Java:嵌入在 AsyncTask 中的 WebService

Java : a WebService asking embeded in a AsyncTask(Java:嵌入在 AsyncTask 中的 WebService)

问题描述

.作为一名年轻的 android 开发人员，我正在寻找一种从服务器获取 JSON 响应的方法.我开始研究 AsyncTask，但每次我需要询问 WebService 时，我都不愿意编写 AsyncTask.

. Hi, as a young android developer i was looking at a way to get a JSON response from a server. I started looking at AsyncTask but i not feeling comfortable to code an AsyncTask for each time i needed to ask a WebService.

然后我开始编写一个类(扩展 AsyncTask)来查询 URL(POST 或 GET)并提供包含来自服务器的响应的回调.我想得到一些反馈，它真的有用吗，而不是 AsyncTask 的无用覆盖，因为我一开始就错过了一些理解.我越编码，我就越怀疑.

Then i started to code a class (extends AsyncTask) that query an URL (POST or GET) and provide a callback containing the response from the server. I wanted to have some feedback, is it really useful, and not an useless overlay of an AsyncTask cause i missed understand something at the beginning. The more i code it, the more i doubt.

提前感谢您的反馈.

这是我用来查询我的班级服务器的代码:

Here's the code i use to query a server with my class :

HashMap<String, String> parameters = new HashMap<String, String>();
parameters.put("address", "sidney");
parameters.put("sensor", "false");

WebServiceAsyncTask asyncWS = new WebServiceAsyncTask(MainActivity.this);
asyncWS.setParameters(parameters);
asyncWS.execute(
        "http://maps.googleapis.com/maps/api/geocode/json",
        WebServiceAsyncTask.GET,
        new WebServiceAsyncTaskCallback() {
            @Override
            void callbackMethod(String result) {
                Toast.makeText(getApplicationContext(), result, Toast.LENGTH_SHORT).show();
            }
        }
);

这是我的 WebServiceAsyncTask 的代码:

Here's the code of my WebServiceAsyncTask :

import android.app.ProgressDialog;
import android.content.Context;
import android.net.Uri;
import android.os.AsyncTask;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.StatusLine;
import org.apache.http.client.HttpClient;
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.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.protocol.HTTP;
import org.apache.http.util.EntityUtils;

import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

/**
 * Anthony Raymond
 */
public class WebServiceAsyncTask extends AsyncTask<Object, String, String> {
    public static final String GET = "GET";
    public static final String POST = "POST";

    private static final String PROGRESS_TEXT_PREPARING = "Preparing request";
    private static final String PROGRESS_PERCENT_PREPARING = "25";
    private static final String PROGRESS_TEXT_CONNECTION_SERVER = "Connecting to the server";
    private static final String PROGRESS_PERCENT_CONNECTION_SERVER = "50";
    private static final String PROGRESS_TEXT_PARSING = "Parsing received data";
    private static final String PROGRESS_PERCENT_PARSING = "75";
    private static final String PROGRESS_TEXT_END = "Process ended";
    private static final String PROGRESS_PERCENT_END = "100";


    private Context context;
    private HashMap<String, String> mData = new HashMap<String, String>();
    private ProgressDialog progressDialog;


    private WebServiceAsyncTaskCallback callbackClass;

    /**
     * If a Context is passed, a ProgressDialog will be displayed
     * NEED TO PASS Context LIKE THIS :
     * MyActivity.this
     * DO NOT USE getApplicationContext()
     * @param applicationContext
     */
    public WebServiceAsyncTask(Context applicationContext)
    {
        this.context = applicationContext;
    }

    /**
     * Create a WebServiceAsyncTask.
     * Usage : add request parameter by passing an HashMap<String, String> with the setParameter Method, then call
     * .execute(String url, WebServiceAsyncTask constant (GET or SET), WebServiceAsyncTaskCallback callback)
     * exemple :
     * HashMap<String, String> parameters = new HashMap<String, String>();
     * parameters.put("address", "Sidney");
     * parameters.put("sensor", "false");
     * WebServiceAsyncTask asyncWS = new WebServiceAsyncTask(MainActivity.this);
     * asyncWS.setParameters(parameters);
     * asyncWS.execute(
     *      "http://maps.googleapis.com/maps/api/geocode/json",
     *      WebServiceAsyncTask.GET,
     *      new WebServiceAsyncTaskCallback() {
     *          @Override
     *          void callbackMethod(String result) {
     *              Toast.makeText(getApplicationContext(), result, Toast.LENGTH_SHORT).show();
     *          }
     *      }
     * );
     */
    public WebServiceAsyncTask()
    {
        this.context = null;
    }

    private void prepareProgressDialog()
    {
        if (this.context != null)
        {
            this.progressDialog = new ProgressDialog(this.context);
            this.progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            this.progressDialog.setCancelable(true);
            this.progressDialog.setTitle("Please Wait...");
            this.progressDialog.setMessage(PROGRESS_TEXT_PREPARING);
            this.progressDialog.setProgress(Integer.parseInt(PROGRESS_PERCENT_PREPARING));
        }
    }
    private String getPostResponse(String url)
    {
        byte[] result;
        String str = "";
        HttpClient client = new DefaultHttpClient();

        HttpPost http = new HttpPost(url);
        // set up post data
        List<NameValuePair> nameValuePair = new ArrayList<NameValuePair>();
        for (String key : this.mData.keySet()) {
            nameValuePair.add(new BasicNameValuePair(key, this.mData.get(key)));
        }

