Android程序开发通过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：

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									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"; 

									} 

									} 

									}