public static String formUpload(String urlStr, Map<String, String> textMap, Map<String, String> fileMap, String uri) {
   String res = "";
   HttpURLConnection conn = null;
   String BOUNDARY = "---------------------------123821742118716"; // boundary就是request头和上传文件内容的分隔符
   try {
      URL url = new URL(urlStr);
      conn = (HttpURLConnection) url.openConnection();
      conn.setConnectTimeout(5000);
      conn.setReadTimeout(30000);
      conn.setDoOutput(true);
      conn.setDoInput(true);
      conn.setUseCaches(false);
      conn.setRequestMethod("POST");
      conn.setRequestProperty("Connection", "Keep-Alive");
      conn.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows; U; Windows NT 6.1; zh-CN; rv:1.9.2.6)");
      conn.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + BOUNDARY);

      OutputStream out = new DataOutputStream(conn.getOutputStream());
      // text
      if (textMap != null) {
         StringBuilder strBuilder = new StringBuilder();
         for (Object o : textMap.entrySet()) {
            Map.Entry entry = (Map.Entry) o;
            String inputName = (String) entry.getKey();
            String inputValue = http://www.mamicode.com/(String) entry.getValue();
            if (inputValue =http://www.mamicode.com/= null) {
               continue;
            }
            strBuilder.append("\r\n").append("--").append(BOUNDARY).append("\r\n");
            strBuilder.append("Content-Disposition: form-data; name=\"").append(inputName).append("\"\r\n\r\n");
            strBuilder.append(inputValue);
         }
         out.write(strBuilder.toString().getBytes());
      }

      // file
      if (fileMap != null) {
         for (Object o : fileMap.entrySet()) {
            Map.Entry entry = (Map.Entry) o;
            String inputName = (String) entry.getKey();
            String inputValue = http://www.mamicode.com/(String) entry.getValue();
            if (inputValue =http://www.mamicode.com/= null) {
               continue;
            }

            InputStream inputStream = new URL(uri).openStream();
            File file = new File(inputValue);
            String filename = file.getName();
            String contentType = new MimetypesFileTypeMap().getContentType(file);
            if (filename.endsWith(".png")) {
               contentType = "image/png";
            }
            if (contentType == null || contentType.equals("")) {
               contentType = "application/octet-stream";
            }

            StringBuilder strBuilder = new StringBuilder();
            strBuilder.append("\r\n").append("--").append(BOUNDARY).append("\r\n");
            strBuilder.append("Content-Disposition: form-data; name=\"").append(inputName).append("\"; filename=\"").append(filename).append("\"\r\n");
            strBuilder.append("Content-Type:").append(contentType).append("\r\n\r\n");

            out.write(strBuilder.toString().getBytes());

            DataInputStream in = new DataInputStream(inputStream);
            int bytes;
            byte[] bufferOut = new byte[1024];
            while ((bytes = in.read(bufferOut)) != -1) {
               out.write(bufferOut, 0, bytes);
            }
            in.close();
         }
      }

      byte[] endData = http://www.mamicode.com/("\r\n--" + BOUNDARY + "--\r\n").getBytes();
      out.write(endData);
      out.flush();
      out.close();

      // 读取返回数据
      StringBuilder strBuilder = new StringBuilder();
      BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
      String line;
      while ((line = reader.readLine()) != null) {
         strBuilder.append(line).append("\n");
      }
      res = strBuilder.toString();
      reader.close();
   } catch (Exception e) {
      System.out.println("发送POST请求出错。" + urlStr);
      e.printStackTrace();
   } finally {
      if (conn != null) {
         conn.disconnect();
      }
   }
   return res;
}

上传文件实现方法