Tomcat 10.0.4 Doesn't Load Servlets (@Webservlet Classes) with 404 Error

Tomcat 10.0.4 doesn't load servlets (@WebServlet classes) with 404 error

I had the same issue while reproducing the problem reported at IntelliJ IDEA forums.

It didn't work with Tomcat 10 for the reasons described in the answer by Piotr P. Karwasz, but it works just fine with Tomcat 9.0.44 and earlier versions.

Servlet 5.0 JAR throws compile error on javax.servlet.* but Servlet 4.0 JAR does not

When I place the .class file in the corresponding Tomcat directory, start the server and try to interact with the app, I get the following exception:

java.lang.ClassNotFoundException: javax.servlet.http.HttpServlet

I tried placing the javax.servlet-api-4.0.1 in the Tomcat/lib directory, but then I get:

java.lang.ClassCastException: class com.example.controllers.BeerSelect
                       cannot be cast to class jakarta.servlet.Servlet

The jakarta.servlet.Servlet is part of Servlet API version 5.0 which in turn is part of Jakarta EE version 9. Your servlet is actually extending from javax.servlet.Servlet which in turn is part of an older JEE version which is actually not supported by your target runtime (Tomcat 10.x).

You have 2 options:

1. Replace the javax.servlet.* imports in your code by jakarta.servlet.* ones.

   import jakarta.servlet.*;
   import jakarta.servlet.http.*;
   

   Then you can just compile against the libraries from a Servlet 5.0 based target runtime.

2. Or, downgrade the servlet container from Servlet API version 5.0 to a previous version, at least the one still having the javax.servlet.* package name. Tomcat 9.x is the latest one still having the old package.

The technical reason is that during the step from Java/Jakarta EE 8 to Jakarta EE 9 all javax.* packages have been renamed to jakarta.* packages. So there is no backwards compatibility anymore since Jakarta EE 9.

So, when following any servlet tutorials which still use the old javax.servlet.* package while you're using Tomcat 10 or newer, then you need to manually swap out the package used in code examples for the jakarta.servlet.* one. Generally it'll work just fine.

See also:

• Apache Tomcat - versions
• Tomcat casting servlets to javax.servlet.Servlet instead of jakarta.servlet.http.HttpServlet (this answer contains complete examples of proper pom.xml declarations for Tomcat 10+, Tomcat 9-, JEE 9+ and JEE 8-, just in case you're using Maven).

Deploying Spring 5.x on Tomcat 10.x

TL;DR: Spring MVC 5 does not run on Tomcat 10 because of the package renaming from javax.* to jakarta.*.

After further research, I was able to find the answer to my question. Spring MVC 5 does not work on Tomcat 10. This is because Tomcat 10 is based on Jakarta EE 9 where package names for APIs have changed from javax.* to jakarta.*.

Tomcat 10 mentioned this on the download webpage:

Users of Tomcat 10 onwards should be aware that, as a result of the
move from Java EE to Jakarta EE as part of the transfer of Java EE to
the Eclipse Foundation, the primary package for all implemented APIs
has changed from javax.* to jakarta.*. This will almost certainly
require code changes to enable applications to migrate from Tomcat 9
and earlier to Tomcat 10 and later.

For Spring MVC 5, the Spring MVC DispatcherServlet has a dependency on the javax.servlet.* package namespace. This is using the Java EE 8 javax package naming. Since Tomcat 10 is based on Jakarta EE 9, the packages for javax naming are not supported. This explains why Spring MVC 5 does not work on Tomcat 10.

There are GitHub issues filed against the Spring Framework regarding this:

Spring core 5 is not starting on Tomcat 10

Support for Jakarta EE 9 (annotations and interfaces in jakarta.* namespace)

In my case, instead of migrating to Tomcat 10, I will stay on Tomcat 9 until the Spring framework is upgraded to Jakarta EE 9.

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