Feature and Usage of Application.properties

Certainly! Let's consider an example where we want to access custom properties defined in the application.properties file. We'll demonstrate how to access these properties using the @Value annotation and @ConfigurationProperties approach.

Step-by-Step Example

1. Define Properties in application.properties

First, add some custom properties to your application.properties file:

propertiesCopy code# application.properties

myapp.feature.enabled=true
myapp.default-role=USER
myapp.title=My Application
myapp.version=1.0.0

2. Access Properties Using @Value

You can directly inject these properties into your Spring components using the @Value annotation.

MyComponent.java:

javaCopy codepackage com.example.demo;

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

@Component
public class MyComponent {

    @Value("${myapp.feature.enabled}")
    private boolean featureEnabled;

    @Value("${myapp.default-role}")
    private String defaultRole;

    @Value("${myapp.title}")
    private String title;

    @Value("${myapp.version}")
    private String version;

    public void printProperties() {
        System.out.println("Feature Enabled: " + featureEnabled);
        System.out.println("Default Role: " + defaultRole);
        System.out.println("Title: " + title);
        System.out.println("Version: " + version);
    }
}

3. Access Properties Using @ConfigurationProperties

For a more structured and type-safe approach, you can use the @ConfigurationProperties annotation.

MyAppProperties.java:

javaCopy codepackage com.example.demo;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

@Component
@ConfigurationProperties(prefix = "myapp")
public class MyAppProperties {

    private boolean featureEnabled;
    private String defaultRole;
    private String title;
    private String version;

    // Getters and setters

    public boolean isFeatureEnabled() {
        return featureEnabled;
    }

    public void setFeatureEnabled(boolean featureEnabled) {
        this.featureEnabled = featureEnabled;
    }

    public String getDefaultRole() {
        return defaultRole;
    }

    public void setDefaultRole(String defaultRole) {
        this.defaultRole = defaultRole;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getVersion() {
        return version;
    }

    public void setVersion(String version) {
        this.version = version;
    }

    public void printProperties() {
        System.out.println("Feature Enabled: " + featureEnabled);
        System.out.println("Default Role: " + defaultRole);
        System.out.println("Title: " + title);
        System.out.println("Version: " + version);
    }
}

4. Enable Configuration Properties

Make sure to enable configuration properties in your Spring Boot application class.

SpringbootProjectApplication.java:

javaCopy codepackage com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.properties.EnableConfigurationProperties;

@SpringBootApplication
@EnableConfigurationProperties(MyAppProperties.class)
public class SpringbootProjectApplication {

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

5. Use the Properties in Your Application

Finally, you can use these properties in your application logic. For example, let's use MyComponent and MyAppProperties to print the properties.

DemoApplication.java:

javaCopy codepackage com.example.demo;

import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;

@Component
public class DemoApplication implements CommandLineRunner {

    private final MyComponent myComponent;
    private final MyAppProperties myAppProperties;

    public DemoApplication(MyComponent myComponent, MyAppProperties myAppProperties) {
        this.myComponent = myComponent;
        this.myAppProperties = myAppProperties;
    }

    @Override
    public void run(String... args) throws Exception {
        // Using @Value approach
        myComponent.printProperties();

        // Using @ConfigurationProperties approach
        myAppProperties.printProperties();
    }
}

Summary

In this example, we've demonstrated two approaches to accessing properties from the application.properties file in a Spring Boot application:

1. Using the @Value annotation to inject individual properties.

2. Using @ConfigurationProperties to bind a group of properties to a POJO (Plain Old Java Object).

Both approaches have their use cases, and you can choose one based on your specific needs. The @ConfigurationProperties approach is generally preferred for complex configurations because it provides better type safety and is easier to manage.