1. Vaadin UI Not Rendering Properly

Understanding the Issue

The user interface does not load correctly, components do not appear, or layout styles are broken.

Root Causes

• Incorrect dependency versions or missing dependencies.
• CSS or JavaScript files not loaded properly.
• Issues with frontend bundling in Vaadin 14+ (Flow).

Fix

Ensure all required dependencies are included in pom.xml:

<dependency>
  <groupId>com.vaadin</groupId>
  <artifactId>vaadin-core</artifactId>
  <version>24.1.0</version>
</dependency>

Clear the frontend cache and rebuild the project:

mvn clean install
mvn vaadin:build-frontend

Ensure static resources are properly served by checking:

src/main/resources/META-INF/resources/frontend/

2. Vaadin Components Not Updating

Understanding the Issue

UI components do not reflect state changes, or updates are delayed.

Root Causes

• Missing UI.getCurrent().access() when modifying UI components from background threads.
• Incorrect usage of data binding.
• Session timeouts affecting UI state.

Fix

Ensure UI updates are wrapped inside an access method:

UI.getCurrent().access(() -> {
    myLabel.setText("Updated Text");
});

Use proper data binding with Vaadin’s Binder:

Binder<Person> binder = new Binder<>(Person.class);
binder.bind(nameField, Person::getName, Person::setName);

Verify session timeout settings in application.properties:

server.servlet.session.timeout=30m

3. Vaadin Performance Issues

Understanding the Issue

Vaadin applications experience slow UI rendering, high memory usage, or long server response times.

Root Causes

• Too many UI components created dynamically.
• Large datasets being loaded at once.
• Blocking operations inside UI event listeners.

Fix

Use lazy loading with Vaadin Grid:

grid.setItems(query -> personService.fetchPersons(query.getOffset(), query.getLimit()));

Avoid synchronous blocking calls inside UI event listeners:

CompletableFuture.runAsync(() -> performExpensiveOperation());

Enable production mode for optimized rendering:

mvn clean package -Pproduction

4. Vaadin Session and Authentication Issues

Understanding the Issue

Users get logged out unexpectedly, or authentication does not persist across views.

Root Causes

• Session timeout configuration is too short.
• Incorrect usage of VaadinSession for storing authentication data.
• Spring Security configuration conflicts.

Fix

Set a longer session timeout in application.properties:

server.servlet.session.timeout=60m

Ensure authentication state is stored correctly:

VaadinSession.getCurrent().setAttribute(User.class, loggedInUser);

Verify Spring Security settings for Vaadin:

@Bean
public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
    return http.authorizeHttpRequests(auth -> auth.anyRequest().authenticated())
        .formLogin().defaultSuccessUrl("/home", true)
        .and().build();
}

5. Vaadin and Third-Party Library Conflicts

Understanding the Issue

Vaadin does not work correctly when integrated with other frameworks such as Spring Boot or Hibernate.

Root Causes

• Conflicting dependency versions.
• Issues with automatic frontend compilation.
• Incorrect annotation placement for Vaadin views.

Fix

Ensure dependencies are aligned in pom.xml:

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
</dependency>

Manually trigger frontend compilation:

mvn vaadin:build-frontend

Ensure proper placement of Vaadin view annotations:

@Route("/dashboard")
@PageTitle("Dashboard")
public class DashboardView extends VerticalLayout {}

Conclusion

Vaadin simplifies Java-based web application development, but troubleshooting UI rendering, performance slowdowns, session handling, integration conflicts, and frontend build failures is essential for a smooth experience. By optimizing session management, lazy loading data, and ensuring proper dependency management, developers can create efficient and scalable Vaadin applications.

FAQs

1. Why is my Vaadin UI not rendering?

Ensure dependencies are correct, clear frontend caches, and rebuild using mvn vaadin:build-frontend.

2. How do I fix Vaadin session timeout issues?

Increase session timeout in application.properties and verify authentication state storage.

3. How can I improve Vaadin performance?

Use lazy loading in grids, enable production mode, and avoid blocking operations in event listeners.

4. Why are my Vaadin components not updating?

Wrap UI updates inside UI.getCurrent().access() when modifying from background threads.

5. How do I resolve Vaadin dependency conflicts?

Align dependency versions in pom.xml and manually trigger frontend builds.