and more.

By default, Heroku stores 1500 lines of logs from your application, but the full log stream is available as a service. Several add-on providers have logging services that provide things such as log persistence, search, and email and SMS alerts.

In this step, you provision one of these logging add-ons, Papertrail.

Provision the Papertrail logging add-on:

$ heroku addons:create papertrail
Creating papertrail on ⬢ peaceful-inlet-84135... free
Welcome to Papertrail. Questions and ideas are welcome (technicalsupport@solarwinds.com). Happy logging!
Created papertrail-slippery-84785 as PAPERTRAIL_API_TOKEN
Use heroku addons:docs papertrail to view documentation

The add-on is now deployed and configured for your application. You can list add-ons for your app with this command:

$ heroku addons

To see this particular add-on in action, visit your application’s Heroku URL a few times. Each visit generates more log messages, which get routed to the Papertrail add-on. Visit the Papertrail console to see the log messages:

$ heroku addons:open papertrail

Your browser opens up a Papertrail web console that shows the latest log events. The interface lets you search and set up alerts.

Use a Database

Heroku provides managed data services for Postgres and Redis, and the add-on marketplace provides additional data services, including MongoDB and MySQL.

Use the heroku addons command for an overview of the database provisioned for your app:

$ heroku addons

Add-on                                       Plan         Price     State
───────────────────────────────────────────  ───────────  ────────  ───────
heroku-postgresql (postgresql-fitted-70383)  essential-0  $5/month  created
 └─ as DATABASE

papertrail (papertrail-slippery-84785)       choklad      free      created
 └─ as PAPERTRAIL

Listing the config vars for your app displays the URL that your app uses to connect to the database, DATABASE_URL:

$ heroku config
=== peaceful-inlet-84135 Config Vars
DATABASE_URL:         postgres://avhrhofbiyvpct:3ab23026d0fc225bde4544cedabc356904980e6a02a2418ca44d7fd19dad8e03@ec2-23-21-4-7.compute-1.amazonaws.com:5432/d8e8ojni26668k
PAPERTRAIL_API_TOKEN: ChtIUu9fHbij1cBn7y6z

The heroku pg command provides more in-depth information on your app’s Heroku Postgres databases:

$ heroku pg
=== DATABASE_URL
Plan:                  Essential 0
Status:                Available
Connections:           0/20
PG Version:            15.5
Created:               2024-05-01 13:22 UTC
Data Size:             8.6 MB/1.00 GB (0.84%) (In compliance)
Tables:                0
Fork/Follow:           Unsupported
Rollback:              Unsupported
Continuous Protection: Off
Add-on:                postgresql-fitted-70383

Running this command for your app indicates that the app has an essential-0 Postgres database running Postgres 15.5, with no tables.

The example app you deployed already has database functionality, which you can reach by visiting your app’s /database path.

$ heroku open /database

You see something like this:

Database Output

* Read from DB: 2023-03-09 16:58:55.816605
* Read from DB: 2023-03-09 16:58:56.728701
* Read from DB: 2023-03-09 16:58:57.064755

Assuming that you have Postgres installed locally, use the heroku pg:psql command to connect to the remote database and see all the rows:

$ heroku pg:psql
--> Connecting to postgresql-fitted-70383
psql (15.2, server 14.7 (Ubuntu 14.7-1.pgdg20.04+1))
SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, compression: off)
Type "help" for help.

peaceful-inlet-84135::DATABASE=> SELECT * FROM ticks;
            tick
----------------------------
 2023-03-09 16:58:55.816605
 2023-03-09 16:58:56.728701
 2023-03-09 16:58:57.064755
(3 rows)

peaceful-inlet-84135::DATABASE=> \q

The code in the example app looks like this:

private final DataSource dataSource;

@Autowired
public GettingStartedApplication(DataSource dataSource) {
    this.dataSource = dataSource;
}

@GetMapping("/database")
String database(Map<String, Object> model) {
    try (Connection connection = dataSource.getConnection()) {
        final var statement = connection.createStatement();
        statement.executeUpdate("CREATE TABLE IF NOT EXISTS ticks (tick timestamp)");
        statement.executeUpdate("INSERT INTO ticks VALUES (now())");

        final var resultSet = statement.executeQuery("SELECT tick FROM ticks");
        final var output = new ArrayList<>();
        while (resultSet.next()) {
            output.add("Read from DB: " + resultSet.getTimestamp("tick"));
        }

        model.put("records", output);
        return "database";

    } catch (Throwable t) {
        model.put("message", t.getMessage());
        return "error";
    }
}

The database method adds a row to the tick table when you access your app using the /database route. It then returns all rows to render in the output.

The DataSource shown in the example app code is automatically configured and injected by the Spring Boot framework. It refers to the values in the src/main/resources/application.properties file for the database connection configuration.

The example app has spring.datasource.url set to the value in the JDBC_DATABASE_URL environment variable to establish a pool of connections to the database:

spring.datasource.url: ${JDBC_DATABASE_URL}

The official Heroku Java buildpack that’s automatically added to your app sets this JDBC_DATABASE_URL environment variable when a dyno starts up. This variable is dynamic and doesn’t appear in your list of configuration variables when running heroku config. You can view it by running the following command:

$ heroku run echo \$JDBC_DATABASE_URL

Read more about Heroku PostgreSQL. You can also install Redis or other data add-ons via heroku addons:create.

Prepare the Local Environment

You must install your app’s dependencies before you can run your app locally.

Run ./mvnw clean install in your local directory. This command installs the dependencies to your local environment, preparing your system to run the app locally.

$ ./mvnw clean install
...
[INFO] Installing /Users/example-user/java-getting-started/pom.xml to /Users/example-user/.m2/repository/com/heroku/java-getting-started/1.0.0-SNAPSHOT/java-getting-started-1.0.0-SNAPSHOT.pom
[INFO] Installing /Users/example-user/java-getting-started/target/java-getting-started-1.0.0-SNAPSHOT.jar to /Users/example-user/.m2/repository/com/heroku/java-getting-started/1.0.0-SNAPSHOT/java-getting-started-1.0.0-SNAPSHOT.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  1.125 s
[INFO] Finished at: 2023-03-09T17:24:39+01:00
[INFO] ------------------------------------------------------------------------

The Maven process compiles and builds a JAR, with dependencies, placing it into your application’s target directory. The spring-boot-maven-plugin in the pom.xml provides this process.

After installing dependencies, you can run your app locally but it still requires a Postgres database. Create a local Postgres database and update your local .env file.

heroku local, the command used to run apps locally, automatically sets up your environment based on the .env file in your app’s root directory. Set the JDBC_DATABASE_URL environment variable with your local Postgres database’s connection string:

JDBC_DATABASE_URL=jdbc:postgresql://localhost:5432/java_database_name

Your local environment is now ready to run your app and connect to the database.

Run the App Locally

Ensure you’ve already run ./mvnw clean install before running your app locally.

Start your application locally with the heroku local CLI command:

$ heroku local --port 5001
...
5:26:58 PM web.1 |  2023-03-09T17:26:58.009+01:00  INFO 39665 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 5001 (http)
5:26:58 PM web.1 |  2023-03-09T17:26:58.014+01:00  INFO 39665 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
5:26:58 PM web.1 |  2023-03-09T17:26:58.014+01:00  INFO 39665 --- [           main] o.apache.catalina.core.StandardEngine    : Starting Servlet engine: [Apache Tomcat/10.1.5]
5:26:58 PM web.1 |  2023-03-09T17:26:58.055+01:00  INFO 39665 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
5:26:58 PM web.1 |  2023-03-09T17:26:58.056+01:00  INFO 39665 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 497 ms
5:26:58 PM web.1 |  2023-03-09T17:26:58.175+01:00  INFO 39665 --- [           main] o.s.b.a.w.s.WelcomePageHandlerMapping    : Adding welcome page template: index
5:26:58 PM web.1 |  2023-03-09T17:26:58.278+01:00  INFO 39665 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 5001 (http) with context path ''
5:26:58 PM web.1 |  2023-03-09T17:26:58.288+01:00  INFO 39665 --- [           main] c.heroku.java.GettingStartedApplication  : Started GettingStartedApplication in 0.931 seconds (process running for 1.119)

Just like the Heroku platform, heroku local examines your Procfile to determine what command to run.

To see your app running locally, open http://localhost:5001 with your web browser

If you want to access the app’s /database route locally, ensure that your local Postgres database is running before you visit the URL.

To stop the app from running locally, go back to your terminal window and press Control+C to exit.

Push Local Changes

In this step, you make local changes to your app and deploy them to Heroku.

Modify pom.xml to include a dependency for jscience by adding the following code inside the <dependencies> element:

In the file pom.xml, add the following dependency to the <dependencies> element:

<dependency>
  <groupId>org.jscience</groupId>
  <artifactId>jscience</artifactId>
  <version>4.3.1</version>
</dependency>

In the file src/main/java/com/heroku/java/GettingStartedApplication.java, add the following import statements for the library:

import org.jscience.physics.amount.Amount;
import org.jscience.physics.model.RelativisticModel;
import javax.measure.unit.SI;

In the file GettingStartedApplication.java, add the following convert method:

@GetMapping("/convert")
String convert(Map<String, Object> model) {
    RelativisticModel.select();
    var energy = Amount.valueOf("12 GeV");

    model.put("result", "E=mc^2: " + energy + " = " + energy.to(SI.KILOGRAM));
    return "convert";
}

Finally, create a src/main/resources/templates/convert.html file with these contents:

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org" th:replace="~{fragments/layout :: layout (~{::body},'hello')}">
<body>

<div class="container">
    <p th:text="${result}"/>
</div>

</body>
</html>

Here’s the final source code for GettingStartedApplication.java. Ensure that your changes look similar. Here’s a diff of all the local changes made.

Test your changes locally:

$ ./mvnw clean install
...
[INFO] Installing /Users/example-user/java-getting-started/pom.xml to /Users/example-user/.m2/repository/com/heroku/java-getting-started/1.0.0-SNAPSHOT/java-getting-started-1.0.0-SNAPSHOT.pom
[INFO] Installing /Users/example-user/java-getting-started/target/java-getting-started-1.0.0-SNAPSHOT.jar to /Users/example-user/.m2/repository/com/heroku/java-getting-started/1.0.0-SNAPSHOT/java-getting-started-1.0.0-SNAPSHOT.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  1.211 s
[INFO] Finished at: 2023-03-09T18:04:10+01:00
[INFO] ------------------------------------------------------------------------

$ heroku local --port 5001
...
6:05:29 PM web.1 |  2023-03-09T18:05:29.514+01:00  INFO 69174 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 492 ms
6:05:29 PM web.1 |  2023-03-09T18:05:29.628+01:00  INFO 69174 --- [           main] o.s.b.a.w.s.WelcomePageHandlerMapping    : Adding welcome page template: index
6:05:29 PM web.1 |  2023-03-09T18:05:29.726+01:00  INFO 69174 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 5001 (http) with context path ''
6:05:29 PM web.1 |  2023-03-09T18:05:29.736+01:00  INFO 69174 --- [           main] c.heroku.java.GettingStartedApplication  : Started GettingStartedApplication in 0.911 seconds (process running for 1.099)

Visit your application’s /convert path at http://localhost:5001/convert, which displays some scientific conversions:

E=mc^2: 12 GeV = (2.139194076302506E-26 ± 1.4E-42) kg

After testing, deploy your changes. Almost every Heroku deployment follows this same pattern. First, use the git add command to stage your modified files for commit:

$ git add .

Next, commit the changes to the repository:

$ git commit -m "Add convert endpoint"

Now deploy as you did before:

$ git push heroku main

Finally, check that your updated code successfully deployed by opening your browser to that route:

$ heroku open /convert

Define Config Vars

Heroku lets you externalize your app’s configuration by storing data such as encryption keys or external resource addresses in config vars.

