Application.properties basics in Spring Boot - Mini Project: Build & Apply

Application.properties basics

📖 Scenario: You are creating a simple Spring Boot application that needs configuration settings for the server port and application name.

🎯 Goal: Learn how to set up and use the application.properties file to configure basic Spring Boot application properties.

📋 What You'll Learn

Create an application.properties file with specific properties

Add a property for server.port with value 8085

Add a property for spring.application.name with value MyApp

Access these properties in a Spring Boot component using @Value annotation

Print the configured values inside a CommandLineRunner bean

💡 Why This Matters

🌍 Real World

Setting application properties is essential for configuring Spring Boot apps without changing code. It helps manage environments and customize behavior.

💼 Career

Understanding application.properties and property injection is a fundamental skill for Spring Boot developers working on real-world backend services.

1

Create application.properties file with server port

Create an application.properties file and add the line server.port=8085 to set the server port.

Spring Boot

# Your application.properties file
# Add server.port=8085 below

Need a hint?

The application.properties file is where Spring Boot reads configuration values. Setting server.port changes the port your app runs on.

2

Add application name property

In the same application.properties file, add the line spring.application.name=MyApp to set the application name.

Spring Boot

server.port=8085
# Add spring.application.name=MyApp below

Need a hint?

The spring.application.name property helps identify your app in logs and monitoring.

3

Create a Spring Boot component to read properties

Create a Java class named AppConfigReader annotated with @Component. Use @Value to inject server.port into an int serverPort field and spring.application.name into a String appName field.

Spring Boot

server.port=8085
spring.application.name=MyApp

// Create AppConfigReader class with @Component
// Use @Value to inject server.port and spring.application.name
// Your code here

Need a hint?

Use @Value("${property.name}") to inject property values into fields.

4

Print properties using CommandLineRunner

In your main Spring Boot application class, create a CommandLineRunner bean that injects AppConfigReader and prints the serverPort and appName values.

Spring Boot

server.port=8085
spring.application.name=MyApp

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

@Component
public class AppConfigReader {

    @Value("${server.port}")
    private int serverPort;

    @Value("${spring.application.name}")
    private String appName;

    public int getServerPort() {
        return serverPort;
    }

    public String getAppName() {
        return appName;
    }
}

import org.springframework.boot.CommandLineRunner;
import org.springframework.context.annotation.Bean;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.SpringApplication;

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

    // Create CommandLineRunner bean to print serverPort and appName
    // Your code here

Need a hint?

Use a CommandLineRunner bean to run code after the app starts. Inject your AppConfigReader to access properties.