我有一个简单的servlet页面，它推送到一个jsp页面，当你选择你想要的记录时，它应该从数据库中删除它并重新加载页面。然而，在控制台中它会打印正确的sql delete语句，但是 1）它不会删除而且2）不会重新加载页面
这是servlet代码
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
/**
* Servlet implementation class StudentModify
*/
@WebServlet("/StudentModify")
public class StudentModify extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public StudentModify() {
super();
// TODO Auto-generated constructor stub
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
sendBack(request, response);
}
private void sendBack(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
HttpSession session = request.getSession(true);
//Set data you want to send back to the request (will be forwarded to the page)
//Can set string, int, list, array etc.
String sql = "SELECT ul.id, s.name, l.time, l.day, l.room,l.id" +
" FROM lab l, subject s, user_lab ul" +
" WHERE ul.user_id=" + (Integer)session.getAttribute("id") +" AND ul.lab_id ="+ "l.id"+" AND l.subject_id ="+"s.id";
try{
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/wae","root","");
System.out.println("got boob");
System.out.println(session.getAttribute("id"));
Statement stmt = con.createStatement();
ResultSet res = stmt.executeQuery(sql);
System.out.println(res);
ArrayList<String> list1 = new ArrayList<String>();
ArrayList<String> list2 = new ArrayList<String>();
ArrayList<String> list3 = new ArrayList<String>();
if (res.next()){
do{
list1.add(res.getString(1));
list2.add(res.getString(2) + " " + res.getString(3) +" "+ res.getString(4) +" "+res.getString(5));
list3.add(res.getString(6));
}while(res.next());
String[] arr = list1.toArray(new String[list1.size()]);
String[] arr1 = list2.toArray(new String[list2.size()]);
String[] arr2 = list3.toArray(new String[list3.size()]);
request.setAttribute("res", arr);
request.setAttribute("res1", arr1);
request.setAttribute("res2", arr2);
}
}catch (SQLException e) {
}
catch (Exception e) {
}
//Decides what page to send the request data to
RequestDispatcher view = request.getRequestDispatcher("StudentModify.jsp");
//Forward to the page and pass the request and response information
view.forward(request, response);
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.getSession(true);
int user_id = Integer.parseInt((String)request.getParameter("user_id"));
int lab_id = Integer.parseInt((String)request.getParameter("lab_id"));
int id = Integer.parseInt((String)request.getParameter("id"));
System.out.println(request.getParameter("user_id")+" "+request.getParameter("lab_id"));
String message = null;
try {
Class.forName("com.mysql.jdbc.Driver");
Connection con =
DriverManager.getConnection("jdbc:mysql://localhost:3306/wae","root","");
System.out.println("got connection");
Statement s = con.createStatement();
String sql = "DELETE FROM user_lab" +
" WHERE id= " + id + " AND user_id= " + user_id + " AND lab_id= " + lab_id;
System.out.println(sql);
int i = s.executeUpdate(sql);
if (i==1) {
message = "Successfully Enrolled In lab.";
response.sendRedirect("Student_manage.jsp");
}
s.close();
con.close();
}
catch (SQLException e) {
message = "Error." + e.toString();
}
catch (Exception e) {
message = "Error." + e.toString();
}
if (message!=null) {
PrintWriter out = response.getWriter();
out.println("<B>" + message + "</B><BR>");
out.println("<HR><BR>");
}
}
// TODO Auto-generated method stub
}
和jsp页面
<%@ 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>Mars University Lab System</title>
<link rel="stylesheet" href="style.css" type="text/css" media="screen">
</head>
<body>
<jsp:include page="headerStudent.jsp"/>
<tr>
<td>
</td>
</tr>
<tr>
<td>
<div id = "centrecontent">
<br>
<h3>Enrol into Labs</h3>
<% if (session.getAttribute("id") == null) {
System.out.println("error");
}
else{ %>
<% String[] list1 = (String[])request.getAttribute("res");
String[] list2 = (String[])request.getAttribute("res1");
String[] list3 = (String[])request.getAttribute("res2");%>
<p>Please Choose a Class</p>
<form name="StudentModify" ACTION="StudentModify" method="post">
<%
for(int i=0; i<list1.length; i++)
{ %>
<input type="hidden" name="id" value=<%=list3[i]%>>
<input type="hidden" name="user_id" value=<%=session.getAttribute("id")%>>
<%out.print(list2[i] + " ");%>
<input type="radio" name="lab_id" value=<%out.println(list1[i]);%>><br>
<%
}
}
%>
<input type=SUBMIT value="Submit" name="Submit"/>
</form>
</div>
<jsp:include page="footer.jsp"/>
</body>
</html>
答案 0 :(得分：0)
尝试更改
<input type=SUBMIT value="Submit" name="Submit"/>
到
<input type="submit" value="Submit" name="Submit"/>
答案 1 :(得分：0)
你尝试过使用提交吗？如果在运行查询后不提交更改，则更改将不会反映在数据库中。
答案 2 :(得分：0)
问题是HTTP specification禁止重定向DELETE / POST / PUT：
“10.3重定向3xx
此类状态代码表示用户代理需要采取进一步操作才能完成请求。当且仅当第二个请求中使用的方法是GET或HEAD时，所需的操作可以由用户代理执行而不与用户交互。 “
目前尚不清楚为什么数据库删除不起作用，但可能是您没有提交事务。 （OTOH，如果连接已设置自动提交，则不需要提交。）