选课系统(后端)

package com.dao;

import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;

import com.entity.Message1;
import com.entity.Message2;
import com.entity.Message3;
import com.util.DBUtil;

public class MessageDao {
    //登录
    public int login(String username, String password,String shenfen) {
        String sql=null;
        if(shenfen.equals("student")) {
            sql="select * from d2 where num='"+username+"'and password='"+password+"'";
        }else if(shenfen.equals("teacher")) {
            sql="select * from d1 where num='"+username+"'and password='"+password+"'";
        }else if(shenfen.equals("manage")) {
            sql="select * from d4 where username='"+username+"'and password='"+password+"'";
        }
         Connection conn=DBUtil.getConn();
         Statement st=null;
         ResultSet rs=null;
         int row=0;
         try {
             st=conn.createStatement();
             rs=st.executeQuery(sql);
             if (rs.next()) {
                row=1;
            }else {
                row=0;
            }
        } catch (Exception e) {
            // TODO: handle exception
        }
        return row;
    }
   //添加
    public boolean add1(Message1 message) {
        String sql = "insert into d1(num,tname,tsex,txueyuan,tzhicheng,password)"+"values('" + message.getNum() + "','"
                + message.getTname() + "','" + message.getTsex() + "','" + message.getTxueyuan() + "','"
                + message.getTzhicheng() + "','"+message.getPassword()+"')";
        // 创建数据库链接
        Connection conn = DBUtil.getConn();
        Statement state = null;
        boolean f = false;
        int a = 0;

        try {
            state = conn.createStatement();
            state.executeUpdate(sql);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 关闭连接
            DBUtil.close(state, conn);
        }

        if (a > 0) {
            f = true;
        }
        return f;
    }
    public boolean add2(Message2 message) {
        String sql = "insert into d2(num,sname,ssex,sclass,smajor,password)"+"values('" + message.getNum() + "','"
                + message.getSname() + "','" + message.getSsex() + "','" + message.getSclass() + "','"
                + message.getSmajor() + "','"+message.getPassword()+"')";
        // 创建数据库链接
        Connection conn = DBUtil.getConn();
        Statement state = null;
        boolean f = false;
        int a = 0;

        try {
            state = conn.createStatement();
            state.executeUpdate(sql);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 关闭连接
            DBUtil.close(state, conn);
        }

        if (a > 0) {
            f = true;
        }
        return f;
    }
    public boolean add3(Message3 message) {
        String sql = "insert into d3(cnum,cname,cpnum,cteacher)"+"values('" + message.getCnum() + "','"
                + message.getCname() + "','" + message.getCpnum() + "','" + message.getCteacher() + "')";
        // 创建数据库链接
        Connection conn = DBUtil.getConn();
        Statement state = null;
        boolean f = false;
        int a = 0;

        try {
            state = conn.createStatement();
            state.executeUpdate(sql);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 关闭连接
            DBUtil.close(state, conn);
        }

        if (a > 0) {
            f = true;
        }
        return f;
    }
     public static boolean num1(String num) {
            boolean flag = false;
            String sql = "select * from d1 where num = '" + num + "'";
            Connection conn = DBUtil.getConn();
            Statement state = null;
            ResultSet rs = null;
            
            try {
                state = conn.createStatement();
                rs = state.executeQuery(sql);
                while (rs.next()) {
                    flag = true;
                }
            } catch (SQLException e) {
                e.printStackTrace();
            } finally {
                DBUtil.close(rs, state, conn);
            }
            return flag;
        }
     public static boolean num2(String num) {
            boolean flag = false;
            String sql = "select * from d2 where num = '" + num + "'";
            Connection conn = DBUtil.getConn();
            Statement state = null;
            ResultSet rs = null;
            
            try {
                state = conn.createStatement();
                rs = state.executeQuery(sql);
                while (rs.next()) {
                    flag = true;
                }
            } catch (SQLException e) {
                e.printStackTrace();
            } finally {
                DBUtil.close(rs, state, conn);
            }
            return flag;
        }
     public static boolean num3(String cnum) {
            boolean flag = false;
            String sql = "select * from d3 where cnum = '" + cnum + "'";
            Connection conn = DBUtil.getConn();
            Statement state = null;
            ResultSet rs = null;
            
