【超全必看】JavaWeb中Request、Response、ServletContext对象的使用详解（附示例代码）

其他 2020-03-31 10:21:53 阅读次数: 0

Request

获取请求行数据

  1. 获取请求方式
    String getMethod()
  2. (*)获取虚拟目录
    String getContextPath()
  3. 获取Servlet路径
    String getServletPath()
  4. 获取get方式请求参数
    String getQueryString()
  5. (*)获取请求URI和URL
    String getRequestURI()
    StringBuffer getRequestURL()
  6. 获取协议及版本
    String getProtocol()
  7. 获取客户机的IP地址
    String getRemoteAddr()

MyServlet类

@WebServlet("/demo1")
public class MyServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        String method = req.getMethod();
        System.out.println("请求方式"+method);
        String contextPath = req.getContextPath();
        System.out.println("虚拟目录"+contextPath);
        String servletPath = req.getServletPath();
        System.out.println("servlet路径"+servletPath);
        String queryString = req.getQueryString();
        System.out.println("get方式请求参数"+queryString);
        String requestURI = req.getRequestURI();
        System.out.println("请求URI"+requestURI);
        StringBuffer requestURL = req.getRequestURL();
        System.out.println("请求URL"+requestURL);
        String protocol = req.getProtocol();
        System.out.println("协议及版本"+protocol);
        String remoteAddr = req.getRemoteAddr();
        System.out.println("客户机IP地址"+remoteAddr);
    }


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

登录页：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <form action="demo1" method="post">
        <input name="username" >
        <input type="submit" value="submit">
    </form>
</body>
</html>

启动tomcat服务器（虚拟目录为/root）,访问login.html输入abc并提交
在这里插入图片描述
idea输出结果:

请求方式:  POST
虚拟目录:  /root
servlet路径:  /demo1
get方式请求参数:  null
请求URI:  /root/demo1
请求URL:  http://localhost:8080/root/demo1
协议及版本:  HTTP/1.1
客户机IP地址:  0:0:0:0:0:0:0:1

将form中post换成get方式，再次提交，结果：

请求方式:  GET
虚拟目录:  /root
servlet路径:  /demo1
get方式请求参数:  username=abc
请求URI:  /root/demo1
请求URL:  http://localhost:8080/root/demo1
协议及版本:  HTTP/1.1
客户机IP地址:  0:0:0:0:0:0:0:1

获取请求头数据

通过请求头的名称获取请求头的值
String getHeader(String name)
获取所有的请求头名称
Enumeration<String> getHeaderNames()

@WebServlet("/demo1")
public class MyServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        Enumeration<String> headerNames = req.getHeaderNames();
        while (headerNames.hasMoreElements()){
            //请求头的名称
            String requestName = headerNames.nextElement();
            System.out.print("请求头的名称:"+requestName);
            //请求头的值
            String header = req.getHeader(requestName);
            System.out.println("请求头的值："+header);
        }

    }


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

结果：

请求头的名称:host请求头的值：localhost:8080
请求头的名称:connection请求头的值：keep-alive
请求头的名称:upgrade-insecure-requests请求头的值：1
请求头的名称:user-agent请求头的值：Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.87 Safari/537.36
请求头的名称:sec-fetch-user请求头的值：?1
请求头的名称:accept请求头的值：text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3
请求头的名称:sec-fetch-site请求头的值：same-origin
请求头的名称:sec-fetch-mode请求头的值：navigate
请求头的名称:referer请求头的值：http://localhost:8080/root/login.html
请求头的名称:accept-encoding请求头的值：gzip, deflate, br
请求头的名称:accept-language请求头的值：zh-CN,zh;q=0.9
请求头的名称:cookie请求头的值：JSESSIONID=97917D6D1FAD1D35757576268BD7DED3; Idea-fe3516c6=7bffffd5-2036-45b3-9613-35358f80bd96; Webstorm-cca88c1f=3ab543cf-2131-4475-9a5b-d0cd0e5d216b; Hm_lvt_eaa57ca47dacb4ad4f5a257001a3457c=1573474754,1573523933,1573525590,1573526587

获取请求体数据

请求体：只有POST请求方式，才有请求体，在请求体中封装了POST请求的请求参数
步骤：

  1. 获取流对象
    BufferedReader getReader()获取字符输入流，只能操作字符数据
    ServletInputStream getInputStream()获取字节输入流，可以操作所有类型数据
  2. 再从流对象中拿数据

