Elisp: can't read buffer content with with-current-buffer

[Alessandro Bertulli <alessandro.bertulli96@gmail.com>]

Hi all!
I'm trying to set up some custom Elisp function to help me run Java
programs. Since it's possible I have different classes containing a main
method (for instance, when developing multi process or client-server
applications) I wanted to use completing-read. Therefore, I need a
list/function for completion. To do so, I need to scan the project I'm
working on, and search for the main methods that can be run. No problem
here, I can do that using grep and regexp. But then I don't know how to
collect those results in a list!

Specifically, let's say I have the directory "my_project" containing
some Java files. I want a list of strings, each one being one of the
files returned by grep, like:
'("~/my_project/src/main/java/ClassOne.java"
  "~/my_project/src/main/java/ClassTwo.java")

In this function I wrote, however, it seems I can't do that:

(defun get-main-method-list ()
  "Scan the project for main methods to run."
  (interactive)
  (let* ((project-root (projectile-acquire-root))
	 (output-buffer (get-buffer-create "*java-grep*")))
    (async-shell-command (format "grep --include=\\*.java -rnwl \'%s\' -e \'%s\'"
				 project-root
				 "public[[:space:]]\\+static[[:space:]]\\+void[[:space:]]\\+main")
			 output-buffer
			 output-buffer)
    (with-current-buffer output-buffer
      (let ((buffer-content (buffer-string)))
	(print buffer-content) ;; debug
	(set-text-properties 0 (length buffer-content) nil buffer-content)
	(split-string buffer-content "\n")))))

See where I put a debug (print): it prints nothing or newlines, and the
function seems to return '(""). Is this a problem in using
with-current-buffer? If no, what am I getting wrong? Is this the
preferred way to tokenize a buffer into a list of strings?

Thanks for your time, have a nice day!

Alessandro