            try {
                state = conn.createStatement();
                rs = state.executeQuery(sql);
                while (rs.next()) {
                    flag = true;
                }
            } catch (SQLException e) {
                e.printStackTrace();
            } finally {
                DBUtil.close(rs, state, conn);
            }
            return flag;
        }
    //查询
     public  Message1 search(String name) {
            String sql = "select * from d1 where name = '" + name + "'";       
            Connection conn = DBUtil.getConn();
            Statement state = null;
            ResultSet rs = null;
            Message1 bean=null;
            try {
                state = conn.createStatement();
                rs = state.executeQuery(sql);
                while (rs.next()) {
                    int id2=rs.getInt("id");
                    String name2 = rs.getString("name");
                    String sex2 = rs.getString("sex");
                    String nation2 = rs.getString("nation");
                    String date2 = rs.getString("date");
                    String age2=rs.getString("age");
                    String politics2=rs.getString("politics");
                    /*bean = new Message1(id2,name2,sex2,nation2,date2,age2,politics2);*/
                }
            } catch (SQLException e) {
                e.printStackTrace();
            } finally {
                DBUtil.close(rs, state, conn);
            }       
            return bean;
        }
     //删除
         public boolean delete(String name){
                String sql="delete from d1 where name='" + name + "'";
                Connection conn = DBUtil.getConn();
                Statement state = null;
                int a = 0;
                boolean f = false;
                try {
                    state = conn.createStatement();
                    a = state.executeUpdate(sql);
                } catch (SQLException e) {
                    e.printStackTrace();
                } finally {
                    DBUtil.close(state, conn);
                }
                
                if (a > 0) {
                    f = true;
                }
                return f;
            }
        //通过姓名查找
         public static Message1 getMessageBynum1(String num) {
                String sql = "select * from d1 where num ='" + num + "'";
                Connection conn = DBUtil.getConn();
                Statement state = null;
                ResultSet rs = null;
                Message1 message = null;            
                try {
                    state = conn.createStatement();
                    rs = state.executeQuery(sql);
                    while (rs.next()) {
                        String num1 = rs.getString("num");
                        String tname = rs.getString("tname");
                        String tsex = rs.getString("tsex");
                        String txueyuan=rs.getString("txueyuan");
                        String tzhicheng=rs.getString("tzhicheng");      
                        String password=rs.getString("password");    
                        message = new Message1(num1,tname,tsex,txueyuan,tzhicheng,password);                 
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    DBUtil.close(rs, state, conn);
                }
                
                return message;
            }
         public static Message2 getMessageBynum2(String num) {
                String sql = "select * from d2 where num ='" + num + "'";
                Connection conn = DBUtil.getConn();
                Statement state = null;
                ResultSet rs = null;
                Message2 message = null;            
                try {
                    state = conn.createStatement();
                    rs = state.executeQuery(sql);
                    while (rs.next()) {
                        String num1 = rs.getString("num");
                        String tname = rs.getString("sname");
                        String tsex = rs.getString("ssex");
                        String txueyuan=rs.getString("sclass");
                        String tzhicheng=rs.getString("smajor");      
                        String password=rs.getString("password");    
                        message = new Message2(num1,tname,tsex,txueyuan,tzhicheng,password);                 
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    DBUtil.close(rs, state, conn);
                }
                
                return message;
            }
         public static String getMessageBynum3(String num) {
                String sql = "select * from d1 where num ='" + num + "'";
                Connection conn = DBUtil.getConn();
                Statement state = null;
                ResultSet rs = null;
                Message1 message = null;            
                try {
                    state = conn.createStatement();
                    rs = state.executeQuery(sql);
                    while (rs.next()) {
                        String num1 = rs.getString("num");
                        String tname = rs.getString("tname");
                        String tsex = rs.getString("tsex");
                        String txueyuan=rs.getString("txueyuan");
                        String tzhicheng=rs.getString("tzhicheng");      
                        String password=rs.getString("password");    
                        message = new Message1(num1,tname,tsex,txueyuan,tzhicheng,password);                 
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    DBUtil.close(rs, state, conn);
                }
                
                return message.getTname();
            }
         //修改
         public static boolean update12(Message1 message,String name) {
                
             String sql = "update d1 set num='" + message.getNum() + "', tname='" + message.getTname()+"',tsex='"+message.getTsex()+"',txueyuan='"+message.getTxueyuan()+"', tzhicheng='" + message.getTzhicheng() + "', password='" + message.getPassword() + "'where num ='" + name + "'";
                Connection conn = DBUtil.getConn();
                Statement state = null;
                boolean f = false;
                int a = 0;
                
                try {
                    state = conn.createStatement();
                    a = state.executeUpdate(sql);
                } catch (SQLException e) {
                    e.printStackTrace();
                } finally {
                    DBUtil.close(state, conn);
                }
                
                if (a > 0) {
                    f = true;
                }
                return f;
            }
         public static boolean update22(Message2 message,String name) {
                
             String sql = "update d2 set num='" + message.getNum() + "', sname='" + message.getSname()+"',ssex='"+message.getSsex()+"',Sclass='"+message.getSclass()+"', Smajor='" + message.getSmajor() + "', password='" + message.getPassword() + "'where num ='" + name + "'";
                Connection conn = DBUtil.getConn();
                Statement state = null;
                boolean f = false;
                int a = 0;
                
                try {
                    state = conn.createStatement();
                    a = state.executeUpdate(sql);
                } catch (SQLException e) {
                    e.printStackTrace();
                } finally {
                    DBUtil.close(state, conn);
                }
                
                if (a > 0) {
                    f = true;
                }
                return f;
            }
         //显示全部
         public List<Message3> list()
            {
                String sql = "select * from d3";
                List<Message3> list = new ArrayList<>();
                Connection conn = DBUtil.getConn();
                Statement state = null;
                ResultSet rs = null;            
                try {
                    state = conn.createStatement();
                    rs = state.executeQuery(sql);
                    while (rs.next()) {
                        Message3 bean = null;
                        String cnum=rs.getString("cnum");
                        String cname = rs.getString("cname");
                        String cpnum = rs.getString("cpnum");
                        String cteacher = rs.getString("cteacher");                
                        bean =new Message3(cnum,cname,cpnum,cteacher);                        
                        list.add(bean);
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                } finally {
                    DBUtil.close(rs, state, conn);
                }
                
                return list;
            }    
         
}

package com.entity;
//tnum tname tsex txueyaun tzhicheng
public class Message1 {
private String num;
private String tname;
private String tsex;
private String txueyuan;
private String tzhicheng;
private String password;
public String getNum() {
    return num;
}
public void setNum(String num) {
    this.num = num;
}
public String getTname() {
    return tname;
}
public void setTname(String tname) {
    this.tname = tname;
}
public String getTsex() {
    return tsex;
}
public void setTsex(String tsex) {
    this.tsex = tsex;
}
public String getTxueyuan() {
    return txueyuan;
}
public void setTxueyuan(String txueyuan) {
    this.txueyuan = txueyuan;
}
public String getTzhicheng() {
    return tzhicheng;
}
public void setTzhicheng(String tzhicheng) {
    this.tzhicheng = tzhicheng;
}
public String getPassword() {
    return password;
}
public void setPassword(String password) {
    this.password = password;
}
public Message1(String num, String tname, String tsex, String txueyuan, String tzhicheng, String password) {
    super();
    this.num = num;
    this.tname = tname;
    this.tsex = tsex;
    this.txueyuan = txueyuan;
    this.tzhicheng = tzhicheng;
    this.password = password;
}
public Message1() {
    super();
    // TODO 自动生成的构造函数存根
}

}

package com.entity;

public class Message2 {
    //num sname ssex sclass smajor
    private String num;
    private String sname;
    private String ssex;
    private String sclass;
    private String smajor;
    private String password;
    public String getNum() {
        return num;
    }
    public void setNum(String num) {
        this.num = num;
    }
    public String getSname() {
        return sname;
    }
    public void setSname(String sname) {
        this.sname = sname;
    }
    public String getSsex() {
        return ssex;
    }
    public void setSsex(String ssex) {
        this.ssex = ssex;
    }
    public String getSclass() {
        return sclass;
    }
    public void setSclass(String sclass) {
        this.sclass = sclass;
    }
    public String getSmajor() {
        return smajor;
    }
    public void setSmajor(String smajor) {
        this.smajor = smajor;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public Message2(String num, String sname, String ssex, String sclass, String smajor, String password) {
        super();
        this.num = num;
        this.sname = sname;
        this.ssex = ssex;
        this.sclass = sclass;
        this.smajor = smajor;
        this.password = password;
    }
}

package com.entity;

public class Message3 {
    public String cnum;
    public String cname;
    public String cpnum;
    public String cteacher;
    public String getCnum() {
        return cnum;
    }
    public void setCnum(String cnum) {
        this.cnum = cnum;
    }
    public String getCname() {
        return cname;
    }
    public void setCname(String cname) {
        this.cname = cname;
    }
    public String getCpnum() {
        return cpnum;
    }
    public void setCpnum(String cpnum) {
        this.cpnum = cpnum;
    }
    public String getCteacher() {
        return cteacher;
    }
    public void setCteacher(String cteacher) {
        this.cteacher = cteacher;
    }
    public Message3(String cnum, String cname, String cpnum, String cteacher) {
        super();
        this.cnum = cnum;
        this.cname = cname;
        this.cpnum = cpnum;
        this.cteacher = cteacher;
    }
    
}

package com.service;

import java.util.List;

import com.dao.MessageDao;
import com.entity.Message1;
import com.entity.Message2;
import com.entity.Message3;

//服务层
public class MessageService {

    MessageDao mDao = new MessageDao();
    //登录
    public int login(String username,String password,String shenfen) {
        return mDao.login(username,password,shenfen);
    }
    //添加
    public boolean add1(Message1 message) {
        boolean f = false;
        if(!mDao.num1(message.getNum())) {
            mDao.add1(message);
            f = true;
        }
        return f;
    }
    public boolean add2(Message2 message) {
        boolean f = false;
        if(!mDao.num2(message.getNum())) {
            mDao.add2(message);
            f = true;
        }
        return f;
    }
    public boolean add3(Message3 message) {
        boolean f = false;
        if(!mDao.num3(message.getCnum())) {
            mDao.add3(message);
            f = true;
        }
        return f;
    }
    //查找
    public Message1 search(String name) {
        return mDao.search(name);
    }
    //删除
    public boolean delete(String name) {
        
           mDao.delete(name);
               return true;
            }
    public Message1 getMessageBynum(String num)
    {
        return mDao.getMessageBynum1(num);
    }
    //修改
    public  void update(Message1 message,String num) {
        mDao.update12(message,num);
    }
    //显示所有
    public List<Message3> list()
    {
        return mDao.list();
    }
}

package com.servlet;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.dao.MessageDao;
import com.entity.Message1;
import com.entity.Message2;
import com.entity.Message3;
import com.service.MessageService;

@WebServlet("/MessageServlet")
public class MessageServlet extends HttpServlet {
    static String wen=null; 
    static String mo=null;
    private static final long serialVersionUID = 1L;

    MessageService service = new MessageService();
    
    /**
     * 方法选择
     */
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        String method = req.getParameter("method");
        
