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在瀏覽器裡頭有實做AJAX query，這讓網頁有了更大的發揮空間，

程式人員可以讓網頁就像一般應用程式一樣有趣。

那如果，一般應用程式也可以發出HTTP query，

進而取得web service吐出的東西，那又會擦出怎樣的火花呢？ 先賣個關子～

本篇只講在Android上，要如何寫一個發出HTTP query，又接回HTTP response的程式。

關鍵字：Android & HttpClient

在Android SDK裡有引入org.apache.http.client，

這package是這程式的靈魂，詳情可以看本篇的參考。

底下是程式：

流程：
1.建一個text view

2.呼叫HTTPGetQuery

2.1.建一個HTTP client

2.2.建一個HTTP get物件，並在初始化的參數帶入URL

2.3.建一個HTTP reponse handler物件

2.4.HTTP client實際對web service query，並帶入HTTP get

2.5.取回reponse，再從response取出status code、header、cookie、content字串

2.6.因為HTTP是socket IO，所以用try catch包起來，以防IO錯誤時沒有處理到

2.7.回傳結果

3.將結果放到text view

4.畫出這個程式畫面

程式碼：

package androidajax.example.android;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.http.Header;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.*;
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;

public class AndroidAJAX extends Activity {
    private Document xmldoc;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // Have a text view on the scene.
        TextView tv = new TextView(this);
        // Put the answer string returned by the HTTP query on the scene.
        // Change the red url by yourself.
        Map map = HTTPGetQuery("http://test.com.url?account=牛蛙");
        //Map map = HTTPPostQuery("http://test.com.url");
        tv.setText(map.get("status").toString() + ": " + map.get("content").toString());
        // Render the scene.
        setContentView(tv);
    }
    
    /** Method: Do the HTTP query according to hostURL with "get" method. */
    private Map<String, String> HTTPGetQuery(String hostURL) {
        // Declare a content string prepared for returning.
        String content = "";
        // Have an HTTP client to connect to the web service.
        HttpClient httpClient = new DefaultHttpClient();
        // Have an HTTP response container.
        HttpResponse httpResponse = null;
        // Have map container to store the information.
        Map<String, String> map = new HashMap<String, String>();
        
        // This try & catch is prepared for the IO exception in case.
        try {
            // Have a post method class with the query URL.
            HttpGet httpQuery = new HttpGet(hostURL);
            // The HTTP client do the query and have the string type response.
            httpResponse = httpClient.execute(httpQuery);
            
            // Read the HTTP headers and into content.
            //for (Header header : httpResponse.getAllHeaders()) {
            //     content += "\n" + header.toString();
            //}
            // Read the HTTP response content as an encoded string.
            content += EntityUtils.toString(httpResponse.getEntity());
        }
        // Catch the HTTP exception.
        catch(ClientProtocolException ex) {
            content = "ClientProtocolException:" + ex.getMessage();
        }
        // Catch the any IO exception.
        catch(IOException ex) {
            content = "IOException:" + ex.getMessage();
        }
        // The HTTP connection must be closed any way.
        finally    {
            httpClient.getConnectionManager().shutdown();
        }
        
        // Check the HTTP connection is executed or not.
        if (httpResponse != null) {
            // Put the status code with status key.
            map.put("status", Integer.toString(httpResponse.getStatusLine().getStatusCode()));
            // Put the response content with content key
            map.put("content", content);
        }
        else {
            // Put the dummy with status key.
            map.put("status", "");
            // Put the dummy with content key
            map.put("content", "");
        }
        
        // Return result.
        return map;
    }
    
    /** