Question

我需要获取HashTable中存在的所有密钥。我使用以下代码执行此操作：

protected void doGet(HttpServletRequest request,
    HttpServletResponse response) throws ServletException, IOException {
// Important: doGet get the 4 input. 
// Parameter name: "Standard", "Section", "Name", "Rollno"
// But i am dealing with only 3 input to test the code. (not considering "Rollno" as of now, So RollNo will be empty string as of now.) 

String output = "";
response.setContentType("text/html");

// referer tag in the header tells that which page sent the request.
// If this request is sent by Search.jsp page, the look at which button
// made the request and process the request accordingly.

if (request.getHeader("referer") != null
        && (request.getHeader("referer").endsWith("Search.jsp"))) {

    Enumeration<String> parma_names = request.getParameterNames();
    while ((parma_names != null) && (parma_names.hasMoreElements())) {
        String ele_name = parma_names.nextElement();
        if (ele_name.equalsIgnoreCase("data1")) {
            output = requestMadeForDialog(request, ele_name);
            response.getWriter().write(output);
        } else {
 // See here...
            output = requestMadeForReport(request, ele_name);
            response.getWriter().write(output);
            break;
        }
    }
} else {
      // something here...
}

}

如果请求是针对报告的，那么下面是报告的代码。

private String requestMadeForReport(HttpServletRequest request,
        String ele_name) {
    log("requestMadeForReport and element name is " + ele_name);
    // received parameter may be empty, If param is empty then it should not
    // be included in where clause.
    String standard = request.getParameter("standard");
    String section = request.getParameter("section");
    String name = request.getParameter("name");
    String rollno = request.getParameter("rollno");
    Hashtable<String, String> param = new Hashtable<>();
    if (standard != null && (!standard.isEmpty())) {
        param.put("standard", standard);
    }
    if (section != null && (!section.isEmpty())) {
        param.put("section", section);
    }
    if (name != null && (!name.isEmpty())) {
        param.put("name", name);
    }
    if (rollno != null && (!rollno.isEmpty())) {
        param.put("rollno", rollno);
    }

    generateReport(param);
    return null;
}

//只有非空和非空参数才会移交给实际的报告生成器方法。

private void generateReport(Hashtable<String, String> param) {
    // TODO Auto-generated method stub
    Enumeration<String> keyset = param.keys();
    while (keyset.hasMoreElements()) {
        String e = keyset.nextElement();
    }
}

但是在得到最后一个元素时我得到NoSuchElementException。我的HashTable包含密钥{“Section”，“Name”，“Standard”} 并且在while循环'e'中只获得值“Section”和“Standard”。并且第三次抛出异常。

我也尝试过，[link]（Get keys from HashMap in Java）但是同样的问题发生在这里。

java.util.NoSuchElementException：Hashtable枚举器

0 个答案: