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Learn the basics of Hilla application development: creating a project, defining and accessing Endpoints, and building views.

1. What you need

  • About 10–20 minutes, depending on if you decide to do every part step by step.

  • Node 16.14 or later.

  • JDK 11 or later, for example, Eclipse Temurin JDK.

Visual Studio Code is used in this tutorial. See the setup instructions on YouTube. You can use any IDE that supports Java, TypeScript, HTML, and CSS.

This tutorial is intended for developers with a basic understanding of Java, JavaScript, HTML, and CSS. You don’t need to be an expert by any means, but understanding the syntax and basic concepts makes it easier to follow along.

2. Create a Hilla project

Use the Hilla CLI to create a new project:

npx @hilla/cli init --preset hilla-tutorial hilla-todo

Alternatively, you can download the starter as a zip-file and extract it.

Unpack the downloaded zip into a folder on your computer, and import the project in the IDE of your choice.

If you open one of the .ts files inside the frontend/views folder, you might see red underlines for unresolved imports. They get resolved when you start the development server for the first time, when all dependencies are downloaded.

Importing into VS Code

Import the project by either:

  • navigating to the project folder and running code . (note the period), or

  • choosing File  Open…​ in VS Code and selecting the project folder.

You should install the following extensions to VS Code for an optimal development experience:

VS Code should automatically suggest these for you when you open the project.

Project architecture and structure

Hilla projects are based on Spring Boot and use Maven for dependency management and build configuration.

Project structure

The following lists the key folders and files in a Hilla application project:

frontend

The folder where your views and front-end code live.

src

The folder where your Java back-end code lives.

pom.xml

The project configuration file, which defines dependencies.

frontend/index.html

The bootstrap page. You don’t usually need to edit this.

frontend/index.ts

Your application routes are defined here.

src/main/java/com/example/application/Application.java

The Java class which runs the Spring Boot application.

See Application architecture for more details.

3. Define the data model and service layer

Begin by setting up the data model and services for accessing the database. You can do this in two steps:

  1. Define an entity.

  2. Create a repository for accessing the database.

This tutorial shows how to use an in-memory H2 database and JPA for persistence. The starter you downloaded already includes the needed dependencies in the pom.xml file.

3.1. Define an entity

Define a JPA entity class for the data model, by creating a new file, Todo.java, in src/main/java/com/example/application with the following content:

package com.example.application;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.validation.constraints.NotBlank;

@Entity // (1)
public class Todo {

  @Id
  @GeneratedValue
  private Integer id;

  private boolean done = false;

  @NotBlank // (2)
  private String task;

  public Todo() {}

  public Todo(String task) {
    this.task = task;
  }

  public Integer getId() {
    return id;
  }

  public void setId(Integer id) {
    this.id = id;
  }

  public boolean isDone() {
    return done;
  }

  public void setDone(boolean done) {
    this.done = done;
  }

  public String getTask() {
    return task;
  }

  public void setTask(String task) {
    this.task = task;
  }
}
  1. Turn the class into a JPA entity with an @Entity annotation.

  2. Add a @NotBlank Java bean validation annotation to enforce validity both in the view and on the server.

3.2. Create a repository

Next, create a repository for accessing the database. You only need to define an interface with type information: Spring Data takes care of the implementation. Create a new file, TodoRepository.java, in src/main/java/com/example/application, with the following contents:

package com.example.application;

import org.springframework.data.jpa.repository.JpaRepository;

public interface TodoRepository extends JpaRepository<Todo, Integer> {
}

You now have all the necessary back-end code in place to start building a UI.

Hilla can generate TypeScript versions of the Java files you created. To achieve this, run the project from the command line:

.\mvnw

The first time you run the application, it may take up to a few minutes, as Hilla downloads all the dependencies and builds a front-end bundle. Subsequent builds don’t download dependencies, so that they are much faster.

When the build has finished, you should see the application running on http://localhost:8080.

Running project

4. Create a typed server endpoint

One of the key features of Hilla is type-safe server access through endpoints. When you define an @Endpoint, Hilla creates the needed REST-like endpoints, secures them, and generates TypeScript interfaces for all the data types and public methods used. Having full-stack type safety helps you stay productive through autocomplete and helps guard against breaking the UI when you change the data model on the server.

