非常簡單的小例子，註釋的很清楚。話不多少，看代碼

FileController.java

package com.imooc;

import org.apache.commons.io.IOUtils;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
 
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.multipart.MultipartFile;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
 
import java.io.OutputStream;
import java.util.Date;

/**
 * Created by 敲代碼的卡卡羅特
 * on 2018/4/15 16:52.
 */
@RequestMapping("/file")
@Controller
public class FileController {
    private String folder="E://update";
    @PostMapping
    public void upload(MultipartFile file) throws Exception {

        System.out.println(file.getName());  
 
//file  就是你前臺傳過來的參數名字
        System.out.println(file.getOriginalFilename());  //idea快捷鍵.txt  就是你文件的實際名字
        System.out.println(file.getSize()); //文件的大小

        //這裏只是一個小demo，按理說應該截取傳過來的後綴的，這裏寫死了。
        File localFile = new File(folder, new Date().getTime() + ".txt");
        //復制到這個文件中
        file.transferTo(localFile);
    }

    @GetMapping("/{id}")
    public void download(@PathVariable String id, HttpServletRequest request, HttpServletResponse response) throws Exception {
        //這個是jdk1.7的新用法，把流寫在try的括號裏面，就不用最後關閉流了。幫你做了
        try (InputStream inputStream = new FileInputStream(new File(folder, id + ".txt"));
             OutputStream outputStream = response.getOutputStream();) {
            //設置信息頭
            response.setContentType("application/x-download");
            response.addHeader("Content-Disposition", "attachment;filename=test.txt");//filename 就是你下載到本地的名字

            //意思是把輸入流復制到輸出流中
            IOUtils.copy(inputStream, outputStream);
            outputStream.flush();
        }

    }
}

依賴看引入的包。就不寫了。

springmvc實現上傳和下載