code: public static String coverMap2String(Map<String, String> data) {
  		TreeMap<String, String> tree = new TreeMap<String, String>();
  		Iterator<Entry<String, String>> it = data.entrySet().iterator();
  		while (it.hasNext()) {
  			Entry<String, String> en = it.next();
  			if (SDKConstants.param_signature.equals(en.getKey().trim())) {
  				continue;
  			}
  			tree.put(en.getKey(), en.getValue());
  		}
  		it = tree.entrySet().iterator();
  		StringBuffer sf = new StringBuffer();
  		while (it.hasNext()) {
  			Entry<String, String> en = it.next();
  			sf.append(en.getKey() + SDKConstants.EQUAL + en.getValue()
  					+ SDKConstants.AMPERSAND);
  		}
  		return sf.substring(0, sf.length() - 1);
  	}
docs: 将Map中的数据转换成key1=value1&key2=value2的形式 不包含签名域signature
  
  @param data
  待拼接的Map数据
  @return 拼接好后的字符串