Android端通过HttpURLConnection上传文件到服务器

Android端通过HttpURLConnection上传文件到服务器

一：实现原理

最近在做Android客户端的应用开发，涉及到要把图片上传到后台服务器中，自己选择了做Spring3 MVC HTTP API作为后台上传接口，android客户端我选择用HttpURLConnection来通过form提交文件数据实现上传功能，本来想网上搜搜拷贝一下改改代码就好啦，发现根本没有现成的例子，多数的例子都是基于HttpClient的或者是基于Base64编码以后作为字符串来传输图像数据，于是我不得不自己动手，参考了网上一些资料，最终实现基于HttpURLConnection上传文件的android客户端代码，废话少说，其实基于HttpURLConnection实现文件上传最关键的在于要熟悉Http协议相关知识，知道MIME文件块在Http协议中的格式表示，基本的传输数据格式如下：

其中boundary表示form的边界，只要按照格式把内容字节数写到HttpURLConnection的对象输出流中，服务器端的Spring Controller 就会自动响应接受，跟从浏览器页面上上传文件是一样的。

服务器端HTTP API， 我是基于Spring3 MVC实现的Controller，代码如下： 

@RequestMapping(value = "/uploadMyImage/{token}", method = RequestMethod.POST)
public @ResponseBody String getUploadFile(HttpServletRequest request, HttpServletResponse response,
        @PathVariable String token) {
    logger.info("spring3 MVC upload file with Multipart form");
    logger.info("servlet context path : " + request.getSession().getServletContext().getRealPath("/"));
    UserDto profileDto = userService.getUserByToken(token);
    String imgUUID = "";
    try {
        if (request instanceof MultipartHttpServletRequest && profileDto.getToken() != null) {
            MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest) request;
            logger.info("spring3 MVC upload file with Multipart form");
            // does not work, oh my god!!
            MultipartFile file = multipartRequest.getFiles("myfile").get(0);
            InputStream input = file.getInputStream();
            long fileSize = file.getSize();
            BufferedImage image = ImageIO.read(input);
            // create data transfer object
            ImageDto dto = new ImageDto();
            dto.setCreateDate(new Date());
            dto.setFileName(file.getOriginalFilename());
            dto.setImage(image);
            dto.setCreator(profileDto.getUserName());
            dto.setFileSize(fileSize);
            dto.setType(ImageAttachmentType.CLIENT_TYPE.getTitle());
            dto.setUuid(UUID.randomUUID().toString());
 
            /// save to DB
            imgUUID = imageService.createImage(dto);
            input.close();
        }
    } catch (Exception e) {
        e.printStackTrace();
        logger.error("upload image error", e);
    }
 
    return imgUUID;
}

Android客户端基于HttpURLConnection实现上传的代码，我把它封装成一个单独的类文件，这样大家可以直接使用，只要传入上传的URL等参数即可。代码如下：

package com.demo.http;
 
import java.io.BufferedInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Random;
 
import android.os.Handler;
import android.util.Base64;
import android.util.Log;
 
public class UploadImageTask implements APIURLConstants {
    private String requestURL = DOMAIN_ADDRESS + UPLOAD_DESIGN_IMAGE_URL; // default
    private final String CRLF = "\r\n";
    private Handler handler;
    private String token;
    public UploadImageTask(String token, Handler handler) {
        this.handler = handler;
        this.token = token;
    }
 
    public String execute(File...files) {
        InputStream inputStream = null;
        HttpURLConnection urlConnection = null;
        FileInputStream fileInput = null;
        DataOutputStream requestStream = null;
        handler.sendEmptyMessage(50);
        try {
            // open connection
            URL url = new URL(requestURL.replace("{token}", this.token));
            urlConnection = (HttpURLConnection) url.openConnection();
            // create random boundary
            Random random = new Random();
            byte[] randomBytes = new byte[16];
            random.nextBytes(randomBytes);
            String boundary = Base64.encodeToString(randomBytes, Base64.NO_WRAP);
 
            /* for POST request */
            urlConnection.setDoOutput(true);
            urlConnection.setDoInput(true);
            urlConnection.setUseCaches(false);
            urlConnection.setRequestMethod("POST");
            long size = (files[0].length() / 1024);
            if(size >= 1000) {
                handler.sendEmptyMessage(-150);
                return "error";
            }
            // 构建Entity form
            urlConnection.setRequestProperty("Connection", "Keep-Alive");
            urlConnection.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary);
            urlConnection.setRequestProperty("Cache-Control", "no-cache");
             
            // never try to chunked mode, you need to set a lot of things
            //  if(size > 400) {
            //      urlConnection.setChunkedStreamingMode(0);
            //  }
            //  else {
            //      urlConnection.setFixedLengthStreamingMode((int)files[0].length());
            //  }
            // end comment by zhigang on 2016-01-19
             
            /* upload file stream */
            fileInput = new FileInputStream(files[0]);
            requestStream = new DataOutputStream(urlConnection.getOutputStream());
            String nikeName = "myfile";
            requestStream = new DataOutputStream(urlConnection.getOutputStream());
            requestStream.writeBytes("--" + boundary + CRLF);
            requestStream.writeBytes("Content-Disposition: form-data; name=\"" + nikeName + "\"; filename=\"" + files[0].getName() + "\""+ CRLF);
            requestStream.writeBytes("Content-Type: " + getMIMEType(files[0]) + CRLF);
            requestStream.writeBytes(CRLF);
            // 写图像字节内容
            int bytesRead;
            byte[] buffer = new byte[8192];
            handler.sendEmptyMessage(50);
            while((bytesRead = fileInput.read(buffer)) != -1) {
                requestStream.write(buffer, 0, bytesRead);
            }
            requestStream.flush();
            requestStream.writeBytes(CRLF);
            requestStream.flush();
            requestStream.writeBytes("--" + boundary + "--" + CRLF);
            requestStream.flush();
            fileInput.close();
 
            // try to get response
            int statusCode = urlConnection.getResponseCode();
            if (statusCode == 200) {
                inputStream = new BufferedInputStream(urlConnection.getInputStream());
                String imageuuId = HttpUtil.convertInputStreamToString(inputStream);
                Log.i("image-uuid", "uploaded image uuid : " + imageuuId);
                handler.sendEmptyMessage(50);
                return imageuuId;
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(requestStream != null) {
                try {
                    requestStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(fileInput != null) {
                try {
                    fileInput.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (urlConnection != null) {
                urlConnection.disconnect();
            }
        }
        handler.sendEmptyMessage(50);
        return null;
    }
 
    private String getMIMEType(File file) {
        String fileName = file.getName();
        if(fileName.endsWith("png") || fileName.endsWith("PNG")) {
            return "image/png";
        }
        else {
            return "image/jpg";
        }
    }
 
}