Tag: Spring Boot

In previous articles, we talked about some features of Spring Boot that are very useful in the development phase of our system: we described simplified dependency management and API development, for instance. In this article, we are going to cover functionalities that are related to a production environment.

When a Spring Boot application is finally in production, it needs all the tools to manage and monitor it. This is especially important in complex scenarios like those related to microservice systems. Spring Boot provides an effective solution to provide the required functionalities, the Actuator. The Actuator is a Spring Boot module with a set of features available as HTTP or JMX endpoints, or even with a remote SSH shell.

There are two main ways by which microservice applications can interact with each other: REST services and messaging systems. The REST approach is the most common and will be treated in this article. We will see how Spring boot can make the development process of REST APIs fairly easy, with the use of a set of useful annotations and some implicit background behavior, like the serialization of model objects to JSON format.

Another important issue is related to the documentation and sharing of APIs, and we will see that these concerns are addressed effectively with a solution named Swagger. Integrating Swagger with Spring Boot allows us to generate the documentation from the source code, as a Swagger JSON file, and even browse and manage all the exposed REST services with a web user interface.

We sometimes encounter server errors caused by a user providing input that's longer than the database column size or even a non-existent ENUM value. Do not trust user input is a popular cliche that, if implemented, will save a lot of time and resources down the line.

That is why, in this article, we will be looking at the request-validator library, which is able to compare the user input against a pre-defined set of rules and return errors if any.

What You Will Build

You will build a full-stack reactive web app that sends and receives messages through Kafka. The app uses Spring Boot and Java on the server, Lit and TypeScript on the client, and the Hilla framework for components and communication.

What You Will Need

• 20 minutes
• Java 11 or newer
• Node 16.14 or newer
• An IDE that supports both Java and TypeScript, such as VS Code.

Technology Overview

Kafka

Apache Kafka is a distributed event streaming platform. You can think of it as a publish/subscribe system on steroids. Kafka producers can send messages to a topic, and consumers can then read those messages. However, unlike most pub/sub systems, the messages do not get removed from the topic when you read them. This allows you to perform stream processing to analyze, aggregate, or transform data from different events in real-time.

WebRTC video calls have been added to the AngularPwaMessenger project. The back end supports WebSocket connections that are secured by JWT tokens to enable WebRTC signaling. The current browsers support video calls with WebRTC. The Angular front end supports the WebRTC calls and needs to access the camera and the microphone. The browsers need to be able to connect to each other directly and use the server backend to do that. That means that home/company networks that prevent incoming connections prevent the creation of a video call. Installing the PWA on a smartphone does work because no router/firewall stops the connections. For development, a setup with a self-signed certificate is used that enables testing inside a firewalled network.

WebRTC Documentation

The Mozilla Development Network has WebRTC documentation. The WebRTC protocol is documented here and the AngularPwaMessenger backend provides a STUN server implementation for the ICE protocol. The signaling and video calls are documented here. The diagrams/code show the creation of the connection for the video call.

The AngularAndSpring project uses Kafka for the distributed sign-in of new users and the distributed token revocation for logged-out users.

System Architecture

The AngularAndSpring project needs to be able to be horizontally scaled each with its own database. To enable that, a sign-in needs to be propagated to all instances. Kafka serves as a central event streaming platform to send the sign-in events. Kafka is horizontally scalable to high event loads and can be set up to be highly available.