【发布时间】：2016-07-01 23:14:18
【问题描述】：
我正在尝试从 db 中检索数据并使用 JSP 以表格形式显示它。
问题是当我执行 query.list() 时它返回 null。
数据库中有10条记录。
如何检索所有记录？
下面是我的 DTO
public class TaskDAO {
@SuppressWarnings("unchecked")
public List<Task> getUserTasks(String userName) {
// Task task = getTasksByUserName(userName);
Configuration configuration = new Configuration().configure();
SessionFactory sessionFactory = configuration.buildSessionFactory();
Session session = sessionFactory.openSession();
Transaction transaction = null;
List<Task> task = new LinkedList<Task>();
try {
transaction = session.getTransaction();
transaction.begin();
Query query = session.createQuery("select id, taskDescription from Task where USERNAME='"
+ userName + "'");
task = query.list();
transaction.commit();
} catch (Exception e) {
if (transaction != null) {
transaction.rollback();
}
e.printStackTrace();
} finally {
session.close();
}
return task;
}
}
下面是我的 JSP
<%@page import="java.util.Iterator"%>
<%@page import="com.sk.app.dto.Task"%>
<%@page import="java.util.List"%>
<%@page import="com.sk.app.controller.Success"%>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Home Page</title>
</head>
<body>
<h2>Tasks</h2>
<table>
<%
List tasks = (List)request.getAttribute("taskList");
Iterator iterator = tasks.iterator();
while (iterator.hasNext()){
Task currentTask = (Task) iterator.next();%>
<tr>
<td> <%=currentTask.getId()%></td>
<td> <%=currentTask.getTaskDescription()%></td>
</tr>
<%} %>
</table>
下面是我的 Servlet
public class Success extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
String userName = request.getParameter("userName");
try {
TaskDAO taskDAO = new TaskDAO();
List<Task> taskList = taskDAO.getUserTasks(userName);
request.setAttribute("taskList", taskList);
Iterator<Task> iterator = taskList.iterator();
int count = 0;
while (iterator.hasNext()){
count ++;
}
System.out.println(count);
RequestDispatcher requestDispatcher = request
.getRequestDispatcher("task.jsp");
requestDispatcher.forward(request, response);
} catch (Exception e) {
e.printStackTrace();
}
}
}
下面是我的任务 dto
public class Task {
private int id;
private String taskDescription;
private String USERNAME;
public String getUserName() {
return USERNAME;
}
public void setUserName(String userName) {
this.USERNAME = userName;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getTaskDescription() {
return taskDescription;
}
public void setTaskDescription(String taskDescription) {
this.taskDescription = taskDescription;
}
@Override
public String toString() {
return "Task [id=" + id + ", taskDescription=" + taskDescription
+ ", USERNAME=" + USERNAME + "]";
}
}
【问题讨论】：
-
这是一个巨大的“不要那样做”的集合。不要使用 scriptlet，不要使用字符串粘贴来生成查询，不要手写事务管理或 DAO，不要手动编写 servlet。我可以用大约 10 行 Spring 和 10 行 HTML 模板替换你的整个代码。
-
@chrylis 我是新手，从头开始学习。尝试实施我学到的东西。
标签： java mysql hibernate servlets dao