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(), setValueSeparator(), or setEscapeCharacter() to customize the placeholder syntax. In addition, the default escape character can be changed or disabled globally by setting the spring.placeholder.escapeCharacter.default property via a JVM system property (or via the SpringProperties mechanism).

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`