@WebServlet annotation with Tomcat 7

Question

In my application, I had a servlet which was defined like this in the web.xml:

<servlet>
    <display-name>Notification Servlet</display-name>
    <servlet-name>NotificationServlet</servlet-name>
    <servlet-class>com.XXX.servlet.NotificationServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>NotificationServlet</servlet-name>
    <url-pattern>/notification/*</url-pattern>
</servlet-mapping>

After moving to use Tomcat 7, I would like to use the @WebServlet annotation that will do the job.
Here is the way I did it:

@WebServlet( name="NotificationServlet", displayName="Notification Servlet", urlPatterns = {"/notification"}, loadOnStartup=1)
public class NotificationServlet extends HttpServlet {

And it does not work. Could someone please tell me what I did wrong?

Solution 1

Provided that you're sure that you're using Tomcat 7 or newer, the webapp's web.xml has to be declared conform Servlet 3.0 spec in order to get Tomcat to scan and process the annotations. Otherwise Tomcat will still run in a fallback modus matching the Servlet version in web.xml. The support for servlet API annotations was only added in Servlet 3.0 (Tomcat 7).

So, the root declaration of your web.xml must look like below (make sure you remove any DOCTYPE from web.xml too, otherwise it will still be interpreted as Servlet 2.3!).

<web-app 
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    version="3.0">

Further, there's a minor difference in the URL pattern. The URL pattern /notifications will let the servlet only listen on requests on exactly that path. It does not kick in on requests with an extra path like /notifications/list or something. The URL pattern /notifications/* will let the servlet listen on requests with extra path info as well.

The minimum @WebServlet annotation should thus look like this

@WebServlet("/notifications/*")

The rest of attributes are optional and thus not mandatory to get the servlet to function equally.

See also:

• Our servlets wiki page

Solution 2

One may also want to check for having two classes with an annotations with the same name:

@WebServlet(name = "Foo", urlPatterns = {"/foo"})
public class Foo extends HttpServlet {
    //...
}

And:

@WebServlet(name = "Foo", urlPatterns = {"/bar"})
public class Bar extends HttpServlet {
    //...
}

In this cases, one of the servlets will not work. If you don't use the name, leave it out, like @BalusC suggests. I got the strange behavior that one of the servlets only worked right after changing and compiling it, but not after compilation without changes.

Solution 3

Additionally, in order to use these annotations and compile your code you must import the corresponding dependency in your pom.xml, but as provided cause your "Servlet 3.0" compliant server already has this.

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>3.0.1</version>
    <scope>provided</scope>
</dependency>

Comments

[Nicolas Zozol]

You may need to add <web-app (...) metadata-complete="false"></webapp>.

[destan]

One doesn't have to use web.xml at all when using @WebServlet annotation. It works without web.xml.

[BalusC]

@destan: that's correct. However, if you have one, as in OP's case, it must be at least 3.0. You eventually need one because not everything can be annotated.

[Aniket]

@BalusC but on servlet wiki en.wikipedia.org/wiki/Java_Servlet it showing support from version 2.5. Although I tested its not working with version 2.5 it requires version 3.0. But i am little bit confused after reading servlet wiki page

[BalusC]

@Aniket: So you say that information on Wikipedia is more reliable than the information in Oracle's own Servlet specification document? Why exactly?

[Herbert]

I had the strange effect that the servlet worked when it was just changed, compiled and redeployed to glassfish 4. When I recompiled again without changes, and deployed, it did not work. I added the metadata-complete="false" attribute and minimized the webservlet-annotation, and now it works. Other servlets were working the whole time though.

[Herbert]

If you down vote, leave a comment, otherwise nobody will be able to respond to, correct or learn from it. Thank you.