Accessing Spring Properties

Spring’s IoC is wonderful, and annotating classes for auto-configuration and wiring is exceptionally useful. But when you have a primitive value to set on an object, it can be tedious to manually define the bean in your context.xml. Here is an example:

@Service
public class MainframeHealthService implements IMainframeHealthService {

        private String host;
        private String port;
        private String healthCheckEndpoint = "/mainframe/health";

        public String getHealthStatus() {
                /* operation to check the status and return */
        }
}

Now, I could set the host as a bean in the context.xml:

<bean id="mainframeHealthSvc" class="main.MainframeHealthService" p:host="${mainframe.host}" p:url="${mainframe.port}"/>

But, here is another option — the Value annotation! It uses the same formatting as using the property placeholder but directly inside the class.

@Service
public class MainframeHealthService implements IMainframeHealthService {
        @Value("${mainframe.host}")
        private String host;
        @Value("${mainframe.port}")
        private String port;
        private String healthCheckEndpoint = "/mainframe/health";

        public String getHealthStatus() {
                /* operation to check the status and return */
        }
}

This does create a hard-coded dependency on that property. If it isn’t found by the container during bean processing, an IllegalArgumentException (“Could not resolve placeholder…”) is thrown.