Servlet无法转发-Servlet异常 [英] Servlet not forwarding - Servlet exception

问题描述

我的servlet无法正确转发.我不断尝试Tomcat-8.5 404或500错误页面.当我收到500错误时，它只是说servlet抛出了一个异常.

My servlet is not forwarding correctly. I keep getting forwarded to the Tomcat-8.5 404 or 500 error pages depending what I try. When I get the 500 error, it just says the servlet threw an exception.

我正在尝试检索定位标记的名称(在导航栏中)，然后根据该名称将其转发到正确的JSP.一旦开始工作，我将使用该servlet检查现有会话或启动新会话.

I'm attempting to retrieve the name of an anchor tag (in a nav bar), and based on the name forward it to the correct JSP. Once I get this working I will use this servlet to check for existing sessions or start new ones.

非常感谢您的帮助.

下面是我的servlet映射:

Below is my servlet mapping:

<servlet>
    <servlet-name>SessionTracker</servlet-name>
    <servlet-class>SessionTracker</servlet-class>
</servlet>

<!-- Servlet Maps -->
<servlet-mapping>
    <servlet-name>SessionTracker</servlet-name>
    <url-pattern>/donate/*</url-pattern>
</servlet-mapping>

以下是定位标记:

<li><a href="/donate/donate.jsp" name="donate">Donate</a></li>

请注意，我还在锚标记上尝试了以下方法:

Note, I have also tried the following on the anchor tag:

<li><a href="/donate/donate.jsp?name=donate" name="donate">Donate</a</li>

下面是相应的Java函数:

Below are the respective Java functions:

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    ServletContext sc = getServletContext();
    String url = forwardRequest(request, response, sc);

    sc.getRequestDispatcher(url).forward(request, response);
}

private static String forwardRequest(HttpServletRequest request, HttpServletResponse response, ServletContext sc){
    String url = new String("");
    String name = request.getParameter("name");

    switch(name){ //switch state to determine which
        case "donate":
            url = "/donate/donate.jsp";
            break;

        case "mission":
            url = "/about/missionStatement.jsp";
            break;
    }

    return url;
}

推荐答案

好，让我们分析一下代码:

Ok Let's analyze your code:

1.- dd(web.xml)

1.- dd (web.xml)

<servlet-class>SessionTracker</servlet-class>

尽量不要使用默认软件包(尽管这里没有问题)

Try not to use Default package, (Although there is no problem here)

<url-pattern>/donate/*</url-pattern>

哦，男孩，这是个问题，您是在对容器说，嘿，如果有人使用url

Oh Boy, here is a problem, you're saying to the Container, HEY, If someone uses the url http://localhost:8080/mysite/donate/whateverIDon'tCare call the Servlet SessionTracker, so I can use this diferents paths and it will call the same Servlet

/mysite/donate/some
/mysite/donate/hereWeGo
/mysite/donate/lol

这不好，请尝试将其更改为

So that is not good, try to change it to

<url-pattern>/donate/SesionTrackerServlet</url-pattern>

2.-看看您的

<li><a href="/donate/donate.jsp?name=donate" name="donate">Donate</a</li>

您看到失败了吗?是的，正如我所说，当用户单击此处时，它将调用您的Servlet，因此您的Servlet将调用您的方法forwardRequest，您认为会发生什么?是的，它将转向url ="/donate/donate.jsp";但是等等，你看到我的观点1了吗?您将再次调用servlet，并再次调用方法，并一次又一次地调用booooom....Estado HTTP 500-Servlet执行引发了异常，因为您创建了循环.

can you see the failure? yes as I said , when a user click here it will call your Servlet, so your servlet will call your method forwardRequest and What do you think will happen? yes it will foward to url = "/donate/donate.jsp"; but wait, did you see my point 1? your will call again the servlet and again the method and again and again and again and booooom....Estado HTTP 500 - Servlet execution threw an exception because you made a Loop.

但我对此表示更改:

Web.xml

<servlet>
<servlet-name>SessionTracker</servlet-name>
<servlet-class>SessionTracker</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>SessionTracker</servlet-name>
<url-pattern>/donate/SessionTrackerServlet</url-pattern>
</servlet-mapping>

现在输入此网址(当然，如果需要，请更改端口)

Now enter this url (of course change your port if you need)

http://localhost:8080/Test/donate/SessionTrackerServlet?name = donate

还有woooala =)

And woooala =)

[![enter image description here][1]][1]
[![enter image description here][2]][2]
[![enter image description here][3]][3]
[![enter image description here][4]][4]


  [1]: https://i.stack.imgur.com/9hhTO.png
  [2]: https://i.stack.imgur.com/Hqha7.png
  [3]: https://i.stack.imgur.com/uUvn4.png
  [4]: https://i.stack.imgur.com/Tge2x.png

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