項目搭建準備工作

1. 搭建一個maven web項目

2. 配置tomcat

3. 測試項目是否可以運行

4. 導入項目中需要的jar包

  <dependencies>
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>servlet-api</artifactId>
      <version>2.5</version>
    </dependency>
    <dependency>
      <groupId>javax.servlet.jsp</groupId>
      <artifactId>javax.servlet.jsp-api</artifactId>
      <version>2.3.3</version>
    </dependency>
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.47</version>
    </dependency>
    <!--JSTL表達式依賴-->
    <dependency>
      <groupId>jstl</groupId>
      <artifactId>jstl</artifactId>
      <version>1.2</version>
    </dependency>
    <!--Standard標簽庫-->
    <dependency>
      <groupId>taglibs</groupId>
      <artifactId>standard</artifactId>
      <version>1.1.2</version>
    </dependency>

  </dependencies>

5. 創(chuàng)建項目包結構

6. 編寫實體類

• ORM映射：表——類映射

7. 編寫基礎公共類

• 數據庫配置文件
  此文件注意不要亂加；

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://127.0.0.1:3306/?useUnicode=true&characterEncoding=UTF-8&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC
username=root
password=11232020

• 數據庫公共類

//操作數據的公共類
public class BaseDao {

    private static String driver;
    private static String url;
    private static String username;
    private static String password;

    //靜態(tài)代碼塊，類加載就初始化
    static {
        Properties properties = new Properties();
        //通過類加載器讀取對應的資源
        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");
    }

    //獲得數據庫連接
    public static Connection getConnection() {
        Connection connetion = null;
        try {
            Class.forName(driver);
            connetion = DriverManager.getConnection(url,username,password);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return connetion;
    }

    //編寫查詢公共類
    public static ResultSet execute(Connection connection,String sql,Object[] params,ResultSet resultSet,PreparedStatement preparedStatement) throws SQLException {
        //預編譯的sql后面直接執(zhí)行就行
        preparedStatement = connection.prepareStatement(sql);

        for (int i = 0; i < params.length; i++) {
            //setObject冷溶，占位符從一開始，但我們的數組是從0開始借杰！
            preparedStatement.setObject(i+1,params[i]);
        }
        resultSet = preparedStatement.executeQuery();
        return resultSet;
    }

    //編寫增刪改查公共方法
    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，占位符從一開始进泼，但我們的數組是從0開始蔗衡！
            preparedStatement.setObject(i+1,params[i]);
        }
        int updateRows = preparedStatement.executeUpdate();
        return updateRows;
    }

    //釋放資源
    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();
                //回收失敗
                flag = false;
            }
        }
        if (preparedStatement != null) {
            try {
                preparedStatement.close();
                //GC回收
                preparedStatement = null;
            } catch (SQLException e) {
                e.printStackTrace();
                //回收失敗
                flag = false;
            }
        }
        if (connection != null) {
            try {
                connection.close();
                //GC回收
                connection = null;
            } catch (SQLException e) {
                e.printStackTrace();
                //回收失敗
                flag = false;
            }
        }
        return flag;
    }
}

• 編寫字符編碼過濾器

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

    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        request.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");

        chain.doFilter(request,response);
    }

    public void destroy() {

    }
}

    <!--    字符編碼過濾器-->
    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.vigil.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

8. 導入靜態(tài)資源

登錄功能實現

1. 編寫前端頁面

2. 設置歡迎頁面

    <welcome-file-list>
        <welcome-file>login.jsp</welcome-file>
    </welcome-file-list>

3. 編寫dao層登錄用戶登錄的接口

public interface UserDao {
    //得到要登錄的用戶
    public User getLoginUser(Connection connection, String userCode) throws SQLException;
}

4. 編寫dao接口的實現類

public class UserDaoImpl implements UserDao {
    public User getLoginUser(Connection connection, String userCode) throws SQLException {

        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        User user = null;

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

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

        return user;
    }
}

5.業(yè)務層接口

public interface UserService {
    public User login(String userCode, String password);
}

6. 實現業(yè)務層接口

public class UserServiceImpl implements UserService {

    //業(yè)務層都會調用dao層，所以要引入dao層
    private UserDao userDao = null;
    public UserServiceImpl() {
        userDao = new UserDaoImpl();
    }

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

        try {
            connection = BaseDao.getConnection();
            //通過業(yè)務層乳绕，調用對應的具體的數據庫操作
            user = userDao.getLoginUser(connection,userCode);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        finally {
            BaseDao.closeResource(connection,null,null);
        }
        return user;
    }
}

7. 編寫Servlet

public class LoginServlet extends HttpServlet {

    //控制層绞惦，調用業(yè)務層代碼
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("LoginServlet run----start");
        //獲得用戶登錄名和密碼
        String userCode = req.getParameter("userCode");
        String userPassword = req.getParameter("userPassword");

        //和數據庫中的密碼進行對比
        UserServiceImpl userService = new UserServiceImpl();
        User user = userService.login(userCode, userPassword);//通過查詢得到登錄的人全部在數據庫的信息對應的保存在一個JavaBean類中

        if(user != null && user.getUserPassword() != null && user.getUserPassword().equals(userPassword)) {//查有此人并且密碼正確
            //將用戶的信息存放到Session中
            req.getSession().setAttribute(Constants.USER_SESSION,user);
            //跳轉到主頁
            resp.sendRedirect("jsp/frame.jsp");
        } else {//查無此人
            //轉發(fā)回登錄頁面，順帶提示洋措，用戶名或者密碼錯誤
            req.setAttribute("error","用戶名或者密碼錯誤");
            req.getRequestDispatcher("login.jsp").forward(req,resp);
        }


    }

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

8. 配置Servlet

    <!--Servlet-->
    <servlet>
        <servlet-name>LoginServlet</servlet-name>
        <servlet-class>com.vigil.servlet.user.LoginServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/dologin.html</url-pattern>
    </servlet-mapping>

9. 測試功能是否全部實現

登錄功能優(yōu)化

注銷功能

• 思路：移除Session济蝉，返回登錄頁面

1. servlet

public class LogoutServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //移除用戶的Constants.USER_SESSION
        req.getSession().removeAttribute(Constants.USER_SESSION);
        resp.sendRedirect(req.getContextPath()+"/login.jsp");//返回登錄頁面
    }

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

2. 配置xml

    <servlet>
        <servlet-name>LogoutServlet</servlet-name>
        <servlet-class>com.vigil.servlet.user.LogoutServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>LogoutServlet</servlet-name>
        <url-pattern>/user/logout.html</url-pattern>
    </servlet-mapping>

登錄攔截優(yōu)化

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

    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) request;
        HttpServletResponse resp = (HttpServletResponse) response;

        //過濾器，從Session獲取用戶
        User user = (User) req.getSession().getAttribute(Constants.USER_SESSION);
        if(user == null) {
            resp.sendRedirect("/smbms/error.jsp");
        } else {
            chain.doFilter(request,response);
        }

    }

    public void destroy() {

    }
}

    <!--    用戶登錄過濾器-->
    <filter>
        <filter-name>SysFilter</filter-name>
        <filter-class>com.vigil.filter.SysFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>SysFilter</filter-name>
        <url-pattern>/jsp/*</url-pattern>
    </filter-mapping>

密碼修改

1. 導入前端素材

2. 寫項目菠发，從底層往上寫

• 從dao層開始寫起王滤，再寫業(yè)務層service，再寫控制層servlet滓鸠，再和視圖層jsp作聯(lián)系雁乡。要思考好一個事務和數據庫的邏輯關系，分別實現不同層次的代碼糜俗。

3. UserDao接口

public interface UserDao {
    //得到要登錄的用戶
    public User getLoginUser(Connection connection, String userCode) throws SQLException;

    //修改當前用戶密碼
    public int updatePwd(Connection connection,int id,String password) throws SQLException;
}

4. UserDao接口實現類

    //修改當前用戶密碼
    public int updatePwd(Connection connection, int id, String 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,sql,params);
            BaseDao.closeResource(null,pstm,null);
        }
        return execute;

