code: @Override
  	protected String sendGetRequest(HttpRequest httpRequest) throws AbstractCosException {
  		String url = httpRequest.getUrl();
  		HttpGet httpGet = null;
  		String responseStr = "";
  		int retry = 0;
  		int maxRetryCount = this.config.getMaxFailedRetry();
  		while (retry < maxRetryCount) {
  			try {
  				URIBuilder urlBuilder = new URIBuilder(url);
  				for (String paramKey : httpRequest.getParams().keySet()) {
  					urlBuilder.addParameter(paramKey, httpRequest.getParams().get(paramKey));
  				}
  				httpGet = new HttpGet(urlBuilder.build());
  			} catch (URISyntaxException e) {
  				String errMsg = "Invalid url:" + url;
  				LOG.error(errMsg);
  				throw new ParamException(errMsg);
  			}
  
  			httpGet.setConfig(requestConfig);
  			setHeaders(httpGet, httpRequest.getHeaders());
  
  			try {
  				HttpResponse httpResponse = httpClient.execute(httpGet);
  				;
  				int responseStatusCode = httpResponse.getStatusLine().getStatusCode();
  				if (responseStatusCode == 200 || responseStatusCode == 400) {
  					responseStr = EntityUtils.toString(httpResponse.getEntity(), "UTF-8");
  					return responseStr;
  				} else {
  					String errMsg = getErrorHttpResponseMsg(httpRequest, httpResponse.getStatusLine());
  					throw new NetworkException(errMsg);
  				}
  			} catch (ParseException | IOException e) {
  				++retry;
  				if (retry == maxRetryCount) {
  					String errMsg = getExceptionMsg(httpRequest, e.toString());
  					throw new ServerException(errMsg);
  				}
  			} finally {
  				httpGet.releaseConnection();
  			}
  		}
  		return responseStr;
  
  	}
docs: Get请求函数
  
  @param url
  @param headers
  额外添加的Http头部
  @param params
  GET请求的参数
  @return Cos服务器返回的字符串
  @throws Exception