构造HTTP消息体采用HttpConnection实现文件上传
自己构造http消息体，用HttpConnection实现文件上传， 后台用的是Sinatra框架搞定服务端，很简洁，几行代码，比起servlet快捷不少
package com.hoot.regx;import java.io.File;import java.io.FileInputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.net.HttpURLConnection;import java.net.URL;import java.util.List;import java.util.Map;import java.util.Map.Entry;public class Regx {private static final String BOUNDARY = "-----------------7d4a6d158c9";private static final String TWO_HYPHENS = "--";private static final String END = "\r\n";/** * @param args * @throws IOException */public static void main(String[] args) throws IOException {URL url = new URL("http://localhost:4567/upload");HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setDoOutput(true);conn.setDoInput(true);conn.setRequestMethod("POST");conn.setRequestProperty("Connection", "Keep-Alive");conn.setRequestProperty("Charset", "UTF-8");conn.setRequestProperty("Content-Type","multipart/form-data;boundary=" + BOUNDARY);StringBuffer sb = new StringBuffer();//分解符sb.append(TWO_HYPHENS + BOUNDARY + END);//设置与上次文件相关信息sb.append("Content-Disposition: form-data; name=\"myfile\"; filename=\"test.txt\""+ END);//上传文件信息和文件的内容间必须有一个空行sb.append(END);//Map<String, List<String>> props = conn.getRequestProperties();//for(Entry<String, List<String>> prop : props.entrySet()){//System.out.println(prop.getKey() + ":" );//for(String str : prop.getValue()){//System.out.print(str);//}//System.out.println();//}System.out.println(sb.toString());byte[] data = sb.toString().getBytes();OutputStream os = conn.getOutputStream();os.write(data);//一下是文件数据FileInputStream fis = new FileInputStream(new File("test.txt"));byte[] buf = new byte[1024];int len = 0;while ((len = fis.read(buf)) > 0) {os.write(buf, 0, len);}String endStr = END + TWO_HYPHENS + BOUNDARY + TWO_HYPHENS + END;byte[] end_data = endStr.getBytes();System.out.println("<this is file content>");System.out.println(endStr);os.write(end_data);os.flush();os.close();fis.close();InputStream is = conn.getInputStream();while ((len = is.read(buf)) > 0) {System.out.write(buf, 0, len);}is.close();}}服务器端：
需要安装几个gem
sinatra haml
require 'rubygems'require 'sinatra'require 'haml' get '/' do 'Hello world' end# Handle GET-request (Show the upload form)get "/upload" do haml :uploadend # Handle POST-request (Receive and save the uploaded file)post "/upload" do logger.info "#{params}" unless params[:myfile] && (tmpfile = params[:myfile][:tempfile]) && (name = params[:myfile][:filename]) @error = "No file selected" logger.info "params #{@error} file: #{tmpfile} name: #{name} #{params}" return haml(:error) end directory = 'uploads' path = File.join(directory, name) File.open(path, "wb") do |f| f.write(tmpfile.read) end #File.copy(tempfile.path, path) @msg = "#{name}The file was successfully uploaded!"end够简洁吧，下面我吧两个haml文件也贴一下（haml文件放在在同级目录的views目录下）
upload.haml
%html %body %h1 File uploader! %form(method="post" enctype='multipart/form-data') %input(type='file' name='myfile') %br %input(type='submit' value='Upload!')
error.haml
%html %body %h1 File uploader error!
总结：自己构造Post请求有些繁琐，分隔符间空格很重要，如过看不明白可以用抓包工具传两个小文件 然后看看浏览器构造的请求体是什么格式，然后我们用字符串片接方式构造相同的结构，发送给服务器。
参考资料http://my.oschina.net/u/226973/blog/48897 sinatrarb.comhaml.info