5. UserService接口

public interface UserService {
    //得到要登錄的用戶
    public User login(String userCode, String password);

    //根據用戶ID更改密碼
    public boolean updatePwd(int id,String pwd);

}

6. UserService實現

    //根據用戶ID更改密碼
    public boolean updatePwd(int id, String pwd) {
        Connection connection = null;
        boolean flag = false;
        try {
            connection = BaseDao.getConnection();
            if(userDao.updatePwd(connection,id,pwd) > 0) {
                flag = true;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        finally {
            BaseDao.closeResource(connection,null,null);
        }
        return flag;
    }

7. 編寫Servlet

//實現Servlet的復用
public class UserServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String method = req.getParameter("method");
        if("savepwd".equals(method)) {//修改用戶密碼
            this.savepwd(req,resp);
        } else if("pwdmodify".equals(method)) {
            this.pwdmodify(req,resp);
        }
    }

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

    //修改用戶密碼（包含了舊密碼驗證踱稍，刪去也行）
    public void savepwd(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //從Session里面拿id，得到用戶的實體類對象User
        Object o = req.getSession().getAttribute(Constants.USER_SESSION);
        String newpassword = req.getParameter("newpassword");
        String oldpassword = req.getParameter("oldpassword");
        boolean flag = false;
        //用戶Session中有這個用戶吩跋，并且新舊密碼不空寞射，不為0長度
        if(o != null && (newpassword != null && newpassword.length() > 0) && (oldpassword != null && oldpassword.length() > 0)) {
            User user = (User)o;
            if((user.getUserPassword().equals(oldpassword))) {//舊密碼是是一致的
                UserService userService = new UserServiceImpl();
                flag = userService.updatePwd(user.getId(),newpassword);
                if (flag) {
                    req.setAttribute("message", "修改密碼成功，請退出锌钮，使用新密碼登錄");
                    //密碼修改成功引矩，移除當前Session
                    req.getSession().removeAttribute(Constants.USER_SESSION);
                } else {
                    req.setAttribute("message", "修改密碼失敗");
                }
            } else {
                req.setAttribute("message", "修改密碼失敗");
            }
        } else {
            req.setAttribute("message", "修改密碼失敗");
        }
        req.getRequestDispatcher("/jsp/pwdmodify.jsp").forward(req,resp);
    }

    //驗證舊密碼梁丘，利用session中的用戶User實例對象（登錄就會有）
    public void pwdmodify(HttpServletRequest req, HttpServletResponse resp) {
        //從Session里面拿id值漫，得到用戶的實體類對象User
        Object o = req.getSession().getAttribute(Constants.USER_SESSION);
        String oldpassword = req.getParameter("oldpassword");

        Map<String, String> resultMap = new HashMap<String, String>();

        if(o == null) {//session過期了
            resultMap.put("result","sessionerror");
        } else if(oldpassword == null) {//舊密碼輸入為空
            resultMap.put("result","error");
        } else if(!((User)o).getUserPassword().equals(oldpassword)) {//舊密碼輸入不正確
            resultMap.put("result","false");
        } else {//舊密碼輸入正確
            resultMap.put("result","true");
        }

        try {
            resp.setContentType("application/json");
            PrintWriter writer = resp.getWriter();
            /*
            JSONArray,工具類酱塔，轉換格式蕊玷，將map轉換為json
             */
            writer.write(JSONArray.toJSONString(resultMap));
            writer.flush();
            writer.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

• json工具包導入

    <dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>fastjson</artifactId>
      <version>1.2.75</version>
    </dependency>

8. 配置xml

    <servlet>
        <servlet-name>UserServlet</servlet-name>
        <servlet-class>com.vigil.servlet.user.UserServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>UserServlet</servlet-name>
        <url-pattern>/user/pwd.html</url-pattern>
    </servlet-mapping>

     <!--session默認過期時間剪勿，真實業(yè)務處理-->
    <session-config>
        <session-timeout>30</session-timeout>
    </session-config>

