post发送请求

public static String sendPost(String url, Map<String, String> params) {        URL u = null;        HttpURLConnection con = null;        // 构建请求参数        StringBuffer sb = new StringBuffer();        if (params != null) {            for (Entry<String, String> e : params.entrySet()) {                sb.append(e.getKey());                sb.append("=");                sb.append(e.getValue());                sb.append("&");            }            sb.substring(0, sb.length() - 1);        }        // 尝试发送请求        try {            u = new URL(url);            con = (HttpURLConnection) u.openConnection();            con.setRequestMethod("POST");            con.setDoOutput(true);            con.setDoInput(true);            con.setUseCaches(false);            con.setRequestProperty("Content-Type",                    "application/x-www-form-urlencoded");            OutputStreamWriter osw = new OutputStreamWriter(                    con.getOutputStream(), "UTF-8");            osw.write(sb.toString());            osw.flush();            osw.close();        } catch (Exception e) {            e.printStackTrace();        } finally {            if (con != null) {                con.disconnect();            }        }        // 读取返回内容        StringBuffer buffer = new StringBuffer();        try {            BufferedReader br = new BufferedReader(new InputStreamReader(                    con.getInputStream(), "UTF-8"));            String temp;            while ((temp = br.readLine()) != null) {                buffer.append(temp);                buffer.append("\n");            }        } catch (Exception e) {            e.printStackTrace();        }        return buffer.toString();    }