public static String doGet(String url, Map<String, String> params,
			String charset) {
		try {
			if (params != null && !params.isEmpty()) {
				List<NameValuePair> pairs = new ArrayList<NameValuePair>(
						params.size());
				for (Map.Entry<String, String> entry : params.entrySet()) {
					String value = entry.getValue();
					if (value != null) {
						pairs.add(new BasicNameValuePair(entry.getKey(), value));
					}
				}
				url += "?"
						+ EntityUtils.toString(new UrlEncodedFormEntity(pairs,
								charset));
			}
			HttpGet httpGet = new HttpGet(url);
			CloseableHttpResponse response = httpClient.execute(httpGet);
			int statusCode = response.getStatusLine().getStatusCode();
			if (statusCode != 200) {
				httpGet.abort();
				throw new RuntimeException("HttpClient,error status code :"
						+ statusCode);
			}
			HttpEntity entity = response.getEntity();
			String result = null;
			if (entity != null) {
				result = EntityUtils.toString(entity, "utf-8");
			}
			EntityUtils.consume(entity);
			response.close();
			return result;
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}