Madness. Smbms (supermarket order management system)

SMBMS( Supermarket order management system )

Code ：（ It is suggested that static resources and sql Bring them here to use , Others write it for yourself to practice . Pay attention to modifying relevant configuration files .）

link :https://pan.baidu.com/s/12MmpF9msJVjLT1U77XYfRw
Extraction code :11fv

database ：

How to build a project ？

Consider whether to use Maven？ rely on , jar package .

1. Preparation for project construction

1. Building a maven web project .
2. To configure Tomcat.
3. Test whether the project can run .
4. Pom.xml Import what is needed in the project jar package .(jsp,Servlet,mysql drive ,jstl,standard…)

<dependencies>
  <dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
  </dependency>
  <!-- servlet rely on  -->
  <dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
  </dependency>
  <!-- JSP rely on  -->
  <dependency>
    <groupId>javax.servlet.jsp</groupId>
    <artifactId>javax.servlet.jsp-api</artifactId>
    <version>2.3.3</version>
  </dependency>
  <!--  Connect to database  -->
  <dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.47</version>
  </dependency>
  <!-- JSTL The dependency of expressions  -->
  <dependency>
    <groupId>javax.servlet.jsp.jstl</groupId>
    <artifactId>jstl-api</artifactId>
    <version>1.2</version>
  </dependency>
  <!-- standard Tag library  -->
  <dependency>
    <groupId>taglibs</groupId>
    <artifactId>standard</artifactId>
    <version>1.1.2</version>
  </dependency>
  <!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
  <dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.80</version>
  </dependency>
</dependencies>

5. Create project package structure .

6. Write entity class .(pojo)
   ROM mapping : surface — Class mapping .

7. Public class writing .

   1、 Database configuration file ：

driver = com.mysql.jdbc.Driver
url = jdbc:mysql://localhost:3306/smbms?useUnicode=true&characterEncoding=utf8&useSSL=true
username = root
password = newpass

​ 2、 Write the public class of the database ：

package com.kuang.dao;

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

// Public classes that operate databases .
public class BaseDao {
    

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

    // Static code block , Class is initialized when it is loaded .
    static {
    
        Properties properties = new Properties();
        // Read the corresponding resources through the class loader .
        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");
    }

  
    // Get a link to the database .
    public static Connection getConnection(){
    
        Connection connection = null;
        try {
    
            Class.forName(driver);
            connection = DriverManager.getConnection(url,username,password);
        } catch (Exception e) {
    
            e.printStackTrace();
        }
        return connection;
    }

  
    // Write query tool classes .
    public static ResultSet execute(Connection connection,PreparedStatement preparedStatement,ResultSet resultSet,String sql,Object[] params) throws SQLException {
    
        preparedStatement = connection.prepareStatement(sql);
        for (int i = 0; i < params.length; i++) {
    
            //setObject, Placeholders from 1 Start , But our array is from 0 At the beginning .
            preparedStatement.setObject(i+1,params[i]);
        }
        resultSet = preparedStatement.executeQuery();
        return resultSet;
    }

  
    // Write, add, delete and modify public methods .
    public static int execute(Connection connection,PreparedStatement preparedStatement,String sql,Object[] params) throws SQLException {
    
        preparedStatement = connection.prepareStatement(sql);
        for (int i = 0; i < params.length; i++) {
    
            //setObject, Placeholders from 1 Start , But our array is from 0 At the beginning .
            preparedStatement.setObject(i+1,params[i]);
        }
        int updateRows = preparedStatement.executeUpdate();
        return updateRows;
    }

  
    // Release resources .
    public static  boolean closeResourse(Connection connection,PreparedStatement preparedStatement,ResultSet resultSet){
    
        boolean flag = true;
        if (resultSet != null){
    
            try {
    
                resultSet.close();
                //GC Recycling 
                resultSet = null;
            } catch (SQLException throwables) {
    
                throwables.printStackTrace();
                flag = false;
            }
        }
        if (preparedStatement != null){
    
            try {
    
                preparedStatement.close();
                //GC Recycling 
                preparedStatement = null;
            } catch (SQLException throwables) {
    
                throwables.printStackTrace();
                flag = false;
            }
        }
        if (connection != null){
    
            try {
    
                connection.close();
                //GC Recycling 
                connection = null;
            } catch (SQLException throwables) {
    
                throwables.printStackTrace();
                flag = false;
            }
        }
        return false;
    }

}

​ 3、 Write a character encoding filter ( Don't forget to register filters )

package com.kuang.filter;

import javax.servlet.*;
import java.io.IOException;

public class CharacterEncodingFilter implements Filter {
    // Don't miss the wrong package. .

