Question

我的数据库结构如下：

enter image description here

这是Controller Servlet的doGet（）：

protected void doGet(HttpServletRequest request,
                    HttpServletResponse response) throws ServletException, IOException {
    getSubjects(request, response);
}

和getSubjects（请求，响应）是：

private void getSubjects(HttpServletRequest request,
                    HttpServletResponse response) throws ServletException{
            try {
                    List<Subject> subjects = subjectDAO.subjectList();// I'm sending subjects List as Arttribute and, Please SEE *** below
                    ### HERE by passing subject ID Here.
                    List<Page> pages = pageDAO.topicList(subjectId); // Now I want to send pages List as Arttribute as well and, Please SEE### below
                    request.setAttribute("subjects", subjects);
                    request.setAttribute("pages", pages);
                    getServletContext().getRequestDispatcher("/view.jsp").forward(
                                    request, response);
            } catch (Exception e) {                        
                    throw new ServletException("Error ", e.getCause());
            }
    }

这是我的JSP

<ul class="subjects">    *** HERE below I'm getting that subjects List.
                        <c:forEach items="${subjects}" var="subject">
                          <li
                            <c:catch>
                              <c:choose>
                                <c:when test="${subject.subjectId == param.subj_id}">
                                <c:out value=" class=\"selected\""/>
                                </c:when>
                              </c:choose>    
                            </c:catch>><a href='/contexct/super-controller?action=view-content&subj_id=
                           <c:out value="${subject.subjectId}"/>'>
                           <c:out value="${subject.subjectName}" />
                           </a></li>
                           <ul class="pages">
                            ### HERE below I can get that pages List .But how can I get value of subjectId So that I can get pages from DB, Please SEE$$$ above.
                            <c:forEach items="${pages}" var="page">
                                <li
                                  <c:catch>
                                     <c:choose>
                                        <c:when test="${page.pageId == param.topic_id}">
                                        <c:out value=" class=\"selected\""/>
                                       </c:when>
                                     </c:choose>    
                                   </c:catch>><a href='/contexct/super-controller?action=view-content&amp;topic_id=
                             <c:out value="${page.pageId}"/>'>
                             <c:out value="${page.pageName}" />
                           </a></li>
                         </c:forEach>
                       </ul>
                     </c:forEach>
                    </ul>

因为我在jsp中获得了主题数据：

<c:forEach items="${subjects}" var="subject">

现在我如何在getSubjects（）中将主题ID传递给这一行：

 List<Page> pages = pageDAO.topicList(subjectId);

这样我就可以获得与主题相对应的页面并将该列表设置为：

 request.setAttribute("pages", pages);

希望你现在能理解我的问题

更新

我以这种方式调试：

private void getSubjects(HttpServletRequest request,
        HttpServletResponse response) throws ServletException{
    try {
        List<Subject> subjects = subjectDAO.subjectList();
        List<Page> pages = null;
        for (int i = 0; i < subjects.size(); i++) {
            pages = pageDAO.topicList(subjects.get(i).getSubjectId());
            System.out.println("List id is " + subjects.get(i).getSubjectId());
                            for (int i = 0; i < subjects.size(); i++) {
            pages = pageDAO.topicList(subjects.get(i).getSubjectId());
            System.out.println("List id is " + subjects.get(i).getSubjectId());
            for (int j = 0; j < pages.size(); j++) {                    
                System.out.println("Topics are " +pages.get(j).getTopicName());
            }
        }
        }
        request.setAttribute("subjects", subjects);
        request.setAttribute("pages", pages);
        getServletContext().getRequestDispatcher("/content.jsp").forward(
                request, response);
    } catch (Exception e) {             
        throw new ServletException("Cannot obtain subjects from DB", e.getCause());
    }
}

我得到了Console：

List id is 1
Topics are App User Interface
List id is 2
Topics are Java Basics
Topics are OOP
List id is 3
List id is 4

这是正确的，但无法完成这项工作

<c:forEach items="${pages}" var="page">
     <li
       <c:catch>
         <c:choose>
           <c:when test="${page.pageId == param.topic_id}">...

以上给出..

意味着没有任何东西返回。

Answer 1

好的，我必须执行类似的任务。我使用了一个控制器servlet。然后是一个数据库对象，它使用类来处理从数据库中检索数据。您似乎没有检查＆＃34;操作＆＃34;参数被发送到servlet。

if (action.equalsIgnoreCase("getTopic")){
            int SubjectId = Integer.parseInt(request.getParameter("SubjectId"));
            dao.getTopic(SubjectId);
            forward = "myjsp.jsp";
            request.setAttribute("subjects", dao.getAllSubjects());    
        } else if (action.equalsIgnoreCase("listSubjects")){
            forward = "myjsp.jsp";
            request.setAttribute("categories", dao.getAllSubjects());

        } else {
            forward = "myjsp.jsp";
        }

        RequestDispatcher view = request.getRequestDispatcher(forward);
        view.forward(request, response);
    }

Answer 2

如果您想从Map获取页面，请尝试以下方法（未测试）：

private void getSubjects(HttpServletRequest request, HttpServletResponse response) 
throws ServletException{

    try {
        List<Subject> subjects = subjectDAO.subjectList();
        List<Page> pages = null;
        Map<String, ArrayList<Page>> subjectPageMap = null;

        if(subjects!= null && subjects.size() > 0){
            subjectPageMap = new HashMap<String, ArrayList<Page>>();
            for(Subject subject : subjects){
                pages = pageDAO.topicList(subject.getSubjectId());
                pages = pages != null && pages.size() > 0 ? pages : new ArrayList<Page>();
                subjectPageMap.put(subject.getSubjectId(), pages);
            }
        }

        request.setAttribute("subjects", subjects);
        request.setAttribute("subjectPageMap", subjectPageMap);
        getServletContext().getRequestDispatcher("/view.jsp").forward(
                                request, response);
    } catch (Exception e) {
        throw new ServletException("Error ", e.getCause());
    }
}

在这种情况下如何在jsp中传递参数

更新

2 个答案: