Question

问题是当我填写它调用servlet的表单时，它显示正确的信息，当用户单击后退按钮时，它似乎在该页面上调用值为null的servlet。如何制作它以便重新加载页面，以便用户可以重新填写表单。

SetTimeZone.xhtml

 <html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title>SetTimeZone</title>
    <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
</head>
<body>
    <div>
        <form name ="SetTimeZone" method="post" action="SetTimeZoneServlet">
            Set Time Zone: <input type="text" name="timeZone"/><br></br><br></br>
            <input type ="submit" value="Submit" name="submit"/>
        </form>
    </div>
</body>

public class SetTimeZoneServlet extends HttpServlet {

/**
 * Handles the HTTP <code>POST</code> method.
 *
 * @param request servlet request
 * @param response servlet response
 * @throws ServletException if a servlet-specific error occurs
 * @throws IOException if an I/O error occurs
 */
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    TimeZoneBean bean = new TimeZoneBean();
    String city = request.getParameter("timeZone");
    bean.setCity(city);
    String temp = bean.checkCity();
    String value = "";

    if ("error".equals(temp)) {
        value = "Sorry no information is availible for " + city;
    } else {
        value = "The current time in " + city + " is " + bean.getTime();
    }

    try (PrintWriter out = response.getWriter()) {

        response.setContentType("text/html;charset=UTF-8");

        /* TODO output your page here. You may use following sample code. */
        out.println("<!DOCTYPE html>");
        out.println("<html>");
        out.println("<head>");
        out.println("<title>Servlet OrderFormServlet</title>");
        out.println("</head>");
        out.println("<body>");
        out.println("<p>" + value + "</p>");
        out.println("<form name=\"SetTimeZone.xhtml\" method=\"post\" name=\""
                + "SetTimeZoneRedirectServlet\"> ");
        out.println("<input type =\"submit\" value=\"Back\"/ name=\"back\">");
        out.println("</form>");
        out.println("</body>");
        out.println("</html>");
    }
}

public class SetTimeZoneRedirectServlet extends HttpServlet {

/**
 * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
 * methods.
 *
 * @param request servlet request
 * @param response servlet response
 * @throws ServletException if a servlet-specific error occurs
 * @throws IOException if an I/O error occurs
 */
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.sendRedirect("SetTimeZone.xhtml");
}
}

重定向到页面后得到的输出是; 对不起，没有关于null的信息。

Answer 1

尝试使用GET而不是POST 这可以解决您的问题

Answer 2

通过对表单使用POST方法，您可能会遇到此问题。正如@visray建议的那样，您需要覆盖doGet() Servlet方法才能使GET方法正常工作。

在处理数据库更改时应该使用

POST方法，因此在您的情况下GET是合适的。

Java Servlet重定向到页面自动调用其表单servlet

2 个答案: