Resolving 404 Error for Java Spring MVC Applications on Tomcat

Discover how to troubleshoot and fix the common `404` error encountered while deploying Java Spring MVC apps on Tomcat, ensuring your application's main page loads correctly.
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Troubleshooting the 404 Error in Your Java Spring MVC App on Tomcat

If you're deploying a Java Spring MVC application on Tomcat and facing the frustrating 404 error with the message "The requested resource is not available," you're not alone—a lot of developers encounter this issue during deployment. In this guide, we'll explore the common causes of this error and how to resolve it, ensuring your application runs smoothly.

Understanding the Problem

When you deploy a Spring MVC app and navigate to the designated URL (like http://localhost:8080/demo-mvc/ in your case), receiving a 404 error indicates that the Tomcat server cannot find the resource you are trying to access. This could be due to various reasons related to configuration files, project structure, or conflicting files in the web application directory.

Common Causes of 404 Error Include:

Incorrect deployment or absence of app directory in Tomcat's webapps folder.

Misconfiguration in the web.xml or servlet mapping.

Default files (like index.html) conflicting with Spring's request mappings.

Resolving the 404 Error

Step 1: Verify Deployment

First and foremost, check whether your application is correctly deployed on Tomcat:

Navigate to the Tomcat/webapps directory.

Ensure your app's directory (e.g., demo-mvc) exists there.

If it's missing, deploy your WAR file again from your IDE or manually place it inside the webapps directory.

Step 2: Examine Your Configuration Files

Ensure your configuration files are set up correctly. Two important files are:

web.xml (for servlet and URL mapping configuration)

spring-mvc-demo-servlet.xml (for Spring MVC configuration)

Here’s a quick checklist for these files:

web.xml: Make sure your servlet and servlet-mapping are defined and mapped accurately. Here’s an essential snippet:

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spring-mvc-demo-servlet.xml: Ensure component scanning and view resolver configuration are defined correctly, allowing Spring to look for controllers and views in the proper locations. The context should highlight your bean definitions similar to:

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Step 3: Check View Rendering

If your app was deployed correctly and configurations are accurate, verify your view files (e.g., main-menu.jsp) exist in the specified directory (WEB-INF/view). Also, ensure your controllers return the correct view names as configured:

HomeController should refer to the main-menu view:

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

Step 4: Remove Conflicting Files

A significant step that resolved the issue in this specific case was removing a default index.html file created by the IDE (NetBeans). This file can conflict with your application's URL mapping. Always ensure that if you have custom request mappings, no default HTML files are interfering:

Locate and delete any unwanted index.html or similar files in your webapp directory.

Redeploy your application and try accessing your main page again.

Conclusion

By following the steps outlined above, you should be able to successfully resolve the 404 error with your Java Spring MVC application running on Tomcat. Good practices include keeping your directory structure clean, ensuring configuration files are set up correctly, and removing any potential conflicts. Don’t let deployment issues keep you from enjoying the full capabilities of your application. Happy coding!

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