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我需要获取我的HashTable. 我用以下代码做到这一点：

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...
}

}

如果请求报告，则下面是报告代码。

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交给实际的报表生成器方法。

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

但是我得到NoSuchElementException了最后一个元素。MyHashTable包含键 {"Section"、"Name"、"Standard"} 并且在 while 循环中 'e' 仅获得值 "Section" 和 "Standard"。第三次抛出异常。

我也试过，[链接]（从 Java 中的 HashMap 获取密钥）但同样的问题发生在这里。

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