At runtime, config vars are exposed to your app as environment variables. For example, modify GettingStartedApplication.java so that the method obtains an energy value from the ENERGY environment variable:

In the file src/main/java/com/heroku/java/GettingStartedApplication.java, change the convert method:

@GetMapping("/convert")
String convert(Map<String, Object> model) {
    RelativisticModel.select();

    final var result = java.util.Optional
            .ofNullable(System.getenv().get("ENERGY"))
            .map(Amount::valueOf)
            .map(energy -> "E=mc^2: " + energy + " = " + energy.to(SI.KILOGRAM))
            .orElse("ENERGY environment variable is not set!");

    model.put("result", result);
    return "convert";
}

Recompile the app to integrate this change by running ./mvnw clean install.

heroku local automatically sets up your local environment based on the .env file in your app’s root directory. Your sample app already includes a .env file with the following contents:

ENERGY=20 GeV

Your local .env file also includes the JDBC_DATABASE_URL variable if you set it during the Run the App Locally step.

Run the app with heroku local --port 5001 and visit http://localhost:5001/convert to see the conversion value for 20 GeV.

Now that you know it works as expected locally, set this variable as a config var on your app running on Heroku. Execute the following:

$ heroku config:set ENERGY="20 GeV"
Setting ENERGY and restarting ⬢ peaceful-inlet-84135... done, v9
ENERGY: 20 GeV

View the app’s config vars using heroku config to verify it’s set correctly:

$ heroku config
=== peaceful-inlet-84135 Config Vars
DATABASE_URL:         postgres://avhrhofbiyvpct:3ab23026d0fc225bde4544cedabc356904980e6a02a2418ca44d7fd19dad8e03@ec2-23-21-4-7.compute-1.amazonaws.com:5432/d8e8ojni26668k
ENERGY:               20 GeV
PAPERTRAIL_API_TOKEN: ChtIUu9fHbij1cBn7y6z

To see your changes in action, deploy your local changes to Heroku and visit the /convert route :

$ git add .
$ git commit -m "Use ENERGY environment variable"
$ git push heroku main
$ heroku open /convert

Start a One-off Dyno

The heroku run command lets you run maintenance and administrative tasks on your app in a one-off dyno. It also lets you launch a REPL process attached to your local terminal for experimenting in your app’s environment or your deployed application code:

$ heroku run java -version
Running java -version on ⬢ peaceful-inlet-84135... up, run.4406 (Eco)
openjdk version "17.0.6" 2023-01-17 LTS
OpenJDK Runtime Environment Zulu17.40+19-CA (build 17.0.6+10-LTS)
OpenJDK 64-Bit Server VM Zulu17.40+19-CA (build 17.0.6+10-LTS, mixed mode, sharing)

If you receive an error, Error connecting to process, configure your firewall.

Remember to type exit to exit the shell and terminate the dyno.

Next Steps

Congratulations! You now know how to deploy an app, change its configuration, scale it, view logs, attach add-ons, and run it locally.

Here’s some recommended reading to continue your Heroku journey:

• How Heroku Works provides a technical overview of the concepts encountered while writing, configuring, deploying, and running apps.
• The Java category provides more in-depth information on developing and deploying Java apps.
• The Deployment category provides a variety of powerful integrations and features to help streamline and simplify your deployments.

Delete Your App and Add-on

Remove the app and database from your account. You’re only charged for the resources you used.

$ heroku addons:destroy heroku-postgresql
 ▸    WARNING: Destructive Action
 ▸    This command will affect the app peaceful-inlet-84135
 ▸    To proceed, type peaceful-inlet-84135 or re-run this command with
 ▸    --confirm peaceful-inlet-84135

>

$ heroku apps:destroy
 ▸    WARNING: This will delete ⬢ peaceful-inlet-84135 including all add-ons.
 ▸    To proceed, type peaceful-inlet-84135 or re-run this command with
 ▸    --confirm peaceful-inlet-84135

>

You can confirm that your add-on and app are gone with these commands:

$ heroku addons --all
$ heroku apps --all