E015Web学习笔记-Request和Respons（三）

╰+攻爆jí腚メ 2024-04-18 16:28 72阅读 0赞

# 一、ServletContext对象 #

## 1、概念 ##

代表整个web项目，可以和web项目的容器（服务器）通信；

### 2、功能 ###

①获取MIME类型；

②域对象：共享数据；

③获取文件的真实（服务器）路径

## 3、获取ServletContext对象 ##

### ①通过request获取： ###

req.getServletContext();

### ②通过HttpServlet获取： ###

getServletContext();
    因为MyServlet extends HttpServlet

备注：两种方式获取的是同一个ServletContext对象

## 4、ServletContext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 比如：text/html、image/jpeg

## 5、域对象 ##

### 方法： ###

1、void setAttribute(String name, Object value);
    2、Object getAttribute(String name);
    3、void removeAttribute(String name);

### ServletContext对象范围： ###

所有用户所有请求的数据；

**备注：使用的时候很谨慎！**

## 6、获取文件的真实（服务器）路径 ##

String getRealPath(String path);

### 读取文件代码示例： ###

package com.zibo.servlet;
    
    import javax.servlet.ServletContext;
    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.File;
    import java.io.FileInputStream;
    import java.io.IOException;
    
    @WebServlet("/my")
    public class MyServlet extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            System.out.println("doGet……");
            System.out.println("转到doPost……");
            this.doPost(req,resp);
        }
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            System.out.println("doPost……");
            ServletContext servletContext = req.getServletContext();
            //b.txt
            String realPath_b = servletContext.getRealPath("/b.txt");
            System.out.println(realPath_b);
            //D:\MyFiles\IdeaProjects\web\out\artifacts\web_war_exploded\b.txt
            File file_b = new File(realPath_b);
            FileInputStream fileInputStream_b = new FileInputStream(file_b);
            byte[] bytes_b = fileInputStream_b.readAllBytes();
            System.out.println("b.txt读取到内容："+new String(bytes_b));
            //c.txt
            String realPath_c = servletContext.getRealPath("/WEB-INF/c.txt");
            System.out.println(realPath_c);
            //D:\MyFiles\IdeaProjects\web\out\artifacts\web_war_exploded\WEB-INF\c.txt
            File file_c = new File(realPath_c);
            FileInputStream fileInputStream_c = new FileInputStream(file_c);
            byte[] bytes_c = fileInputStream_c.readAllBytes();
            System.out.println("c.txt读取到内容："+new String(bytes_c));
            //a.txt
            String realPath_a = servletContext.getRealPath("/WEB-INF/classes/a.txt");
            System.out.println(realPath_a);
            //D:\MyFiles\IdeaProjects\web\out\artifacts\web_war_exploded\WEB-INF\classes\a.txt
            File file_a = new File(realPath_a);
            FileInputStream fileInputStream_a = new FileInputStream(file_a);
            byte[] bytes_a = fileInputStream_a.readAllBytes();
            System.out.println("a.txt读取到内容："+new String(bytes_a));
        }
    }

### 运行结果： ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzI5Njg5MzQz_size_16_color_FFFFFF_t_70][]

### 文件位置备注： ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzI5Njg5MzQz_size_16_color_FFFFFF_t_70 1][]

# 二、文件下载 #

## 1、说明 ##

如果超链接指向的资源可以被浏览器解析，则会展示在浏览器里面，否则弹出下载框，询问下载；

## 2、通过响应头设置资源的打开方式 ##

conten-disposition:attachment;filename=xxx

## 3、步骤 ##

**第一步：定义页面，编辑超链接href属性，指向Servlet，传递资源名称filename；**

**第二步：定义Servlet**

第一步：获取文件名称；
    
    第二步：使用字节输入流，加载文件进内存；
    
    第三步：指定response的响应头：content-disposition:attachment;filename=xxx；
    
    第四步：将数据写到response输出流；

## 4、代码演示 ##

### html文件代码： ###

<!DOCTYPE html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Title</title>
    </head>
    <body>
        <a href="/my?filename=1.jpg">下载图片</a>
    </body>
    </html>

### 服务器代码： ###

package com.zibo.servlet;
    
    import javax.servlet.ServletContext;
    import javax.servlet.ServletException;
    import javax.servlet.ServletOutputStream;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.IOException;
    
