JAVA错误 这是什么错误 求大神指教

Question

错误提示java.lang.StringIndexOutOfBoundsException: String index out of range: -8 java.lang.String.substring
给出一部分代码：
public void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
//取消乱码了
//String s=new String(request.getParameter("userName").getBytes("ISO-8859-1"),"UTF-8");
//System.out.println(s);
String url = request.getRequestURI();
String action = url.substring(url.lastIndexOf("/"),url.lastIndexOf("."));
//HttpSession session1 = request.getSession();
User user=new User();
UserDao userDao= new UserDao();
DeleteUserDao deleteUserDao=new DeleteUserDao();
FindDao findDao =new FindDao();
FindByNameDao findByNameDao=new FindByNameDao();
UpdateDao updateDao=new UpdateDao();
//增加用户
if("/add".equals(action)){
//user.setId(Integer.parseInt(request.getParameter("id")));
user.setUserName(new String(request.getParameter("userName").getBytes("ISO-8859-1"),"UTF-8"));
user.setPwd(new String(request.getParameter("pwd").getBytes("iso-8859-1"),"utf-8"));
user.setAge(Integer.parseInt(request.getParameter("userAge")));
user.setSex(new String(request.getParameter("sex").getBytes("ISO-8859-1"),"UTF-8"));
user.setHobby(new String(request.getParameter("hobby").getBytes("ISO-8859-1"),"UTF-8"));
user.setEdu(new String(request.getParameter("edu").getBytes("ISO-8859-1"),"UTF-8"));

Answer 1

StringIndexOutOfBoundsException是越界异常，看你代码应该是
String action = url.substring(url.lastIndexOf("/"),url.lastIndexOf("."));出错；

url.lastIndexOf("/")和url.lastIndexOf(".")有可能会返回-1的

Answer 2

数组越界，应该是有些地址，不是符合你假设的 url 的情况追问

那应该怎么解决

追答

你都采纳别人了，还问我……

在前面增加判断咯，先判断是否符合格式之类的
或者，判断两个 lastIndexOf 是否为 >= 0, 也行