Why Are My Servlets Failing to Load in Tomcat 10 (404 Error)?

Tomcat 10.0.4 Won't Load Servlets (404 Error)

In this scenario, a Servlet 4.0 application that utilizes annotations to define servlets is experiencing 404 errors when attempting to access these servlets. Upon investigation, it is discovered that these annotations are ignored in Tomcat 10 due to a transition from the javax.* to the jakarta.* API namespace.

Cause of Namespace Incompatibility

Tomcat 10 is incompatible with the Servlet 4.0 API namespace due to the adoption of Servlet 5.0. This results in:

• Compile errors when compiling Servlet 4.0 applications against Tomcat 10's API jars
• Class not found errors when starting Servlet 4.0 applications that use a web.xml descriptor
• Error messages indicating that the servlet class is not a jakarta.servlet.Servlet
• Servlet annotations defined with the javax.* namespace being ignored
• Issues with ServletContainerInitializers (e.g., Spring applications) failing to start

Solution: Namespace Migration

To resolve this issue, it is recommended to migrate the application to use the jakarta.* namespace. One recommended approach is to utilize the Tomcat Migration Tool for Jakarta EE, which automates this process.

Important Note

The Tomcat documentation includes a warning regarding this namespace change. Ensuring that this is acknowledged and addressed during migration can help prevent this issue.

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