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
    
        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        servletResponse.setContentType("text/html");

        filterChain.doFilter(servletRequest,servletResponse);
    }

    @Override
    public void destroy() {
    

    }
}

<!-- Character encoding filter -->
<filter>
    <filter-name>CharacterEncodingFilter</filter-name>
    <filter-class>com.kuang.filter.CharacterEncodingFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

8. Import static resources (js,css,img,calendar)

2. Login function realization

1. Write front page ( Take it directly jsp Come and use )
2. Set the home page

<!-- Set up the welcome page -->
<welcome-file-list>
    <welcome-file>login.jsp</welcome-file>
</welcome-file-list>

3. To write dao Layer login user login interface

// adopt userCode and userPassword, Get the user to log in .
public User getLoginUser(Connection connection,String userCode,String userPassword) throws SQLException;

4. To write dao Implementation class of layer interface

// adopt userCode and userPassword, Get the user to log in .
@Override
public User getLoginUser(Connection connection, String userCode,String userPassword) throws SQLException {
    
    PreparedStatement pstm = null;
    ResultSet rs = null;
    User user = null;

    if (connection!=null){
    
        String sql = "select * from smbms_user where userCode = ? and userPassword = ?";
        Object[] params = {
    userCode,userPassword};
        rs = BaseDao.execute(connection,pstm,rs,sql,params);
        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.closeResourse(null,pstm,rs);
    }
    return user;
}

5. Business layer interface

// The user login .
public User login(String userCode,String userPassword);

6. Business layer implementation classes

// The business layer calls dao layer , So we're going to introduce Dao layer .
private UserDao userDao;
public UserServiceImpl() {
    // Parameterless constructors .
    userDao = new UserDaoImpl();
}


// The user login 
@Override
public User login(String userCode, String userPassword) {
    
    Connection connection = null;
    User user = null;
    try {
    
        connection = BaseDao.getConnection();
        // Call the corresponding specific database operation through the business layer .
        user = userDao.getLoginUser(connection, userCode,userPassword);
    } catch (SQLException throwables) {
    
        throwables.printStackTrace();
    }finally {
    
        BaseDao.closeResourse(connection,null,null);
    }
    return user;
}

7. To write Servlet

package com.kuang.servlet.user;

import com.kuang.pojo.User;
import com.kuang.service.user.UserServiceImpl;
import com.kuang.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;

//Servlet： Control layer , Call the business layer code .
public class LoginServlet extends HttpServlet {
    

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        System.out.println("LoginServlet---start...");

        // Get user name and password .
        String userCode = req.getParameter("userCode");
        String userPassword = req.getParameter("userPassword");

        // Compare it to the password in the database , Call the business layer ;
        UserServiceImpl userService = new UserServiceImpl();
        User user = userService.login(userCode, userPassword);// The person who logged in has been found here .

        if (user!=null){
    // Find this person , You can log in .
            // Put the user's information in Session in ;
            req.getSession().setAttribute(Constants.USER_SESSION,user);
            // Jump to home .
            resp.sendRedirect("jsp/frame.jsp");
        }else {
    // Check no one , Unable to log in .
            // Forward back to the login page , By the way, remind it , Wrong username or password .
            req.setAttribute("error"," Wrong username or password ！");
            req.getRequestDispatcher("login.jsp").forward(req,resp);
        }
    }

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

8. register Servlet

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

9. Test access , Ensure that the above functions can be successful

3. Login function optimization

Logout function :

Ideas ： remove session, Return to login page .

package com.kuang.servlet.user;

import com.kuang.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, HttpServletResponse resp) throws ServletException, IOException {
    
        // Remove the user's Constants.USER_SESSION
        req.getSession().removeAttribute(Constants.USER_SESSION);
        resp.sendRedirect(req.getContextPath()+"/login.jsp");// Return to landing page .
    }

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

register xml:

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

4. Login blocking optimization

So that users can not directly enter the successful login page .

Write a filter , And register .

package com.kuang.filter;

import com.kuang.pojo.User;
import com.kuang.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, FilterChain Chain) throws IOException, ServletException {
    
        HttpServletRequest request = (HttpServletRequest)req;
        HttpServletResponse response = (HttpServletResponse)resp;

        // filter ： from Session Get users .
        User user = (User)request.getSession().getAttribute(Constants.USER_SESSION);

        if (user==null){
    // Has been removed or logged off , Or login .
            response.sendRedirect("/SMBMS/error.jsp");
        }else{
    
            Chain.doFilter(req,resp);
        }
    }

    @Override
    public void destroy() {
    }
  
}

register xml

<!-- User login filter -->
<filter>
    <filter-name>SysFilter</filter-name>
    <filter-class>com.kuang.filter.SysFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>SysFilter</filter-name>
    <url-pattern>/jsp/*</url-pattern>
</filter-mapping>

test , Sign in , Cancellation , jurisdiction , Make sure that OK.

5. Password change

1. Import front-end material

<li><a href="${pageContext.request.contextPath }/jsp/pwdmodify.jsp"> Password change </a></li>

2. Write project , It is suggested to write from the bottom up

3. UserDao Interface

// Change the current user password .
public int updatePwd(Connection connection,int id,String password)throws SQLException;

4. UserDao Interface implementation class

// Change the current user password .
@Override
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.closeResourse(null,pstm,null);
    }
    return execute;
}

5. UserService layer

// According to the user id Change Password .
public boolean updatePwd(int id,String password)throws SQLException;

6. UserService Implementation class

// According to the user id Change Password .
@Override
public boolean updatePwd(int id, String pwd) throws SQLException {
    
    Connection connection = null;
    boolean flag = false;
    // Change Password .
    try {
    
        connection = BaseDao.getConnection();
        if (userDao.updatePwd(connection,id,pwd)>0){
    
            flag = true;
        }
    } catch (SQLException throwables) {
    
        throwables.printStackTrace();
    } finally {
    
        BaseDao.closeResourse(connection,null,null);
    }
    return flag;
}

7. servlet Remember to implement reuse , To extract the method ！

// Realization Servlet Reuse 
@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);
        }else if (method.equals("query")){
    
            this.query(req,resp);
        }else if (method.equals("add")){
    
            this.add(req,resp);
        }else if (method.equals("modifyexe")){
    
            this.modify(req,resp);
        }else if (method.equals("deluser")){
    
            this.delUser(req,resp);
        }else if (method.equals("ucexist")){
    
            this.userCodeExist(req, resp);
        }else if (method.equals("getrolelist")){
    
            this.getRoleList(req, resp);
        }else if (method.equals("view")){
    
            this.getUserById(req,resp,"userview.jsp");
        }else if (method.equals("modify")){
    
            this.getUserById(req,resp,"usermodify.jsp");
        }
}


// Change Password 
public void updatePwd(HttpServletRequest req, HttpServletResponse resp){
    
    // from Session Take it inside id;
    Object o = req.getSession().getAttribute(Constants.USER_SESSION);
    String newpassword = req.getParameter("newpassword");

    boolean flag = false;

    if (o!=null && !StringUtils.isNullOrEmpty(newpassword)){
    
        UserServiceImpl userService = new UserServiceImpl();

        try {
    
            flag = userService.updatePwd(((User)o).getId(),newpassword);
        } catch (SQLException throwables) {
    
            throwables.printStackTrace();
        }

        if (flag){
    
            req.setAttribute("message"," Password changed successfully , Please exit , Log in with the new password ！");
            // Password changed successfully , Remove current Session.
            req.getSession().removeAttribute(Constants.USER_SESSION);
        }else {
    
            req.setAttribute("message"," Password change failed .");
        }
    }else {
    
        req.setAttribute("message"," There is a problem with the new password .");
    }

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

register xml

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

8. test

6. Optimize password modification Ajax

1. alibaba.com fastjson（ Import ）

<!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
<dependency>
  <groupId>com.alibaba</groupId>
  <artifactId>fastjson</artifactId>
  <version>1.2.80</version>
</dependency>

2. Background code modification

// Verify old password ,session There is the user's password in .
public void pwdModify(HttpServletRequest req, HttpServletResponse resp){
    
    // from Session Take it inside id;
    Object o = req.getSession().getAttribute(Constants.USER_SESSION);
    String oldpassword = req.getParameter("oldpassword");

    // Omnipotent Map： Result set 
    Map<String, String> resultMap = new HashMap<String, String>();

    if (o==null){
    //Session It doesn't work ,session Out of date .
        resultMap.put("result","sessionerror");
    }else if (StringUtils.isNullOrEmpty(oldpassword)){
    // The password entered is empty .
        resultMap.put("result","error");
    }else {
    
        String userPassword = ((User)o).getUserPassword();//Session User's password in .
        if (oldpassword.equals(userPassword)){
    
            resultMap.put("result","true");
        }else {
    
            resultMap.put("result","false");
        }
    }

    try {
    
        resp.setContentType("application/json");
        PrintWriter writer = resp.getWriter();
        //JSONArray  alibaba.com JSON Tool class , Transformation format .
        /* resultMap = ["reslut","sessionerror","reslut","error"] Json Format  = {key:value} */
        writer.write(JSONArray.toJSONString(resultMap));
        writer.flush();
        writer.close();
    } catch (IOException e) {
    
        e.printStackTrace();
    }
}

3. test

7. User management implementation

1. Import paging tool class ——PageSupport
2. User list page import ——userlist.jsp

1、 Get the number of users

1. UserDao

// Query the total number of users according to user name or role .
public int getUserCount(Connection connection,String username,int userRole) throws  SQLException;

2. UserDaoImpl

// Query the total number of users according to user name or role .（ The hardest thing to understand sql）
@Override
public int getUserCount(Connection connection,String username,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 u,smbms_role r where u.userRole = r.id");
        ArrayList<Object> list = new ArrayList<Object>();// Store our parameters .

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

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

        // How to handle list Convert to array .
        Object[] params = list.toArray();

        System.out.println("getUserCount Of sql sentence ："+sql.toString());// Output the last complete sql sentence .
        rs = BaseDao.execute(connection, pstm, rs, sql.toString(), params);

        if (rs.next()){
    
            count = rs.getInt("count");// Get the final parameters from the result set .
        }
        BaseDao.closeResourse(null,pstm,rs);
    }
    return count;
}

3. UserService

// Number of query records .
public int getUserCount(String username,int userRole);

4. UserServiceImpl

// Number of query records .
@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 throwables) {
    
        throwables.printStackTrace();
    } finally {
    
        BaseDao.closeResourse(connection,null,null);
    }
    return count;
}

2、 Get the list of users

1. UserDao

// Query users by criteria .（ Pagination ）
public List<User> getUserList(Connection connection, String userName, int userRole, int currentPageNo, int pageSize) throws Exception;

2. UserDaoImpl

// Query users by criteria .（ Pagination ）
@Override
public List<User> getUserList(Connection connection, String userName, int userRole, int currentPageNo, int pageSize) throws Exception {
    

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

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

        // stay mysql In the database , Paging using  limit startIndex,pageSize ;  total 
        sql.append(" order by creationDate DESC limit ?,?");
        currentPageNo = (currentPageNo - 1) * pageSize;
        list.add(currentPageNo);
        list.add(pageSize);

        Object[] params = list.toArray();
        System.out.println("getUserList Of sql sentence ：" + sql.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.closeResourse(null, pstm, rs);
    }
    return userList;
}

3. UserService

// Query the user list according to the criteria .
public List<User> getUserList(String queryUserName, int queryUserRole, int currentPageNo, int pageSize);

4. UserServiceImpl

// Query the user list according to the criteria 
@Override
public List<User> getUserList(String queryUserName, int queryUserRole, int currentPageNo, int pageSize) {
    
    Connection connection = null;
    List<User> userList = null;

    try {
    
        connection = BaseDao.getConnection();
        userList = userDao.getUserList(connection, queryUserName, queryUserRole, currentPageNo, pageSize);
    } catch (Exception e) {
    
        e.printStackTrace();
    } finally {
    
        BaseDao.closeResourse(connection, null, null);
    }
    return userList;
}

3、 Get role operation

For the unity of our duties , We can put the operation of the role in a separate package , and pojo class .

