Android从restful服务读取json

Question

我正在尝试从服务获取响应（响应来自 json）。 我检查了设备是否已连接，现在我需要向服务发出 http 请求。我在其他问题上发现了我必须使用后台线程，但我不确定我是否有工作示例。

所以我需要找出如何连接到给定的 uri 并读取响应。 我的服务需要获取内容标头 application/json 才能返回 json，因此在请求之前我还需要设置此标头。

提前谢谢你

更新

package com.example.restfulapp;

import android.app.AlertDialog;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.provider.Settings;
import org.apache.http.HttpResponse;
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 org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;

import java.io.InputStreamReader;
import java.util.concurrent.ExecutionException;


public class MainActivity extends Activity {

    private int code = 0;
    private String value = "";
    private ProgressDialog mDialog;
    private Context mContext;
    private String mUrl ="http://192.168.1.13/myservice/upfields/";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        if (!isOnline())
        {
            displayNetworkOption ("MyApp", "Application needs network connectivity. Connect now?");
        }

        try {
            JSONObject s = getJSON(mUrl);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }

    }

    public class Get extends AsyncTask<Void, Void, String> {
        @Override
        protected String doInBackground(Void... arg) {
            String linha = "";
            String retorno = "";

            mDialog = ProgressDialog.show(mContext, "Please wait", "Loading...", true);

            HttpClient client = new DefaultHttpClient();
            HttpGet get = new HttpGet(mUrl);

            try {
                HttpResponse response = client.execute(get);

                StatusLine statusLine = response.getStatusLine();
                int statusCode = statusLine.getStatusCode();

                if (statusCode == 200) { // Ok
                    BufferedReader rd = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));

                    while ((linha = rd.readLine()) != null) {
                        retorno += linha;
                    }
                }
            } catch (ClientProtocolException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

            return retorno;
        }

        @Override
        protected void onPostExecute(String result) {
            mDialog.dismiss();
        }
    }

    public JSONObject getJSON(String url) throws InterruptedException, ExecutionException {
        setUrl(url);

        Get g = new Get();

        return createJSONObj(g.get());
    }

    private void displayNetworkOption(String title, String message){
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder
                .setTitle(title)
                .setMessage(message)
                .setPositiveButton("Wifi", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialogInterface, int i) {
                        startActivity(new Intent(Settings.ACTION_WIFI_SETTINGS));
                    }
                })
                .setNeutralButton("Data", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialogInterface, int i) {
                        startActivity(new Intent(Settings.ACTION_DATA_ROAMING_SETTINGS));
                    }
                })
                .setNegativeButton("No", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialogInterface, int i) {
                        return;
                    }
                })
                .show();
    }

    private boolean isOnline() {
        ConnectivityManager cm =
                (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo netInfo = cm.getActiveNetworkInfo();
        if (netInfo != null && netInfo.isConnectedOrConnecting()) {
            return true;
        }
        return false;
    }


}

这会引发错误： Gradle：找不到符号方法 setUrl(java.lang.String) Gradle：找不到符号方法 createJSONObj(java.lang.String)

Answer 1

在 EvZ 认为他生来无所不知的贬损回应之后，我最终得到了一个 MyTask 子类，我在我的 Activity 的 onCreate 中这样调用它。

new MyTask().execute(wserviceURL);



private class MyTask extends AsyncTask<String, Void, String> {
            @Override
            protected String doInBackground(String... urls) {
                URL myurl = null;
                try {
                    myurl = new URL(urls[0]);
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                }
                URLConnection connection = null;
                try {
                    connection = myurl.openConnection();
                } catch (IOException e) {
                    e.printStackTrace();
                }

                connection.setConnectTimeout(R.string.TIMEOUT_CONNECTION);
                connection.setReadTimeout(R.string.TIMEOUT_CONNECTION);

                HttpURLConnection httpConnection = (HttpURLConnection) connection;
                httpConnection.setRequestProperty("Content-Type", getString(R.string.JSON_CONTENT_TYPE));

                int responseCode = -1;
                try {
                    responseCode = httpConnection.getResponseCode();
                } catch (SocketTimeoutException ste) {
                    ste.printStackTrace();
                }
                catch (Exception e1) {
                    e1.printStackTrace();
                }
                if (responseCode == HttpURLConnection.HTTP_OK) {
                    StringBuilder answer = new StringBuilder(100000);

                    BufferedReader in = null;
                    try {
                        in = new BufferedReader(new InputStreamReader(httpConnection.getInputStream()));
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                    String inputLine;

                    try {
                        while ((inputLine = in.readLine()) != null) {
                            answer.append(inputLine);
                            answer.append("\n");
                        }
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                    try {
                        in.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                    httpConnection.disconnect();
                    return answer.toString();
                }
                else
                {
                    //connection is not OK
                    httpConnection.disconnect();
                    return null;
                }

            }

            @Override
            protected void onPostExecute(String result) {
                String userid = null;
                String username = null;
                String nickname = null;
                if (result!=null)
                {
                    try {
                        //do read the JSON here
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
                //stop loader dialog
                mDialog.dismiss();


            }

        }

lory105 的回答引导我找到答案附近的某个地方，thanx。

Answer 2

这里是一个如何处理 HTTP 响应并转换为 JSONObject 的示例：

/**
 * convert the HttpResponse into a JSONArray
 * @return JSONObject
 * @param response
 * @throws IOException 
 * @throws IllegalStateException 
 * @throws UnsupportedEncodingException 
 * @throws Throwable
 */
public static JSONObject processHttpResponse(HttpResponse response) throws UnsupportedEncodingException, IllegalStateException, IOException  {
    JSONObject top = null;
    StringBuilder builder = new StringBuilder();
    try {
            BufferedReader reader = new BufferedReader(
                                        new InputStreamReader(response.getEntity().getContent(), "UTF-8"));

            for (String line = null; (line = reader.readLine()) != null;) {
                builder.append(line).append("\n");
                }

        String decoded = new String(builder.toString().getBytes(), "UTF-8");
        Log.d(TAG, "decoded http response: " + decoded);

        JSONTokener tokener = new       JSONTokener(Uri.decode(builder.toString()));

        top = new JSONObject(tokener);



  } catch (JSONException t) {
        Log.w(TAG, "<processHttpResponse> caught: " + t + ", handling as string...");

    } catch (IOException e) {
        Log.e(TAG, "caught: " + e, e);
    } catch (Throwable t) {
        Log.e(TAG, "caught: " + t, t);
    }
     return top;
}

Answer 3

从 Android 3+ 开始，http 连接必须在单独的线程中完成。 Android 提供了一个名为 AsyncTask 的类来帮助您完成这项工作。

Here 你可以找到一个很好的 AsyncTask 示例，它执行 http 请求并接收 JSON 响应。

请记住，在 doInBackgroud(..) 方法中，您不能修改 UI，例如启动 Toast、更改活动或其他。您必须使用 onPreExecute() 或 onPostExecute() 方法来执行此操作。

添加

对于mDialog和mContext变量，添加下面的代码，创建JSONTask的时候写new JSONTask(YOUR_ACTIVITY)

public abstract class JSONTask extends AsyncTask<String, Void, String> {

  private Context context = null;
  ProgressDialog mDialog = new ProgressDialog();

  public JSONTask(Context _context){ context=_context; }

..