Store List of Objects in Session Scope Spring MVC's ApplicationListener

Question

I am trying to store a list of objects in my Spring MVC application's session so that I may iterate through them within my JSPs to create options in a drop down.

After about two hours of reading through posts and blogs I am very confused. In fact, I don't even know where to start. Can anyone point me in the direction of a Spring based solution [documentation, tutorials, examples] that meets the following criteria?

1. Values for the list are pulled from a database table.
2. The list is loaded during application startup.
3. It does not directly access the session within a controller.

Answer 1

You should define a spring bean. You can see how to run code within the bean at startup in the answer to this question. Something like an ApplicationListener should work. In that startup code you can load the table into memory (it sounds like that is what you are looking for.)

Within your controller you inject the spring bean which has a method to get the values you need. You then add those values to the Model (not the session) in your request handler and the Model is used by the view (your JSP page) which can iterate over the values and display them.

Answer 2

Create a class which reads the values and puts in list by implementing org.springframework.beans.factory.InitializingBean interface e.g.:

      public class ListLoader implements InitializingBean{
       ....
       ....
       public List<String> getMyList(){
         ...
         ...
       }
     }

Add the bean in configuration file:

   <bean id="myListLoader" class="com.....ListLoader">
    ...
   </bean>

To access it:

   ListLoader myListLoader= (ListLoader)context.getBean("myListLoader");
   List<String> myValues= = myListLoader.getMyList();

Answer 3

Just to provide some further clarity into how I resolved this problem, I have chosen to answer my own question.

1. As suggested in DigitalJoel's answer, I created an ApplicationListener bean. This Listener is fired each time the context is refreshed.

LookupLoader.java

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;
import org.tothought.entities.SkillCategory;
import org.tothought.repositories.SkillCategoryRepository;

public class LookupLoader implements ApplicationListener<ContextRefreshedEvent> {

    @Autowired
    SkillCategoryRepository repository;

    private List<SkillCategory> categories;


    public List<SkillCategory> getCategories() {
        return categories;
    }

    public void setCategories(List<SkillCategory> categories) {
            this.categories = categories;           
    }

    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        if(this.categories == null){
            this.setCategories(repository.findAll());               
        }
    }
}

2. Next, I registered this bean in my application configuration.

application-context.xml (Spring-Config)

<bean id="lookupLoader"
    class="org.tothought.controllers.initializers.LookupLoader" />

3. Then to place this bean in each request I created a HandlerInterceptorAdapter that is executed each time a request is received. In this bean I autowired the LookupLoader and set my list in the request.

LookupHandlerInterceptor.java

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;
import org.tothought.controllers.initializers.LookupLoader;

public class LookupHandlerInterceptor extends HandlerInterceptorAdapter {
    @Autowired
    LookupLoader loader;

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        request.setAttribute("skillCategories", loader.getCategories());
        return super.preHandle(request, response, handler);
    }
}

4. Register the HandlerInterceptor within the Spring MVC web application configuration

servlet-context.xml

<!-- Intercept request to blog to add paging params -->
<mvc:interceptors>
    <mvc:interceptor>
        <mvc:mapping path="/**"/>
        <bean class="org.tothought.controllers.interceptors.LookupHandlerInterceptor" />
    </mvc:interceptor>
</mvc:interceptors>

5. Access the list via JSP & JSTL

<c:forEach var="category" items="${skillCategories}">
    ${category.name}
</c:forEach>