注册页

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <form action="demo1" method="post">
        <input name="username" type="text" >
        <input type="submit" value="注册">
    </form>
</body>
</html>

@WebServlet("/demo1")
public class MyServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        System.out.println(req.getMethod());
        //获取字符输入流
        BufferedReader reader = req.getReader();
        String line=null;
        //读取数据输出结果
        while((line=reader.readLine())!=null){
            System.out.println(line);
        }
    }


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

启动tomcat服务器，访问register.html注册页面，输入tkrs
在这里插入图片描述
结果：

POST
username=tkrs

获取请求参数通用方式

不论get还是post请求方式都可以使用下列方法来获取请求参数

  1. String getParameter(String name)根据参数名称获取参数值
  2. String[] getParameterValues(String name)根据参数名称获取参数值的数组
  3. Enumeration<String> getParameterNames()获取所有请求的参数名称
  4. Map<String,String[]> getParameterMap()获取所有参数的map集合

注册页：

扫描二维码关注公众号，回复： 10332907 查看本文章 
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <form action="demo1" method="post">
        <input name="username" type="text" placeholder="姓名："><br>
        <input name="password" type="password" placeholder="密码："><br>
        <input type="checkbox" name="hobby" value="game">游戏
        <input type="checkbox" name="hobby" value="sport">体育<br>
        <input type="submit" value="注册">
    </form>
</body>
</html>

servlet：

@WebServlet("/demo1")
public class MyServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        //1.  `String getParameter(String name)`根据参数名称获取参数值
        String name = req.getParameter("username");
        System.out.println("username的值为： "+name);
        System.out.println("-----------------");
        //2. `String[] getParameterValues(String name)`根据参数名称获取参数值的数组
        String[] hobbies = req.getParameterValues("hobby");
        System.out.println("hobby的值为: "+ Arrays.toString(hobbies));
        System.out.println("-----------------");
        //3. `Enumeration<String> getParameterNames()`获取所有请求的参数名称
        Enumeration<String> parameterNames = req.getParameterNames();
        System.out.println("所有请求参数为： ");
        while (parameterNames.hasMoreElements()){
            String s = parameterNames.nextElement();
            System.out.println(s);
        }
        System.out.println("-----------------");
        //4. `Map<String,String[]> getParameterMap()`获取所有参数的map集合
        Map<String, String[]> parameterMap = req.getParameterMap();
        System.out.println("所有参数map集合为： ");
        Set<String> set = parameterMap.keySet();
        for(String key:set){
            System.out.println("参数："+key);
            System.out.println("值：");
            String[] strings = parameterMap.get(key);
            for (String s : strings) {
                System.out.println(s);
            }
        }
        System.out.println("-----------------");
    }


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

运行：
在这里插入图片描述
结果：

username的值为： tkrs
-----------------
hobby的值为: [game, sport]
-----------------
所有请求参数为： 
username
password
hobby
-----------------
所有参数map集合为： 
参数：username
值：
tkrs
参数：password
值：
123
参数：hobby
值：
game
sport
-----------------

中文乱码问题：
get方式：tomcat 8 已经将get方式乱码问题解决了
post方式：会乱码
解决：在获取参数前，设置request的编码 request.setCharacterEncoding("utf-8");

请求转发

一种在服务器内部的资源跳转方式

  1. 步骤：
    1. 通过request对象获取请求转发器对象：
    RequestDispatcher getRequestDispatcher(String path)
    2. 使用RequestDispatcher对象来进行转发：
    forward(ServletRequest request, ServletResponse response)
  2. 特点：
    1. 浏览器地址栏路径不发生变化
    2. 只能转发到当前服务器内部资源中
    3. 转发是一次请求
		@WebServlet("/demo2")
		public class MyRes2 extends HttpServlet {
		    @Override
		    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
		        System.out.println("demo2被访问了");
		        req.getRequestDispatcher("/demo3").forward(req,resp);
		    }
		
		    @Override
		    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
		        this.doPost(req,resp);
		    }
		}
		------------
		@WebServlet("/demo3")
		public class MyRes3 extends HttpServlet {
		    @Override
		    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
		        System.out.println("demo3被访问了");
		    }
		
		    @Override
		    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
		        this.doPost(req,resp);
		    }
		}

访问demo2：

demo2被访问了
demo3被访问了

共享数据

  • 域对象：一个有作用范围的对象，可以在范围内共享数据
  • request域：代表一次请求的范围，一般用于请求转发的多个资源中共享数据
  • 方法：
    1. void setAttribute(String name,Object obj):存储数据
    2. Object getAttitude(String name):通过键获取值
    3. void removeAttribute(String name):通过键移除键值对
@WebServlet("/demo2")
public class MyRes2 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
        System.out.println("demo2被访问了");
        req.setAttribute("msg","demo2设置的消息");
        req.getRequestDispatcher("/demo3").forward(req,resp);
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
        this.doPost(req,resp);
    }
}
------------------
@WebServlet("/demo3")
public class MyRes3 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
        System.out.println("demo3被访问了");
        Object msg = req.getAttribute("msg");
        System.out.println(msg);
    }

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

访问demo2，输出：

demo2被访问了
demo3被访问了
demo2设置的消息

获取ServletContext

ServletContext getServletContext()

巩固Request知识的案例：用户登陆

  • 用户登录案例需求：

    1.编写login.html登录页面 username & password 两个输入框
    2.使用Druid数据库连接池技术,操作mysql，test数据库中user表
    3.使用JdbcTemplate技术封装JDBC
    4.登录成功跳转到SuccessServlet展示：登录成功！用户名,欢迎您
    5.登录失败跳转到FailServlet展示：登录失败，用户名或密码错误

  • 导入jar包，lib包要放在web下的WEB-INF目录内
    在这里插入图片描述

  • 在数据库test中创建user表

    CREATE TABLE USER(
	id INT PRIMARY KEY AUTO_INCREMENT,
	username VARCHAR(32) UNIQUE NOT NULL,
	`PASSWORD` VARCHAR(32) NOT NULL
);

  • 创建封装数据的User类

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

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    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;
    }

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

  • 创建JDBCUtils工具类

    public class JDBCUtils {
    //使用druid连接池
    private static DataSource source = null;
    static{
        try {
            Properties pros = new Properties();
            InputStream is = new FileInputStream("druid.properties");
            pros.load(is);
            //根据提供的DruidDataSourceFactory创建对应的DataSource对象
            source = DruidDataSourceFactory.createDataSource(pros);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    public static Connection getConnection() throws Exception {
        Connection conn = source.getConnection();
        return conn;
    }
    public static DataSource getDataSource() {
    	return source;
	}
}

    properties文件：

    url=jdbc:mysql://localhost:3306/test?serverTimezone=UTC&rewriteBatchedStatements=true
username=root
password=sjh2019
driverClassName=com.mysql.cj.jdbc.Driver
initialSize=10
maxActive=20
maxWait=1000
filters=wall

  • UserDao类

    	public class UserDao {
    
    private JdbcTemplate template = new JdbcTemplate(JDBCUtils.getDataSource());
    
    public User login(User user) throws Exception {
        try{
            //获取用户名
            String name = user.getUsername();
            //获取密码
            String password = user.getPassword();
            //1.编写sql
            String sql = "select * from user where username = ? and password = ?";
            //2.调用query方法
            User loginuser = template.queryForObject(sql,
                    new BeanPropertyRowMapper<>(User.class),
                    name, password);
            return loginuser;
        }catch (Exception e){
            e.printStackTrace();
            return null;
        }
    }
    
}

  • 登陆的Servlet

    @WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //设置字符集编码
        request.setCharacterEncoding("utf-8");
        //获取用户输入的用户名和密码
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        User user = new User();
        user.setUsername(username);
        user.setPassword(password);
        try {
            //查询该用户在数据库是否存在
            User loginuser = new UserDao().login(user);
            if(loginuser!=null){
                request.setAttribute("user",loginuser);
                request.getRequestDispatcher("/SuccessServlet").forward(request,response);
            }else {
                request.getRequestDispatcher("/FailServlet").forward(request,response);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }
}

  • SuccessServlet

    @WebServlet("/SuccessServlet")
public class SuccessServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        User user = (User) request.getAttribute("user");
        String name = user.getUsername();
        //设置编码
        response.setContentType("text/html;charset=utf-8");
        //输出
        response.getWriter().write("登录成功！"+name+",欢迎您");

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }
}

  • FailServlet

    @WebServlet("/FailServlet")
public class FailServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //设置编码
        response.setContentType("text/html;charset=utf-8");
        //输出
        response.getWriter().write("抱歉，用户名或密码错误");
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }
}

  • 测试
    插入一条用户记录

    INSERT INTO USER VALUES
(1,'fanxian','123');

