Environment variables in configuration in Spring Boot - Mini Project: Build & Apply

Environment variables in configuration

📖 Scenario: You are building a Spring Boot application that needs to use environment variables to configure its behavior. This is common when deploying apps to different environments like development, testing, and production.

🎯 Goal: Create a Spring Boot application that reads a custom environment variable and uses it in the configuration to display a greeting message.

📋 What You'll Learn

Create a property in application.properties that reads an environment variable

Create a Spring Boot @Component class that uses @Value to inject the property

Write a method that returns the greeting message using the injected property

Add a @RestController with a GET endpoint to return the greeting message

💡 Why This Matters

🌍 Real World

Using environment variables for configuration is essential for deploying Spring Boot applications across different environments without changing code.

💼 Career

Many companies use environment variables to manage secrets, API keys, and environment-specific settings in their Spring Boot microservices.

1

Create application.properties with environment variable placeholder

Create a file named application.properties and add a property called app.greeting that reads the environment variable GREETING_MESSAGE with a default value of Hello, World!.

Spring Boot

# Your code here

Need a hint?

Use the syntax property=${ENV_VAR:defaultValue} to read environment variables in Spring Boot.

2

Create GreetingService component with @Value injection

Create a class named GreetingService annotated with @Component. Inject the property app.greeting into a private String field called greeting using @Value. Add a public method getGreeting() that returns the greeting string.

Spring Boot

app.greeting=${GREETING_MESSAGE:Hello, World!}

// Your code here

Need a hint?

Use @Value("${app.greeting}") to inject the property into the field.

3

Create GreetingController with GET endpoint

Create a class named GreetingController annotated with @RestController. Inject GreetingService via constructor. Add a GET mapping method greet() mapped to /greet that returns the greeting string from GreetingService.getGreeting().

Spring Boot

app.greeting=${GREETING_MESSAGE:Hello, World!}

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class GreetingService {

    @Value("${app.greeting}")
    private String greeting;

    public String getGreeting() {
        return greeting;
    }
}

// Your code here

Need a hint?

Use constructor injection for GreetingService and @GetMapping("/greet") for the endpoint.

4

Add main Spring Boot application class

Create a class named DemoApplication annotated with @SpringBootApplication. Add the main method that runs SpringApplication.run(DemoApplication.class, args).

Spring Boot

app.greeting=${GREETING_MESSAGE:Hello, World!}

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class GreetingService {

    @Value("${app.greeting}")
    private String greeting;

    public String getGreeting() {
        return greeting;
    }
}

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class GreetingController {

    private final GreetingService greetingService;

    public GreetingController(GreetingService greetingService) {
        this.greetingService = greetingService;
    }

    @GetMapping("/greet")
    public String greet() {
        return greetingService.getGreeting();
    }
}

// Your code here

Need a hint?

The main class must have @SpringBootApplication and a main method to start the app.