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 "";
    }  
}