Question

尽管我正在研究Murach的Java Servlet和JSP，但对HTML格式哈哈有疑问

在index.jsp上提交表单后，将调用EmailListServlet，它会进行一些验证，如果一切正常，则将调用thank.jsp。

Index.jsp文件

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>Murach's Java Servlets and JSP</title>
    <link rel="stylesheet" href="styles/main.css" type="text/css"/>
</head>
<body>
    <h1>Join our email list</h1>
    <p>To join our email list, enter your name and
       email address below.</p>
    <p><i>${message}</i></p>
    <form action="emailList" method="post">
        <input type="hidden" name="action" value="add">        
        <label class="pad_top">Email:</label>
        <input type="email" name="email" value="${user.email}" 
               required><br>
        <label class="pad_top">First Name:</label>
        <input type="text" name="firstName" value="${user.firstName}" 
               required><br>
        <label class="pad_top">Last Name:</label>
        <input type="text" name="lastName" value="${user.lastName}"  
               required><br>        
        <label>&nbsp;</label>
        <input type="submit" value="Join Now" class="margin_left">
    </form>
</body>
</html>

EmailLisServlet

package murach.email;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

import murach.business.User;
import murach.data.UserDB;

public class EmailListServlet extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request,
            HttpServletResponse response)
            throws ServletException, IOException {
        String url = "/index.html";
        
        // get current action
        String action = request.getParameter("action");
        if (action == null) {
            action = "join";  // default action
        }

        // perform action and set URL to appropriate page
        if (action.equals("join")) {
            url = "/index.jsp";    // the "join" page
        } 
        else if (action.equals("add")) {
            // get parameters from the request
            String firstName = request.getParameter("firstName");
            String lastName = request.getParameter("lastName");
            String email = request.getParameter("email");

            // store data in User object
            User user = new User(firstName, lastName, email);

            // validate the parameters
            String message;
            if (UserDB.emailExists(user.getEmail())) {
                message = "This email address already exists.<br>" +
                          "Please enter another email address.";
                url = "/index.jsp";
            }
            else {
                message = "";
                url = "/thanks.jsp";
                UserDB.insert(user);
            }
            request.setAttribute("user", user);
            request.setAttribute("message", message);
        }
        getServletContext()
                .getRequestDispatcher(url)
                .forward(request, response);
    }    
}

thanks.jsp

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>Murach's Java Servlets and JSP</title>
    <link rel="stylesheet" href="styles/main.css" type="text/css"/>    
</head>

<body>
    <h1>Thanks for joining our email list</h1>

    <p>Here is the information that you entered:</p>

    <label>Email:</label>
    <span>${user.email}</span><br>
    <label>First Name:</label>
    <span>${user.firstName}</span><br>
    <label>Last Name:</label>
    <span>${user.lastName}</span><br>

    <p>To enter another email address, click on the Back 
    button in your browser or the Return button shown 
    below.</p>

    <form action="" method="post">
        <input type="hidden" name="action" value="join">
        <input type="submit" value="Return">
    </form>

</body>
</html>

问题是我不明白为什么当我在thank.jsp上提交表单时，一旦action元素为空，它将返回index.jsp。你能告诉我我放手吗？

为什么表单动作为空返回上一页？

0 个答案: