用Spring注入bean时的nullPointerException

Question

我是Spring3.2.5的新手，我正尝试将一个bean作为属性注入另一个bean中，但当我想使用该属性时，它总是为空。

我使用的配置如下：

ApplicationContext.xml：

<bean id="subscriptionService" class="fake.services.SubscriptionService">
</bean>

<bean id="restController" class="fake.RestController">
    <property name="subscriptionService" ref="subscriptionService"></property>
</bean>

restController.java：

@Path("/")
@Secured("ROLE_USER")
public class RestController {

protected ISubscriptionService subscriptionService;



/**
 * @return the subscriptionService
 */
public ISubscriptionService getSubscriptionService() {
    return subscriptionService;
}

/**
 * @param subscriptionService the subscriptionService to set
 */
public void setSubscriptionService(ISubscriptionService subscriptionService) {
    this.subscriptionService = subscriptionService;
}

}

ISubScriptionService.java：

public interface ISubscriptionService {

public UUID subscribe();

}

 public class SubscriptionService implements ISubscriptionService {

/**
 * 
 */
public SubscriptionService() {
}

/**
 * Subscribes a user and returns a uuid for the queue
 * @return  the uuid for the queue
 */
public UUID subscribe() {
    return UUID.randomUUID();
}

}

我得到的错误是：

Answer 1

是否实现了isubscriptionservice接口？applicationcontext.xml中的subscriptionservicebean应该引用该接口的实现。