Loading a property or system property using spring @Value
In the previous tutorial we saw how you can load properties from a file. In this tutorial we will show you how to inject these properties or system properties into a spring bean using the spring @Value annotation.
Example application.properties file
Here are some properties that we want to inject into a bean.
application.environment = PRODUCTIONLoad Properties with Spring Property Placeholder
As you saw in the previous tutorial you can load the properties using the <context:property-placeholder> element.
The PropertyPlaceholderConfigurer looks by default not only in the properties file you specify but also searches for Java System properties if it cannot find a property in the specified properties file. If you want you can customize this behavior by setting the system-properties-mode attribute of the property-placeholder with one of the following values:
- NEVER (0): this will never check the system properties.
- FALLBACK (1): [default] this will check system properties if no property could be found in the specified properties file.
- OVERRIDE (2): this will check system properties first, if no suitable system property is found then it’ll search in the specified properties file.
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd">
<context:component-scan base-package="com.memorynotfound"/>
<context:property-placeholder location="classpath:application.properties"/>
</beans>Injecting a Property or a System Property using spring @Value annotation
The spring @Value annotation can be placed on fields, methods and method/constructor parameters to specify a default value. In this example we are first loading a property from the application.properties file. Then we also load a system property both using the spring expression language.
package com.memorynotfound;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
@Component
public class Config {
@Value("${application.environment}")
private String fileProperty;
@Value("${java.version}")
private String systemProperty;
@Override
public String toString() {
return "Config{" +
"fileProperty='" + fileProperty + '\'' +
", systemProperty='" + systemProperty + '\'' +
'}';
}
}Bootstrap Spring and test properties
package com.memorynotfound;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Main {
public static void main(String... args){
ApplicationContext context = new ClassPathXmlApplicationContext("app-config.xml");
Config config = context.getBean(Config.class);
System.out.println(config);
}
}Output
Config{fileProperty='PRODUCTION', systemProperty='1.7.0_67'}
