title: Regexp for a string to contain only letters , numbers and space in Java
body: <p>Requirement: String should contain only letters , numbers and space.<br>
               I have to pass a clean name to another API.</p>
  
  <p>Implementation: Java</p>
  
  <p>I came up with this for my requirement</p>
  
  <pre>
  public static String getCleanFilename(String filename) {
      if (filename == null) {
          return null;
      }
      return filename.replaceAll("[^A-Za-z0-9 ]","");
  }
  </pre>
  
  <p>This works well for few of my testcase , but want to know am I missing any boundary conditions, or any better way (in performance) to do it.</p>