SMBMS(超市管理项目)

  • 项目结构

image-20230707232311327

  • 数据库

image-20230707232655439

img

1. 项目搭建准备

1.1 新建Maven Web项目

1.2 配置Tomcat

1.3 测试启动

image-20230707233531008

1.4 导入依赖

1.4.1 pom.xml

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<!-- servlet 依赖 -->
<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
</dependency>
<!-- JSP 依赖 -->
<dependency>
    <groupId>javax.servlet.jsp</groupId>
    <artifactId>jsp-api</artifactId>
    <version>2.2</version>
</dependency>
<!-- JSTL 依赖 -->
<dependency>
    <groupId>javax.servlet.jsp.jstl</groupId>
    <artifactId>jstl-api</artifactId>
    <version>1.2</version>
</dependency>
<!-- JSTL 实现 -->
<dependency>
    <groupId>taglibs</groupId>
    <artifactId>standard</artifactId>
    <version>1.1.2</version>
</dependency>
<!-- MySQL 依赖 -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.19</version>
</dependency>

1.4.2 web.xml

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<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                             http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">
</web-app>

1.4.3 index.jsp

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<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
    <head>
        <title>Index.jsp</title>
    </head>
    <style>
        h1 {
            text-align: center;
            color: red;
        }
    </style>
    <body>
        <h1>Hello World!</h1>
    </body>
</html>

1.5 构建项目结构

image-20230707233908335

1.6 编写实体类 ORM

  • 对象关系映射（Object Relational Mapping，简称ORM）- 表-类映射

1.7 编写基本公共类

1.7.1 数据库配置文件 db.properties

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driver=com.mysql.jdbc.Driver
#在和mysql传递数据的过程中，使用unicode编码格式，并且字符集设置为utf-8
url=jdbc:mysql://127.0.0.1:3306/smbms?useSSL=false&useUnicode=true&characterEncoding=utf-8
user=root
password=root

1.7.2 编写数据库的公共类 BaseDao

  • DAO（Data Access Object）
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package com.bayyy.dao;

import java.io.InputStream;
import java.sql.*;
import java.util.Properties;

public class BaseDao {
    private static String driver;   // 数据库驱动
    private static String url;      // 数据库连接地址
    private static String username; // 数据库用户名
    private static String password; // 数据库密码

    // 静态代码块, 类加载时执行
    static {
        Properties properties = new Properties();
        // 通过类加载器加载db.properties文件
        InputStream is = BaseDao.class.getClassLoader().getResourceAsStream("db.properties");

        try {
            properties.load(is);
        } catch (Exception 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;
    }

    // 编写查询公共方法
    public static ResultSet execute(Connection connection, String sql, Object[] params, ResultSet resultSet, PreparedStatement preparedStatement) throws SQLException {
        preparedStatement = connection.prepareStatement(sql);
        for (int i = 0; i < params.length; i++) {
            // setObject占位符从1开始, 而数组下标从0开始
            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, String sql, Object[] params, PreparedStatement preparedStatement) throws SQLException {
        preparedStatement = connection.prepareStatement(sql);
        for (int i = 0; i < params.length; i++) {
            // setObject占位符从1开始, 而数组下标从0开始
            preparedStatement.setObject(i + 1, params[i]);
        }
        return preparedStatement.executeUpdate();
    }

    // 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;
    }
}

1.7.2 编写字符编码Filter

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

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletResponse.setCharacterEncoding("UTF-8");
        servletRequest.setCharacterEncoding("UTF-8");
        filterChain.doFilter(servletRequest, servletResponse); // 放行: 交给下一个过滤器
    }

    @Override
    public void destroy() {
    }
}

1.8 导入静态代码

jsp、html、css、js…

2. 登录功能实现

image-20230709223919042

2.1 编写前端首页

…

2.2 设置首页 xml

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

2.3 编写Dao层用户接口

DAO （Data Access Object 数据访问对象）

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public interface UserDao {
    // 得到登录的用户
    public User getLoginUser(Connection connection, String serCode) throws SQLException;
}

