Spring 3.0 - Application Context - three ways to get the context

In searching Google for “Spring ApplicationContextAware“, you come across a lot of recommendations and I also see a lot of folks continuing to complain saying that their setApplicationContext method does not get invoked. So to help clarify, I’m blogging a few notes in hope that it helps clarify a few things.

Two Ways to Get Application Context:

Method #1: In your class you implement ApplicationContextAware class like this:

public class MyClass implements ApplicationContextAware {
    static final long serialVersionUID = 02L;
    ApplicationContext applicationContext = null;
    public void doSomething(){
        if (applicationContext != null && applicationContext.containsBean("accessKeys")){
            MyBean beanA = (MyBean) applicationContext.getBean("mybean");
            //Do something with this AccessBean
        }
        return null;
    }
    @Override
    public void setApplicationContext(final ApplicationContext applicationContext) throws BeansException {
        System.out.println("setting context");
        this.applicationContext = applicationContext;
    }
}

Method #2: If you are in a Java Servlet, you can do the following:

public class gzservlet extends HttpServlet {
    static final long serialVersionUID = 02L;
    ApplicationContext applicationContext = null;
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        if (applicationContext == null){
            System.out.println("setting context in get");
            applicationContext = WebApplicationContextUtils.getWebApplicationContext(this.getServletContext());
        }
        if (applicationContext != null && applicationContext.containsBean("accessKeys")){
            AccessBean thisAccessBean = (AccessBean) applicationContext.getBean("accessKeys");
            req.setAttribute("keys", thisAccessBean.toString());
            System.out.println("setting keys");
        }
        req.getRequestDispatcher("/index2.jsp").include(req,resp);
    }
}

So the question one would ask is when to use what? And the answer is. Depends on how you are invoking Spring.

What works for Method #1: when you invoke Spring you are using the DispatcherServlet link this. Then Method #1 will resolve the implementation of ApplicationContextAware and call the setApplicationContext() method to set the context.

In web.xml.
<servlet>
	<servlet-name>dispatchservlet</servlet-name>
	<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
	<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
	<servlet-name>dispatchservlet</servlet-name>
	<url-pattern>/*</url-pattern>
</servlet-mapping>

If you are not using the DispatcherServlet and you are initializing Spring using a Listener and you have your own Servlet that’s driving the RequestResponse scope then use Method #2. Below is an example of how the web.xml will look like in this case.

<listener>
   <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<servlet>
  <servlet-name>MyOwnServlet</servlet-name>
  <servlet-class>com.something.myservlet</servlet-class>
  <load-on-startup>2</load-on-startup>
</servlet>
<servlet-mapping>
  <servlet-name>MyOwnServlet</servlet-name>
  <url-pattern>*.do</url-pattern>
</servlet-mapping>

I hope this clarifies why sometimes even though you have implemented the ApplicationContextAware interface, your setter does not get invoked.

[09/12/2010] Here is a third way to get your context:

Create the following class with a static method to get your context:

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
public class ApplicationContextProvider implements ApplicationContextAware{
 private static ApplicationContext ctx = null;
 public static ApplicationContext getApplicationContext() {
return ctx;
 }
 public void setApplicationContext(ApplicationContext ctx) throws BeansException {
this.ctx = ctx;
 }
}

and in your spring bean configuration xml file add the following:

<bean id="applicationContextProvider" class="ApplicationContextProvider"></bean>

And now in your classes, you can do the following:

ApplicationContext ctx = ApplicationContextProvider.getApplicationContext();

That’s it!!!

Cheers.

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