java - 无法从 Java Servlet 获取变量

Question

我有一个 html 表单，询问用户简历的详细信息:

<form action = "processdetails.html" method = "post">
    <table>
        <tr><td style = "font-weight: bold">Personal Details:</td></tr>
        <tr>
            <td>Name:</td>
            <td><input type = "text" name = "applicant"/></td>
        </tr>
        <tr>
            <td>Mobile No.:</td>
            <td><input type = "text" name = "mobile"/></td>
        </tr>
        <tr>
            <td>E-mail:</td>
            <td><input type = "text" name = "email"/></td>
        </tr>
    </table>
    <br/>
    <input style = "width: 150px" type = "submit" value = "Generate CV"/>
</form>

点击“生成简历”按钮后，它会转到显示输入详细信息的 Servlet:

@WebServlet("/processdetails.html")
public class ProcessDetailsServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    String applicantName = "";
    String mobileNo = "";
    String emailAdd = "";

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");

        if(request.getParameter("applicant") != null) {
            applicantName = request.getParameter("applicant");
        }

        if(request.getParameter("mobile") != null) {
            mobileNo = request.getParameter("mobile");          
        }

        if(request.getParameter("email") != null) {
            emailAdd = request.getParameter("email");           
        }

        PrintWriter out = response.getWriter();

        // other necessary html/css here

        out.print("<form action = 'generatepdf.html' method = 'post'>");
        out.print("<table>");
        out.print("<tr><td style = 'font-weight: bold'>Personal Details:</td></tr>");
        out.print("<tr>");
        out.print("<td>Name:</td>");
        out.print("<td>" + applicantName + "</td>");
        out.print("</tr>");
        out.print("<tr>");
        out.print("<td>Mobile No.:</td>");
        out.print("<td>" + mobileNo + "</td>");
        out.print("</tr>");
        out.print("<tr>");
        out.print("<td>E-mail:</td>");
        out.print("<td>" + emailAdd + "</td>");
        out.print("</tr>");
        out.print("</table>");      
        out.print("<br/>");
        out.print("<input style = 'width: 150px' type = 'submit' value = 'Generate PDF'/>");
        out.print("</form>");

        // other html

        out.close();
    }
}

点击“生成PDF”按钮后，跳转到另一个Servlet:

@WebServlet("/generatepdf.html")
public class GeneratePdfServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        generatePdf();
    }

    protected void generatePdf() {
        System.out.println("This is generatePdf().");

        ProcessDetailsServlet pds = new ProcessDetailsServlet();
        System.out.println("Name: " + pds.applicantName);       
    }
}

为了检查 generatePdf() 是否获取详细信息，我将其打印到控制台。
但是，applicantName 未打印:



为什么applicantName 无法被访问？

Answer 1

1. 当您点击“生成简历”时，您的表单将提交至 ProcessDetailsS​​ervlet
2. ProcessDetailsS​​ervlet 显示结果
3. 当您点击“生成 PDF”时，您将再次提交给 GeneratePdfServlet。

嗯，基本上您不会获得 GeneratePdfServlet 的任何用户详细信息，因为当您单击“生成 PDF”时，您没有向 GeneratePdfServlet 提交任何值。

在您设法将用户数据保存在 HttpSession 或某个安全的地方之前，用户数据不会在下一个请求中保留。

您的替代方案(如果您不想使用HttpSession)是，您可以使用不可编辑的输入字段而不是表格，使用ProcessDetailsS​​ervlet 生成表单。因此，下次用户单击“生成 PDF”时，您可以重新提交他们的数据并将其放入 servlet 中以生成 PDF。

编辑: 仅输入字段以表单形式提交。因此表值不会到达 Servlet。