2.4 编写dao层接口的实现类

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

        if (connection != null) {
            String sql = "select * from user where userCode=?";
            Object[] params = {serCode};
            resultSet = BaseDao.execute(connection, sql, params, resultSet, preparedStatement);
            if (resultSet.next()) {
                user = new User();
                user.setId(resultSet.getInt("id"));                           // id
                user.setUserCode(resultSet.getString("userCode"));    // 用户编码
                user.setUserName(resultSet.getString("userName"));    // 用户名称
                user.setUserPassword(resultSet.getString("userPassword"));    // 用户密码
                user.setGender(resultSet.getInt("gender"));                   // 性别
                user.setBirthday(resultSet.getDate("birthday"));              // 出生日期
                user.setPhone(resultSet.getString("phone"));                  // 电话
                user.setAddress(resultSet.getString("address"));              // 地址
                user.setUserRole(resultSet.getInt("userRole"));    // 用户角色
                user.setCreatedBy(resultSet.getInt("createdBy")); // 创建者
                user.setCreationDate(resultSet.getTimestamp("creationDate")); // 创建时间
                user.setModifyBy(resultSet.getInt("modifyBy"));     // 更新者
                user.setModifyDate(resultSet.getTimestamp("modifyDate"));     // 更新时间
            }
            BaseDao.closeResource(null, preparedStatement, resultSet);
            return user;
        }
        return null;
    }
}

2.5 业务层接口 UserService

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public interface UserService {
    // 用户登录
    public User login(String userCode, String userPassword);
}

2.6 业务层实现类 UserServiceImpl

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public class UserServiceImpl implements UserService{
    // 业务层都会调用dao层, 通过用户编码获取用户信息
    private UserDao userDao;
    public UserServiceImpl() {
        userDao = new UserDaoImpl();
    }

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

        try {
            connection = BaseDao.getConnection();
            user = userDao.getLoginUser(connection, userCode);
        } catch (SQLException e) {
            throw new RuntimeException(e);
        } finally {
            BaseDao.closeResource(connection, null, null);
        }
        return user;
    }
}

2.7 编写LoginServlet并注册

  • .java
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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
        UserService userService = new UserServiceImpl();
        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 {
            // 转发回登录页面, 并提示错误信息
            req.setAttribute("error", "用户名或密码不正确");
            req.getRequestDispatcher("login.jsp").forward(req, resp);
        }

    }
}
  • web.xml
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<!-- Servlet: 注销 -->
<servlet>
    <servlet-name>LogoutServlet</servlet-name>
    <servlet-class>com.bayyy.servlet.user.LogoutServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>LogoutServlet</servlet-name>
    <url-pattern>/jsp/logout.do</url-pattern>
</servlet-mapping>

2.8 登录拦截优化

  • SysFilter

    1. 将 ServletRequest/ServletResponse 强转为 HttpServletRequest/HttpServletResponse

      ServletRequest 没有 getSession 方法

      ServletResponse 没有 sendRedirect 方法

      无法实现获取Session和重定向功能

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public class SysFilter implements Filter {
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse respone = (HttpServletResponse) servletResponse;

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

        if (user == null) { // Session失效, 用户不存在(注销或者未登录)
            // 已经被移除或者注销了, 或者未登录
            respone.sendRedirect("/error.jsp"); // 跳转到错误页面
        } else {
            filterChain.doFilter(servletRequest, servletResponse);  // 放行
        }
    }
}
  1. xml 注册
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<!-- Filter: 登录验证 -->
<filter>
    <filter-name>SysFilter</filter-name>
    <filter-class>com.bayyy.filter.SysFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>SysFilter</filter-name>
    <url-pattern>/jsp/*</url-pattern>
</filter-mapping>

3. 密码修改

3.1 导入前端素材

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<li><a href="${pageContext.request.contextPath }/jsp/pwdmodify.jsp">密码修改</a></li>

3.2 项目->从底层向顶层写

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graph LR
	程序员 --> 前端JSP --请求--> Servlet --调用--> Service --调用--> Dao --查询--> 数据库

3.3 UserDao接口

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public interface UserDao {
    // 得到登录的用户
    public User getLoginUser(Connection connection, String serCode) throws SQLException;

