title: Why is this URL returning error 400 from Tomcat?
body: <p>I have a Tomcat server running Java servlets. I'm trying to make a servlet that returns stored files, given their encrypted IDs.</p>
  
  <p>ID: 100</p>
  
  <p>Encrypted ID: +e4/E5cR/aM=</p>
  
  <p>URL-encoded ID: %2Be4%2FE5cR%2FaM%3D</p>
  
  <p>Resulting URL: <a href="http://localhost/file/demo/%2Be4%2FE5cR%2FaM%3D" rel="noreferrer">http://localhost/file/demo/%2Be4%2FE5cR%2FaM%3D</a></p>
  
  <p>When I try to follow that link, I don't even get into my servlet's code - the server returns this error: <strong>Failed to load resource: the server responded with a status of 400 (Bad Request)</strong></p>
  
  <p>What's wrong with this URL that's making Tomcat reject it before reaching my code? I ran it though a URL-encoder, and I don't see any invalid characters in it.</p>