SpringMVC教程之文件上传与下载详解

<form action="" enctype="multipart/form-data" method="post">
    <input type="file" name="file"/>
    <input type="submit">
</form>

try {
    processedRequest = checkMultipart(request);
    multipartRequestParsed = (processedRequest != request);
    ...

<form action="" enctype="multipart/form-data" method="post">
   <input type="file" name="file"/>
   <input type="submit">
</form>

<!--文件上传-->
<dependency>
   <groupId>commons-fileupload</groupId>
   <artifactId>commons-fileupload</artifactId>
   <version>1.3.3</version>
</dependency>

<!--文件上传配置-->
<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
   <!-- 请求的编码格式，必须和jSP的pageEncoding属性一致，以便正确读取表单的内容，默认为ISO-8859-1 -->
   <property name="defaultEncoding" value="utf-8"/>
   <!-- 上传文件大小上限，单位为字节（10485760=10M） -->
   <property name="maxUploadSize" value="10485760"/>
   <property name="maxInMemorySize" value="40960"/>
</bean>

<form action="/upload" enctype="multipart/form-data" method="post">
 <input type="file" name="file"/>
 <input type="submit" value="upload">
</form>

package com.wang.controller;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.multipart.commons.CommonsMultipartFile;
import javax.servlet.http.HttpServletRequest;
import java.io.*;
@Controller
public class FileController {
    //@RequestParam("file") 将name=file控件得到的文件封装成CommonsMultipartFile 对象
    //批量上传CommonsMultipartFile则为数组即可
    @RequestMapping("/upload")
    public String fileUpload(@RequestParam("file") CommonsMultipartFile file , HttpServletRequest request) throws IOException {
        //获取文件名 : file.getOriginalFilename();
        String uploadFileName = file.getOriginalFilename();
        //如果文件名为空，直接回到首页！
        if ("".equals(uploadFileName)){
            return "redirect:/index.jsp";
        }
        System.out.println("上传文件名 : "+uploadFileName);
        //上传路径保存设置
        String path = request.getServletContext().getRealPath("/upload");
        //如果路径不存在，创建一个
        File realPath = new File(path);
        if (!realPath.exists()){
            realPath.mkdir();
        }
        System.out.println("上传文件保存地址："+realPath);
        InputStream is = file.getInputStream(); //文件输入流
        OutputStream os = new FileOutputStream(new File(realPath,uploadFileName)); //文件输出流
        //读取写出
        int len=0;
        byte[] buffer = new byte[1024];
        while ((len=is.read(buffer))!=-1){
            os.write(buffer,0,len);
            os.flush();
        }
        os.close();
        is.close();
        return "redirect:/index.jsp";
    }
}

/*
 * 采用file.Transto 来保存上传的文件
 */
@RequestMapping("/upload2")
public String  fileUpload2(@RequestParam("file") CommonsMultipartFile file, HttpServletRequest request) throws IOException {
    //上传路径保存设置
    String path = request.getServletContext().getRealPath("/upload");
    File realPath = new File(path);
    if (!realPath.exists()){
        realPath.mkdir();
    }
    //上传文件地址
    System.out.println("上传文件保存地址："+realPath);
    //通过CommonsMultipartFile的方法直接写文件（注意这个时候）
    file.transferTo(new File(realPath +"/"+ file.getOriginalFilename()));
    return "redirect:/index.jsp";
}

@GetMapping("/download1")
@ResponseBody
public R download1(HttpServletResponse response){
    FileInputStream fileInputStream = null;
    ServletOutputStream outputStream = null;
    try {
        // 这个文件名是前端传给你的要下载的图片的id
        // 然后根据id去数据库查询出对应的文件的相关信息，包括url，文件名等
        String  fileName = "wang.jpg";

        //1、设置response 响应头，处理中文名字乱码问题
        response.reset(); //设置页面不缓存,清空buffer
        response.setCharacterEncoding("UTF-8"); //字符编码
        response.setContentType("multipart/form-data"); //二进制传输数据
        //设置响应头，就是当用户想把请求所得的内容存为一个文件的时候提供一个默认的文件名。
        //Content-Disposition属性有两种类型：inline 和 attachment 
        //inline ：将文件内容直接显示在页面 
        //attachment：弹出对话框让用户下载具体例子：
        response.setHeader("Content-Disposition",
                           "attachment;fileName="+ URLEncoder.encode(fileName, "UTF-8"));

		// 通过url获取文件
        File file = new File("D:/upload/"+fileName);
        //2、 读取文件--输入流
        fileInputStream = new FileInputStream(file);
        //3、 写出文件--输出流
        outputStream = response.getOutputStream();

        byte[] buffer = new byte[1024];
        int len;
        //4、执行写出操作
        while ((len = fileInputStream.read(buffer)) != -1){
            outputStream.write(buffer,0,len);
            outputStream.flush();
        }

        return R.success();
    } catch (IOException e) {
        e.printStackTrace();
        return R.fail();
    }finally {
        if( fileInputStream != null ){
            try {
                // 5、关闭输入流
                fileInputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if( outputStream != null ){
            try {
                // 5、关闭输出流
                outputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

@GetMapping("/download2")
public ResponseEntity<byte[]> download2(){
    try {
        String fileName = "wang.jpg";
        byte[] bytes = FileUtils.readFileToByteArray(new File("D:/upload/"+fileName));
        HttpHeaders headers=new HttpHeaders();
        // Content-Disposition就是当用户想把请求所得的内容存为一个文件的时候提供一个默认的文件名。
        headers.set("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName, "UTF-8"));
        headers.set("charsetEncoding","utf-8");
        headers.set("content-type","multipart/form-data");
        ResponseEntity<byte[]> entity=new ResponseEntity<>(bytes,headers, HttpStatus.OK);
        return entity;
    } catch (IOException e) {
        e.printStackTrace();
        return null;
    }
}