userlogin.jsp
<%@ page language="java" contentType="text/html; charset=gb2312"
pageEncoding="gb2312"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="gb2312">
<title>管理员登陆</title>
</head>
<body>
<script type="text/javascript">
function jump() {
window.open("userregister.jsp");
}
</script>
<form action="loginServlet" method="get">
<table border="2">
<tr><th>
用户名:<input type="text" name="UserName" />
</th>
<tr><td>
密码:<input type="password" name="UserPassword"/>
</td></tr>
<tr><td>
<input type="submit" name="login" value="登陆"/>
<input type="button" name="register" value="注册" onclick="jump()"/>
</td></tr>
</table>
</form>
</body>
</html>
loginServlet.java
package java_zhuyoukai.web.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.hamcrest.core.StringEndsWith;
import java_zhuyoukai.DAO.UserDAO;
import java_zhuyoukai.domain.User;
import java_zhuyoukai.service.UserService;
import java_zhuyoukai.service.UserServiceImpl;
/**
* Servlet implementation class logins
*/
public class loginServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public loginServlet() {
super();
// TODO Auto-generated constructor stub
}
@Override
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
String name=request.getParameter("UserName");
String password=request.getParameter("UserPassword");
System.out.println(name+password);
UserService us=new UserServiceImpl();
PrintWriter out = response.getWriter();
if(us.login(name, password)){
out.print("success");
}
else {
out.print("false");
}
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
UserDao.java
package java_zhuyoukai.DAO;
import java.sql.*;
import javax.servlet.http.HttpServlet;
import java_zhuyoukai.domain.User;
public class UserDAO {
public Connection getConnection() {
Connection con=null;
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
try {
con=DriverManager.getConnection("jdbc:mysql://localhost:3306/user","root","password");
System.out.println(con);
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return con;
}
public ResultSet executeQuery(String sql) {
// TODO Auto-generated method stub
Connection con = getConnection();
ResultSet res = null;
Statement state = null;
if (con !=null) {
try {
state = con.createStatement();
res = state.executeQuery(sql);
} catch (SQLException e) {
return null;
}
}
return res;
}
}
UserServiceImpl.java
package java_zhuyoukai.service;
import java.sql.ResultSet;
import java.sql.SQLException;
import java_zhuyoukai.DAO.UserDAO;
public class UserServiceImpl implements UserService {
public boolean login(String uname ,String upassword) {
boolean a=false;
String sql="select * from user_list where name='mizhonghao'";
UserDAO userDAO=new UserDAO();
ResultSet rs=userDAO.executeQuery(sql);
try {
if (rs.next()) {
a=true;
}
else {
System.out.println("no");
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return a;
}
}
报错信息:Cannot invoke "java.sql.ResultSet.next()" because "rs" is null