用戶管理實現

• 思路：

• 導入分頁的工具類

• 用戶列表頁面導入

• 獲取用戶數量

1. UserDao

    //根據用戶名或者角色查詢用戶總數
    public int getUserCount(Connection connection,String username,int userRole) throws SQLException;

2. UserDaoImpl

//根據用戶名或者角色查詢用戶總數
    public int getUserCount(Connection connection, String username, int userRole) throws SQLException {
        PreparedStatement pstm = null;
        ResultSet rs = null;
        int count = 0;
        //sql語句通過StringBuffer追加
        if(connection != null) {
            StringBuffer sql = new StringBuffer();
            ArrayList<Object> list = new ArrayList<Object>();
            sql.append("select count(1) as count from smbms_user u,smbms_role r where u.userRole = r.id");

            if(username != null) {//追加username的查詢判斷
                sql.append(" and u.userName like ?");
                list.add("%" + username + "%");//index : 0
            }
            if(userRole > 0) {//追加userRole的查詢判斷
                sql.append(" and u.userRole = ?");
                list.add(userRole);//index : 1
            }

            //list轉化為數組
            Object[] params = list.toArray();

            System.out.println("UserDaoImpl.getUserCount.SQL:" + sql);//輸出sql查詢語句
            System.out.println(list.toString());

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

            if(rs.next()) {//從結果集中獲取最終的數量
                count = rs.getInt("count");
            }
        }
        //關閉資源
        BaseDao.closeResource(null,pstm,rs);

        return count;
    }

3. Service

    //根據用戶名或者角色查詢用戶總數
    public int getUserCount(String username,int userRole);

4. ServiceImpl

    //根據用戶名或者角色查詢用戶總數
    public int getUserCount(String username, int userRole) {

        Connection connection = BaseDao.getConnection();
        int count = 0;
        try {
            count = userDao.getUserCount(connection, username, userRole);
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            BaseDao.closeResource(connection,null,null);
        }
        return count;
    }

    @Test
    public void test() {//測試
        UserServiceImpl userService = new UserServiceImpl();
        int count = userService.getUserCount("李四",1);
        System.out.println(count);
    }

• 獲得用戶列表

1. UserDao

    //通過條件查詢獲得用戶列表
    public List<User> getUserList(Connection connection,String userName,int userRole,int currentPageNo,int pageSize) throws SQLException;

2. UserDaoImpl

//通過條件查詢獲得用戶列表
    public List<User> getUserList(Connection connection, String userName, int userRole, int currentPageNo, int pageSize) throws SQLException {
        PreparedStatement pstm = null;
        ResultSet rs = 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");
            List<Object> list = new ArrayList<Object>();
            if(userName != null && userName.length() > 0) {
                sql.append(" and u.userName like ?");
                list.add("%" + userName + "%");
            }
            if(userRole > 0) {
                sql.append(" and u.userRole = ?");
                list.add(userRole);
            }

            //在數據庫中定踱，分頁使用    limit(傳的兩個數值分別是開始位和總數)   startIndex畅哑，pageSize 呵恢；總數
            //startIndex  = （當前頁-1）*頁面大小--->對應前端頁面的第幾頁
            //0，5            1 - 1 = 0 * 01234
            //5挥唠，5            2 - 1 = 1 * 5唤锉，56789
            //10，5           3 - 1 = 2 * 10 10听系，11，12脑豹，13，14
            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" + sql.toString());
            System.out.println("sql--->?" + list.toString());

            rs = BaseDao.execute(connection,pstm,rs,sql.toString(),params);
            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,pstm,rs);
        }
        return userList;
    }

3. Service

    //根據條件查詢用戶列表
    public List<User> getUserList(String queryUserName, int queryUserRole,int currentPageNo, int pagaSize);

4. ServiceImpl

    //根據條件查詢用戶列表
    public List<User> getUserList(String queryUserName, int queryUserRole, int currentPageNo, int pagaSize) {
        Connection connection = null;
        List<User> userList = null;
        System.out.println("queryUserName-->" + queryUserName);
        System.out.println("queryUserRole-->" + queryUserRole);
        System.out.println("currentPageNo-->" + currentPageNo);
        System.out.println("pagaSize-->" + pagaSize);