Create a new TodoEndpoint.java file in src/main/java/com/example/application with the following content:

package com.example.application;

import java.util.List;

import com.vaadin.flow.server.auth.AnonymousAllowed;
import dev.hilla.Endpoint;
import dev.hilla.Nonnull;


@Endpoint // (1)
@AnonymousAllowed // (2)
public class TodoEndpoint {
  private TodoRepository repository;

  public TodoEndpoint(TodoRepository repository) { // (3)
    this.repository = repository;
  }

  public @Nonnull List<@Nonnull Todo> findAll() { // (4)
    return repository.findAll();
  }

  public Todo save(Todo todo) {
    return repository.save(todo);
  }
}
  1. Annotating a class with @Endpoint exposes it as a service for client-side views. All public methods of an endpoint are callable from TypeScript.

  2. By default, endpoint access requires an authenticated user. @AnonymousAllowed enables access for anyone. See Configuring Security for more information on endpoint security.

  3. Use Spring to automatically inject the TodoRepository dependency for database access.

  4. Using the @Nonnull annotation ensures that the TypeScript generator doesn’t interpret these values as possibly undefined.

5. Build the Todo view

Hilla uses the Lit library for client-side views. Lit is a lightweight and highly performant library for building reactive components with declarative templates.

Next, you create a view for adding and viewing to-do items. You can choose to build it step by step, learning some concepts along the way, or to copy the complete view implementation if you are in a hurry. When you’re ready, you can learn more about creating components.

Build the view step by step

Open the frontend/views/todo/todo-view.ts file and replace its contents with the following:

import { html } from 'lit';
import { customElement, state } from 'lit/decorators.js';
// (1)
import '@vaadin/button';
import '@vaadin/checkbox';
import '@vaadin/text-field';
import { Binder, field } from '@hilla/form';
import Todo from 'Frontend/generated/com/example/application/Todo';
import TodoModel from 'Frontend/generated/com/example/application/TodoModel';
import { TodoEndpoint } from 'Frontend/generated/endpoints';
import { View } from '../view';

@customElement('todo-view') // (2)
export class TodoView extends View { // (3)
}
  1. Import the UI components, helpers, and generated TypeScript models required for building the view.

  2. Register the new component with the browser. This makes it available as <todo-view>. The routing in index.ts is already set up to show it when you navigate to the application.

  3. Define the component class that extends from View.

Define the view state

Inside the TodoView class, define the view state as follows:

@state()
private todos: Todo[] = []; // (1)
private binder = new Binder(this, TodoModel); // (2)
  1. The list of Todo items is private and decorated with @state(), so Lit observes it for changes.

  2. A Hilla Binder is used to handle the form state for creating new Todo objects. TodoModel is automatically generated by Hilla. This describes the data types and validations that Binder needs. Read more about forms in Binding Data to Forms.

Define styles

Define some padding on the view. Web Components have a default display value of inline, which is rarely what you want. Set it to block instead by adding the following code to the themes/hilla-todo/styles.css file, which is where you define styles in a Hilla application, as explained in Styling.

todo-view {
  display: block;
  padding: var(--lumo-space-m) var(--lumo-space-l); /* <1> */
}
  1. The padding property is defined using the spacing properties to be consistent with the rest of the app.

Define the HTML template

Go back to the todo-view.ts file and define a render() method that returns an html template literal inside the class.

render() {
  return html`

  `;
}

Add the following code within the html template:

<div class="form">
  <vaadin-text-field
    ${field(this.binder.model.task) /* <1> */ }
  ></vaadin-text-field>
  <vaadin-button
    theme="primary"
    @click=${this.createTodo /* <2> */}
    ?disabled=${this.binder.invalid /* <3> */}
  >
    Add
  </vaadin-button>
</div>
  1. The Text Field component is bound to the task property of a Todo using ${field(this.binder.model.task)}. You can read more about forms in Binding Data to Forms.

  2. The click event of the Add button is bound to the createTodo() method.

  3. The button is disabled if the form is invalid.

Right underneath the previous <div>, add the following code:

<div class="todos">
  ${this.todos.map((todo) => /* <1> */ html`
      <div class="todo">
        <vaadin-checkbox
          ?checked=${todo.done /* <2> */}
          @checked-changed=${(e: CustomEvent) => // (3)
            this.updateTodoState(todo, e.detail.value)}
        ></vaadin-checkbox>
        <span>${todo.task}</span>
      </div>
    `
  )}
</div>
  1. The existing todo items are shown by mapping the todos array to Lit templates. The template for a single Todo contains a checkbox and the task text.

  2. Bind the checked boolean attribute to the done property on the todo.

  3. Call the updateTodoState() method, with the todo and the new value, whenever the checked value changes.

Update the view state and call the backend

Below the render() method in the TodoView class, add a connectedCallback() lifecycle callback to initialize the view when it’s attached to the DOM.

async connectedCallback() { // (1)
  super.connectedCallback(); // (2)
  this.todos = await TodoEndpoint.findAll(); // (3)
}
  1. Use an async function to make it easier to handle asynchronous code.

  2. Remember to call the superclass method.

  3. The getTodos() method is automatically generated by Hilla based on the method in TodosEndpoint.java. The method was imported in the head of the file. The await keyword waits for the server response without blocking the UI.

Below the connectedCallback(), add another method to handle the creation of a new Todo.

async createTodo() {
  const createdTodo = await this.binder.submitTo(TodoEndpoint.save); // (1)
  if (createdTodo) {
    this.todos = [...this.todos, createdTodo]; // (2)
    this.binder.clear(); // (3)
  }
}
  1. Use binder to submit the form to TodoEndpoint. The Binder validates the input before posting it, and the server revalidates it.

  2. Update the state with a new array that includes the saved Todo. This re-renders the view.

  3. Clear the form input.

Finally, add a method for updating the todo state right below createTodo():

updateTodoState(todo: Todo, done: boolean) {
  todo.done = done;
  const updatedTodo = { ...todo }; // (1)
  this.todos = this.todos.map((t) => (t.id === todo.id ? updatedTodo : t)); // (2)
  TodoEndpoint.save(updatedTodo); // (3)
}
  1. Create a new Todo with the updated done state.

  2. Update the local todos array with the new state. The map operator creates a new array where the changed todo is swapped out. This re-renders the view.

  3. Save the updated todo to the server.

Get the complete view implementation

Open the frontend/views/todo/todo-view.ts file and replace its contents with the following:

import { html } from 'lit';

import { customElement, state } from 'lit/decorators.js';

import '@vaadin/button';
import '@vaadin/checkbox';
import '@vaadin/text-field';
import { Binder, field } from '@hilla/form';
import Todo from 'Frontend/generated/com/example/application/Todo';
import TodoModel from 'Frontend/generated/com/example/application/TodoModel';
import { TodoEndpoint } from 'Frontend/generated/endpoints';
import { View } from '../view';

@customElement('todo-view')
export class TodoView extends View {
  @state()
  private todos: Todo[] = [];

  private binder = new Binder(this, TodoModel);

  render() {
    return html`
      <div class="form">
        <vaadin-text-field ${field(this.binder.model.task)}></vaadin-text-field>
        <vaadin-button theme="primary" @click=${this.createTodo} ?disabled=${this.binder.invalid}>
          Add
        </vaadin-button>
      </div>
      <div class="todos">
        ${this.todos.map(
          (todo) => html`
            <div class="todo">
              <vaadin-checkbox
                ?checked=${todo.done}
                @checked-changed=${(e: CustomEvent) => this.updateTodoState(todo, e.detail.value)}></vaadin-checkbox>
              <span>${todo.task}</span>
            </div>
        `)}
      </div>
    `;
  }

  async connectedCallback() {
    super.connectedCallback();
    this.todos = await TodoEndpoint.findAll();
  }

  async createTodo() {
    const createdTodo = await this.binder.submitTo(TodoEndpoint.save);
    if (createdTodo) {
      this.todos = [...this.todos, createdTodo];
      this.binder.clear();
    }
  }

  updateTodoState(todo: Todo, done: boolean) {
    todo.done = done;
    const updatedTodo = { ...todo };
    this.todos = this.todos.map((t) => (t.id === todo.id ? updatedTodo : t));
    TodoEndpoint.save(updatedTodo);
  }
}

6. Run the application

Run the project from the command line with the following command:

.\mvnw

The first time you run the application, it may take up to a few minutes, as Hilla downloads all the dependencies and builds a front-end bundle. Subsequent builds don’t download dependencies, so that they are much faster.

When the build has finished, you should see the application running on http://localhost:8080.

You should now have a fully functional to-do application. Notice that when you refresh the browser, it keeps the same todo items, as they are persisted in the database.

The to-do application running in a web browser