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

3.4 UserDao接口实现类

  • UserDaoImpl.java
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@Override
public int updatePwd(Connection connection, int id, String password) throws SQLException {
    PreparedStatement preparedStatement = null;
    int execute = 0;

    if (connection != null) {
        Object prams[] = {password, id};
        String sql = "update smbms_user set userPassword=? where id=?";
        execute = BaseDao.execute(connection, sql, prams, preparedStatement);
        BaseDao.closeResource(null, preparedStatement, null);
        return 0;
    }
    return execute;
}

3.5 UserService层

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public interface UserService {
    // 用户登录
    public User login(String userCode, String userPassword);

    // 根据用户id修改密码
    public boolean updatePwd(int id, String password);
}

3.6 UserServive实现类

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public boolean updatePwd(int id, String password) {
    Connection connection = null;
    boolean flag = false;

    // 修改密码
    try {
        connection = BaseDao.getConnection();
        if (userDao.updatePwd(connection, id, password) > 0) {
            flag = true;
        }
    } catch (SQLException e) {
        throw new RuntimeException(e);
    } finally {
        BaseDao.closeResource(connection, null, null);
    }
    return flag;
}

3.7 Servlet复用，提取方法

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protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    String method = req.getParameter("method");
    if ("savepwd".equals(method)) {
        this.updatePwd(req, resp);
    }
}

public void updatePwd(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    // 从Session里面获取用户信息
    Object userSession = req.getSession().getAttribute(Constants.USER_SESSION);

    String newpassword = req.getParameter("newpassword");

    boolean flag = false;

    if (userSession != null && !StringUtils.isNullOrEmpty(newpassword)) {
        UserService userService = new UserServiceImpl();
        flag = userService.updatePwd(((User) userService).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");
    }
    req.getRequestDispatcher("pwdmodify.jsp").forward(req, resp);
}

3.8 密码修改 - Ajax

3.8.1 阿里巴巴的包

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<!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>2.0.35</version>
</dependency>

3.8.2 UserServlet 代码修改

  • 增加 pqdmodify 部分
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// 实现Servlet复用
public class UserServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String method = req.getParameter("method");
        if (method.equals("savepwd")) {
            this.updatePwd(req, resp);
        } else if (method.equals("pwdmodify")) {
            this.pwdModify(req, resp);
        }
    }

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

    // 修改密码
    public void updatePwd(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 从Session里面获取用户信息
        Object userSession = req.getSession().getAttribute(Constants.USER_SESSION);

        String newpassword = req.getParameter("newpassword");

        boolean flag = false;

        if (userSession != null && !StringUtils.isNullOrEmpty(newpassword)) {
            UserService userService = new UserServiceImpl();
            flag = userService.updatePwd(((User) userSession).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");
        }
        req.getRequestDispatcher("pwdmodify.jsp").forward(req, resp);
    }

    // 验证旧密码
    public void pwdModify(HttpServletRequest req, HttpServletResponse resp) {
        // 1. 从Session里面获取用户信息
        Object userSession = req.getSession().getAttribute(Constants.USER_SESSION);
        String oldpassword = req.getParameter("oldpassword");

        // 使用 Map
        HashMap<String, String> resultMap = new HashMap<String, String>();
        if (userSession == null) {  // Session 过期或不存在
            resultMap.put("result", "sessionerror");
        } else if (StringUtils.isNullOrEmpty(oldpassword)) {  // 旧密码输入为空
            resultMap.put("result", "error");
        } else {
            String userPassword = ((User) userSession).getUserPassword();
            if (oldpassword.equals(userPassword)) {  // 旧密码输入正确
                resultMap.put("result", "true");
            } else {  // 旧密码输入错误
                resultMap.put("result", "false");
            }
        }

        try {
            resp.setContentType("application/json");
            PrintWriter writer = resp.getWriter();
            // JSONArray 阿里巴巴的 JSON 工具类, 转换格式
            writer.write(JSONArray.toJSONString(resultMap));
            writer.flush();
            writer.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

4. 用户管理实现

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graph LR
	id1(客户) --发起请求--> id2["Servlet\n1.处理请求\n2.调用业务\n3.返回页面"]
	id2 --返回前端页面--> id1
	id2 --> id3(用户列表)
	id3 --> id6[Service]
	id6 --> id9[Dao]
	id2 --> id4(角色列表)
	id4 --> id7[Service]
	id7 --> id10[Dao]
	id2 --> id5["分页\npageSize(固定的)\n总数(数据库查)"]
	id5 --> id8[Service]
	id8 --> id11[Dao]
	id9 --> id12{数据库}
	id10 --> id12
	id11 --> id12