        UrlEncodedFormEntity urlEncodedFormEntity;
        try
        {

            urlEncodedFormEntity = new UrlEncodedFormEntity(nameValuePair);
            http.setEntity(urlEncodedFormEntity);
            this.publishProgress(PROGRESS_TEXT_CONNECTION_SERVER, PROGRESS_PERCENT_CONNECTION_SERVER);
            HttpResponse response = client.execute(http);
            StatusLine statusLine = response.getStatusLine();

            if(statusLine.getStatusCode() == HttpURLConnection.HTTP_OK)
            {
                this.publishProgress(PROGRESS_TEXT_PARSING, PROGRESS_PERCENT_PARSING);
                result  = EntityUtils.toByteArray(response.getEntity());
                str     = new String(result, HTTP.UTF_8);
            }
        }
        catch (UnsupportedEncodingException e)
        {
            e.printStackTrace();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        return str;
    }
    private String getGetResponse(String url)
    {
        byte[] result;
        String str = "";
        HttpClient client = new DefaultHttpClient();

        try
        {
            // set up get data and URL
            Uri.Builder uri = Uri.parse(url).buildUpon();

            for (String key : this.mData.keySet()) {
                uri.appendQueryParameter(key, this.mData.get(key));
            }

            HttpGet http = new HttpGet(String.valueOf(uri));
            this.publishProgress(PROGRESS_TEXT_CONNECTION_SERVER, PROGRESS_PERCENT_CONNECTION_SERVER);
            HttpResponse response = client.execute(http);
            StatusLine statusLine = response.getStatusLine();

            if(statusLine.getStatusCode() == HttpURLConnection.HTTP_OK)
            {
                this.publishProgress(PROGRESS_TEXT_PARSING, PROGRESS_PERCENT_PARSING);
                result  = EntityUtils.toByteArray(response.getEntity());
                str     = new String(result, HTTP.UTF_8);
            }
        }
        catch (UnsupportedEncodingException e)
        {
            e.printStackTrace();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        return str;
    }
    public void setParameters(HashMap<String, String> httpRequestParameters)
    {
        this.mData = httpRequestParameters;
    }



    @Override
    protected String doInBackground(Object... params)
    {
        // Ensure that we got, URL, http method and Callback
        if (params.length != 3)
        {
            this.cancel(true);
        }
        else
        {
            if ((params[2] instanceof WebServiceAsyncTaskCallback))
            {
                this.callbackClass = ((WebServiceAsyncTaskCallback)params[2]);
            }
            else
            {
                this.cancel(true);
            }
            try {
                URL url = new URL((String)params[0]);
            } catch (MalformedURLException e) {
                this.callbackClass.onError("First param must be a valid URL. (" + params[0] + " given)");
                this.cancel(true);
            }
            if (!((String)params[1]).equals(POST) && !((String)params[1]).equals(GET))
            {
                this.callbackClass.onError("Second parameters must be " + this.getClass().getName() + " POST or GET constant");
                this.cancel(true);
            }
        }

        String str          = "";

        //IS OUR REQUEST A POST
        if (params.length > 1)
        {
            if (((String)params[1]).toUpperCase().equals(WebServiceAsyncTask.POST))
            {
                str = getPostResponse(((String)params[0]));
            }
            else if(((String)params[1]).toUpperCase().equals(WebServiceAsyncTask.GET)) //THEN GET
            {
                str = getGetResponse(((String)params[0]));
            }
        }

        return str;
    }

    @Override
    protected void onPostExecute(String result)
    {
        this.mData = null;

        if (this.context != null)
        {
            this.publishProgress(PROGRESS_TEXT_END, PROGRESS_PERCENT_END);
            this.progressDialog.dismiss();
        }
        if (this.callbackClass != null)
        {
            this.callbackClass.callbackMethod(result);
        }
    }

    @Override
    protected void onPreExecute()
    {
        if (this.context != null)
        {
            this.prepareProgressDialog();
            this.progressDialog.show();
        }
    }

    @Override
    protected void onProgressUpdate(String... values) {
        if (this.context != null)
        {
            this.progressDialog.setMessage(values[0]);
            this.progressDialog.setProgress(Integer.parseInt(values[1]));
        }
    }


}

/**
 * Allow to easily get the server response
 */
abstract class WebServiceAsyncTaskCallback{
    /**
     * Return the server response as String
     * @param result server response as a String
     */
    abstract void callbackMethod(String result);

    /**
     * This method is design to report simple errors for development phase.
     * @param errMessage contains error message
     */
    protected void onError(String errMessage){};

    ;
}

推荐答案

您对 AsyncTask 的使用似乎很合适.您可能知道.. 对于网络通信，您必须使用 AsyncTask 或您自己的线程(扩展 HandlerThread.)

Your use of AsyncTask appears appropriate. As you may be aware.. for network communications you must use AsyncTask or your own thread (extend HandlerThread.)

如果您的应用经常调用 AsyncTask 或同时执行 AsyncTask，那么创建您自己的线程会更高效(所有 AsyncTask 请求在 API 13 及更高版本中使用单个线程.)

If your app is frequently calling AsyncTask or is executing simultaneous AsyncTask then creating your own thread will be more efficient (all AsyncTask requests use a single thread in API 13 and up.)

我不熟悉您的应用及其运作方式.您的用户是否需要这些后台网络传输的对话框和状态反馈?

I'm unfamiliar with your app and how it functions.. do your users require the dialogs and status feedback for thses background network transmissions?

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