文件上传、下载

待我称王封你为后i 2022-10-29 13:29 270阅读 0赞

### 文章目录 ###

*   *  文件上传
     *   *  jsp
         *  servlet
     *  文件下载

## 文件上传 ##

### jsp ###

jsp需要做如下配置：

1.  <input>标签的 `type="file"`，需要带上name属性
2.  <form>表单的 `method="post"`
3.  <form>表单的`enctype="multipart/form-data"`,表示以二进制流传输

### servlet ###

方法一：底层方法读写

protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
    
            InputStream inputStream = req.getInputStream(); // 获取字节流
            Reader reader = new InputStreamReader(inputStream); //将inputStream 字节流 转化成 字符流
            BufferedReader bufferedReader = new BufferedReader(reader); // 建立一个缓冲字符流，
    
            String path = req.getServletContext().getRealPath("file/copy.txt"); //获取文件的绝对路径
            OutputStream outputStream = new FileOutputStream(path); // 输出字节流
            Writer writer = new OutputStreamWriter(outputStream);  // 输出字符流
            BufferedWriter bufferedWriter = new BufferedWriter(writer);// 输出字符缓冲流
    
    
            String str = "";
            while((str = bufferedReader.readLine())!=null)
            { 
                bufferedWriter.write(str);
                bufferedWriter.flush();
    
            }
            bufferedWriter.close();
            writer.close();
            outputStream.close();
            bufferedReader.close();
            reader.close();
            inputStream.close();
        }

这种方法读取会包含一些浏览器的信息，以字节流读取可换行，字符流读取无法换行

--------------------

方法二：利用apache提供的包：`commons-fileupload`、`commons-io` 利用面向对象的思想去读写，包需要自己下载和配置到项目中。

fileupload包可将所有的请求信息解析为FileItem对象，通过对FileItem对象的操作完成读写功能。

protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
    
          DiskFileItemFactory diskFileItemFactory = new DiskFileItemFactory();
            ServletFileUpload servletFileUpload = new ServletFileUpload(diskFileItemFactory);
            try { 
                List<FileItem> list = servletFileUpload.parseRequest(req);
                for(FileItem item:list)
                { 
    // System.out.println(item.getName()); //文件名
    // System.out.println(item.getFieldName()); // input组件里的属性名字
                    if(item.isFormField()) //输入框
                    { 
                        String name = item.getFieldName();
                        String value = item.getString("UTF-8");
                        System.out.println(name+":"+value);
                    }
                    else //文件
                    { 
                        String name = item.getName();
                        long size = item.getSize();
                        System.out.println(name+":"+size+"Byte");
                        InputStream inputStream = item.getInputStream();
    // Reader reader = new InputStreamReader(inputStream);
    // BufferedReader bufferedReader = new BufferedReader(reader);
    
                        String path = req.getServletContext().getRealPath("file/"+name); //获取文件的绝对路径
                        OutputStream outputStream = new FileOutputStream(path); 
    // Writer writer = new OutputStreamWriter(outputStream);
    // BufferedWriter bufferedWriter = new BufferedWriter(writer);
                        int tmp = 0;
                        while ((tmp=inputStream.read())!= -1)
                        { 
                            outputStream.write(tmp);
                        }
    
    // String tmp = "";
    // while ((tmp = bufferedReader.readLine())!=null)
    // { 
    // bufferedWriter.write(tmp);
    // }
    // bufferedWriter.close();
    // writer.close();
                        outputStream.close();
    // bufferedReader.close();
    // reader.close();
                        inputStream.close();
                        System.out.println("上传成功");
                    }
                }
            } catch (FileUploadException e) { 
                e.printStackTrace();
            }
     }

以字节流读取、保存，可适用任何文件，字符流只是针对文本信息

## 文件下载 ##

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
    <html>
    <head>
        <title>Title</title>
    </head>
    <body>
     <a href="/download?type=jpg"> 1.jpg </a>
     <a href="/download?type=txt"> 1.txt </a>
    </body>
    </html>

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
            resp.setContentType("application/octet-stream"); //设置响应方式
            String type = req.getParameter("type");
            String fileName = "";
            if(type.equals("txt"))
            { 
                fileName = "1.txt";
            }
            if(type.equals("jpg"))
            { 
                fileName = "1.jpg";
            }
            resp.setHeader("Content-Disposition","attachment;filename="+fileName);//设置下载后的文件名
            OutputStream outputStream = resp.getOutputStream();//获取输出流
            String path  = req.getServletContext().getRealPath("file/"+fileName);//获取资源路径
    
            InputStream inputStream = new FileInputStream(path);
            int tmp =0;
            while ((tmp=inputStream.read())!=-1)
            { 
                outputStream.write(tmp);
            }
    
            inputStream.close();
            outputStream.close();
    
    
        }