    登陆登陆页面
    输入fanxian 123
    在这里插入图片描述

    在这里插入图片描述
    输入其他则报错：
    在这里插入图片描述
    在这里插入图片描述
    可使用beanutils包简化数据的封装，需要导入一个beanutils的jar包
    然后修改LoginServlet如下：

    @WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //设置字符集编码
        request.setCharacterEncoding("utf-8");
        User user = new User();
        Map<String, String[]> parameterMap = request.getParameterMap();
        try {
            //使用beanutils封装表单提交的数据
            BeanUtils.populate(user,parameterMap);
            //查询该用户在数据库是否存在
            User loginuser = new UserDao().login(user);
            if(loginuser!=null){
                request.setAttribute("user",loginuser);
                request.getRequestDispatcher("/SuccessServlet").forward(request,response);
            }else {
                request.getRequestDispatcher("/FailServlet").forward(request,response);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }
}

在这里插入图片描述

Response

功能：设置响应消息

  • 设置响应行

    1. 格式：HTTP/1.1 200 ok
    2. 设置状态码：setStatus(int sc)

  • 设置响应头：setHeader(String name, String value)

  • 设置响应体：

    1. 获取输出流
      字符输出流：PrintWriter getWriter()
      字节输出流：ServletOutputStream getOutputStream()
    2. 使用输出流，将数据输出到客户端浏览器

重定向案例

请求的Servlet

@WebServlet("/RequestServlet")
public class RequestServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //第一种方法 设置状态码和响应头
        //response.setStatus(302);
        //response.setHeader("location","ResponseServlet");//相对路径 相当于./ResponseServlet
        //或者response.setHeader("location","/root/ResponseServlet");（/root是我的虚拟目录）绝对路径


        //第二种方法
        response.sendRedirect("ResponseServlet");
        System.out.println("准备进行重定向");
    }

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

响应的Servlet

@WebServlet("/ResponseServlet")
public class ResponseServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("重定向成功");
    }

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

在浏览器访问
在这里插入图片描述
结果：
在这里插入图片描述
控制台输出：
在这里插入图片描述

  • 重定向的特点:redirect

    地址栏发生变化
    重定向可以访问其他站点(服务器)的资源
    重定向是两次请求。不能使用request对象来共享数据

  • 转发的特点：forward

    转发地址栏路径不变
    转发只能访问当前服务器下的资源
    转发是一次请求，可以使用request对象来共享数据

路径写法：

  • 路径分类
    • 相对路径：通过相对路径不可以确定唯一资源

      如：./index.html
      不以/开头，以.开头路径
      规则：找到当前资源和目标资源之间的相对位置关系
      ./：当前目录
      …/:后退一级目录

    • 绝对路径：通过绝对路径可以确定唯一资源
      • 如：http://localhost/day15/responseDemo2 /day15/responseDemo2
      • 以/开头的路径
  • 规则：判断定义的路径是给谁用的？判断请求将来从哪儿发出

    • 给客户端浏览器使用：需要加虚拟目录(项目的访问路径)

      • 建议虚拟目录动态获取：request.getContextPath()
      • <a> , 重定向…

      之前的重定向例子请求servlet代码可改为

      		String contextPath = request.getContextPath();
        response.sendRedirect(contextPath+"/ResponseServlet");
        System.out.println("准备进行重定向");

    • 给服务器使用：不需要加虚拟目录

      转发路径

      见上文Request中的转发案例

服务器输出字符数据到浏览器

  • 步骤：
    1. 获取字符输出流
    2. 输出数据
  • 乱码问题：
    1. PrintWriter pw = response.getWriter();获取的流的默认编码是ISO-8859-1
    2. 设置该流的默认编码
    3. 告诉浏览器响应体使用的编码
@WebServlet("/OutServlet")
public class OutServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //1.设置浏览器编码格式
        //方式一：response.setHeader("content-type","text/html;charset=utf-8");
        //方式二：
        response.setContentType("text/html;charset=utf-8");
        //3.获取输出流
        PrintWriter writer = response.getWriter();
        //4.输出
        writer.write("你好 response");

    }

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

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服务器输出字节数据到浏览器

  • 步骤：
    1. 获取字节输出流
    2. 输出数据
@WebServlet("/OutServlet2")
public class OutServlet2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //1.设置浏览器编码格式
        //方式一：response.setHeader("content-type","text/html;charset=utf-8");
        //方式二：
        response.setContentType("text/html;charset=utf-8");
        //3.获取输出流
        ServletOutputStream writer = response.getOutputStream();
        //4.输出
        writer.write("你好 response".getBytes(StandardCharsets.UTF_8));

