spring @value

Posted 2023-02-18 空白-键

转自：http://www.mkyong.com/spring3/spring-value-default-value/

In this tutorial, we will show you how to set a default value for @Value

1. @Value Examples

To set a default value in Spring expression, use Elvis operator :

	#expression?:default value

Few examples :

	@Value("#systemProperties['mongodb.port'] ?: 27017")
	private String mongodbPort;

	@Value("#config['mongodb.url'] ?: '127.0.0.1'")
	private String mongodbUrl;	
	
	@Value("#aBean.age ?: 21")
	private int age;

P.S @Value has been available since Spring 3.0

2. @Value and Property Examples

To set a default value for property placeholder :

	$property:default value

Few examples :

	//@PropertySource("classpath:/config.properties")
	//@Configuration
	
	@Value("$mongodb.url:127.0.0.1")
	private String mongodbUrl;
	
	@Value("#'$mongodb.url:172.0.0.1'")
	private String mongodbUrl;
	
	@Value("#config['mongodb.url']?:'127.0.0.1'")
	private String mongodbUrl;

config.properties

mongodb.url=1.2.3.4
mongodb.db=hello

For “config” bean.

	<util:properties id="config" location="classpath:config.properties"/>

Follow up
Must register a static PropertySourcesPlaceholderConfigurer bean in either XML or annotation, so that Spring @Valueknow how to interpret $

  //@PropertySource("classpath:/config.properties")
  //@Configuration

  @Bean
  public static PropertySourcesPlaceholderConfigurer propertyConfigIn() 
	return new PropertySourcesPlaceholderConfigurer();