Question

我在音乐商店工作，允许您使用由Servlet，JSP和JavaBeans组成的MVC框架购买歌曲。我有一个ControllerServlet，它根据JSP中表单的操作值将请求分派给相关的JSP视图。在同一个包中有另一个名为CartBean的类，它作为2个数组列表的模型，包含有关歌曲和专辑的信息（每个调用另外两个不同的JavaBeans，称为SongBean和AlbumBean）。以下是servlet的开始，其中3种类型的bean被声明为全局变量，因此它们暴露给整个类，而不仅仅是在doGet和doPost中。

/**
 * Servlet implementation class ControllerServlet
 */
@WebServlet(urlPatterns="/search", displayName="ControllerServlet")
public class ControllerServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    Logger logger = Logger.getLogger(this.getClass().getName());

    // make the SongBean and AlbumBean global variables so the parsed data is available
    // to whole class (not just doGet) as long as class exists
    public ArrayList<SongBean> songs = new ArrayList<SongBean>();
    public ArrayList<AlbumBean> albums = new ArrayList<AlbumBean>();
    public CartBean cart = new CartBean();

在doPost方法中，我有以下内容，如果用户尝试向购物车添加内容，他应该能够在从doGet返回的搜索结果JSP视图中选择一些复选框时这样做

                } else if (action.equals("add")) {

                    String selected[] = request.getParameterValues("checkbox-anything-songs"); 

                    // iterate through the songs selected in results.jsp for matching songs in order to add to cart
                    for (int i = 0; i < selected.length; i++) {
                        System.out.println("You selected song with songID: " + selected[i]);

                        // iterate through SongBeans in global variable, songs
                        for (SongBean song : songs) {
                            // selected song is added to cart using songID to match with SongBean's songID & break out of for loop
                            if (song.getSongID().matches(selected[i])) {
                                cart.addSong(song);
                                break;
                            }
                        }   

                    } 
                    ArrayList<SongBean> songsInCart = cart.getSongs();
                    System.out.println("You added " + selected.length + " songs to your cart and have a total of " + cart.getSongs().size() + " songs in your cart now!");
                    System.out.println("Songs in cart now: " + songsInCart);

                    request.setAttribute("songsCart", songsInCart);
                    RequestDispatcher requestdispatcher = request.getRequestDispatcher("/cart.jsp");   
                    requestdispatcher.forward(request, response);

我试图将cart或songsInCart的对象带到cart.jsp视图，以便我可以在其中显示已保存的数据。我知道正确的数据保存在对象中，就像我在控制台打印中看到的那样，并知道它正在保存正确的数据。问题是，当我在将请求发送到那里并使用getAttribute获取songsCart对象后尝试在cart.jsp视图中显示它时，它一直给我以下错误：

HTTP Status 500 - An exception occurred processing JSP page /cart.jsp at line 182

type Exception report

message An exception occurred processing JSP page /cart.jsp at line 182

description The server encountered an internal error that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException: An exception occurred processing JSP page /cart.jsp at line 182

179:    
180:    <!-- Message about whether the shopping cart is empty or not -->
181:    <c:choose>
182:        <c:when test="<%= songbean.size() == 0 && albumbean.size() == 0 %>">
183:            <h2><small>Your shopping cart is empty.</small></h2>
184:        </c:when>
185:        <c:when test="<%= songbean.size() >= 1 || albumbean.size() >= 1 %>">

我怀疑它与cart.jsp顶部的代码有关，如下所示，我收到一条警告信息＆＃34;类型安全：未选中从Object转换为ArrayList＆＃34;对于该行：＆＃34; ArrayList songbean =（ArrayList）session.getAttribute（＆＃34; songsCart＆＃34;）;＆＃34;：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ page import="edu.unsw.comp9321.*, java.util.*" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%
    // initialize session

    // get the beans from importing edu.unsw.comp9321.*
    CartBean cartBean;
    SongBean songBean;
    AlbumBean albumBean;

    // check the session status to see if session has been initialized and shopping cart activated
    if (session.getAttribute("shopping") == null) {
        cartBean = new CartBean();
        songBean = new SongBean();
        albumBean = new AlbumBean();
        session.setAttribute("shopping", cartBean);
        session.setAttribute("songBean", songBean);
        session.setAttribute("albumBean", albumBean);
        System.out.println("cart.jsp: Creating New Session.");
    } else {
        System.out.println("cart.jsp: Already In Session.");
    }

    cartBean = (CartBean) session.getAttribute("shopping");

    // get SongBeans and AlbumBeans so can fetch CartBean attributes from them
    ArrayList<SongBean> songbean = (ArrayList<SongBean>) session.getAttribute("songsCart");

    ArrayList<AlbumBean> albumbean = cartBean.getAlbums();
%>

我不知道出了什么问题，我怀疑它与songsCart对象没有被正确转换为包含所有歌曲的ArrayList有关。无论是那个还是与c标签有关，或者没有正确地执行getAttributes。有谁知道出了什么问题？

类型安全：未选中从Object转换为ArrayList

0 个答案: