Sling (sort of) Requires Javax Servlet

Recently I was refactoring some Maven POM’s to reduce the number of dependencies and manage the dependency version from the reactor POM. After I removed the duplicate dependencies I ran the build and almost immediately ran into this error:

[ERROR] BUILD FAILURE  
[INFO] ------------------------------------------------------------------------  
[INFO] Compilation failure  
{...Class}.java:[178,50] cannot access javax.servlet.http.HttpServletRequest class file for javax.servlet.http.HttpServletRequest not found
		RequestPathInfo requestInfo = httpRequest.getRequestPathInfo() ;

Since the error was related to Java Servlets, I assumed it was an issue with the servlet project. After spending time going down the rabbit hole, I noticed the error was actually coming out of another project, and being triggered by a Sling Pipeline Rewriter.

So why would code which isn’t a servlet code be throwing an error for missing a javax.servlet class? Well, the error is triggered by:

RequestPathInfo requestInfo = context.getRequest().getRequestPathInfo();

Well, it turns out that the Sling API declares the Java Servlet API as a provided dependency, meaning it’s included in the compilation of the Sling API, but not transitive. The simple solution is that if you interact with any of the Sling Servlet code, aka the SlingHttpServletRequest or the SlingHttpServletResponse, you need to add the javax.servlet.servlet-api as a dependency in your project.