Android开发中Post方式上传文件（头像之类的）

/**
 * 文件上传
 * @param actionUrl:上传接口地址
 * @param files:需上传的文件集合
 * @return
 * @throws IOException
 */
public static String upLoadFilePost(String actionUrl, Map files) throws IOException {
    String BOUNDARY = java.util.UUID.randomUUID().toString();
    String PREFIX = "--", LINEND = "\r\n";
    String MULTIPART_FROM_DATA = "multipart/form-data";
    String CHARSET = "UTF-8";
    URL uri = new URL(actionUrl);
    HttpURLConnection conn = (HttpURLConnection) uri.openConnection();
    conn.setReadTimeout(5 * 1000);
    conn.setDoInput(true);// 允许输入
    conn.setDoOutput(true);// 允许输出
    conn.setUseCaches(false);
    conn.setRequestMethod("POST"); // Post方式
    conn.setRequestProperty("connection", "keep-alive");
    conn.setRequestProperty("Charsert", "UTF-8");
    conn.setRequestProperty("Content-Type", MULTIPART_FROM_DATA
            + ";boundary=" + BOUNDARY);

    DataOutputStream outStream = new DataOutputStream(conn.getOutputStream());
    // 发送文件数据
    if (files != null)
        for (Map.Entry file : files.entrySet()) {
            StringBuilder sb1 = new StringBuilder();
            sb1.append(PREFIX);
            sb1.append(BOUNDARY);
            sb1.append(LINEND);
            sb1.append("Content-Disposition: form-data; name=\"file\"; filename=\""
                            + file.getKey() + "\"" + LINEND);
            sb1.append("Content-Type: application/octet-stream; charset="
                    + CHARSET + LINEND);
            sb1.append(LINEND);
            outStream.write(sb1.toString().getBytes());
            InputStream is = new FileInputStream(file.getValue());
            byte[] buffer = new byte[1024];
            int len = 0;
            while ((len = is.read(buffer)) != -1) {
                outStream.write(buffer, 0, len);
            }

            is.close();
            outStream.write(LINEND.getBytes());
        }

    // 请求结束标志
    byte[] end_data = (PREFIX + BOUNDARY + PREFIX + LINEND).getBytes();
    outStream.write(end_data);
    outStream.flush();

    // 得到响应码
    int res = conn.getResponseCode();
    if (res == 200) {
        InputStream in = conn.getInputStream();
        InputStreamReader isReader = new InputStreamReader(in);
        BufferedReader bufReader = new BufferedReader(isReader);
        String line = "";
        String data = "";
        while ((line = bufReader.readLine()) != null) {
            data += line;
        }
        outStream.close();
        conn.disconnect();
        return data;
    }
    outStream.close();
    conn.disconnect();
    return "";
}

PS：在子线程中调用。