4.1 导入前端界面和相关方法

4.1.1 导入分页工具类

  • PageSupport.java

4.1.2 用户列表页面导入

  • userlist.jap
  • rollpage.jsp

4.2 获取用户数量

4.2.1 UserDao接口

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

4.2.2 Dao接口实现类

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// 查询用户名或者角色查询用户总数
@Override
public int getUserCount(Connection connection, String userName, int userRole) throws SQLException {
    PreparedStatement preparedStatement = null;
    ResultSet resultSet = null;
    int count = 0;

    if (connection != null) {
        StringBuffer sql = new StringBuffer();
        sql.append("select count(1) as count from smbms_user u,smbms_role r where u.userRole=r.id");
        // 存放参数
        ArrayList<Object> list = new ArrayList<Object>();
        if (!StringUtils.isNullOrEmpty(userName)) {
            sql.append(" and u.userName like ?");
            list.add("%" + userName + "%");
        }
        if (userRole != 0) {
            sql.append(" and u.userRole=?");
            list.add(userRole);
        }
        Object[] objects = list.toArray();
        System.out.println("UserDaoImpl->getUserCount:" + sql.toString());  // 输出最终的sql语句
        System.out.println("UserDaoImpl->getUserCount:" + list.toString()); // 输出最终的参数
        resultSet = BaseDao.execute(connection, sql.toString(), objects, resultSet, preparedStatement);
        if (resultSet.next()) {
            count = resultSet.getInt("count");
        }
        BaseDao.closeResource(null, preparedStatement, resultSet);
    }
    return count;
}

4.2.3 UserService 接口

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

4.2.4 Service接口实现类

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@Override
public int getUserCount(String userName, int userRole) {
    Connection connection = null;
    int count = 0;

    try {
        connection = BaseDao.getConnection();
        count = userDao.getUserCount(connection, userName, userRole);
    } catch (SQLException e) {
        throw new RuntimeException(e);
    } finally {
        BaseDao.closeResource(connection, null, null);
    }
    return count;
}

4.3 获取用户列表

4.3.1 UserDao接口

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// 获取用户列表(通过条件查询-userList)
public List<User> getUserList(Connection connection, String userName, int userRole, int currentPageNo, int pageSize) throws SQLException;

4.3.2 Dao接口实现类

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public List<User> getUserList(Connection connection, String userName, int userRole, int currentPageNo, int pageSize) throws SQLException {
    PreparedStatement preparedStatement = null;
    ResultSet resultSet = null;
    List<User> userList = new ArrayList<User>();
    if (connection != null) {
        StringBuffer sql = new StringBuffer();
        sql.append("select u.*,r.roleName as userRoleName from smbms_user u,smbms_role r where u.userRole=r.id");
        ArrayList<Object> list = new ArrayList<Object>();
        if (!StringUtils.isNullOrEmpty(userName)) {
            sql.append(" and u.userName like ?");
            list.add("%" + userName + "%");
        }
        if (userRole != 0) {
            sql.append(" and u.userRole=?");
            list.add(userRole);
        }
        // 在数据库中，分页使用limit startIndex,pageSize; 总数
        sql.append(" order by creationDate DESC limit ?,?");
        currentPageNo = (currentPageNo - 1) * pageSize;
        list.add(currentPageNo);
        list.add(pageSize);

        Object[] params = list.toArray();
        System.out.println("UserDaoImpl->getUserList:" + sql.toString());  // 输出最终的sql语句
        resultSet = BaseDao.execute(connection, sql.toString(), params, resultSet, preparedStatement);

        while (resultSet.next()) {
            User _user = new User();
            _user.setId(resultSet.getInt("id"));                           // id
            _user.setUserCode(resultSet.getString("userCode"));    // 用户编码
            _user.setUserName(resultSet.getString("userName"));    // 用户名称
            _user.setGender(resultSet.getInt("gender"));
            _user.setBirthday(resultSet.getDate("birthday"));
            _user.setPhone(resultSet.getString("phone"));
            _user.setUserRole(resultSet.getInt("userRole"));
            _user.setUserRoleName(resultSet.getString("userRoleName"));
            userList.add(_user);
        }
        BaseDao.closeResource(null, preparedStatement, resultSet);
    }
    return userList;
}

4.3.3 UserService接口

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// 查询用户列表
public List<User> getUserList(String userName, int userRole, int currentPageNo, int pageSize);

4.3.4 Service接口实现类

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public List<User> getUserList(String userName, int userRole, int currentPageNo, int pageSize) {
    Connection connection = null;
    List<User> userList = null;
    try {
        connection = BaseDao.getConnection();
        userList = userDao.getUserList(connection, userName, userRole, currentPageNo, pageSize);
    } catch (SQLException e) {
        throw new RuntimeException(e);
    } finally {
        BaseDao.closeResource(connection, null, null);
    }
    return userList;
}

4.4 获取角色操作

  • 为了职责统一，将角色操作单独放在一个包中，和 enity(pojo) 类对应

4.4.1 RoleDao

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

}

4.4.2 RoleDaoIpml实现类

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public class RoleDaoImpl implements RoleDao {
    // 获取角色列表
    @Override
    public List<Role> getRoleList(Connection connection) throws SQLException {
        ArrayList<Role> roleList = new ArrayList<Role>();
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        if (connection != null) {
            String sql = "select * from smbms_role";
            Object[] params = {};
            resultSet = BaseDao.execute(connection, sql, params, resultSet, preparedStatement);
            while (resultSet.next()) {
                Role _role = new Role();
                _role.setId(resultSet.getInt("id"));
                _role.setRoleCode(resultSet.getString("roleCode"));
                _role.setRoleName(resultSet.getString("roleName"));
                roleList.add(_role);
            }
            BaseDao.closeResource(null, preparedStatement, resultSet);
        }
        return roleList;
    }
}

4.4.3 RoleService

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

4.4.4 RoleServiceImpl实现类

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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 e) {
            throw new RuntimeException(e);
        } finally {
            BaseDao.closeResource(connection, null, null);
        }
        return roleList;
    }
}

4.5 用户显示 - UserServlet

  • 获取用户前端的数据（查询）
  • 判断请求是否需要执行，看参数的值判断
  • 为了实现分页，需要计算出当前页面和总页面，页面大小…
  • 用户列表展示
  • 返回前端
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// 查询用户列表
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
    UserService userService = new UserServiceImpl();
    List<User> userList = null;

    // 第一次走这个请求, 一定是第一页, 页面大小固定的
    int pageSize = 5;
    int currentPageNo = 1;

    if (queryUserName == null) {
        queryUserName = "";
    }
    if (temp != null && !temp.equals("")) { // 前端获取数据出错
        queryUserRole = Integer.parseInt(temp);
    }
    if (pageIndex != null) {
        currentPageNo = Integer.parseInt(pageIndex);
    }
    System.out.println("queryUserName servlet: " + queryUserName);
    System.out.println("queryUserRole servlet: " + queryUserRole);

    // 获取用户总数(分页: 上一页, 下一页)
    int totalCount = userService.getUserCount(queryUserName, queryUserRole);
    // 总页数支持
    PageSupport pageSupport = new PageSupport();
    pageSupport.setPageSize(pageSize); // 设置页面容量
    pageSupport.setTotalCount(totalCount); // 总数量(表)
    pageSupport.setCurrentPageNo(currentPageNo); // 当前页码

    int totalPageCount = pageSupport.getTotalPageCount();

    // 控制首页和尾页
    if (currentPageNo < 1) {
        currentPageNo = 1;
    } else if (currentPageNo > totalPageCount) {
        currentPageNo = totalPageCount;
    }

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

    RoleService roleService = new RoleServiceImpl();
    List<Role> roleList = roleService.getRoleList();
    req.setAttribute("roleList", roleList);

    req.setAttribute("totalCount", totalCount);
    req.setAttribute("currentPageNo", currentPageNo);
    req.setAttribute("totalPageCount", totalPageCount);
    req.setAttribute("queryUserName", queryUserName);
    req.setAttribute("queryUserRole", queryUserRole);

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

4.6 小黄鸭调试法