Question

我试图将数据从servlet传递给没有表单的JSP。我在Servlet中设置数据，并通过Dispatcher将其传递给JSP文件。现在，当我运行JSP文件时，我收到错误消息我甚至尝试过使用JSTL，我的问题不在于JSTL或JSP，问题是当JSP运行时我无法直接获取servlet传递的数据，所以问题是我是否可以直接运行JSP文件并在没有表单的UI上获得结果。我想在UI上显示数据库内容，我将在servlet中准备连接，然后在JSP中传递结果集，这将在没有表单的UI上显示我不想提交任何表单想要在UI上显示数据库的数据，但是通过servlet，帮助我。

Below is the code:

        Servlet:
        import java.io.IOException;
        import java.util.ArrayList;
        import javax.servlet.ServletException;
        import javax.servlet.http.HttpServlet;
        import javax.servlet.http.HttpServletRequest;
        import javax.servlet.http.HttpServletResponse;
        public class NewClass extends HttpServlet {
           @Override
           protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        ArrayList<String> myList;
         myList = new ArrayList<>();
        myList.add("one");
        myList.add("Two");
        myList.add("Three");
        request.setAttribute("MyList", myList);
        request.getRequestDispatcher("/ToTestPage.jsp").forward(request, response);
        //request.getRequestDispatcher("/ToTestPage.jsp").include(request, response);
           }
        }

JSP文件。 ToTestJSP：

    <%@page import="java.util.Iterator"%>
    <%@page import="java.util.List"%>
    <%@page import="java.util.ArrayList"%>
    <%@page contentType="text/html" pageEncoding="UTF-8"%>
    <!DOCTYPE html>
    <html>
        <head>
            <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
            <title>JSP Page</title>
        </head>
        <body>
          <body>      
        <%

            ArrayList<String> list = (ArrayList<String>) request.getAttribute("MyList");
            Iterator itr = list.iterator();
            while(itr.hasNext()) {
                String value =  (String) itr.next();
                out.println(value);
            }

        %>
    </body>
        </body>
    </html>

当我刚刚运行时，我收到以下错误消息 - ToTestPage.jsp文件：

       org.apache.jasper.JasperException: An exception occurred processing JSP page /ToTestPage.jsp at line 22

      19:     <%
      20:        
      21:         ArrayList<String> list = (ArrayList<String>)    request.getAttribute("MyList");
      22:         Iterator itr = list.iterator();
      23:         while(itr.hasNext()) {
      24:             String value =  (String) itr.next();
      25:             out.println(value);

以下是我的Web配置文件：

    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>  
    <servlet>
        <servlet-name>NewClass</servlet-name>
        <servlet-class>NewClass</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>NewClass</servlet-name>
        <url-pattern>/NewClass</url-pattern>
    </servlet-mapping>
</web-app>

完成堆栈跟踪：

Stacktrace:
          org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:580)
        org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:477)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

root cause 
java.lang.NullPointerException
    org.apache.jsp.ToTestPage_jsp._jspService(ToTestPage_jsp.java:103)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:439)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

如何在JSP页面加载

0 个答案: