Proof of concept: Spring Boot and Vue application

Executing the project

You need:

(Required) Java 11
(Optional) Maven 3

If you have Maven installed, on the root of the project run:

mvn clean package
mvn -pl backend spring-boot:run

If you don't have Maven installed, you can use one of the provided wrappers for your OS. On Windows use mvnw.cmd and on macOS and Linux use mvnw. Example on macOS:

./mvnw clean package
./mvnw -pl spring-boot:run

Then open the project: http://localhost:8080/

Application's behavior

Once the application is up and running, the following is true:

Going to localhost:8080 serves Vue's home page.
Route navigation through page components (e.g. links) works.
Route navigation by directly typing in browser nav bar works.
The frontend can talk with the backend without CORS config.

Both the frontend and the backend exist in the same origin.

Setup overview

The project is a two-module Maven project; one sub-module for the backend, another one for the frontend.

The idea for having both the frontend and backend in the same origin boils down to having the backend serve the SPA's (Single Page Application) entry file (index.html) and let the SPA deal with everything frontend related (data fetching, state management, routing, etc.), whilst the backend merely forwards non-API requests to the SPA and attends API requests.

How to make Spring Boot serve the SPA

By default, when the root URL is visited, Spring Boot serves the following file:

src/main/resources/public/index.html

By default, when a Vue application is built, it outputs the following directory:

dist
├── css/
├── img/
├── js/
├── favicon.ico
└── index.html

The idea is to copy the output of Vue's build into the place where Spring Boot expects to find the index.html. This is done with the maven-resources-plugin (see the pom.xml of the backend sub-module). This plugin does the copying during the generate-resources phase, which comes before the compile phase. For reference on the Maven phases, see Lifecycles Reference.

Additionally, how can the frontend be built by Maven? Otherwise, the frontend would be required to be built through a npm invocation before Maven can use the output. This is done with the frontend-maven-plugin (see the pom.xml of the frontend sub-module).

Heroku configuration

Create the following config vars in the settings page of your Heroku app:

BASE_URL=<heroku-url-for-you-app>
MAVEN_CUSTOM_GOALS=clean package

This config vars are read as environment vars by the application.

BASE_URL is used by the Spring configuration and the Vue router.
MAVEN_CUSTOM_GOALS tells Heroku how to build the project.

In the root of the project, the Procfile defines the command used to execute the project. Notice that entire application can be executing through a JAR and that the heroku profile is being used.

Heroku assigns a port to the application to bind to, this is provided by Heroku through the env variable PORT. In the Spring configuration this env var is read to configure execution.

Other configurations

Vue's dev server. With the setup described above, running the project requires Maven to re-build the frontend and re-compile the backend, which can be lengthy. To accelerate frontend development, a dev server is created at localhost:8081 after running npm run serve in the frontend sub-module. This does require CORS to talk to the backend, but frontend reload is much faster. CORS is configured in Spring Boot for the dev server (see class WebConfiguration).
Spring Boot's route forwarding. Spring Boot automatically serves src/main/resources/public/index.html when the root URL is visited, however it does not automatically delegate routing to Vue. To allow Vue to handle all the routing, forwarding is required for every route except /index.html and api/* routes. See the class FrontendForwarderController.