        if ("add1".equals(method)) {
            add1(req, resp);
        }else if ("login".contentEquals(method)) {
            login(req, resp);
        }else if ("add2".equals(method)) {
            add2(req, resp);
        }else if ("add3".equals(method)) {
            add3(req, resp);
        }else if ("update11".equals(method)) {
            update11(req, resp);
        }else if ("update12".equals(method)) {
            update12(req, resp);
        }else if ("update21".equals(method)) {
            update21(req, resp);
        }else if ("update22".equals(method)) {
            update22(req, resp);
        }else if ("list".equals(method)) {
            list(req, resp);
        }
    }
  //登录
      private void login(HttpServletRequest req,HttpServletResponse resp) throws IOException, ServletException {
          req.setCharacterEncoding("utf-8");
          String username=req.getParameter("username");
          String password=req.getParameter("password");
          String shenfen=req.getParameter("shenfen");
          int message=service.login(username,password,shenfen);
          if(message == 0) {
              req.setAttribute("message", "帐号或密码错误！");
              req.getRequestDispatcher("login.jsp").forward(req,resp);
              } else {
                  Cookie cookie=new Cookie("username", username);
                cookie.setPath("/");
                cookie.setMaxAge(60*60*24);
                resp.addCookie(cookie);
                     req.setAttribute("message", "登陆成功");
                     req.getRequestDispatcher(shenfen+".jsp").forward(req,resp);
              }
      }
 //添加
    private void add1(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
        req.setCharacterEncoding("utf-8");
        //获取数据num tname tsex txueyaun tzhicheng
        String num = req.getParameter("num");
        String tname = req.getParameter("tname");
        String tsex = req.getParameter("tsex");
        String txueyuan = req.getParameter("txueyuan");
        String tzhicheng = req.getParameter("tzhicheng");
        String password = req.getParameter("password");
        Message1 message = new Message1(num,tname,tsex,txueyuan,tzhicheng,password);
        
        //添加后消息显示
        if(service.add1(message)) {
            req.setAttribute("message", "添加成功");
            req.getRequestDispatcher("manage.jsp").forward(req,resp);
        } else {
            req.setAttribute("message", "工号重复，请重新录入");
            req.getRequestDispatcher("add1.jsp").forward(req,resp);
        }
    }
    private void add2(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
        req.setCharacterEncoding("utf-8");
        //snum sname ssex sclass smajor
        String num = req.getParameter("num");
        String sname = req.getParameter("sname");
        String ssex = req.getParameter("ssex");
        String sclass = req.getParameter("sclass");
        String smajor = req.getParameter("smajor");
        String password = req.getParameter("password");
        Message2 message = new Message2(num,sname,ssex,sclass,smajor,password);
        
        //添加后消息显示
        if(service.add2(message)) {
            req.setAttribute("message", "添加成功");
            req.getRequestDispatcher("manage.jsp").forward(req,resp);
        } else {
            req.setAttribute("message", "学号重复，请重新录入");
            req.getRequestDispatcher("add2.jsp").forward(req,resp);
        }
    }
    private void add3(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
        req.setCharacterEncoding("utf-8");
        //snum sname ssex sclass smajor
        String cnum = req.getParameter("cnum");
        String cname = req.getParameter("cname");
        String cpnum = req.getParameter("cpnum");
        String cteacher = req.getParameter("cteacher");
        Message3 message = new Message3(cnum,cname,cpnum,cteacher);
        
        //添加后消息显示
        if(service.add3(message)) {
            req.setAttribute("message", "添加成功");
            req.getRequestDispatcher("teacher.jsp").forward(req,resp);
        } else {
            req.setAttribute("message", "课程编号重复，请重新录入");
            req.getRequestDispatcher("add3.jsp").forward(req,resp);
        }
    }
    //查询
    private void search(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException{
        req.setCharacterEncoding("utf-8");
        String name = req.getParameter("name");       
        Message1 message = service.search(name);
        if(message == null) {
            req.setAttribute("message", "查无此用户！");
            req.getRequestDispatcher("search.jsp").forward(req,resp);
        } else {
            req.setAttribute("message", message);
            req.getRequestDispatcher("search1.jsp").forward(req,resp);
        }
    }
    private void search1(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException{
        req.setCharacterEncoding("utf-8");
        String name = req.getParameter("name");       
        Message1 message = service.search(name);
        if(message == null) {
            req.setAttribute("message", "查无此用户！");
            req.getRequestDispatcher("search.jsp").forward(req,resp);
        } else {
            req.setAttribute("message", message);
            req.getRequestDispatcher("search2.jsp").forward(req,resp);
        }
    }
    
    //删除
    private void delete(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException{
        req.setCharacterEncoding("utf-8");
        