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

        return userList;
    }

    @Test
    public void test() {//測試
        UserServiceImpl userService = new UserServiceImpl();
        List<User> userList = userService.getUserList(null,3,1,5);
        System.out.println(userList.size());
        for (User user : userList) {
            System.out.println(user.getUserName()+user.getId());
        }
    }

• 獲得角色列表

為了職責分明清晰衡查，可以把角色的操作單獨放到一個包中瘩欺，和pojo一一對應

1. RoleDao

public interface RoleDao {
    //獲得角色列表
    public List<com.vigil.pojo.Role> getRoleList(Connection connection) throws SQLException;

}

2. RoleDaoImpl

public class RoleDaoImpl implements RoleDao {

    //獲得角色列表
    public List<com.vigil.pojo.Role> getRoleList(Connection connection) throws SQLException {

        PreparedStatement pstm = null;
        ResultSet rs = null;
        ArrayList<com.vigil.pojo.Role> roleList = new ArrayList<com.vigil.pojo.Role>();

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

        return roleList;
    }

}

3. RoleService

public interface RoleService {
    //獲得角色列表
    public List<Role> getRoleList();

}

4. RoleServiceImpl

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

    //獲得角色列表
    public List<Role> getRoleList() {

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

    }

    @Test
    public void test() {
        RoleServiceImpl roleService = new RoleServiceImpl();
        List<Role> roleList = roleService.getRoleList();
        System.out.println(roleList.size());
        for(Role role : roleList) {
            System.out.println(role.getId()+role.getRoleName()+role.getRoleCode());
        }
    }
}

5. Servlet

1. 查詢獲得用戶列表

2. 從前端獲取數據

3. 獲得用戶的總數（分頁：上一頁、下一頁的情況）

4. 控制首頁和尾頁，如果頁面要小于1俱饿，就顯示第一頁的東西

5. 獲取用戶列表展示

6. 返回前端

//
    public void query(HttpServletRequest req, HttpServletResponse resp) {
        //查詢獲得用戶列表
        UserServiceImpl userService = new UserServiceImpl();
        List<User> userList = null;

        //第一次請求歌粥，是可以固定頁面大寫和頁數的,還有下拉欄默認值，建議把這些數值寫到配置文件拍埠，方便后期修改
        int pageSize = 5;
        int currentPageNo = 1;
        int queryUserRole = 0;

        //從前端獲取數據
        String queryUserName = req.getParameter("queryUserName");
        String tempUR = req.getParameter("queryUserRole");
        String pageIndex = req.getParameter("pageIndex");
        System.out.println("queryUserName:" + queryUserName + " tempUR: " + tempUR + " pageIndex: " + pageIndex);
        if (queryUserName == null) {
            queryUserName = "";
        }
        if(tempUR != null && !tempUR.equals("")) {//賦值0失驶，1，2
            queryUserRole = Integer.parseInt(tempUR);
        }
        if(pageIndex != null) {
            currentPageNo = Integer.parseInt(pageIndex);
        }

        //獲得用戶的總數（分頁：上一頁枣购、下一頁的情況）
        int totalCount = userService.getUserCount(queryUserName, queryUserRole);
        //總頁數支持
        PageSupport pageSupport = new PageSupport();
        pageSupport.setCurrentPageNo(currentPageNo);//當前頁面
        pageSupport.setPageSize(pageSize);//頁面大小
        pageSupport.setTotalCount(totalCount);//用戶總數

        int totalPageCount = pageSupport.getTotalPageCount();//總頁數
        //控制首頁和尾頁
        //如果頁面要小于1嬉探，就顯示第一頁的東西
        if(currentPageNo < 1) {
            currentPageNo = 1;
        } else if (currentPageNo > totalPageCount) {//當前頁大于最后一頁
            currentPageNo = totalPageCount;
        }

        //獲取用戶列表展示
        userList = userService.getUserList(queryUserName, queryUserRole, currentPageNo, pageSize);
        req.setAttribute("userList",userList);

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

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