Question

我正在尝试运行https://developers.google.com/appengine/docs/java/gettingstarted/usingjsps上提供的App Engine教程。根据教程的要求，我已将新的servlet SignGuestbookServlet.java映射到web.xml中的url-pattern“/ sign”，但是当我尝试访问localhost：8888 / sign上的资源时，出现404错误。

Web.xml中：

<?xml version="1.0" encoding="utf-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">
<servlet>
    <servlet-name>SignGuestbookServlet</servlet-name>
    <servlet-class>guestbook.SignGuestbookServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>SignGuestbookServlet</servlet-name>
    <url-pattern>/sign</url-pattern>
</servlet-mapping>
<servlet>
    <servlet-name>Guestbook</servlet-name>
    <servlet-class>guestbook.GuestbookServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>Guestbook</servlet-name>
    <url-pattern>/guestbook</url-pattern>
</servlet-mapping>


<welcome-file-list>
    <welcome-file>guestbook.jsp</welcome-file>
</welcome-file-list>
</web-app>

SignGuestbookServlet.java：

package guestbook;

import java.io.IOException;
import java.util.logging.Logger;
import javax.servlet.http.*;

import com.google.appengine.api.users.User;
import com.google.appengine.api.users.UserService;
import com.google.appengine.api.users.UserServiceFactory;

@SuppressWarnings("serial")
public class SignGuestbookServlet extends HttpServlet {

private static final Logger log = Logger.getLogger(SignGuestbookServlet.class.getName());

@Override
public void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws IOException {
 resp.getWriter().println("Hello");
    /*UserService userService = UserServiceFactory.getUserService();
    User user = userService.getCurrentUser();


    String content = req.getParameter("content");
    if (content == null) {
        content = "(No greeting)";
    }
    if (user != null) {
        log.info("Greeting posted by user " + user.getNickname() + ": " + content);
    } else {
        log.info("Greeting posted anonymously: " + content);
    }
    resp.sendRedirect("/guestbook.jsp");
    */
}
}

为什么会发生这种情况的原因？任何帮助将不胜感激。

P.S。：我使用get方法从表单发送数据，所以我使用了doGet（）而不是doPost（）。

Answer 1

您的Servlet类的名称和web.xml中的完全限定名称不匹配。您的servlet类名是SignGuestbookServlet

public class SignGuestbookServlet extends HttpServlet

但在您的web.xml中，它被指定为GuestbookServlet

<servlet-class>guestbook.GuestbookServlet</servlet-class>

使用正确的servlet类名更新web.xml

<servlet-class>guestbook.SignGuestbookServlet</servlet-class>

Answer 2

您的Java代码没有任何问题。问题是由于您启动本地开发服务器，web.xml中存在错误的（额外）条目，因此存在错误，因此上下文未正确初始化。因此，虽然服务器正在运行，但在尝试访问/ sign端点时会出现错误。

要解决此问题，请执行以下操作：

目前，您的web.xml显示如下：

<?xml version="1.0" encoding="utf-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">
<servlet>
   <servlet-name>SignGuestbookServlet</servlet-name>
   <servlet-class>guestbook.SignGuestbookServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>SignGuestbookServlet</servlet-name>
  <url-pattern>/sign</url-pattern>
</servlet-mapping>
<servlet>
   <servlet-name>Guestbook</servlet-name>
   <servlet-class>guestbook.GuestbookServlet</servlet-class>
</servlet>
<servlet-mapping>
   <servlet-name>Guestbook</servlet-name>
   <url-pattern>/guestbook</url-pattern>
</servlet-mapping>
<welcome-file-list>
   <welcome-file>guestbook.jsp</welcome-file>
</welcome-file-list>
</web-app>

删除以下条目：

<servlet>
   <servlet-name>Guestbook</servlet-name>
   <servlet-class>guestbook.GuestbookServlet</servlet-class>
</servlet>
<servlet-mapping>
   <servlet-name>Guestbook</servlet-name>
   <url-pattern>/guestbook</url-pattern>
</servlet-mapping>

您的最终web.xml应如下所示：

<?xml version="1.0" encoding="utf-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">
<servlet>
   <servlet-name>SignGuestbookServlet</servlet-name>
   <servlet-class>guestbook.SignGuestbookServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>SignGuestbookServlet</servlet-name>
  <url-pattern>/sign</url-pattern>
</servlet-mapping>

<welcome-file-list>
   <welcome-file>guestbook.jsp</welcome-file>
</welcome-file-list>
</web-app>

保存您的web.xml。停止本地服务器。再次启动本地服务器。一切都应该没问题。

警告：找不到以下文件：/ sign

2 个答案: