spring @value

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

@Value

know how to interpret

${}

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

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