ApplicationContext vs WebApplicationContext and ServletContext

[Tomasz Nawrot]

Hi,
I found in Spring spec the following sentence:
"Spring MVC looks for a file named [servlet-name]-servlet.xml in the WEB-INF directory of your web application and creates the beans defined there, overriding the definitions of any beans defined with the same name in the global scope."

According that sentence I assume that every bean defined in ApplicationContext should be overwritten by beans with the same name in WebApplicationContext ?
Thus could anybody explain me why I got the error in the following code:


First I declared my ApplicationContext, WebApplicationContext and my own DispatcherServlet in web.xml:

web.xml
------------

<context-param>
	 <param-name>contextConfigLocation</param-name>
	 <param-value>/WEB-INF/myApplicationContext.xml</param-value>
  </context-param>

  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>

  <servlet>
    <servlet-name>controller</servlet-name>
    <servlet-class>com.my.MyDispatcherServlet</servlet-class>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>/WEB-INF/myWebApplicationContext.xml</param-value>
    </init-param>
  </servlet>

  <servlet-mapping>
    <servlet-name>controller</servlet-name>
    <url-pattern>/app/*</url-pattern>
  </servlet-mapping>

Then I created bean "user" in AppContext and the same in WebAppContext:

myApplicationContext.xml
--------------------------------

  <bean id="user" class="com.my.UserBean"> 
    <property name="name" value="tom"></property>
  </bean>

myWebApplicationContext.xml
-----------------------------------

<bean id="user" class="com.my.UserBean"> 
    <property name="name" value="john"></property>
  </bean>

At the end I implemented my version of DispatcherServlet where I retrieved bean "user":

class MyDispatcherServlet extends DispatcherServlet{
  public void service(...){
      ServletContext servletContext = this.getServletContext();

      WebApplicationContext applicationContext = WebApplicationContextUtils.getWebApplicationContext(servletContext);
      UserBean user = (UserBean)applicationContext.getBean("user");
      System.out.println("userBean=" + user.getName());
  }
}

When I run the code I got userName: TOM. So the bean "user" was taken from ApplicationContext - and this is my first WHY ? (it should be taken from WebAppContext so I should get value "JOHN")

After that I change the bean name in AppContext to userBis. And during running the code I got: org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'user' is defined
And this is my second WHY? - it means that beans from WebAppContext weren't loaded ?

Thanks for any explanations.
Tom

[Maciek Kaminski]

Im not 100% sure - please correct me if You know better - but in fact myApplicationContext.xml is Your ROOT WebApplicationContext, not just ApplicationContext.

Now take a look at javadoc of WebApplicationContextUtils.getWebApplicationContext(servletContext):

Find the ROOT WebApplicationContext for this web application, which is typically loaded via ContextLoaderListener or ContextLoaderServlet.

That is why it gives You application context from myApplicationContext.xml instead of myWebApplicationContext.xml.

[H Paul]

Mechanically, given your MyDispatcherServlet is a MVC DispatcherServlet, you can use

public void service(...){
...
this.getWebApplicationContext(); // refer to myWebApplicationContext.xml
...
}