Why is my Spring MVC Controller Not Being Called? Understanding and Resolving 404 Errors

Описание: Discover why your Spring MVC Controller isn't processing requests and learn how to fix 404 errors effectively with simple troubleshooting steps.
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Why is my Spring MVC Controller Not Being Called? Understanding and Resolving 404 Errors

As developers working with Spring MVC, encountering a 404 error when trying to access the default page can be a frustrating issue. Despite seeing the startup logs indicating that the controller is successfully mapped, navigating to your application's URL can result in a 404 error. If you've faced this situation, you're not alone. Let's delve into the problem and outline the solution.

Understanding the Problem

When working with Spring MVC, the goal is to have your controller handle incoming requests correctly. The symptoms of the issue include:

A 404 Not Found error when accessing your application URL.

The logs indicate that the controller is mapped correctly via RequestMappingHandlerMapping.

For example, when accessing http://localhost:8080/inventory-scan/, the expected response should be served by the controller. However, receiving a 404 indicates that Spring can't find the requested resource.

Common Reasons for 404 Errors

Incorrect URL Mapping: The URL pattern that your controller handles might not be defined correctly.

Programmatic Issues: Missing the necessary files or resources in your configured paths, like missing JSP pages Layout.

Tiles Configuration: Issues with the Tiles view resolution can lead to errors in rendering views, affecting the controller response.

The Solution: Step-by-Step Resolution

Step 1: Verify Controller Mapping

Check your controller class to ensure it has the correct @ RequestMapping annotations. Here’s an example of a simple controller in Spring:

[[See Video to Reveal this Text or Code Snippet]]

Make sure that the method is mapped to handle both "/" and "" paths to properly route requests.

Step 2: Update the Request Mapping (if necessary)

If your route still leads to a 404 error, you might want to modify the @ RequestMapping:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Check Tiles and JSP Files

A common cause of issues with view resolution in Spring MVC is missing files in your Tiles configuration. Here's how to verify this:

Ensure that your layout.jsp is present in the specified directory, often WEB-INF/views/.

Check your tiles-defs.xml to confirm that the layout file is correctly referenced, which might look something like this:

[[See Video to Reveal this Text or Code Snippet]]

Step 4: Testing

After making the changes:

Restart your server (Tomcat).

Access your application URL again: http://localhost:8080/inventory-scan/.

If everything is correctly set up, you should now see the intended page rather than the dreaded 404 error.

Conclusion

404 errors in Spring MVC can be perplexing, but with a methodical approach, you can quickly identify and correct the issue. By ensuring your controller is properly mapped, confirming that all required JSP files are present, and checking your configuration settings, you can resolve these common pitfalls.

Remember, debugging is a part of the development process — support from logging can provide critical insights into your application’s behavior. Happy coding!