deployment Descriptor Servlet mapping

[Pratik D mehta]

In the following code from the book headfirst jsp and servlets

<servlet>
<servlet-name>Chapter1 Servlet</servlet-name>
<servlet-class>Ch1Servlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Chapter1 Servlet</servlet-name>
<url-pattern>/serv1</url-pattern>
</servlet-mapping>

Basically we are using a servlet-name to refer to the java class and than mapping that name to the url pattern which the client will see
So My question is cant we directly map the class to the url .
some what like

<servlet-mapping>
<servlet-class>Chapter1 Servlet</servlet-class>
<url-pattern>/serv1</url-pattern>
</servlet-mapping>

[Pete Nelson]

No. You must use both the <servlet> and the <servlet-mapping> section.

[William Brogden]

<servlet-class>Ch1Servlet</servlet-class> 

Class needs to be the fully qualified package plus class name so the servlet container can find it. Classes used in servlets MUST be in packages to avoid all sorts of problems.

Way back at the beginning of the servlet API it was thought that it would be cool to allow for directly naming a servlet class in the URL. Thus we got the Invoker servlet.

These days everybody recognizes that this was a really really really bad idea since it prevented use of the full servlet API.

Bill

[Pratik D mehta]

yup
Thank you peter Nelson and William Brogden (the link was good read)

[Javin Paul]

Guys , but what are the benefits of having mapping in this way , did I miss anything ?

I still don't understand the motive behind such mapiing , having servlet mapped to name first and then name mapped to class or url-pattern .

I know this is the way it works but curious on "Why" part , why it was designed like this by Servlet designer.

[Pratik D mehta]

The objective of this kind of mapping is
1 . The actual servlet name and location available on the server would not be visible to the user , which would be necessary for security .
2 . Than there would be an internal name for that servlet know among the deployers which would be Chapter1 Servlet in the above case as specified.
3. The class name would be specific to developers to be known among them .
4. Maintainence would be definately easy as we would not have to keep on changing each and every JSPs if the servlet name or anything else changes , we can directly change the web.xml mapping which is basically global mapping of servlets for that particular application .
This is the basic understanding i got from Head first .

[William Brogden]

Also note that the "name" of a servlet class includes the package and may therefore be quite long.

Would your really like to type the whole com.mysite.stuff.thingee.BigServletWork name when mapping lets you call it "Work"? How prone to error is that?

Not even getting into the security hazard of having your whole package structure exposed everywhere.

Bill

[T. Huy Nguyen]

William Brogden wrote:
Not even getting into the security hazard of having your whole package structure exposed everywhere.

I don't understand how that why separating servlet-class and url-pattern can prevent a security hazard. The 2 <servlet> and <servlet-mapping> are in the same document, any author of web.xml will be able to see the whole class name.

Would you mind explain further? Thanks

[William Brogden]

The full package and class name would be exposed to ALL USERS of your application.

The web.xml file can not be seen by outside users.

Bill

[T. Huy Nguyen]

Perhaps you're referring to the security hazard of using Invoker servlet? If so, then I understand.

If not, then I still haven't understood why separating servlet-class and url-pattern can prevent a security hazard. Thanks though.

[Bear Bibeault]

One reason is because a single servlet can have multiple mappings.

Sure that could still be done via single XML element if you wanted, but it'd be inconsistent with the rest of the XSD.