Java中BasicNameValuePair的使用，为什么不适用Map来代替BasicNameValuePair

1.BasicNameValuePair通常是用来封装post请求中的参数名称和值；

public String httpPost(Map<String, String> requestParams, String urlEncode) {
        HttpPost httpPost = null;
        String resp = "";
        try {
            // 参数设置
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            for (Map.Entry<String, String> entry : requestParams.entrySet()) {
                params.add(new BasicNameValuePair((String) entry.getKey(),
                        (String) entry.getValue()));
            }

            httpPost = new HttpPost(url);
            httpPost.setEntity(new UrlEncodedFormEntity(params, urlEncode));
            HttpResponse response = httpClient.execute(httpPost);
            int statusCode = response.getStatusLine().getStatusCode();
            if (statusCode != 200) 
            {
                return null;
            }
            HttpEntity httpEntity = response.getEntity();
            resp = EntityUtils.toString(httpEntity);
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (httpPost != null) {
                httpPost.abort();
            }
        }
        return resp;
    }pu