Spring @Value("${property:xxx}") 缺省值

雨点打透心脏的1/2处 2022-05-25 14:30 133阅读 0赞

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

##  ##

## 1. @Value Examples ##

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

#{ expression?:default value}

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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;

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*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}

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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;

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config.properties

mongodb.url=1.2.3.4
    mongodb.db=hello

那个 default value，就是前面的property不存在时的默认值。

写个例子测试一下：

app.properties：

last.time=10

spring配置：

<bean id="configProperties"
    		class="org.springframework.beans.factory.config.PropertiesFactoryBean">
    		<property name="fileEncoding" value="UTF-8" />
    		<property name="locations">
    			<list>
    				<value>classpath:app.properties</value>
    			</list>
    		</property>
    	</bean>
    	<bean id="propertyConfigurer"
    		class="org.springframework.beans.factory.config.PreferencesPlaceholderConfigurer">
    		<property name="properties" ref="configProperties" />
    	</bean>

测试代码：

@Value("${last.time:300}")
    	private String lastTime;
    	
    	@Test
    	public void test2() {
    		System.out.println(lastTime);
    	}

输出：10

把app.properties注释

#last.time=10

输出：300