Why Does Tomcat 10.0.4 Return 404 Errors for Servlets Despite Correct Implementation?

Tomcat 10.0.4 Fails to Load Servlets with 404 (Duplicate)

Introduction:
Developers encounter difficulties running servlets in Tomcat 10.0.4, encountering a 404 error. This issue affects servlets defined using the @WebServlet annotation.

Problem Statement:
In the provided scenario, a simple servlet named login throws a 404 error when accessed via a form button. The servlet implementation in login.java appears to be correct, but the request continues to fail.

Cause:
The underlying cause lies in the migration from Java EE to Jakarta EE, which resulted in a change in the package namespace for servlet APIs. Tomcat 10 implements Servlet API 5.0 (using the jakarta.* namespace), while the provided servlet code uses the older Servlet API 4.0 (javax.*).

Solution:
There are several approaches to resolve this issue:

• Manually Update Code: Update the servlet code to use the new Jakarta EE-based packages. This involves replacing javax.servlet with jakarta.servlet throughout the application.
• Use Tomcat Migration Tool: Utilize the Tomcat Migration Tool for Jakarta EE available from the Tomcat website. It can automate the package namespace conversion process.
• Downgrade Tomcat: If it's not feasible to update the code or use the migration tool, consider downgrading to a compatible Tomcat version that supports Servlet API 4.0, such as Tomcat 9.

Recommendation:
To avoid such compatibility issues in the future, it's recommended to keep applications up-to-date with the latest Servlet API specifications.

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