@WebServlet(urlPatterns = "/")

public class HelloServlet extends HttpServlet {

    protected void doGet(HttpServletRequest req, HttpServletResponse resp)

            throws ServletException, IOException {

        // 设置响应类型:

        resp.setContentType("text/html");

        //create resp flush buffer:

        PrintWriter pw = resp.getWriter();

        //  ?&df=32& name=&name =Bob&name=null&name=gg&=gg

        Map<String,String[]> namesMap = req.getParameterMap();

//        String name = req.getParameter("name");//get first para of names,全字段匹配/包含空格,may get null

        boolean hasName =false;

        for(String key:namesMap.keySet())

            for(String val:namesMap.get(key)){

//                if(val==null)break;

//                pw.format("<p>%s:%s",key,val);

                if("name".equals(key.strip())){

                    if(val.isEmpty() || val.isBlank())break;

                    pw.format("<h1>Hello, %s!</h1>",val);

                    hasName = true;

                }

            }

        if(!hasName)pw.write("<h1>Hello, World!</h1>");

//        System.out.println(pw.getClass().getName());

        // flush resp buffer to browser resp:

        pw.flush();

        pw.close();

    }

}

为什么多此亿举?

直接String name = req.getParameter("name");

它不好吗？

 //  ?&df=32& name=&name =Bob&name=null&name=gg&=gg如果要传多个同名参数，用数组阅读性更好些吧

?name[]=xiaoming&name[]=xiaohong

String[] names = request.getParameterValues("name");