Using `@Value`

@Value is typically used to inject externalized properties:

Java
Kotlin

@Component
public class MovieRecommender {

    private final String catalog;

    public MovieRecommender(@Value("${catalog.name}") String catalog) {
        this.catalog = catalog;
    }
}

@Component
class MovieRecommender(@Value("\${catalog.name}") private val catalog: String)

With the following configuration:

Java
Kotlin

@Configuration
@PropertySource("classpath:application.properties")
public class AppConfig { }

@Configuration
@PropertySource("classpath:application.properties")
class AppConfig

And the following application.properties file:

catalog.name=MovieCatalog

In that case, the catalog parameter and field will be equal to the MovieCatalog value.

A default lenient embedded value resolver is provided by Spring. It will try to resolve the property value and if it cannot be resolved, the property name (for example ${catalog.name}) will be injected as the value. If you want to maintain strict control over nonexistent values, you should declare a PropertySourcesPlaceholderConfigurer bean, as the following example shows:

Java
Kotlin

@Configuration
public class AppConfig {

	@Bean
	public static PropertySourcesPlaceholderConfigurer propertyPlaceholderConfigurer() {
		return new PropertySourcesPlaceholderConfigurer();
	}
}

@Configuration
class AppConfig {

	@Bean
	fun propertyPlaceholderConfigurer() = PropertySourcesPlaceholderConfigurer()
}

When configuring a PropertySourcesPlaceholderConfigurer using JavaConfig, the @Bean method must be static.

Using the above configuration ensures Spring initialization failure if any ${} placeholder could not be resolved. It is also possible to use methods like setPlaceholderPrefix, setPlaceholderSuffix, or setValueSeparator to customize placeholders.

Spring Boot configures by default a PropertySourcesPlaceholderConfigurer bean that will get properties from application.properties and application.yml files.

Built-in converter support provided by Spring allows simple type conversion (to Integer or int for example) to be automatically handled. Multiple comma-separated values can be automatically converted to String array without extra effort.

It is possible to provide a default value as following:

Java
Kotlin

@Component
public class MovieRecommender {

    private final String catalog;

    public MovieRecommender(@Value("${catalog.name:defaultCatalog}") String catalog) {
        this.catalog = catalog;
    }
}

@Component
class MovieRecommender(@Value("\${catalog.name:defaultCatalog}") private val catalog: String)

A Spring BeanPostProcessor uses a ConversionService behind the scenes to handle the process for converting the String value in @Value to the target type. If you want to provide conversion support for your own custom type, you can provide your own ConversionService bean instance as the following example shows:

Java
Kotlin

@Configuration
public class AppConfig {

    @Bean
    public ConversionService conversionService() {
        DefaultFormattingConversionService conversionService = new DefaultFormattingConversionService();
        conversionService.addConverter(new MyCustomConverter());
        return conversionService;
    }
}

@Configuration
class AppConfig {

	@Bean
	fun conversionService(): ConversionService {
		return DefaultFormattingConversionService().apply {
			addConverter(MyCustomConverter())
		}
	}
}

When @Value contains a SpEL expression the value will be dynamically computed at runtime as the following example shows:

Java
Kotlin

@Component
public class MovieRecommender {

    private final String catalog;

    public MovieRecommender(@Value("#{systemProperties['user.catalog'] + 'Catalog' }") String catalog) {
        this.catalog = catalog;
    }
}

@Component
class MovieRecommender(
	@Value("#{systemProperties['user.catalog'] + 'Catalog' }") private val catalog: String)

SpEL also enables the use of more complex data structures:

Java
Kotlin

@Component
public class MovieRecommender {

    private final Map<String, Integer> countOfMoviesPerCatalog;

    public MovieRecommender(
            @Value("#{{'Thriller': 100, 'Comedy': 300}}") Map<String, Integer> countOfMoviesPerCatalog) {
        this.countOfMoviesPerCatalog = countOfMoviesPerCatalog;
    }
}

@Component
class MovieRecommender(
	@Value("#{{'Thriller': 100, 'Comedy': 300}}") private val countOfMoviesPerCatalog: Map<String, Int>)

Using @Value

Using `@Value`