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嗨，我对 jsp 和 servlet 很陌生，所以我很难理解为什么我不能做一个简单的查询。该代码用于登录页面，其中用户 servlet 查询用户发送的数据，然后将其与数据库匹配，然后当它找到匹配项时，它返回 login==true 并执行另一个查询以获取匹配的员工 ID 号使用用户名和密码

import java.sql.Connection;
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 javax.sql.*;
import javax.servlet.*;
import java.io.*;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.Driver;
import java.sql.DriverManager;
import javax.servlet.http.HttpSession;


public class Login extends HttpServlet {


    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException{
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        try {
            HttpSession session = request.getSession(); 
            Connection conn = null;
            PreparedStatement prepState = null;
            Statement state = null;
            ResultSet result = null;
            boolean login = false;
            String username = request.getParameter("username");
            String password = request.getParameter("password");                 
            String checkLogin = ("SELECT * FROM users WHERE username = ? AND password = ?");    

            try{

            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/matrix","","");

            prepState = conn.prepareStatement(checkLogin);     
            prepState.setString(1, username);
            prepState.setString(2, password);

            result = prepState.executeQuery();

            login = result.next();

            if(login){
                out.println("login");
                String id = result.getString(1);
                String getUser = ("SELECT empLastName, empFirstName FROM employees WHERE empID = ? ");
                prepState = conn.prepareStatement(getUser);
                prepState.setString(1, id);
                result = prepState.executeQuery();
                String first = result.getString(2);
                String last = result.getString(1);

                                    out.println("<html>");
                                    out.println(first + " " + last);
                                    out.println("</html>");
            }


            }catch(Exception e){      
                out.println("ERROR");
                  e.printStackTrace(System.err);
            }   
        }catch(Exception db){


        } finally {            
            out.close();
        }
    }

这是我得到的错误

INFO: The start() method was called on component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/Matrix]] after start() had already been called. The second call will be ignored.
    java.sql.SQLException: Access denied for user 'root'@'localhost' (using password: YES)
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1075)
        at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566)
        at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498)
        at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:919)
        at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:4004)
        at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1284)
        at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2312)
        at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2122)
        at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:774)
        at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:49)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
        at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
        at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:375)
        at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:289)
        at java.sql.DriverManager.getConnection(DriverManager.java:582)
        at java.sql.DriverManager.getConnection(DriverManager.java:185)
        at Login.processRequest(Login.java:57)
        at Login.doPost(Login.java:119)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
        at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:498)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
        at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:562)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:394)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:243)
        at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:188)
        at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        at java.lang.Thread.run(Thread.java:662)
4

2 回答 2

2

这个类在很多方面都是错误的：

  1. 空捕获块。你永远不会知道是否有问题。
  2. 在 servlet 中打开一个连接，而不是使用连接池。
  3. 硬连线驱动程序类和连接 URL。
  4. 没有用于连接数据库的凭据。
  5. 一个班级什么都做。最好每个班级有一个责任。
  6. 混合 UI（HTML 生成）和数据库访问。
  7. 您不会关闭结果集、语句或连接。
  8. try 嵌套在另一个 try 中；我只推荐一个。

我现在累了。

我不清楚问题是什么。你收到错误了吗？如果是，您可以发布堆栈跟踪吗？如果没有，您观察到什么行为？

于 2012-04-25T01:49:02.220 回答
0

尝试检查您的 MySQL 用户名和密码。MySQL 有默认用户名“root”

尝试将您的代码更改为此

Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/matrix","root","");

这意味着您连接到本地主机（同一台计算机）中的 MySQL 服务器，用户名“root”和密码空字符串“”（这是默认值）

于 2012-05-22T06:59:02.410 回答