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

数据库准备

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');

项目创建与编写

idea上准备工作

创建一个干净的meavn项目

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>

乱码处理

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>