SMBMS(Supermarket Billing Management System )

1. 项目架构

2. 项目搭建的准备工作

1. 搭建一个Maven Web项目

2. 配置Tomcat

3. 测试项目是否能够跑起来

4. 导入项目中需要用到的Jar包:jsp,Servlet,mysql驱动,jstl,standard

5. 创建项目包结构

6. 编写实体类

   ORM映射:表 -- 类映射

7. 编写基础公共类

   1. 数据库配置文件(db.properties)

   driver = com.mysql.jdbc.Driver
   url = jdbc:mysql://localhost:3306/smbms?useUnicode=true&characterEncoding=utf-8
   username = root
   password = 123456
   

   2. 编写数据库公共类

   package com.wang.dao;
   
   import java.io.IOException;
   import java.io.InputStream;
   import java.sql.*;
   import java.util.Properties;
   
   //操作数据库的公共类
   public class BaseDao {
   
       private static String driver;
       private static String url;
       private static String username;
       private static String password;
   
       //静态代码块,类加载的时候就初始化了
       static {
           Properties properties = new Properties();
           //通过类加载器读取对应的资源
           //由于getResourceAsStream中调用了private方法,此处必须用反射来读配置文件
           InputStream is = BaseDao.class.getClassLoader().getResourceAsStream("db.properties");
   
           try {
               properties.load(is);
           } catch (IOException e) {
               e.printStackTrace();
           }
   
           driver = properties.getProperty("driver");
           url = properties.getProperty("url");
           username = properties.getProperty("username");
           password = properties.getProperty("password");
       }
   
       //获取数据库的连接
       public static Connection getConnection() {
           Connection connection = null;
           try {
               Class.forName(driver);
               connection = DriverManager.getConnection(url,username,password);
           } catch (Exception e) {
               e.printStackTrace();
           }
           return connection;
       }
   
       //编写查询公共类
       public static ResultSet execute(Connection connection,String sql,Object[] params,ResultSet resultSet,PreparedStatement preparedStatement) throws SQLException {
           //预编译的sql,在后面直接执行就可以了,不用传参
           preparedStatement = connection.prepareStatement(sql);
   
           //给预编译的sql传参数
           for (int i = 0; i < params.length; i++) {
               //setObject方法,占位符从1开始,但是我们的数组是从0开始的,因此下面写 i+1
               preparedStatement.setObject(i + 1,params[i]);
           }
   
           resultSet = preparedStatement.executeQuery();
           return resultSet;
       }
   
       //编写增删改公共方法
       public static int execute(Connection connection,PreparedStatement preparedStatement) throws SQLException {
           preparedStatement = connection.prepareStatement(sql);
   
           //给预编译的sql传参数
           for (int i = 0; i < params.length; i++) {
               //setObject方法,params[i]);
           }
   
           int updateRows = preparedStatement.executeUpdate();
           return updateRows;
       }
   
       //释放资源
       public static boolean closeResource(Connection connection,PreparedStatement preparedStatement,ResultSet resultSet) {
           boolean flag = true;
   
           if (resultSet != null){
               try {
                   resultSet.close();
                   //GC回收
                   resultSet = null;
               } catch (SQLException e) {
                   e.printStackTrace();
                   flag = false;
               }
           }
   
           if (preparedStatement != null){
               try {
                   preparedStatement.close();
                   //GC回收
                   preparedStatement = null;
               } catch (SQLException e) {
                   e.printStackTrace();
                   flag = false;
               }
           }
   
           if (connection != null){
               try {
                   connection.close();
                   //GC回收
                   connection = null;
               } catch (SQLException e) {
                   e.printStackTrace();
                   flag = false;
               }
           }
           
           return flag;
       }
   
   }
   

   3. 编写字符编码过滤器并注册

   package com.wang.filter;
   
   import javax.servlet.*;
   import java.io.IOException;
   
   public class CharacterEncodingFilter implements Filter {
       @Override
       public void init(FilterConfig filterConfig) throws ServletException {
   
