Java exec method not executing program

I have this program that I am writing that has this method that is supposed to execute a program but does not do anything. The method in question is as follows:

public void findCC_Data(List<String> l7) {

         StringBuffer output = new StringBuffer();

         Process p;
         try {
            for(String sql_file: l7) {
                String command = "cleartool describe " + sql_file;
                p = Runtime.getRuntime().exec(command);
                System.out.println("Executing: " + command);
                p.waitFor();
                BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
                String line = "";
                while ((line = reader.readLine()) != null) {
                    output.append(line + "\n");
                }
                if (reader.readLine() == null) {
                    System.out.println("'reader.readLine()' is equal to null");
                }


            }

        } catch(Exception e) {
            e.printStackTrace();
        }

        System.out.println(output.toString());



     }

Does anyone know why the command does not do anything and the reader.readLine() method always returns null?

I am following a tutorial but using the cleartool program instead of the ping program basically. The tutorial is at this URL:https://www.mkyong.com/java/how-to-execute-shell-command-from-java/

Solution I had the System.out.println(output.toString()) print statement outside of the for loop instead of inside it. Now when I move the SOP statement inside the loop it prints a million plus lines of information on ClearCase version control stuff. To fix put the SOP with the output.toString() inside the loop in the broken code above.