参考示例：http://www.360doc.com/content/18/0409/18/8335678_744234144.shtml
java后端工程一 或者Android端 示例代码

package cn.gdchent.springbootsecurity.utils;

import okhttp3.*;

import java.io.File;
import java.io.IOException;

/**
 * 文件上传
 * http://www.360doc.com/content/18/0409/18/8335678_744234144.shtml
 */
public class OkHttpUploadUtils {

    // 使用OkHttp上传文件
    public static void uploadFile(File file) {
        OkHttpClient client = new OkHttpClient();
        MediaType contentType = MediaType.parse("application/octet-stream"); // 上传文件的Content-Type
        RequestBody fileBody = RequestBody.Companion.create(contentType, file); // 上传文件的请求体
        RequestBody requestBody=new MultipartBody.Builder()
                .setType(MultipartBody.FORM)
                .addFormDataPart("file","test.txt",fileBody)
                .build();
        Request request = new Request.Builder()
                .url("http://192.168.120.58:8086/uploadFile") // 上传地址
                .post(requestBody)
                .build();
        Call call = client.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onResponse(Call call, Response response) throws IOException {
                // 文件上传成功
                if (response.isSuccessful()) {
                    System.out.println("onResponse: " + response.body().string());
                } else {
                    System.out.println("onResponse: " + response.message());
                }
            }

            @Override
            public void onFailure(Call call, IOException e) {
                // 文件上传失败
                System.out.println("onFailure: " + e.getMessage());
            }
        });
    }
}

spring boot 工程后端接收代码如下：

 @PostMapping(path = "/uploadFile", produces = {"multipart/form-data","application/octet-stream"})
    @ResponseBody
    public HttpResultMap uploadFile(@RequestParam(value = "file") MultipartFile file){
        System.out.println("后端响应");
        //before文件夹根路径
        String uploadDirPath= ResourceFilePathUtils.ipaBeforeRootPath+ File.separator;
        File uploadDir=new File(uploadDirPath);
        if(!uploadDir.exists()){
            uploadDir.mkdirs();
        }
        String uploadFileName=file.getOriginalFilename();
        System.out.println("uploadFileName:"+uploadFileName);

        //如果这个文件存在了
        File uploadFile=new File(uploadDir,uploadFileName);
        if(uploadFile.exists()){
            uploadFile.delete(); //先删除再创建
        }
        //文件不存在 创建文件 然后写入数据到文件
        try {
            uploadFile.createNewFile();//创建文件
            Path path= Paths.get(uploadFile.getAbsolutePath());
            byte [] bytes=file.getBytes();
            Files.write(path,bytes);
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            return new HttpResultMap(
                    200,
                    "message",
                    new JSONObject().put("data","data")
            );
        }
    }