Embedded Tomcat, executable jar, ServletContext.getRealPath()

Question

I'm using a standard spring boot approach (a Java project) where we use embedded Tomcat and package as an executable jar.

I place some static resoures e.g index.html in a static folder under src/main/resources of my project. A library we use expects to load some resources using the servlet context by doing servletContext.getRealPath("XXXX").

When I run this project in Eclipse the real path for servletContext.getRealPath("/") resolves to C:\Users\<me>\workspace\springboot-project\src\main\webapp\. I have no idea why it uses this folder when it does not exist in the project? If I create the executable jar and run this then servletContext.getRealPath("/") gives C:\Users\<me>\AppData\Local\Temp\tomcat-docbase.5693809153072003983.8080\. This directory does exist but has nothing in it.

I can obviously see my resources fine if requested via HTTP I just can't get at them as expected via the servlet context.

Any ideas?

Answer 1

Resources in src/main/resources/static aren't served directly by Tomcat. They're served by Spring through its DispatcherServlet and a ResourceHttpRequestHandler that's auto-configured by Spring Boot. By default, this resource handler is configured to serve resources from the following locations:

1. classpath:/META-INF/resources/
2. classpath:/resources/
3. classpath:/static/
4. classpath:/public/

It's 3 that's making your resources in src/main/resources/static available.

Using getRealPath() is always going to be problematic as it requires the resource to be available as a file on the filesystem, i.e. it can't be inside the war or jar that you're running, and there's no guarantee that that will be the case. Using ClassLoader.getResource() or ServletContext.getResource() is a much more robust way to find and load resources within your web application as it doesn't rely on the resource being directly on the filesystem.

You haven't said which library it is that's using getRealPath(). Perhaps it can be updated or be configured to use a different resource loading strategy?