java - 无法从 Servlet 到 JSP 获取错误消息(验证)

Question

我在 Servlet/JSP 方面遇到问题。我正在尝试验证 Java Servlet 类中 JSP 的 HTML 字段，并将该(可能的)错误消息从 Servlet 返回到 JSP。即使我遵循教程，我也无法解决这个问题。

index.jsp:

   <form action="addWine" method="post">
        <p>
            <input type="text" name="name"/>          
            <input type="submit" value="submit">
            <span class="error">${messages.error}</span>
        </p>
    </form>

添加Wines.java

public class AddingWines extends HttpServlet {

...

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {


   Map<String, String> messages = new HashMap<String, String>();
   request.setAttribute("messages", messages);

    String name = request.getParameter("name");
    if(name.trim().isEmpty()){
        messages.put("name", "give a name");
    }

    //No errors in HTML field

    if (messages.isEmpty()) {
        messages.put("noErrors", String.format("Welcome blabla"));
    }

    request.getRequestDispatcher("greatSucceess.jsp").forward(request, response);

web.xml

    <servlet>
    <servlet-name>AddingWines</servlet-name>
    <servlet-class>Servlets.AddingWines</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>AddingWines</servlet-name>
    <url-pattern>/addWine</url-pattern>
</servlet-mapping>

NetBeans 没有抛出任何错误。即使 HTML 字段为空，它也只是定向到greatSuccesss.jsp。该怎么办？ (顺便说一句，有足够的信息吗？)

Answer 1

在您的 servlet 中，您将每个请求重定向到greatSuccess.jsp，请参阅最后一行:

request.getRequestDispatcher("greatSucceess.jsp").forward(request, response);

您应该按如下方式更改代码:

if (messages.isEmpty()) {
    request.getRequestDispatcher("greatSucceess.jsp").forward(request, response);
} else {
    // show page with form
}