       }
   
       @Override
       public void doFilter(ServletRequest request,ServletResponse response,FilterChain chain) throws IOException,ServletException {
           request.setCharacterEncoding("utf-8");
           response.setCharacterEncoding("utf-8");
   
           chain.doFilter(request,response);
       }
   
       @Override
       public void destroy() {
   
       }
   }
   

   <!--字符编码过滤器-->
   <filter>
       <filter-name>CharacterEncodingFilter</filter-name>
       <filter-class>com.wang.filter.CharacterEncodingFilter</filter-class>
   </filter>
   <!--所有的url都会被过滤-->
   <filter-mapping>
       <filter-name>CharacterEncodingFilter</filter-name>
       <url-pattern>/*</url-pattern>
   </filter-mapping>
   

8. 导入静态资源

3. 登陆功能实现

1. 编写前端页面

2. 设置首页

<!--设置欢迎页面-->
<welcome-file-list>
    <welcome-file>login.jsp</welcome-file>
</welcome-file-list>

3. 编写Dao层,用户登录的接口

package com.wang.dao.user;

import com.wang.pojo.User;

import java.sql.Connection;
import java.sql.SQLException;

public interface UserDao {

    //得到登录的用户
    public User getLoginUser(Connection connection,String userCode) throws SQLException;

}

4. 编写Dao接口的实现类

package com.wang.dao.user;

import com.wang.dao.BaseDao;
import com.wang.pojo.User;

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

public class UserDaoImpl implements UserDao {
    @Override
    public User getLoginUser(Connection connection,String userCode) throws SQLException {
        PreparedStatement pstm = null;
        ResultSet rs = null;
        User user = null;

        if (connection != null) {
            String sql = "select * from smbms_user where userCode = ?";
            Object[] params = {userCode};

           rs = BaseDao.execute(connection,sql,params,rs,pstm);

           if (rs.next()) {
               user = new User();
               user.setId(rs.getInt("id"));
               user.setUserCode(rs.getString("userCode"));
               user.setUserName(rs.getString("userName"));
               user.setUserPassword(rs.getString("userPassword"));
               user.setGender(rs.getInt("gender"));
               user.setBirthday(rs.getDate("birthday"));
               user.setPhone(rs.getString("phone"));
               user.setAddress(rs.getString("address"));
               user.setUserRole(rs.getInt("userRole"));
               user.setCreatedBy(rs.getInt("createdBy"));
               user.setCreationDate(rs.getTimestamp("creationDate"));
               user.setModifyBy(rs.getInt("modifyBy"));
               user.setModifyDate(rs.getTimestamp("modifyDate"));
           }
           BaseDao.closeResource(null,pstm,rs);

        }

        return user;

    }
}

5. 业务层接口

package com.wang.service.user;

import com.wang.pojo.User;

public interface UserService {

    //用户登录
    public User login(String userCode,String password);

}

6. 业务层实现

package com.wang.service.user;

import com.wang.dao.BaseDao;
import com.wang.dao.user.UserDao;
import com.wang.dao.user.UserDaoImpl;
import com.wang.pojo.User;
import org.junit.Test;

import java.sql.Connection;
import java.sql.SQLException;

public class UserServiceImpl implements UserService {

    //业务层都会调用dao层,因此我们要引入dao层
    private UserDao userDao;
    public  UserServiceImpl() {
        userDao = new UserDaoImpl();
    }

    @Override
    public User login(String userCode,String password) {
        Connection connection = null;
        User user = null;

        try {
            connection = BaseDao.getConnection();
            //通过业务层调用对应的具体的数据库操作
            user = userDao.getLoginUser(connection,userCode);
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            BaseDao.closeResource(connection,null,null);
        }
        return user;
    }

    @Test
    public void test() {
        UserServiceImpl userService = new UserServiceImpl();
        User admin = userService.login("admin","1234567");
        System.out.println(admin.getUserPassword());
    }

}

7. 编写Servlet

package com.wang.servlet.user;

import com.wang.pojo.User;
import com.wang.service.user.UserServiceImpl;
import com.wang.util.Constants;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class LoginServlet extends HttpServlet {

    //Servlet:控制层,调用业务层代码
    @Override
    protected void doGet(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException {
        System.out.println("LoginServlet -- start ......");

        //获取用户名和密码
        String userCode = req.getParameter("userCode");
        String userPassword = req.getParameter("userPassword");

        //和数据库中的密码进行对比,调用业务层
        UserServiceImpl userService = new UserServiceImpl();
        //这里已经把登录的人给查出来了
        User user = userService.login(userCode,userPassword);

        if (user != null) {
            //查有此人,可以登录
            //将用户的信息放到session中
            req.getSession().setAttribute(Constants.USER_SESSION,user);
            //跳转到主页
            resp.sendRedirect("jsp/frame.jsp");
        }else {
            //查无此人,无法登陆
            //转发会登录页面,顺带提示用户名或密码错误
            req.setAttribute("error","用户名或密码不正确");
            req.getRequestDispatcher("login.jsp").forward(req,resp);

        }
    }

    @Override
    protected void doPost(HttpServletRequest req,IOException {
        doGet(req,resp);
    }
}

8. 注册Servlet

<!--Servlet-->
<servlet>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>com.wang.servlet.user.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/login.do</url-pattern>
</servlet-mapping>

9. 测试访问,确保以上功能都能实现

4. 登录功能优化

注销功能:

思路:移除Session,返回登录页面

package com.wang.servlet.user;

import com.wang.util.Constants;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class LogoutServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req,IOException {
        //移除用户的Session
        req.getSession().removeAttribute(Constants.USER_SESSION);
        //返回登录页面
        resp.sendRedirect(req.getContextPath() + "/login.jsp");
    }

    @Override
    protected void doPost(HttpServletRequest req,resp);
    }
}

注册xml

<servlet>
    <servlet-name>LogoutServlet</servlet-name>
    <servlet-class>com.wang.servlet.user.LogoutServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>LogoutServlet</servlet-name>
    <url-pattern>/jsp/logout.do</url-pattern>
</servlet-mapping>

登录拦截优化

编写过滤器并注册

package com.wang.filter;

import com.wang.pojo.User;
import com.wang.util.Constants;

import javax.servlet.*;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class SysFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest req,ServletResponse resp,ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) resp;

        //过滤器,从session中获取用户
        User user = (User) request.getSession().getAttribute(Constants.USER_SESSION);

        //已经被移除或者被注销了,或者未登录
        if (user == null) {
            response.sendRedirect("/smbms/error.jsp");
        }else {
            chain.doFilter(req,resp);
        }
    }

    @Override
    public void destroy() {

    }
}

<!--用户登录过滤器-->
<filter>
    <filter-name>SysFilter</filter-name>
    <filter-class>com.wang.filter.SysFilter</filter-class>
</filter>
<!--所有的访问jsp目录下的资源都会被过滤-->
<filter-mapping>
    <filter-name>SysFilter</filter-name>
    <url-pattern>/jsp/*</url-pattern>
</filter-mapping>

5. 密码修改

1. 导入前端素材

2. 写项目,建议从底层向上写

3. UserDao接口

//修改当前用户的密码
public int updatePwd(Connection connection,int id,int password) throws SQLException;

4. UserDao实现类

//修改当前用户的密码,返回受影响的行数
@Override
public int updatePwd(Connection connection,int password) throws SQLException {

    PreparedStatement pstm = null;
    int execute = 0;

    if (connection != null) {
        String sql = "update smbms_user set userPassword = ? where id = ?";
        Object params[] = {password,id};
        execute = BaseDao.execute(connection,pstm);
        BaseDao.closeResource(null,null);
    }

    return execute;

}

5. UserService接口

//根据用户ID修改密码
public boolean updatePwd(int id,int pwd);

6. UserService实现类

@Override
public boolean updatePwd(int id,int pwd) {
    Connection connection = null;
    boolean flag = false;

    //修改密码
    try {
        connection = BaseDao.getConnection();
        if (userDao.updatePwd(connection,id,pwd) > 0) {
            flag = true;
        }
    } catch (SQLException throwables) {
        throwables.printStackTrace();
    } finally {
        BaseDao.closeResource(connection,null);
    }
    return flag;
}

7. 记得实现复用,需要提取出方法!

package com.wang.servlet.user;

import com.mysql.jdbc.StringUtils;
import com.wang.pojo.User;
import com.wang.service.user.UserService;
import com.wang.service.user.UserServiceImpl;
import com.wang.util.Constants;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

//实现Servlet服用
public class UserServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req,IOException {
        String method = req.getParameter("method");
        if (method.equals("savepwd") && method != null) {
            this.updatePwd(req,resp);
        }
    }

    @Override
    protected void doPost(HttpServletRequest req,resp);
    }

    public void updatePwd(HttpServletRequest req,HttpServletResponse resp) {
        //从Session里面拿ID
        Object o = req.getSession().getAttribute(Constants.USER_SESSION);
        String newpassword = req.getParameter("newpassword");

        boolean flag = false;

        if (o != null && !StringUtils.isNullOrEmpty(newpassword)) {
            UserService userService = new UserServiceImpl();
            flag = userService.updatePwd(((User) o).getId(),newpassword);
            if (flag) {
                req.setAttribute("message","修改密码成功,请退出,使用新密码登录");
                //密码修改成功,移除当前Session
                req.getSession().removeAttribute(Constants.USER_SESSION);
            } else {
                req.setAttribute("message","密码修改失败");
            }
        } else {
            req.setAttribute("message","新密码有问题");
        }

        try {
            req.getRequestDispatcher("pwdmodify.jsp").forward(req,resp);
        } catch (ServletException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

8. 注册Servlet

<servlet>
    <servlet-name>UserServlet</servlet-name>
    <servlet-class>com.wang.servlet.user.UserServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>UserServlet</servlet-name>
    <url-pattern>/jsp/user.do</url-pattern>
</servlet-mapping>

6. 优化密码修改:使用AJAX

1. 引入阿里巴巴的fastjson

2. 后台代码修改

//验证旧密码,session中有用户的密码
public void pwdModify(HttpServletRequest req,HttpServletResponse resp) {
    //从Session里面拿ID
    Object o = req.getSession().getAttribute(Constants.USER_SESSION);
    String oldpassword = req.getParameter("oldpassword");

    //万能的map: 结果集
    Map<String,String> resultMap = new HashMap<>();

    if (o == null) {
        //Session失效了,Session过期了
        resultMap.put("result","sessionerror");
    } else if (StringUtils.isNullOrEmpty(oldpassword)) {
        resultMap.put("result","error");
    } else  {
        //Session用户的密码
        String userPassword = ((User) o).getUserPassword();
        if (oldpassword.equals(userPassword)) {
            resultMap.put("result","true");
        } else {
            resultMap.put("result","false");
        }
    }

    try {
        //限定响应返回的格式为json
        resp.setContentType("application/json");
        PrintWriter writer = resp.getWriter();
        //JSONArray 阿里巴巴的JSON工具类转换格式
        /*
        把resultMap转为JSON格式
         */
        writer.write(JSONArray.toJSONString(resultMap));
        writer.flush();
        writer.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

7. 用户管理实现

1. 思路

2. 导入分页的工具类

3. 用户列表页导入

1. userlist.jsp
2. rollpage.jsp

4. 获取用户数量

1. UserDao

//根据用户名或者角色查询用户总数
public int getUserCount(Connection connection,String username,int userRole) throws SQLException;

2. UserDaoImpl

//根据用户名或者角色查询用户总数
@Override
public int getUserCount(Connection connection,int userRole) throws SQLException {

    PreparedStatement pstm = null;
    ResultSet rs = null;
    int count = 0;

    if (connection != null) {
        StringBuffer sql = new StringBuffer();
        sql.append("select count(1) as count from smbms_user as u,smbms_role as r where u.userRole = r.id");
        //存放我们的参数
        ArrayList<Object> list = new ArrayList<>();

        if (!StringUtils.isNullOrEmpty(username)) {
            sql.append(" and u.userName like ?");
            list.add("%" + username + "%");     //index = 0
        }

        if (userRole > 0) {
            sql.append(" and u.userRole like ?");
            list.add(userRole);     //index = 1
        }

