如何获取没有值的URL参数?

Koe*_*err 1 java jsp url-parameters

使用URL访问:

http://127.0.0.1/test.jsp?action=test&abc
Run Code Online (Sandbox Code Playgroud)

要么

http://127.0.0.1/test.jsp?abc
Run Code Online (Sandbox Code Playgroud)

怎么才能得到字符串"abc"?

感谢帮助 :)

Enr*_*que 5

<% java.util.Enumeration names = request.getParameterNames();
    while(names.hasMoreElements()){
        out.println(names.nextElement() + "<br>");
    }
    %>
Run Code Online (Sandbox Code Playgroud)