           //String name=req.getParameter("name");
           //if(MessageDao.name(name))        
            service.delete(mo);
            req.setAttribute("message", "删除成功！");
            req.getRequestDispatcher("delete.jsp").forward(req,resp); 
}  
   //通过姓名查找后删除
   /* private void getMessageByname(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException{
        req.setCharacterEncoding("utf-8");
        String name = req.getParameter("name");
        Message1 message = service.getMessageByname(name);
        mo=name;
        if(message==null)
        {
            req.setAttribute("message", "未找到该用户");
            req.getRequestDispatcher("delete.jsp").forward(req, resp);
        }
        else 
        {
            req.setAttribute("message", message);
            req.getRequestDispatcher("delete1.jsp").forward(req,resp);
        }
    }*/
  
    private void update11(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException{
        req.setCharacterEncoding("utf-8");
        String num = req.getParameter("num");
        Message1 message = MessageDao.getMessageBynum1(num);
        wen=num;
        if(message==null)
        {
            req.setAttribute("message","未找到该用户");
            req.getRequestDispatcher("teacher.jsp").forward(req, resp);
        }
        else
        {
            req.setAttribute("message",message);
            req.getRequestDispatcher("update12.jsp").forward(req,resp);
        }
    }
    private void update21(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException{
        req.setCharacterEncoding("utf-8");
        String num = req.getParameter("num");
        Message2 message = MessageDao.getMessageBynum2(num);
        wen=num;
        if(message==null)
        {
            req.setAttribute("message","未找到该用户");
            req.getRequestDispatcher("update21.jsp").forward(req, resp);
        }
        else
        {
            req.setAttribute("message",message);
            req.getRequestDispatcher("update22.jsp").forward(req,resp);
        }
    }
    //修改
    private void update12(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException{
        req.setCharacterEncoding("utf-8");
         String num3 = req.getParameter("num");
         String tname3 = req.getParameter("tname");
         String tsex3 = req.getParameter("tsex");
         String txueyuan3 = req.getParameter("txueyuan");
         String tzhicheng3 = req.getParameter("tzhicheng");
         String password3 = req.getParameter("password");
         Message1 message = new Message1(num3,tname3,tsex3,txueyuan3,tzhicheng3,password3);
        if(MessageDao.update12(message,wen))
        { 
            req.setAttribute("message","修改成功");
            req.getRequestDispatcher("update11.jsp").forward(req,resp);
        }
        }
    
    private void update22(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException{
        req.setCharacterEncoding("utf-8");
         String num3 = req.getParameter("num");
         String sname3 = req.getParameter("sname");
         String ssex3 = req.getParameter("ssex");
         String sclass3 = req.getParameter("sclass");
         String smajor3 = req.getParameter("smajor");
         String password3 = req.getParameter("password");
         Message2 message = new Message2(num3,sname3,ssex3,sclass3,smajor3,password3);
        if(MessageDao.update22(message,wen))
        { 
            req.setAttribute("message","修改成功");
            req.getRequestDispatcher("update21.jsp").forward(req,resp);
        }
        }
    
    //显示全部
    private void list(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException{
        req.setCharacterEncoding("utf-8");
        
        List<Message3> messages = service.list();
        req.setAttribute("messages", messages);
        req.getRequestDispatcher("allcourse.jsp").forward(req,resp);
    }
}

//DBUtil.java
package com.util;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;



public class DBUtil {
    
    public static String db_url = "jdbc:mysql://localhost:3306/select_system?useSSL=false&serverTimezone=GMT";
    public static String db_user = "root";
    public static String db_pass = "0000";
    
    public static Connection getConn () {
        Connection conn = null;
        
        try {
            Class.forName("com.mysql.jdbc.Driver");//加载驱动
            conn = DriverManager.getConnection(db_url, db_user, db_pass);
        } catch (Exception e) {
            e.printStackTrace();
        }
        
        return conn;
    }
    
    /**
     * 关闭连接
     * @param state
     * @param conn
     */
    public static void close (Statement state, Connection conn) {
        if (state != null) {
            try {
                state.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        
        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
    
    public static void close (ResultSet rs, Statement state, Connection conn) {
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        
        if (state != null) {
            try {
                state.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        
        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) throws SQLException {
        Connection conn = getConn();
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        String sql ="select * from d1";
        pstmt = conn.prepareStatement(sql);
        rs = pstmt.executeQuery();
        if(rs.next()){
            System.out.println("空");
        }else{
            System.out.println("不空");
        }
    }
}