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Question

我正在使用 JDBC 制作注册应用程序。但我收到了这个错误。我认为我的 java.bean 有问题，我的字段为空。

web.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <web-app
 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee  http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xmlns="http://java.sun.com/xml/ns/javaee"
 version="2.5">
 <servlet>
     <servlet-name>login</servlet-name>
     <servlet-class>com.pfa.Servlets.LoginServlet</servlet-class>
 </servlet>

 <servlet-mapping>
     <servlet-name>login</servlet-name>
     <url-pattern>/loginServlet</url-pattern>
 </servlet-mapping>
 <servlet>
     <servlet-name>register</servlet-name>
     <servlet-class>com.pfa.Servlets.RegisterServlet</servlet-class>
 </servlet>

 <servlet-mapping>
     <servlet-name>register</servlet-name>
     <url-pattern>/registerServlet</url-pattern>
  </servlet-mapping>

 <welcome-file-list>
     <welcome-file>login.jsp</welcome-file>
 </welcome-file-list>
 </web-app>

用户.java

package com.pfa.bean;

public class User {

 private String uname,upass,uemail;  

  public String getUname() {  
     return uname;  
  }   

  public void setUname(String uname) {  
     this.uname = uname;  
  }  

  public String getUpass() {  
     return upass;  
  }  

  public void setUpass(String upass) {  
     this.upass = upass;  
  }  

    public String getUemail() {  
     return uemail;  
   }  

   public void setUemail(String uemail) {  
      this.uemail = uemail;  
       }  
 }

注册.Dao

  package com.pfa.Dao;
  import java.sql.DriverManager;
  import java.sql.ResultSet;
  import java.sql.SQLException;
  import javax.swing.JOptionPane;
  import com.mysql.jdbc.Connection;
  import com.mysql.jdbc.PreparedStatement;
  import com.mysql.jdbc.Statement;
  import com.pfa.bean.User;

  public class RegisterDao {
  public static int register(User u) throws ClassNotFoundException{  
    int status=0; 

    try{  
        Class.forName("com.mysql.jdbc.Driver");
            Connection conn = null;          
            conn = (Connection) DriverManager
                    .getConnection("jdbc:mysql://localhost:3306/form",    "root", "");
            Statement ps =  (Statement) conn
                    .createStatement();
            Statement ps1 = (Statement) conn
                    .createStatement();
            ResultSet res = ps
                    .executeQuery("Select * from user");
            // Process the result set
            boolean test = false;
            while (res.next()) {
                if ((res.getString("userName").equals(u.getUname()))
                        || (res.getString("password")
                                .equals(u.getUpass()))||    (res.getString("email").equals(u.getUemail()))) {
                    test = true;
                    status=0;
                     System.out.print("<p style=\"color:red\">Y ou ve a  lreadyy Logged in</p>");  
                }
            }

            if (!test) {
                    String query = "insert into user"
                            + " (userName ,password,email)"
                            + " values ('" + u.getUname() + "','"
                            + u.getUpass() + "','" +u.getUemail()+")";

                    ps1.executeUpdate(query);
                    System.out.println("Insert complete");
                status=1;
            }

        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();

        }

      return status;  
        }  
  }

RegisterServlet.java

 package com.pfa.Servlets;
 import java.io.IOException;
 import java.io.PrintWriter;
 import javax.servlet.RequestDispatcher;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpSession;
 import com.pfa.Dao.LoginDao;
 import com.pfa.Dao.RegisterDao;
 import com.pfa.bean.User;
  public class RegisterServlet extends HttpServlet {
  private static final long serialVersionUID = 102831973239L;
  public void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        String n = request.getParameter("username");
       //String p = request.getParameter("userpass");
       //String q = request.getParameter("useremail");
       HttpSession session = request.getSession(false);
      if (session != null)
        session.setAttribute("name",n);
      User u = new User();
      try {
        if (RegisterDao.register(u)!=0) {
            RequestDispatcher rd =      request.getRequestDispatcher("welcome.jsp");
            rd.forward(request, response);
        } else {
            out.print("<p style=\"color:red\">Sorry u ve already Logged  in</p>");
            RequestDispatcher rd =  request.getRequestDispatcher("register.jsp");
            rd.include(request, response);
        }
    } catch (ClassNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    out.close();
    }
 }

register.jsp

     <%@ page language="java" contentType="text/html; charset=ISO-8859-1"
      pageEncoding="ISO-8859-1"%>

     <html>
     <head>
     <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859- 1">
     <title>Login Application</title>
      </head>
      <body>
      <form action="Process.jsp" method="post">
      <fieldset style="width: 300px">
         <legend> Register to App </legend>
         <table>
             <tr>
                 <td>User ID</td>
                 <td><input type="text" name="username" required="required"                   /></td>
             </tr>
             <tr>
                 <td>Password</td>
                 <td><input type="password" name="userpass"  required="required" /></td>

             </tr>
              <tr>
                 <td>email</td>
                 <td><input type="text" name="useremail" required="required"        /></td>

             <tr>

                    <td><input type="submit" value="Login" /></td>
                 </tr>
              </table>
           </fieldset>
         </form>
       </body>
     </html>

process.jsp

       <%@page import="com.pfa.Dao.*"%>  
       <jsp:useBean id="obj" class="com.pfa.bean.User"/>  
        <jsp:setProperty property="*" name="obj"/>  
     <% 
     int status=RegisterDao.register(obj);  
     if(status>0)  
     out.print("You are successfully registered");    
     %>  

Answer 1

用户名，应该使用setUsername而不是setUname，你可以找到一些关于java反射的资源，还有一些推荐给你，你最好使用preparedstatement来查找结果，例如“select * from user where uname='？ '"，（避免sql注入，效率更高）