Java Web实现用户登录功能

java web 学习记录一下

mvc结构实现mysql 连接
什么是mvc
- MVC是模型（model)、视图（view)、控制（controller）这三个单词上的首字母组成。它是一种应用模型，它的目的是实现Web系统的职能分工。避免all in one 所有代码全部写在一个文件里的一种分工模型。
实现简单登录功能
- 登录成功，进入sccess.jsp界面，失败返回首页，并输出密码错误

数据库简单编写

创建数据库

create database student;

创建表

create table tbl_user(     userId   varchar(11)  not null         primary key,     passWord varchar(255) not null );

导入数据

insert into tbl_user (userId,passWord) values ('admin','1234'); insert into tbl_user (userId,passWord) values ('张三','1234');

idea上准备工作

创建一个干净的meavn项目

Java Web实现用户登录功能

把该项目添加web项目

导入依赖

junit 是为了便于测试
其他是一些基础包
- mysql 连接数据库
- servlet-api servlet服务
- jsp-api
- jstl 写el表达式

<dependencies>         <dependency>             <groupId>mysql</groupId>             <artifactId>mysql-connector-java</artifactId>             <version>8.0.27</version>         </dependency>         <dependency>             <groupId>javax.servlet</groupId>             <artifactId>servlet-api</artifactId>             <version>2.5</version>         </dependency>         <dependency>             <groupId>javax.servlet.jsp</groupId>             <artifactId>jsp-api</artifactId>             <version>2.2.1-b02</version>         </dependency>         <dependency>             <groupId>javax.servlet</groupId>             <artifactId>jstl</artifactId>             <version>1.2</version>         </dependency>         <dependency>             <groupId>junit</groupId>             <artifactId>junit</artifactId>             <version>4.11</version>         </dependency>     </dependencies>

连接数据库

使用idea连接本地数据库

编写实体类User

public class User {     private String userId;     private String passWord;     public String getUserId() {         return userId;     }     public void setUserId(String userId) {         this.userId = userId;     }     public String getPassWord() {         return passWord;     }     public void setPassWord(String passWord) {         this.passWord = passWord;     } }

UserDao层接口

public interface UserDao {     public boolean getUser(String userID,String userPassWord); }

UserDaoImpl实现类

public class UserDaoImpl implements UserDao{      private String driver = "com.mysql.cj.jdbc.Driver";     private String url = "jdbc:mysql://localhost:3306/student";     private String root = "root";     private String password = "123456";      @Override     public boolean getUser(String userID,String userPassWord) {         boolean flag = false;         Connection conn = null;         PreparedStatement pstm = null;         ResultSet rs = null;         String sql = "select * from tbl_user where userId = ? and passWord = ?";         try {             Class.forName(driver);             conn = DriverManager.getConnection(url,root,password);             pstm = conn.prepareStatement(sql);             pstm.setString(1,userID);             pstm.setString(2,userPassWord);             rs = pstm.executeQuery();             if(rs.next()){                 flag = true;             }         } catch (Exception e) {             e.printStackTrace();         }finally{             try {                 rs.close();                 pstm.close();                 conn.close();             } catch (SQLException throwables) {                 throwables.printStackTrace();             }         }         return flag;     } }

UserService层接口

public interface UserService {      public boolean Login(String userId,String userPassWord); }

UserServiceImpl实现类

public class UserServiceImpl implements UserService{     @Override     public boolean Login(String userId, String userPassWord) {         boolean flag = false;         UserDao userDao = new UserDaoImpl();         flag = userDao.getUser(userId,userPassWord);         return flag;     } }

编写LoginServlet服务层

public class LoginServlet extends HttpServlet {     @Override     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {          boolean flag = false;         String userId = req.getParameter("userName");         String userPassWord = req.getParameter("userPassWord");         UserService userService = new UserServiceImpl();         flag = userService.Login(userId,userPassWord);         if(flag){             User user = new User();             user.setUserId(userId);             user.setPassWord(userPassWord);             req.getSession().setAttribute("user",user);             resp.sendRedirect("jsp/success.jsp");         }else{             req.setAttribute("msg","用户错误");             req.getRequestDispatcher("login.jsp").forward(req,resp);         }      }     @Override     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {         doGet(req, resp);     } }

配置web.xml文件

servlet3.0之后可以使用注解，不用配置这个文件，但是是初学者，还是先学会配置web.xml文件

<servlet>         <servlet-name>loginServlet</servlet-name>         <servlet-class>com.hjk.servlet.LoginServlet</servlet-class>     </servlet>     <servlet-mapping>         <servlet-name>loginServlet</servlet-name>         <url-pattern>/login</url-pattern>     </servlet-mapping>

编写login.jsp 界面

简单的写了一下，一个表单的提交功能

<form action="login" method="post">     <table>         <tr><span style="color: aquamarine">${requestScope.msg}</span></tr>         <tr>             <td>用户名：</td><td><input type="text" name="userName"/></td>         </tr>         <tr>             <td>密码</td><td><input type="password" name="userPassWord"/></td>         </tr>         <tr>             <td></td>             <td>             <input type="submit" value="submit"/>             <input type="reset" value="reset">             </td>         </tr>     </table> </form>

写一个登录成功界面sccess.jsp
-这个文件在web问价夹下面，本来想写一个拦截器，没有登录不能直接访问后面的界面，现在还没有写

<h1><span style="text-align: center"><span style="color: deeppink" >欢迎您，${sessionScope.user.userId}登录成功</span></span></h1>

如果登录失败就返回登录界面

idea默认会先访问index.jsp界面，这里在web.xml配置一下，让他直接访问login.jsp

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

已经可以登录了，但是还是存在中文乱码，编写一个过滤器CharacterEncoding，让它处理中文乱码

这个包必须导入import javax.servlet.*;

public class CharacterEncoding implements Filter {     @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");         servletRequest.setCharacterEncoding("utf-8"); 		//不执行filterChain就会一直卡在这里，相当于一直拦截         filterChain.doFilter(servletRequest,servletResponse);     }      @Override     public void destroy() {      } }

为过滤文件配置web.xml

    <filter>         <filter-name>characterEncoding</filter-name>         <filter-class>com.hjk.filter.CharacterEncoding</filter-class>     </filter>     <filter-mapping>         <filter-name>characterEncoding</filter-name>         <url-pattern>/*</url-pattern>     </filter-mapping>