Template Not Found Errors in Spring Boot

When developing a web application with Spring Boot, especially one that leverages templating engines like Thymeleaf, FreeMarker, or Mustache, you might come across the infamous "Template Not Found" error. This error can be a bit frustrating, especially if you're sure that your template exists in the project.

What is this error about? 

The error typically indicates that the Spring Boot application failed to locate the template file for rendering. It's common to see an error message similar to:

TemplateInputException: Error resolving template [templateName], template might not exist or might not be accessible by any of the configured Template Resolvers.

Causes

Incorrect Path: Your template might not be in the default path (src/main/resources/templates/). 

Wrong Extension: Spring Boot expects templates to have certain extensions based on the engine (e.g., .html for Thymeleaf, .ftl for FreeMarker). 

Typo in the Template Name: A simple typo can lead to this error. 

Configuration Errors: Misconfigurations in application.properties or application.yml can lead to template resolution failures. 

Missing Dependencies: If you've missed adding the necessary starter dependencies, Spring Boot might not auto-configure the templating engine. 

Solutions

Verify Template Location: Ensure your templates are in the default location. If you're storing them elsewhere, make sure to update the configuration accordingly. 

By default, Spring Boot expects the template files to be located under the src/main/resources/templates directory. If your template file is not in this location or the directory structure has been modified, the application might not find the template.

Check File Extension: For Thymeleaf, the file should be named templateName.html. For FreeMarker, it would be templateName.ftl. Ensure you're using the right extension. 

Ensure Correct Name Usage: Check the name you're using in your controller when returning the view. It should match the template's name (without the extension). 

Review Configuration: Open application.properties or application.yml and ensure you haven't misconfigured any paths or properties related to your templating engine. 

Add Necessary Dependencies:

For Thymeleaf, ensure you've added:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>

For FreeMarker:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-freemarker</artifactId>
</dependency>

Clean and Rebuild: Sometimes, a clean and rebuild can solve the issue, especially if there's some caching involved. 

Logging: Increase the log level for the templating engine in application.properties to debug. This will provide more insights:

logging.level.org.thymeleaf=DEBUG

Conclusion

Template Not Found errors in Spring Boot are common but easily resolvable with systematic troubleshooting. By understanding the root causes and applying the above solutions, you can ensure a smooth templating experience in your Spring Boot application. Always remember that meticulous attention to configuration and naming conventions will save a lot of debugging time in the long run.