How to Populate a HashMap from a Java Properties File Using Spring @Value Annotation

Is it possible to use Spring's @Value annotation to map values from a properties file to a HashMap?

@Value("#{${service.expiration}}")
private Map<String, String> expirations;

Yes, you can map values from a properties file to a HashMap in a Spring application using the @Value annotation. This allows you to dynamically load key-value pairs defined in your properties file into your Java class. Below is a step-by-step guide on how to achieve this.

@Service
@PropertySource(value = "classpath:my_service.properties")
public class SomeServiceImpl implements SomeService {

    @Value("${service.cache}")
    private boolean useCache;

    @Value("#{${service.expiration}}")
    private Map<String, String> expirations;

}

Causes

• Using the incorrect syntax for referencing multiple properties in Spring.
• Not properly defining the property names in the properties file.

Solutions

• Use SpEL (Spring Expression Language) to map the properties directly to a HashMap.
• Ensure the property names in the properties file match those used in your code.

Mistake: Referencing properties incorrectly without using `${}` for properties.

Solution: Use the correct syntax: `@Value("${property.name}")`.

Mistake: Not using the right SpEL syntax for mapping multiple values.

Solution: Use `#{${property.prefix}}` to refer to a set of properties.