httpclient调用rest接口传参接收不到问题

记录HttpClient调用rest接口遇到的问题。
HttpClientUtil类如下：

package com.bjrxkj.interview

import org.apache.http.HttpResponse
import org.apache.http.NameValuePair
import org.apache.http.client.entity.UrlEncodedFormEntity
import org.apache.http.client.methods.CloseableHttpResponse
import org.apache.http.client.methods.HttpGet
import org.apache.http.client.methods.HttpPost
import org.apache.http.client.utils.URIBuilder
import org.apache.http.entity.ContentType
import org.apache.http.entity.StringEntity
import org.apache.http.impl.client.CloseableHttpClient
import org.apache.http.impl.client.HttpClients
import org.apache.http.message.BasicNameValuePair
import org.apache.http.util.EntityUtils

class HttpClientUtil {

    public static String doGet(String url, Map<String, String> param) {

        // 创建Httpclient对象
        CloseableHttpClient httpclient = HttpClients.createDefault();

        String resultString = "";
        CloseableHttpResponse response = null;
        try {
            // 创建uri
            URIBuilder builder = new URIBuilder(url);
            if (param != null) {
                for (String key : param.keySet()) {
                    builder.addParameter(key, param.get(key));
                }
            }
            URI uri = builder.build();

            // 创建http GET请求
            HttpGet httpGet = new HttpGet(uri);

            // 执行请求
            response = httpclient.execute(httpGet);
            // 判断返回状态是否为200
            if (response.getStatusLine().getStatusCode() == 200) {
                resultString = EntityUtils.toString(response.getEntity(), "UTF-8");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (response != null) {
                    response.close();
                }
                httpclient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return resultString;
    }

    public static String doGet(String url) {
        return doGet(url, null);
    }

    public static String doPost(String url, Map<String, String> param) {
        // 创建Httpclient对象
        CloseableHttpClient httpClient = HttpClients.createDefault();
        CloseableHttpResponse response = null;
        String resultString = "";
        try {
            // 创建Http Post请求
            HttpPost httpPost = new HttpPost(url);
            // 创建参数列表
            if (param != null) {
                List<NameValuePair> paramList = new ArrayList<>();
                for (String key : param.keySet()) {
                    paramList.add(new BasicNameValuePair(key, param.get(key)));
                }
                // 模拟表单
                UrlEncodedFormEntity entity = new UrlEncodedFormEntity(paramList,"utf-8");
                httpPost.setEntity(entity);
            }
            // 执行http请求
            response = httpClient.execute(httpPost);
            resultString = EntityUtils.toString(response.getEntity(), "utf-8");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                response.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        return resultString;
    }

    public static String doPost(String url) {
        return doPost(url, null);
    }

    public static String doPostJson(String url, String json) {
        // 创建Httpclient对象
        CloseableHttpClient httpClient = HttpClients.createDefault();
        CloseableHttpResponse response = null;
        String resultString = "";
        try {
            // 创建Http Post请求
            HttpPost httpPost = new HttpPost(url);
            // 创建请求内容
            StringEntity entity = new StringEntity(json, ContentType.APPLICATION_JSON);
            httpPost.setEntity(entity);
            // 执行http请求
            response = httpClient.execute(httpPost);
            resultString = EntityUtils.toString(response.getEntity(), "utf-8");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                response.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return resultString;
    }

}

使用doPost方法时，参数以Map形式传递，在接口服务端直接getParameter就能得到。
使用doPostJson方法时，参数是json字符串，在接口服务端无法通过getParameter获取。最后直接读流，得到参数：

        BufferedReader br = null;
        try {
            br = new BufferedReader(new InputStreamReader(request.getInputStream()));
        } catch (IOException e1) {
            e1.printStackTrace();
        }
        String line = null;
        StringBuilder sb = new StringBuilder();
        try {
            while((line = br.readLine())!=null){
                sb.append(line);
            }
        } catch (IOException e1) {
            e1.printStackTrace();
        }

        String reqBody = sb.toString();
        println reqBody;