Servlet总结

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简单的登录案例(Servlet)

Servlet学过后忘的太快了，所以，写一篇文章记录一下。下一次自己再忘了，还能再看看。这里复习的是一个简单的登录案例，顺便把JDBC复习一下。主要复习JDBC的JdbcTemplate、和druid连接池。

简单的登录案例实现步骤：

1.创建一个Maven项目

我们这里选的是带模版的Maven项目：

image-20200722205716389

记得一定要选好本地仓库哦~

不然Finsh会创建很慢的哦~

image-20200722205807623

如果在你的创建界面没有出现选择Maven仓库位置，请在下图找取：

image-20200722211509870

当然，要是没学习过Maven…你还是学一下吧，挺重要的…

2.pom.xml文件中需要导入依赖：JdbcTemplate、和druid连接池依赖、servlet依赖、junit依赖

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<dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.1.20</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.springframework/spring-jdbc -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-jdbc</artifactId>
            <version>5.2.7.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-tx</artifactId>
            <version>5.2.7.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>5.2.7.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-beans</artifactId>
            <version>5.2.7.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13</version>
        </dependency>
        <dependency>
            <groupId>commons-logging</groupId>
            <artifactId>commons-logging</artifactId>
            <version>1.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/com.mchange/mchange-commons-java -->
        <dependency>
            <groupId>com.mchange</groupId>
            <artifactId>mchange-commons-java</artifactId>
            <version>0.2.15</version>
        </dependency>
</dependencies>

打开你的Maven，如果这里不暴红，那就说明你导入的依赖很成功。

在这里插入图片描述

3.创建数据库，和SQL语句

这里只是演示如何实现登录案例，所以表较为简单。

就是一个名为user的表，里面只有username和password两个属性。这个建表语句大家应该都会，所以就不再阐述了。

image-20200722212702111

4.创建dao层的包和servlet层的包

在这里插入图片描述

5.先写dao层的代码

1.首先创建一个User类

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package main.liu.dao;

public class User {
    private String username;
    private String password;

    public User() {
    }

    @Override
    public String toString() {
        return "User{" +
                "username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }

    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

2.写一个properties文件用来放关于连接数据库的

在这里插入图片描述

jdbc.properties的内容

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driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql:///db_student?useSSL=false&useUnicode=true&characterEconding=UTF-8
username=root
password=131411
initialSize=5
maxActive=10
maxWait=3000

3.编写一个JDBC工具类:JDBCUtils

工具类一般都会写在一个包中，在dao层下创建一个utils包，写下如下代码。

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package main.liu.utils;

import com.alibaba.druid.pool.DruidDataSourceFactory;

import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;

public class JDBCUtils {
    private static DataSource ds;
    static {
        try {
            Properties properties=new Properties();
            properties.load(JDBCUtils.class.getClassLoader().getResourceAsStream("jdbc.properties"));
            ds= DruidDataSourceFactory.createDataSource(properties);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    
    //获取连接池方法
    public static DataSource getDataSource(){
        return ds;
    }
    //获取连接方法
    public static Connection getConnection() throws SQLException {
        return ds.getConnection();
    }
    //释放资源
    public static void close(Statement statement, Connection connection){
        close(null,statement,connection);
    }
    public static void close(ResultSet resultSet, Statement statement, Connection connection){
        if (resultSet!=null){
            try {
                resultSet.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (statement!=null){
            try {
                statement.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (connection!=null){
            try {
                statement.close();//归还
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

}

4.编写一个UserDao接口

为什么要编写接口呀？

DAO接口
为每个DAO声明接口的好处在于：

  1. 可以在尚未实现具体DAO的时候编写上层代码,如Service里对DAO的调用。
  2. 可以为DAO进行多实现,例如有JDBCDAO实现,MyBatisDAO实现,而不需要更改上层代码。
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package main.liu.dao;

import java.sql.SQLException;

public interface UserDao {
    User findByNamePassword(User loginUser) throws SQLException;
}