        //把list转为数组
        Object[] objects = list.toArray();

        rs = BaseDao.execute(connection,sql.toString(),objects,pstm);

        if (rs.next()) {
            //从结果集中获得最终的结果
            count = rs.getInt("count");
        }

        BaseDao.closeResource(null,rs);

    }

    return count;
}

3. UserService

//查询记录数
public int getUserCount(String username,int userRole);

4. UserServiceImpl

//查询记录数
@Override
public int getUserCount(String username,int userRole) {

    Connection connection = null;
    int userCount = 0;

    try {
        connection = BaseDao.getConnection();
        userCount = userDao.getUserCount(connection,userRole);
    } catch (SQLException throwables) {
        throwables.printStackTrace();
    } finally {
        BaseDao.closeResource(connection,null);
    }

    return userCount;
}

5. 获取用户列表

1. UserDao

//通过条件查询-userlist
public List<User> getUserList(Connection connection,String userName,int userRole,int currentPageNo,int pageSize) throws SQLException;

2. UserDaoImpl

//通过条件查询-userlist
@Override
public List<User> getUserList(Connection connection,int pageSize) throws SQLException {

    PreparedStatement pstm = null;
    ResultSet rs = null;
    ArrayList<User> userList = new ArrayList<>();

    if (connection != null) {
        StringBuffer sql = new StringBuffer();
        sql.append("select u.*,r.roleName userRoleName from smbms_user as u join smbms_role as r on u.userRole = r.id");
        //存放我们的参数
        ArrayList<Object> list = new ArrayList<>();

        if (!StringUtils.isNullOrEmpty(userName)) {
            sql.append(" and u.userName like ?");
            list.add("%" + userName + "%");     //index = 0
        }

        if (userRole > 0) {
            sql.append(" and u.userRole like ?");
            list.add(userRole);     //index = 1
        }

        //在数据库中,分页使用limit   startIndex,pageSize;   总数
        //0,5
        //6,5
        //(当前页-1)*页面大小

        sql.append("order by creationDate desc limit ?,?");
        currentPageNo = (currentPageNo - 1) * pageSize;
        list.add(currentPageNo);
        list.add(pageSize);

        Object[] params = list.toArray();
        rs = BaseDao.execute(connection,pstm);
        while (rs.next()) {
            User _user = new User();
            _user.setId(rs.getInt("id"));
            _user.setUserCode(rs.getString("userCode"));
            _user.setUserName(rs.getString("userName"));
            _user.setGender(rs.getInt("gender"));
            _user.setBirthday(rs.getDate("birthday"));
            _user.setPhone(rs.getString("phone"));
            _user.setUserRole(rs.getInt("userRole"));
            _user.setUserRoleName(rs.getString("userRoleName"));
            userList.add(_user);
        }
        BaseDao.closeResource(null,rs);

    }
    return userList;
}

3. UserService

//根据条件查询用户列表
public List<User> getUserList(String queryUserName,int queryUserRole,int pageSize);

4. UserServiceImpl

//根据条件查询用户列表
@Override
public List<User> getUserList(String queryUserName,int pageSize) {
    Connection connection = null;
    List<User> userList = null;

    try {
        connection = BaseDao.getConnection();
        userList = userDao.getUserList(connection,queryUserName,queryUserRole,currentPageNo,pageSize);
    } catch (SQLException throwables) {
        throwables.printStackTrace();
    } finally {
        BaseDao.closeResource(connection,null);
    }

    return userList;

}

6. 获取角色操作

为了我们职责统一,可以把角色的操作单独放在一个包中,和POJO类对应

RoleDao

public interface RoleDao {
    //获取角色列表
    public List<Role> getRoleList(Connection connection) throws SQLException;
}

RoleDaoImpl

package com.wang.dao.role;

import com.wang.dao.BaseDao;
import com.wang.pojo.Role;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;

public class RoleDaoImpl implements RoleDao{
    //获取角色列表
    @Override
    public List<Role> getRoleList(Connection connection) throws SQLException {

        PreparedStatement pstm = null;
        ResultSet rs = null;
        List<Role> roleList = null;

        if (connection != null) {
            String sql = "select * from smbms_role";
            Object[] params = null;
            rs = BaseDao.execute(connection,pstm);

            while (rs.next()) {
                Role _role = new Role();
                _role.setId(rs.getInt("id"));
                _role.setRoleName(rs.getString("roleName"));
                _role.setRoleCode(rs.getString("roleCode"));
                roleList.add(_role);
            }
            BaseDao.closeResource(null,rs);
        }
        return roleList;
    }
}

RoleService

package com.wang.service.role;

import com.wang.pojo.Role;

import java.util.List;

public interface RoleService {
    //获取角色列表
    public List<Role> getRoleList();
}

RoleServiceImpl

package com.wang.service.role;

import com.wang.dao.BaseDao;
import com.wang.dao.role.RoleDao;
import com.wang.dao.role.RoleDaoImpl;
import com.wang.pojo.Role;

import java.sql.Connection;
import java.sql.SQLException;
import java.util.List;

public class RoleServiceImpl implements RoleService{

    //引入Dao
    private RoleDao roleDao;
    public RoleServiceImpl() {
        roleDao = new RoleDaoImpl();
    }

    @Override
    public List<Role> getRoleList() {
        Connection connection = null;
        List<Role> roleList = null;
        try {
            connection = BaseDao.getConnection();
            roleList = roleDao.getRoleList(connection);
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            BaseDao.closeResource(connection,null);
        }
        return roleList;
    }
}

7. 用户显示的Servlet

1. 获取用户前端的数据(查询)

2. 判断请求是否需要执行,看参数的值判断

3. 为了实现分页,需要计算出当前页面和总页面,页面参数

//重点,难点
public void query(HttpServletRequest req,HttpServletResponse resp) {

    //查询用户列表

    //从前端获取数据
    String queryUserName = req.getParameter("queryname");
    String temp = req.getParameter("queryUserRole");
    String pageIndex = req.getParameter("pageIndex");
    int queryUserRole = 0;

    //获取用户列表
    UserServiceImpl userService = new UserServiceImpl();
    List<User> userList = null;
    //第一次走这个请求,一定是第一页,页面大小是固定的
    //可以把这个写在配置文件中,方便后期修改
    int pageSize = 5;
    int currentPageNo = 1;

    if (queryUserName == null) {
        queryUserName = "";
    }
    if (temp != null && !temp.equals("")) {
        queryUserRole = Integer.parseInt(temp);     //给查询赋值
    } if (pageIndex != null) {
        currentPageNo = Integer.parseInt(pageIndex);
    }

    //获取用户的总数(分页:上一页,下一页)
    int totalCount = userService.getUserCount(queryUserName,queryUserRole);
    //总页数支持
    PageSupport pageSupport = new PageSupport();
    pageSupport.setCurrentPageNo(currentPageNo);
    pageSupport.setPageSize(pageSize);
    pageSupport.setTotalCount(totalCount);

    int totalPageCount = pageSupport.getTotalPageCount();

    //控制首页和尾页
    //如果页面要小于1了,就显示第一页的东西
    if (totalPageCount < 1) {
        currentPageNo = 1;
    } else if (currentPageNo > totalPageCount){
        //当前页面大于最后一页
        currentPageNo = totalPageCount;
    }

    //获取用户列表展示
    userList = userService.getUserList(queryUserName,pageSize);
    req.setAttribute("userList",userList);

    //展示角色列表
    RoleServiceImpl roleService = new RoleServiceImpl();
    List<Role> roleList = roleService.getRoleList();
    req.setAttribute("roleList",roleList);
    req.setAttribute("queryUserName",queryUserName);
    req.setAttribute("queryUserRole",queryUserRole);

    //展示分页
    req.setAttribute("totalCount",totalCount);
    req.setAttribute("currentPageNo",currentPageNo);
    req.setAttribute("totalPageCount",totalPageCount);

    //返回前端
    try {
        req.getRequestDispatcher("userlist.jsp").forward(req,resp);
    } catch (ServletException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

（编辑：李大同）

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