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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：
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@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。
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