Why Do My Servlets Return 404 Errors After Migrating from Tomcat 9 to Tomcat 10?

Tomcat 10.0.4 Fails to Load Servlets with 404 Error: Understanding the Java EE to Jakarta EE Migration

You may encounter issues with accessing servlets in your web application deployed on Tomcat 10.0.4, resulting in a 404 error. This behavior stems from differences between the Java EE and Jakarta EE standards, which have implications for servlets in Tomcat 10:

API Namespace Change:

The API namespace for servlets has changed from javax. in Servlet 4.0 (used by Tomcat 9) to jakarta. in Servlet 5.0 (used by Tomcat 10). This means that:

• Code written for Servlet 4.0 will not compile with Tomcat 10's API jars.
• Servlet 4.0 applications using a web.xml descriptor may throw exceptions and fail to start.
• Servlets using annotations to declare themselves will no longer work, as in your case.

ServletContainerInitializer Dependency:

Applications relying on ServletContainerInitializer, such as Spring and Spring Boot, may fail to start due to @javax.servlet.WebServlet annotations being ignored by the server. Instead, the server scans for @jakarta.servlet.WebServlet.

Solution:

To resolve these issues, consider using the Tomcat Migration Tool for Jakarta EE. This tool simplifies the necessary code changes to ensure compatibility with the new Java EE to Jakarta EE migration:

• Update the project's Maven dependencies or source code to use the jakarta.* API namespace.
• Modify any annotations or XML configuration using the correct Jakarta EE namespace.
• Recompile and test the application.

Warning:

Tomcat's download site includes a warning about the namespace change, highlighting the need for code adjustments when migrating from Tomcat 9 to Tomcat 10 and later.

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