Question

我正在使用一个java Web应用程序，该应用程序使用jsp登录页面的登录servlet。登录页面操作设置为转到servlet，但它无法正常加载，我收到HTTP 500错误。我最初有一个arraylist，它在java类本地存储了用户名和密码，工作正常，没有错误，直到我改变它以使用JDBC从本地mysql数据库中提取登录数据。我的数据库设置为＆＃34; user＆＃34;具有来自用户类的所有字符串数据。

我运行了一个单独的java类来测试数据库，它似乎运行正常但是当我尝试将它实现到我的Web应用程序中时，它在LoginServlet中给出了错误。我设置了我的AuthenicationService类来从数据库中提取用户登录数据并将它们作为对象存储在我的arraylist中。不确定是否有更好的方法可以做到这一点，但我不想弄乱我之前的代码似乎在更改之前正常工作。我确信有更好的方法可以做到这一点，但我有点失去了要改变什么，所以任何帮助都将非常感谢，谢谢。

以下是我设置为业务逻辑层的用户类：

public class User {
private String userName;
private String password;
private String firstName;
private String lastName;
private String email;
private String phoneNumber;


public User(String userName, String pwd, String first, String last, String email, String phone) {
   this.password = pwd;
   this.userName = userName;
   this.firstName = first;
   this.lastName = last;
   this.email = email;
   this.phoneNumber = phone;
}


public String getFirstName() {
    return firstName;
}


public String getLastName() {
    return lastName;
}


public String getUserName() {
    return this.userName;
}

private String getPassword(){
    return this.password;
}

private String getEmail(){
    return this.email;
}

private String getPhoneNumber(){
    return this.phoneNumber;
}

public boolean checkLogin(String userName, String pwd){
    return this.getUserName().equals(userName) && this.getPassword().equals(pwd);
}    
}

另一个从我的数据库中提取用户登录数据的类设置：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.PreparedStatement;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.Iterator;


public class AuthenicationService {
    ArrayList<User> users;


    public AuthenicationService()throws SQLException {
        String userName = null;
        String Password = null;
        String FirstName = null;
        String LastName = null;
        String Email = null;
        String Phone =  null;



        try {

        Connection myConn =   DriverManager.getConnection("jdbc:mysql://localhost:3306/titanbank_db", "root", "sesame");

        Statement myStmt = myConn.createStatement();

        ResultSet result = myStmt.executeQuery("select * from user");

        while (result.next()){
             userName = result.getString("UserName"); 
             Password = result.getString("Password");
             FirstName = result.getString("FirstName");
             LastName = result.getString("LastName");
             Email = result.getString("Email");
             Phone = result.getString("Phone");
             users = new ArrayList<User>();
             users.add(new User(userName, Password, FirstName, LastName, Email, Phone));

     }   

        }
          catch (Exception exc){
            exc.printStackTrace();
    }
}


    public User login(String userName, String pwd){
        User actual = null;
        for (User me : users) {
            if (me.checkLogin(userName, pwd)){
                actual = me;
            }
        }
        return actual;
    }
}

登录Servlet：

import com.titanBank.bll.*;
import java.io.IOException;
import java.sql.SQLException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;



public class LoginServlet extends HttpServlet {


protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {

}


@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
}

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {

    try {
        String userName = request.getParameter("userName");
        String pwd = request.getParameter("password");



        AuthenicationService service = new AuthenicationService();
        User user = service.login(userName, pwd);

        String url = "/accounts/accounts.jsp";
        String errorUrl = "/stderror.jsp";

        request.setAttribute("login", "true");



        if (user != null)
            getServletContext().getRequestDispatcher(url).forward(request, response);
        else
            getServletContext().getRequestDispatcher(errorUrl).forward(request, response);
    } catch (SQLException ex) {
        Logger.getLogger(LoginServlet.class.getName()).log(Level.SEVERE, null, ex);
    }
}


@Override
public String getServletInfo() {
    return "Short description";
}// </editor-fold>

}

我得到的错误：

type Exception report

message

description The server encountered an internal error that prevented it from fulfilling this     request.

exception

java.lang.NullPointerException
com.titanBank.bll.AuthenicationService.login(AuthenicationService.java:56)
com.titanBank.controllers.LoginServlet.doPost(LoginServlet.java:41)
javax.servlet.http.HttpServlet.service(HttpServlet.java:644)
javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
note The full stack trace of the root cause is available in the Apache Tomcat/8.0.9 logs.

Answer 1

   public User login(String userName, String pwd){
    User actual = null;
   if(users!=null){
    for (User me : users) {
        if (me.checkLogin(userName, pwd)){
            actual = me;
        }
    }
    return actual;

   }

   return null; 
   }

Java Login Servlet获取内部错误请求HTTP 500 java.lang.NullPointerException

1 个答案: