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。