    @WebServlet("/my")
    public class MyServlet extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            System.out.println("doGet……");
            System.out.println("转到doPost……");
            this.doPost(req,resp);
        }
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            System.out.println("doPost……");
            ServletContext servletContext = req.getServletContext();
            //1、获取文件名称——取参数
            String filename = req.getParameter("filename");
            //2、使用字节输入流，加载文件进内存——将文件读取到内存
            //1.jpg
            String realPath = servletContext.getRealPath("/img/"+filename);
            File file = new File(realPath);
            FileInputStream fileInputStream = new FileInputStream(file);
            //3、指定response的响应头：content-disposition:attachment;filename=xxx
            //设置响应头类型
            String mimeType = servletContext.getMimeType(filename);
            resp.setHeader("content-type",mimeType);
            //设置响应头打开方式
            resp.setHeader("content-disposition","attachment;filename="+filename);
            //4、将输入流中的数据写到输出流中
            ServletOutputStream stream = resp.getOutputStream();
            byte[] bytes = new byte[1024 * 8];
            int len = 0;
            while ((len = fileInputStream.read(bytes))!=-1){
                stream.write(bytes,0,len);
            }
            fileInputStream.close();
        }
    }

### 运行结果： ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzI5Njg5MzQz_size_16_color_FFFFFF_t_70 2][]

### 文件位置备注： ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzI5Njg5MzQz_size_16_color_FFFFFF_t_70 3][]

## 5、中文文件名乱码问题 ##

### DownloadUtils： ###

package com.zibo.servlet.utils;
    
    import java.io.UnsupportedEncodingException;
    import java.net.URLEncoder;
    import java.nio.charset.StandardCharsets;
    
    
    public class DownloadUtils {
    
        public static String getFileName(String agent, String filename) throws UnsupportedEncodingException {
            if (agent.contains("MSIE")) {
                // IE浏览器
                filename = URLEncoder.encode(filename, StandardCharsets.UTF_8);
                filename = filename.replace("+", " ");
            }else {
                // 其它浏览器
                filename = URLEncoder.encode(filename, StandardCharsets.UTF_8);
            }
            return filename;
        }
    }

### 改造后的服务器代码： ###

package com.zibo.servlet;
    
    import com.zibo.servlet.utils.DownloadUtils;
    
    import javax.servlet.ServletContext;
    import javax.servlet.ServletException;
    import javax.servlet.ServletOutputStream;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.IOException;
    
    @WebServlet("/my")
    public class MyServlet extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            System.out.println("doGet……");
            System.out.println("转到doPost……");
            this.doPost(req,resp);
        }
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            System.out.println("doPost……");
            ServletContext servletContext = req.getServletContext();
            //1、获取文件名称——取参数
            String filename = req.getParameter("filename");
            //2、使用字节输入流，加载文件进内存——将文件读取到内存
            //1.jpg
            String realPath = servletContext.getRealPath("/img/"+filename);
            File file = new File(realPath);
            FileInputStream fileInputStream = new FileInputStream(file);
            //3、指定response的响应头：content-disposition:attachment;filename=xxx
            //设置响应头类型
            String mimeType = servletContext.getMimeType(filename);
            resp.setHeader("content-type",mimeType);
            //设置响应头打开方式
            //解决中文乱码问题
            //1、获取user-agent请求头
            String header = req.getHeader("user-agent");
            //2、使用工具类方法编码文件名
            filename = DownloadUtils.getFileName(header, filename);
            resp.setHeader("content-disposition","attachment;filename="+filename);
            //4、将输入流中的数据写到输出流中
            ServletOutputStream stream = resp.getOutputStream();
            byte[] bytes = new byte[1024 * 8];
            int len = 0;
            while ((len = fileInputStream.read(bytes))!=-1){
                stream.write(bytes,0,len);
            }
            fileInputStream.close();
        }
    }

### 运行结果： ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzI5Njg5MzQz_size_16_color_FFFFFF_t_70 4][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzI5Njg5MzQz_size_16_color_FFFFFF_t_70]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/3914ae4e4c944a71b86c696ad7996a40.jpg
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzI5Njg5MzQz_size_16_color_FFFFFF_t_70 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/12c97df65e4c4225ad1db229e58fc492.jpg
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzI5Njg5MzQz_size_16_color_FFFFFF_t_70 2]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/5ac1c51b6a074c29bb2b5a7cd2b23029.jpg
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzI5Njg5MzQz_size_16_color_FFFFFF_t_70 3]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/b9c11613d1f34c8ba5d2265f8677fdda.jpg
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzI5Njg5MzQz_size_16_color_FFFFFF_t_70 4]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/a7bd3c3fc48f48ac8c591ed87bed0cf0.jpg