Question

我想实现一个单独的JSP标记页面，其形式如下：

JSP：formPay.jsp

<form action="<%=request.getContextPath() + "/Pay.do"%>" method="post" id="guest">
    <table>
        <tr>
            <td width="150"><span class="required">*</span> First Name:</td>
            <td><input type="text" name="firstname" value="<%= request.getAttribute("firstname") %>" />
            </td>
        </tr>
    [...]
    </table>
<input class="button" type="submit" value="Confirm" name="btnConfirm">
</from>

Servlet：PayCommand.java

public class PayCommand implements Command {

    @Override
    public HttpServletRequest execute(HttpServletRequest request)
            throws ServletException, IOException {

        boolean errorWithField = false;

        String paramFirstName = "";
        String paramLastName = "";
        String paramEmail = "";
        String paramCity = "";
        String paramAddress = "";

        try {
            paramFirstName = request.getParameter("firstname");
            paramLastName = request.getParameter("lastname");
            paramEmail = request.getParameter("email");
            paramCity = request.getParameter("city");
            paramAddress = request.getParameter("address");
        } catch (Exception e) {
            request.setAttribute("jsp", "formPay");
            return request;
        }   

        if (paramFirstName==null || paramFirstName.equals("")) {
            errorWithField = true;
        }
        if (paramLastName==null || paramLastName.equals("")) {
            errorWithField = true;
        }
        if (paramEmail==null || paramEmail.equals("")) {
            errorWithField = true;
        }   
        if (paramCity==null || paramCity.equals("")) {
            errorWithField = true;
        }
        if (paramAddress==null || paramAddress.equals("")) {
            errorWithField = true;
        }

        // if errorWithField==true, reload the formPay.jsp
        if (errorWithField) {
            request.setAttribute("message", "You have to fill out all of the fields.");

            request.setAttribute("jsp", "formPay");
            request.setAttribute("firstname", paramFirstName);
            request.setAttribute("lastname", paramLastName);
            request.setAttribute("email", paramEmail);
            request.setAttribute("city", paramCity);
            request.setAttribute("address", paramAddress);

        } else {           
            // if not, go to the confirm page, everything is ok.
            request.setAttribute("jsp", "confirmation");
            request.setAttribute("firstname", paramFirstName);
            request.setAttribute("lastname", paramLastName);
            request.setAttribute("email", paramEmail);
            request.setAttribute("city", paramCity);
            request.setAttribute("address", paramAddress);
        }
        return request;
    }
}

问题是当JSP第一次加载时，我希望它被解释为好像没有错误，但errorWithField结果是true，所以错误信息显示甚至在用户填写表格之前。

第二个问题是JSP将获取已填写的字段的值，但如果没有任何内容，则返回null，包括第一次加载JSP。我该如何对待这个问题？

修改请注意，Pay.do表单操作被重定向到PayCommand.java，这是由前控制器模式处理的。（未显示）

Answer 1

您可以向表单添加隐藏字段，并检查它是否具有值。如果是，那么表格将被回发;否则，它是第一次加载（你应该跳过错误检查的东西）。

Answer 2

第一个问题，我认为你可以使用另一个.do动作来转发到jsp页面而不将属性errorWithField设置为true。
第二个问题，你可以试试这个：

＆lt;％= request.getAttribute（“firstname”）== null？ “”：request.getAttribute（“firstname”）％＆gt;

检测JSP是否第一次加载

2 个答案: