$zjsjname= md5(time().rand(0,9).$_FILES["zjsjurl"]["name"]).'.'.pathinfo($_FILES["zjsjurl"]["name"],PATHINFO_EXTENSION);
move_uploaded_file($_FILES["zjsjurl"]["tmp_name"],"$sjpath/".$zjsjname);
$zjsjurl= "$sjpath/".$zjsjname;
$zjsjurl=!empty($_FILES["zjsjurl"]["name"])?$zjsjurl:null;
现在需要加一个对格式的限制 该怎么弄呢