Why Does Tomcat 10.0.4 Return 404 Errors for Servlets After a Servlet 4.0 to 5.0 Migration?

Tomcat 10.0.4 Neglects Servlet Loading with 404 Error: A Servlet 5.0 Migration Conflict

When attempting to access servlets within a Tomcat 10.0.4 environment, developers may encounter a persistent 404 error. This issue stems from an incompatibility between Servlet 5.0 (implemented by Tomcat 10) and Servlet 4.0 (implemented by Tomcat 9), resulting from a namespace shift from javax. to jakarta. in the Servlet API.

Consequences of the API Namespace Change:

• Compilation errors occur when trying to compile Servlet 4.0 software with Tomcat 10 API jars.
• Servlet 4.0 web applications using a web.xml descriptor may fail to start with numerous ClassNotFoundExceptions.
• Applications utilizing annotations for servlet declaration (as in the given case) stop functioning.
• ServletContainerInitializer-dependent applications (such as Spring projects) fail to initialize because @javax.servlet.WebServlet annotations are overlooked.

Solution:

The most effective solution is to utilize the Tomcat Migration Tool for Jakarta EE. This tool streamlines the transition from Servlet 4.0 to Servlet 5.0 by updating the necessary packages and annotations.

Note:

Tomcat's download page prominently displays a warning regarding this migration, which is often overlooked. It emphasizes the requirement for code modifications to migrate applications from Tomcat 9 and earlier to Tomcat 10 and later due to the API namespace change.

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