Question

我正在解析Json并使用gson库在列表视图上显示。当我插入输入流时，我得到空值。你能告诉我哪里错了我会给你一些步骤我下载了2.3 Gson库。然后我做了getter和setter

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           package com.firstgroup.webservice;

        import java.io.ByteArrayOutputStream;
        import java.io.IOException;
        import java.io.InputStreamReader;
        import java.io.Reader;

        import org.apache.http.HttpResponse;
        import org.apache.http.HttpStatus;
        import org.apache.http.StatusLine;
        import org.apache.http.client.ClientProtocolException;
        import org.apache.http.client.HttpClient;
        import org.apache.http.client.methods.HttpGet;
        import org.apache.http.impl.client.DefaultHttpClient;

        import com.firstgroup.dto.Holder;
        import com.firstgroup.webservicecallback.WebserviceCallBack;
        import com.google.gson.Gson;

        import android.app.ProgressDialog;
        import android.content.Context;
        import android.os.AsyncTask;

        public class RequestTask extends AsyncTask<String, String, String>{
            private  WebserviceCallBack callBack;
            private ProgressDialog progressDialog;
            @Override
            protected void onPreExecute() {
                // TODO Auto-generated method stub
                progressDialog= new ProgressDialog((Context) callBack);
                super.onPreExecute();
                progressDialog.setTitle("Please Wait...");
                progressDialog.setMessage("Webservice Call...");
                progressDialog.setCancelable(true);
                progressDialog.show();
            }

            @Override
            protected String doInBackground(String... uri) {
                HttpClient httpclient = new DefaultHttpClient();
                HttpResponse response;
                String responseString = null;
                try {
                    response = httpclient.execute(new HttpGet(uri[0]));
                    StatusLine statusLine = response.getStatusLine();
                    if(statusLine.getStatusCode() == HttpStatus.SC_OK){
    // I am getting correct result here ...
                        Reader reader = new InputStreamReader(response.getEntity().getContent());
                        Gson gson = new Gson();
                        Holder response1 = gson.fromJson(reader, Holder.class);
                        ByteArrayOutputStream out = new ByteArrayOutputStream();
                        response.getEntity().writeTo(out);
                        out.close();
                        responseString = out.toString();
                    } else{
                        //Closes the connection.
                        response.getEntity().getContent().close();
                        throw new IOException(statusLine.getReasonPhrase());
                    }
                } catch (ClientProtocolException e) {
                    //TODO Handle problems..\
                    progressDialog.hide();
                } catch (IOException e) {
                    //TODO Handle problems..
                    progressDialog.hide();
                }
                return responseString;
            }

            @Override
            protected void onPostExecute(String result) {
                super.onPostExecute(result);
                //Do anything with response..
                if(callBack!=null){
                    callBack.getWebserviceResponse(result);
                }
                progressDialog.hide();
            }
            public void setObserver(WebserviceCallBack callback){
                callBack=callback;
            }


        }


        callback on main activity:

        @Override
        public void getWebserviceResponse(String response) {
            // TODO Auto-generated method stub
            Log.d("response", response);

            //can I used this code ?
// I want to used gson in main activity?
            Reader reader = new InputStreamReader(response.getEntity().getContent());
                Gson gson = new Gson();
                Holder response1 = gson.fromJson(reader, Holder.class);

        }

    }

Answer 1

添加课程：

public class Holder {
    List<deparaturedaseboarddto> data;
}

并更改以下代码：

deparaturedaseboarddto response1 = gson.fromJson(reader, deparaturedaseboarddto.class);

为：

Holder response1 = gson.fromJson(reader, Holder.class);

原因：您的json文本值有一个名为data的根对象，其列表为deparaturedaseboarddto。您正在尝试将此json值反序列化为deparaturedaseboarddto实例，但它是一个具有deparaturedaseboarddto列表的对象。

另外（与您的错误无关）;

1）类名以大写字母开头，字段名称是Java的驼峰。

2）如果java类的字段名称，您不必使用@SerializedName 与json值的字段名称相同。

3）下面的映射可能会阻止错误，因为json值中没有名为Result的字段。 @SerializedName（＆＃34; Result＆＃34;）可以删除或替换为@SerializedName（＆＃34; alertsId＆＃34;）

@SerializedName("Result")
int alertsId;

4）也可能想要替换下面的代码：

ByteArrayOutputStream out = new ByteArrayOutputStream();
response.getEntity().writeTo(out);
out.close();
responseString = out.toString();

使用：

responseString = gson.toJson(response1);

在评论中编辑第二个问题： 如果您想使用AsyncTask中的retrieve Holder实例，请进行以下编辑。

改变这个：

public class RequestTask extends AsyncTask<String, String, String>

用这个：

public class RequestTask extends AsyncTask<String, String, Holder>

和：

protected String doInBackground(String... uri)

用这个：

protected Holder doInBackground(String... uri)

和此：

protected void onPostExecute(String result)

用这个：

protected void onPostExecute(Holder result)

为什么Gson库在调试时显示空值？

1 个答案: