java调用http请求json

最近遇到的问题，java如何调用http请求json：

public class HttpClientUtil {
    private static final String CONTENT_TYPE_TEXT_JSON = "text/json";
    private static final String APPLICATION_JSON = "application/json";

 public static String postJson(String url, String json) {
        CloseableHttpClient httpclient = HttpClients.createDefault();
        HttpPost httppost = new HttpPost(url);
        httppost.addHeader(HTTP.CONTENT_TYPE, APPLICATION_JSON);
        try {
            StringEntity se = new StringEntity(json);
            se.setContentType(CONTENT_TYPE_TEXT_JSON);
            se.setContentEncoding(new BasicHeader(HTTP.CONTENT_TYPE, APPLICATION_JSON));
            httppost.setEntity(se);
            CloseableHttpResponse response = httpclient.execute(httppost);
            try {
                HttpEntity entity = response.getEntity();
                if (entity != null) {
                    return EntityUtils.toString(entity, "UTF-8");
                }
            } finally {
                response.close();
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e1) {
            e1.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            // 关闭连接,释放资源
            try {
                httpclient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return "";
    }
}