@ConfigurationProperties for type-safe config in Spring Boot - Mini Project: Build & Apply

Using @ConfigurationProperties for Type-Safe Configuration in Spring Boot

📖 Scenario: You are building a Spring Boot application that needs to read configuration values from application.properties in a clean and type-safe way.This helps avoid mistakes like typos in property names and makes your code easier to maintain.

🎯 Goal: Create a Spring Boot configuration class using @ConfigurationProperties to map properties from application.properties into a Java class with fields.Use this class to access configuration values in a type-safe manner.

📋 What You'll Learn

Create a Java class named AppConfig with fields appName (String) and maxUsers (int).

Annotate AppConfig with @ConfigurationProperties using prefix app.

Enable configuration properties scanning in the main Spring Boot application class.

Create application.properties with app.appName=MyApp and app.maxUsers=100.

Inject AppConfig into a Spring component and use its fields.

💡 Why This Matters

🌍 Real World

Type-safe configuration helps avoid errors from mistyped property names and makes configuration easier to manage in real Spring Boot applications.

💼 Career

Many Java backend jobs require working with Spring Boot and managing application configuration cleanly and safely using @ConfigurationProperties.

1

Create the configuration properties class

Create a Java class named AppConfig with private fields appName (String) and maxUsers (int). Add public getters and setters for both fields.

Spring Boot

public class AppConfig {
    // Your code here
}

Need a hint?

Define private fields and generate public getters and setters for each.

2

Annotate the class with @ConfigurationProperties

Add the annotation @ConfigurationProperties(prefix = "app") above the AppConfig class declaration. Also add @Component annotation to make it a Spring bean.

Spring Boot

@Component
@ConfigurationProperties(prefix = "app")
public class AppConfig {
    // Your code here
}

Need a hint?

Use @Component and @ConfigurationProperties(prefix = "app") annotations on the class.

3

Enable configuration properties scanning

In your main Spring Boot application class, add the annotation @EnableConfigurationProperties above the class declaration to enable scanning of @ConfigurationProperties beans.

Spring Boot

@Component
@ConfigurationProperties(prefix = "app")
public class AppConfig {
    private String appName;
    private int maxUsers;

    public String getAppName() {
        return appName;
    }

    public void setAppName(String appName) {
        this.appName = appName;
    }

    public int getMaxUsers() {
        return maxUsers;
    }

    public void setMaxUsers(int maxUsers) {
        this.maxUsers = maxUsers;
    }
}

@SpringBootApplication
@EnableConfigurationProperties
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
    // Your code here
}

Need a hint?

Add @EnableConfigurationProperties annotation on the main application class.

4

Use AppConfig in a Spring component

Create a Spring component class named AppInfoPrinter. Inject AppConfig via constructor and add a method printInfo() that returns a String combining appName and maxUsers from AppConfig.

Spring Boot

@Component
public class AppInfoPrinter {
    // Your code here
}

Need a hint?

Inject AppConfig via constructor and use its getters in printInfo().