发送POST请求

/**
 * 请求退款URL
 */
@Value("${request.returnpayurl}")
private String requestReturnpayurl;

//发送退款请求
String returnString = postByString(requestReturnpayurl, params, "text/xml");

/**
 * 发送POST请求
 *
 * @param url
 * @param params
 * @param bodyType
 * @return
 */
private String postByString(String url, String params, String bodyType) {
    HttpClient httpClient = new HttpClient();
    PostMethod postMethod = new PostMethod(url);
    try {
        StringRequestEntity entity = new StringRequestEntity(params, bodyType, "UTF-8");
        postMethod.setRequestEntity(entity);
        httpClient.executeMethod(postMethod);
        if (postMethod.getStatusCode() == HttpStatus.SC_OK) {
            String response = new String(postMethod.getResponseBodyAsString());
            return response;
        } else {
            return null;
        }
    } catch (HttpException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        postMethod.releaseConnection();
    }
    return null;
}