<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>

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

<!--文件上傳配置-->
<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
   <!-- 請求的編碼格式，必須和jSP的pageEncoding屬性一致，以便正確讀取表單的內(nèi)容，默認(rèn)為ISO-8859-1 -->
   <property name="defaultEncoding" value="utf-8"/>
   <!-- 上傳文件大小上限，單位為字節(jié)（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") 將name=file控件得到的文件封裝成CommonsMultipartFile 對象
    //批量上傳CommonsMultipartFile則為數(shù)組即可
    @RequestMapping("/upload")
    public String fileUpload(@RequestParam("file") CommonsMultipartFile file , HttpServletRequest request) throws IOException {
        //獲取文件名 : file.getOriginalFilename();
        String uploadFileName = file.getOriginalFilename();
        //如果文件名為空，直接回到首頁！
        if ("".equals(uploadFileName)){
            return "redirect:/index.jsp";
        }
        System.out.println("上傳文件名 : "+uploadFileName);
        //上傳路徑保存設(shè)置
        String path = request.getServletContext().getRealPath("/upload");
        //如果路徑不存在，創(chuàng)建一個
        File realPath = new File(path);
        if (!realPath.exists()){
            realPath.mkdir();
        }
        System.out.println("上傳文件保存地址："+realPath);
        InputStream is = file.getInputStream(); //文件輸入流
        OutputStream os = new FileOutputStream(new File(realPath,uploadFileName)); //文件輸出流
        //讀取寫出
        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 來保存上傳的文件
 */
@RequestMapping("/upload2")
public String  fileUpload2(@RequestParam("file") CommonsMultipartFile file, HttpServletRequest request) throws IOException {
    //上傳路徑保存設(shè)置
    String path = request.getServletContext().getRealPath("/upload");
    File realPath = new File(path);
    if (!realPath.exists()){
        realPath.mkdir();
    }
    //上傳文件地址
    System.out.println("上傳文件保存地址："+realPath);
    //通過CommonsMultipartFile的方法直接寫文件（注意這個時候）
    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 {
        // 這個文件名是前端傳給你的要下載的圖片的id
        // 然后根據(jù)id去數(shù)據(jù)庫查詢出對應(yīng)的文件的相關(guān)信息，包括url，文件名等
        String  fileName = "wang.jpg";

        //1、設(shè)置response 響應(yīng)頭，處理中文名字亂碼問題
        response.reset(); //設(shè)置頁面不緩存,清空buffer
        response.setCharacterEncoding("UTF-8"); //字符編碼
        response.setContentType("multipart/form-data"); //二進制傳輸數(shù)據(jù)
        //設(shè)置響應(yīng)頭，就是當(dāng)用戶想把請求所得的內(nèi)容存為一個文件的時候提供一個默認(rèn)的文件名。
        //Content-Disposition屬性有兩種類型：inline 和 attachment 
        //inline ：將文件內(nèi)容直接顯示在頁面 
        //attachment：彈出對話框讓用戶下載具體例子：
        response.setHeader("Content-Disposition",
                           "attachment;fileName="+ URLEncoder.encode(fileName, "UTF-8"));

		// 通過url獲取文件
        File file = new File("D:/upload/"+fileName);
        //2、 讀取文件--輸入流
        fileInputStream = new FileInputStream(file);
        //3、 寫出文件--輸出流
        outputStream = response.getOutputStream();

        byte[] buffer = new byte[1024];
        int len;
        //4、執(zhí)行寫出操作
        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、關(guān)閉輸入流
                fileInputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if( outputStream != null ){
            try {
                // 5、關(guān)閉輸出流
                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就是當(dāng)用戶想把請求所得的內(nèi)容存為一個文件的時候提供一個默認(rèn)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;
    }
}