5.有了接口肯定要有实现类呀

实现类一般是在和UserDao处于同一级的一个目录Impl下。

所以，在dao层下建立一个Impl包。

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package main.liu.dao.Impl;
import main.liu.dao.User;
import main.liu.dao.UserDao;
import main.liu.utils.JDBCUtils;
import org.springframework.dao.DataAccessException;
import org.springframework.jdbc.core.BeanPropertyRowMapper;
import org.springframework.jdbc.core.JdbcTemplate;

import java.sql.SQLException;

public class UserDaoImpl implements UserDao {
    //声明JDBCTemplate共用

    @Override
    public User findByNamePassword(User loginUser) throws SQLException {
        try {
            JdbcTemplate template=new JdbcTemplate(JDBCUtils.getDataSource());
            //1.编写sql
            String sql="select * from user where username=? and password=?";
            //2.调用query方法
            User user = template.queryForObject(sql, new BeanPropertyRowMapper<User>(User.class), loginUser.getUsername(), loginUser.getPassword());
            return user;
        } catch (DataAccessException e) {
            e.printStackTrace();
            return null;
        }
    }
}

6.功能已经齐全，那测试一下啊！

在dao层创建一个test包，test包内创建一个test类进行测试一下

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package main.liu.Test;
import main.liu.dao.Impl.UserDaoImpl;
import main.liu.dao.User;
import org.junit.Test;
import java.sql.SQLException;
public class UserDaoTest {
   @Test
    public void Test1() throws SQLException {
       User user=new User();
       user.setUsername("刘畅");
       user.setPassword("131411");
       UserDaoImpl userDao = new UserDaoImpl();
       User user1 = userDao.findByNamePassword(user);
       System.out.println(user1);
   }
}

image-20200722221209721

测试成功后我们就开始编写servlet层的代码

6.编写servlet层代码

1.配置Tomcat运行环境

在这里插入图片描述

2.编写一个登录页面

这就是index.jsp的代码，这是展示了两个输入框和一个提交按钮。

注意：这是jsp文件。你会发现，你用Maven创建后在webapp/WEB-INF/index.jsp并没有下面代码的第一行<%@ page contentType="text/html;charset=UTF-8" language="java" %>。请注意，必须把这一句加上，不然tomcat识别不了这个jsp。

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<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>表单提交</title>
</head>
<body>
<form action="/Servlet_01_war/LoginServlet" method="post">
    <input name="username" placeholder="请输入用户名"><br/>
    <input type="text" name="password" placeholder="请输入密码"><br/>
    <input type="submit" value="提交">
</form>
<a href="/Servlet_01_war/LoginServlet">Servlet01</a>
</body>
</html>

3.创建servlet类

主要实现，当表单提交后跳转到LoginServlet,在LoginServlet中判断用户名和密码是否正确，如果不正确就跳转到defaultServlet类，如果成功就跳转到SuccessServlet类。

1.首先创建一个LoginServlet类

在这里插入图片描述

LoginServlet代码：

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package main.liu.servlet;

import main.liu.dao.Impl.UserDaoImpl;
import main.liu.dao.User;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.sql.SQLException;

@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws UnsupportedEncodingException {
        //设置编码
        request.setCharacterEncoding("utf-8");
        response.setContentType("text/html");
        response.setCharacterEncoding("utf-8");
        //创建userDao对象
        UserDaoImpl userDao = new UserDaoImpl();
        //从表单获取提交信息usernaem和password
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        //把提交的信息放在共享里，好在defaultServlet、SuccessServlet中获取
        request.setAttribute("username",username);
        request.setAttribute("password",password);
        //创建User对象，将username和password用set传进去
        User user=new User();
        user.setUsername(username);
        user.setPassword(password);
        try {
            //调用userDao的方法来查询
            User user1 = userDao.findByNamePassword(user);
            System.out.println(user.getUsername());
            System.out.println(user.getPassword());
            //在dao层，我们能查到就返回user，如果没有就返回null，所以在这里判断是否为空值来代替是否用户名密码正确
            //如果不为空，就跳转到SuccessServlet
            if (user1!=null){
                RequestDispatcher dispatcher = request.getRequestDispatcher("/SuccessServlet");
                dispatcher.forward(request,response);
            }else {
                //如果为空就跳转到defaultServlet
                RequestDispatcher requestDispatcher = request.getRequestDispatcher("/defaultServlet");
                requestDispatcher.forward(request,response);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } catch (ServletException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}
2.defaultServlet
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package main.liu.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/defaultServlet")
public class defaultServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        response.setCharacterEncoding("utf-8");
        response.getWriter().print("登录失败，用户名或密码错误！！！");
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

3.SuccessServlet
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package main.liu.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/SuccessServlet")
public class SuccessServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Object username = request.getAttribute("username");
        response.setContentType("text/html");
        response.setCharacterEncoding("utf-8");
        response.getWriter().print("欢迎用户"+username+"大降光临！！！");
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

7.OK，跑一下看看

在这里插入图片描述

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