Question in Spring Exception Resolver

[Vinayak patil]

Hi,
In my action-servlet.xml file I am specifying the exceptionResolver bean as follows:

 
 
<bean id="exceptionResolver"
 class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">
 
   <property name="exceptionMappings">
<props>
   <prop key="java.lang.Exception">Error</prop>
   <prop key="java.io.IOException">IOEx</prop>
        </props>
   </property>
</bean>

In my controller class, I am throwing an IOException

protected ModelAndView handleRequestInternal(HttpServletRequest request,
HttpServletResponse response) throws Exception {
throw new IOException();
}

I was expecting it to go the "Error" page as java.lang.Exception is specified before java.io.IOException in the mapping. But it redirects to the "IOEx" page.
If I comment out the entry for IOException in action-servlet.xml, it redirects to the "Error" page.

I would like to know how does Spring manage to do this. Does the order of the entry in the bean does not matter?

Thanks in advance,
Vinayak

[Ken Krebs]

When defining your exception handling, you are simply defining inline an instance of java.util.Properties which essentially is a Hashtable for looking up an object via another object which is acting as the key. The ordering of the definitions is irrelevant.

[Christophe Verré]

As Ken said, the order is irrelevant.
Spring will only look at the exception type, look for it in the map, and redirect to the specified location if found.

[Vinayak patil]

Hi,

Thanks for the responses. I still have a doubt with the behaviour though.
I modified the bean definition so that it looks like:
(I removed the entry for IOException)

  
<bean id="exceptionResolver"
 class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">
 
   <property name="exceptionMappings">
<props>
[B]<prop key="java.lang.Exception">Error</prop>[/B]
</props>
   </property>
</bean>
  

Now it redirects to Error page.

So my understanding is this:

When an exception occurs, Spring will search for the exception type in the "exceptionMappings" property.

If it does not find, it tries to search a generic exception type defined and if so, will redirect it to that page.

Thats why, though java.io.IOException was not mapped, it was able to redirect it to the "Error" page.

Is my understanding correct?

-Vinayak

[Ken Krebs]

From the javadoc for SimpleMappingExceptionResolver.setExceptionMappings:

setExceptionMappings

public void setExceptionMappings(Properties mappings)

Set the mappings between exception class names and error view names. The exception class name can be a substring, with no wildcard support at present. A value of "ServletException" would match javax.servlet.ServletException and subclasses, for example.

NB: Consider carefully how specific the pattern is, and whether to include package information (which isn't mandatory). For example, "Exception" will match nearly anything, and will probably hide other rules. "java.lang.Exception" would be correct if "Exception" was meant to define a rule for all checked exceptions. With more unusual exception names such as "BaseBusinessException" there's no need to use a FQN.

That should clarify things. When in doubt, look in the docs and/or write a test.