1. RoleDao

public interface RoleDao {
    
    // Get a list of roles .
    public List<Role> getRoleList(Connection connection)throws SQLException;
}

2. RoleDaoIpml

public class RoleDaoImpl implements RoleDao{
    
  
    // Get a list of roles .
    @Override
    public List<Role> getRoleList(Connection connection) throws SQLException {
    

        PreparedStatement pstm = null;
        ResultSet resultSet = null;
        ArrayList<Role> rolelist = new ArrayList<>();

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

            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.closeResourse(null,pstm,resultSet);
        }
        return rolelist;
    }
}

3. RoleService

public interface RoleService {
    
    // Get a list of roles .
    public List<Role> getRoleList();
}

4. RoleServiceIpml

public class RoleServiceImpl implements RoleService{
    

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

    // Get a list of roles .
    @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.closeResourse(connection,null,null);
        }
        return roleList;
    }

}

4、 The user displays Servlet

1. Get the user's front-end data （ Inquire about ）.
2. Determine whether the request needs to be executed , Judge by the value of the parameter .
3. To achieve paging , You need to calculate the current page and the total page , Page size .
4. User list display .
5. Back to front .

// Query user list （ a key , difficulty ）.
public  void query(HttpServletRequest req, HttpServletResponse resp){
    

    // Get data from the front end ：
    String queryUserName = req.getParameter("queryname");
    String temp = req.getParameter("queryUserRole");
    String pageIndex = req.getParameter("pageIndex");// The default is 1.
    int queryUserRole = 0;

    // Get the list of users 
    UserServiceImpl userService = new UserServiceImpl();
    List<User> userList = null;

    // For the first time, this request , It must be the first page , Fixed page size ：
    int pageSize = 5;// You can configure this into the configuration file , Convenient for later modification ;
    int currentPageNo = 1;

    if (queryUserName==null){
    
        queryUserName = "";
    }
    if (temp!=null && !temp.equals("")){
    
        queryUserRole = Integer.parseInt(temp); // Assign a value to the query ！0,1,2,3
    }
    if (pageIndex!=null){
    
        currentPageNo = Integer.parseInt(pageIndex);
    }

    // Get the total number of users （ Pagination ： The previous page , On the next page ）
    int totalCount = userService.getUserCount(queryUserName,queryUserRole);

    // The total number of pages supports .
    PageSupport pageSupport = new PageSupport();
    pageSupport.setCurrentPageNo(currentPageNo);
    pageSupport.setPageSize(pageSize);
    pageSupport.setTotalCount(totalCount);
    int totalPageCount = pageSupport.getTotalPageCount();// There are several pages .

    // Control the first and last pages .
    // If the page is smaller than 1, Just show the first page .
    if (currentPageNo<1){
    
        currentPageNo = 1;
    }else if (currentPageNo>totalPageCount){
    // The current page is larger than the last page .
        currentPageNo = totalPageCount;
    }

    // Get user list display .
    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);
    req.setAttribute("queryUserName",queryUserName);
    req.setAttribute("queryUserRole",queryUserRole);

    // Back to front 
    try {
    
        req.getRequestDispatcher("userlist.jsp").forward(req,resp);
    } catch (ServletException e) {
    
        e.printStackTrace();
    } catch (IOException e) {
    
        e.printStackTrace();
    }
}

Suggest ： Little yellow duck debugging method ： Think aloud .

Schematic flow chart of the project ：

The code of the remaining two modules is directly CV Come and change it bug Add it （ Too lazy to write. ！）