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"; } } }
经过本人测试，效果杠杠的！！所以请忘记HttpClient这个东西，android开发再也不需要它了。