ServiceHandler类返回null值

Question

以下是代码和响应null。我该如何解决这个问题？

我想与服务器讨论登录，但JSON响应显示null值。我想将数据插入数据库并从数据库中获取数据，因为输出URL是正确的，并且通过该URL我可以插入数据，但是从设备中它无法正常工作。

    package com.example.old_login;

    import org.apache.http.HttpEntity;
    import org.apache.http.HttpResponse;
    import org.apache.http.NameValuePair;
    import org.apache.http.client.ClientProtocolException;
    import org.apache.http.client.entity.UrlEncodedFormEntity;
    import org.apache.http.client.methods.HttpGet;
    import org.apache.http.client.methods.HttpPost;
    import org.apache.http.client.utils.URLEncodedUtils;
    import org.apache.http.impl.client.DefaultHttpClient;
    import org.apache.http.util.EntityUtils;

    import java.io.IOException;
    import java.io.UnsupportedEncodingException;
    import java.util.List;

    public class ServiceHandler {
        public final static int GET = 1;
        public final static int POST = 2;
        static String response = null;

        public ServiceHandler() {
        }

        public String makeServiceCall(String url, int method) {
            return this.makeServiceCall(url, method, null);
        }

        public String makeServiceCall(String url, int method,
                                      List<NameValuePair> params) {
            try {
                // http client
                DefaultHttpClient httpClient = new DefaultHttpClient();
                HttpEntity httpEntity = null;
                HttpResponse httpResponse = null;

                // Checking http request method type
                if (method == POST) {
                    HttpPost httpPost = new HttpPost(url);
                    // adding post params
                    if (params != null) {
                        httpPost.setEntity(new UrlEncodedFormEntity(params));
                    }

                    httpResponse = httpClient.execute(httpPost);

                } else if (method == GET) {
                    // appending params to url
                    if (params != null) {
                        String paramString = URLEncodedUtils
                                .format(params, "utf-8");
                        url += "?" + paramString;
                    }
                    HttpGet httpGet = new HttpGet(url);

                    httpResponse = httpClient.execute(httpGet);

                }
                httpEntity = httpResponse.getEntity();
                response = EntityUtils.toString(httpEntity);

            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            } catch (ClientProtocolException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

            return response;
        }
    }