How to Use the `@Value` Annotation in Java Spring for Property Injection?

How can I use the `@Value` annotation in Java Spring to inject an environment property directly into a field?

// Original implementation
@Component
public class SomeClass {
    @Inject
    private Environment env;

    private String key;

    @PostConstruct
    private void init() {
        key = env.getProperty("SOME_KEY_PROPERTY");
    }
}

In Java Spring, using the `@Value` annotation simplifies the process of injecting environment properties compared to manually retrieving them through the `Environment` interface. This approach allows for cleaner and more concise code.

// Improved implementation
@Component
public class SomeClass {
    @Value("${SOME_KEY_PROPERTY}")
    private String key;
}

Causes

• The original code uses the `Environment` interface to fetch properties manually, making it verbose.
• Spring provides the `@Value` annotation to directly inject property values into class attributes, reducing boilerplate code.

Solutions

• Use the `@Value` annotation directly on the field to inject the property value during bean initialization.
• Replace the use of `Environment` and the `@PostConstruct` method with a direct property injection.

Mistake: Using incorrect keys or syntax with `@Value` leading to null values.

Solution: Ensure the property key is correctly specified in the format `@Value("${PROPERTY_KEY}")` and that the property is defined in application properties or configuration files.

Mistake: Forgetting to define the property in the application properties file.

Solution: Always verify that the property is properly defined in your application.properties or application.yml.