将数据库中的数据存储到java类中并使用JSP进行访问
将数据库中的数据存储到java类中并使用JSP进行访问
提问于 2018-08-12 03:37:38
我在尝试使用模型java类访问存储在数据库中的数据时遇到了问题，我尝试使用该类检索jsp页面上的数据，但编译器给出了一个错误: java.lang.NullPointerException
我想要做的是使用java类、db控制器和jsp页面显示jsp页面上的所有视频。
错误行：
exceptionorg.apache.jasper.JasperException:在第159行处理JSP页/doctorallvideo.jsp时发生异常
</tr>
</thead>
<tbody>
error line---> <% for(int i=0; i<vidlist.size(); i++){
video vid = vidlist.get(i);
%>
<tr>堆栈跟踪：
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:579)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:476)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)根本原因：
java.lang.NullPointerException
org.apache.jsp.doctorallvideo_jsp._jspService(doctorallvideo_jsp.java:271)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)这是我的模型类：
public class video {
private int videoId;
private String videoName;
private String description;
private String category;
private String fileName;
private String filepath;
public video(int videoId, String videoName, String description,String category, String fileName, String filepath) {
super();
this.videoId = videoId;
this.videoName = videoName;
this.description = description;
this.category = category;
this.fileName = fileName;
this.filepath = filepath;
}
public video(String videoName, String description,String category, String fileName, String filepath) {
this.videoName = videoName;
this.description = description;
this.category = category;
this.fileName = fileName;
this.filepath = filepath;
}
public video() {
}
public String getCategory() {
return category;
}
public void setCategory(String category) {
this.category = category;
}
public String getFileName() {
return fileName;
}
public void setFileName(String fileName) {
this.fileName = fileName;
}
public String getFilepath() {
return filepath;
}
public void setFilepath(String filepath) {
this.filepath = filepath;
}
public int getVideoId() {
return videoId;
}
public void setVideoId(int videoId) {
this.videoId = videoId;
}
public String getVideoName() {
return videoName;
}
public void setVideoName(String videoName) {
this.videoName = videoName;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}}
这是db控制器：
public ArrayList<video> getVideos() {
try {
// get person from database
PreparedStatement ps = connection.prepareStatement("select * from video");
ResultSet rs = ps.executeQuery();
ArrayList<video> vidlist = new ArrayList<>();
while (rs.next()) {
// get doctor from database
video vid = new video(rs.getInt("videoId"), rs.getString("videoName"), rs.getString("description"),rs.getString("category"), rs.getString("fileName")
,rs.getString("filepath"));
vidlist.add(vid);
}
return vidlist;
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}servlet文件：
public doctorallvideo() {
super();
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.getWriter().append("Served at: ").append(request.getContextPath());
try {
int personId = (int) session.getAttribute("UserID");
// get doctor details
dbcontroller dbcon = new dbcontroller();
ArrayList<video> vids = dbcon.getVideos();
// add user id in the future
if (vids == null) {
}
RequestDispatcher rs = request.getRequestDispatcher("doctorallvideo.jsp");
request.setAttribute("video", vids);
rs.forward(request, response);
return;
} catch (Exception e) {
// redirect to login
redirectToVideoUpload(request, response);
}
}最后，我在jsp页面上添加了以下内容：
<%@ page
import="multimedia.video, java.util.ArrayList"%>
<%
ArrayList<video> vidlist = (ArrayList<video>)request.getAttribute("video");
%>
<div class="col-sm-9 col-sm-offset-3 main">enter code here
<h3 class="page-header">All Videos</h3>在jsp上是这样的：
<div class="col-sm-9 col-sm-offset-3 main" id="patients" style="display: none;">
<table class="table table-striped table-hover">
<thead>
<tr>
<th>Id</th>
<th>username</th>
<th>Blood Group</th>
</tr>
</thead>
<tbody>
<% for(int i=0; i<vidlist.size(); i++){
video vid = vidlist.get(i);
%>
<tr>
<td><%= vid.getVideoId() %></td>
<td><%= vid.getVideoName() %></td>
</tr>
<%} %>
</tbody>
</table>
</div>回答 1
Stack Overflow用户
发布于 2018-08-12 07:20:41
我看到这个错误的存在是因为您试图访问视频列表，它没有在代码片段中指定我的意思是在代码的这一部分<% code fragment %>
为什么不在你的代码中尝试一下并检查一下。
<tbody>
<%
ArrayList<video> vidlist = (ArrayList<video>)request.getAttribute("video");
for(int i=0; i<vidlist.size(); i++){
video vid = vidlist.get(i);
%>
<tr>
<td><%= vid.getVideoId() %></td>
<td><%= vid.getVideoName() %></td>
</tr>
<%} %>
</tbody>页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/51803122
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