    }

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

在这里插入图片描述
验证码实例：

@WebServlet("/CheckServlet")
public class CheckServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取图片对象
        int width=200;//宽
        int height=100;//高
        BufferedImage image=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
        //设置背景色
        Graphics graphics = image.getGraphics();//得到画笔
        graphics.setColor(Color.PINK);//设置颜色
        graphics.fillRect(0,0,width-1,height-1);//填充颜色
        //画边
        graphics.setColor(Color.blue);
        graphics.drawRect(0,0,width-1,height-1);
        //加验证码
        Random random = new Random();
        String s="qwertyuioplkjhgfdsazxcvbnmQWERTYUIOPLKJHGFDSAZXCVBNM0123456789";
        for (int i = 1; i <=4 ; i++) {
            int index = random.nextInt(s.length());
            char c = s.charAt(index);
            graphics.drawString(c+"",width/5*i,height/2);
        }
        //加干扰线
        graphics.setColor(Color.green);
        for (int i = 1; i <=4 ; i++) {
            int x1=random.nextInt(width);
            int x2=random.nextInt(width);
            int y1=random.nextInt(height);
            int y2=random.nextInt(height);
            graphics.drawLine(x1,y1,x2,y2);
        }
        //输出图片
        ImageIO.write(image,"jpg",response.getOutputStream());
    }

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

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ServletContext

获取

两种方式：
this.getServletContext()
request.getServletContext()

@WebServlet("/Get")
public class Get extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
        ServletContext servletContext1 = request.getServletContext();
        System.out.println(servletContext==servletContext1);
    }

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

打印结果为true

获取MIME类型

  • MIME类型:在互联网通信过程中定义的一种文件数据类型
    • 格式： 大类型/小类型
    • text/html
    • image/jpeg
  • 获取： String getMimeType(String file)
@WebServlet("/Get")
public class Get extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
        String filename="test.jpeg";
        String mimeType = servletContext.getMimeType(filename);
        System.out.println(mimeType);
    }

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

访问
在这里插入图片描述
结果：
在这里插入图片描述

域对象

共享数据
setAttribute(String name,Object value)设置数据
getAttribute(String name)获取数据
removeAttribute(String name)移除数据
作用范围：所有用户所有请求的数据

@WebServlet("/Set")
public class Set extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
        servletContext.setAttribute("msg","肖战是肖恩的孙子");
    }

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

@WebServlet("/Get")
public class Get extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
        String msg = (String) servletContext.getAttribute("msg");
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().write(msg);
    }

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

在这里插入图片描述
在这里插入图片描述

获取文件的真实(服务器)路径

在这里插入图片描述

@WebServlet("/Get")
public class Get extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
        String bPath = servletContext.getRealPath("/b.txt");
        System.out.println("b.txt的真实路径： "+bPath);
        String cPath = servletContext.getRealPath("/WEB-INF/c.txt");
        System.out.println("c.txt的真实路径： "+cPath);
        String aPath = servletContext.getRealPath("/WEB-INF/classes/a.txt");
        System.out.println("a.txt的真实路径： "+aPath);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {![在这里插入图片描述](https://img-blog.csdnimg.cn/20191226180214280.png)
        this.doPost(request, response);
    }
}

访问
在这里插入图片描述
控制台输出：
在这里插入图片描述

文件下载综合案例

在web目录下创建一个images目录存放一张图片
在这里插入图片描述
download.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <a href="/root/DownloadServlet?filename=a.jpg">点击下载图片</a>
</body>
</html>

DownloadServlet

@WebServlet("/DownloadServlet")
public class DownloadServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取文件名
        String filename = request.getParameter("filename");
        //利用servlet对象获取图片真实路径
        ServletContext servletContext = this.getServletContext();
        String realPath = servletContext.getRealPath("/images/"+filename);
        //输入流读取文件
        FileInputStream inputStream = new FileInputStream(realPath);
        //设置响应方式
        String mimeType = servletContext.getMimeType(filename);//获取文件mime类型
        response.setContentType(mimeType);
        response.setHeader("content-disposition","attachment;filename="+filename);//附件下载
        //输出流写出文件
        ServletOutputStream outputStream = response.getOutputStream();
        byte[] bytes=new byte[1024];
        int len=0;
        while((len=inputStream.read(bytes))!=-1){
            outputStream.write(bytes,0,len);
        }
        inputStream.close();//关闭输入流
    }

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

打开页面
在这里插入图片描述
在这里插入图片描述

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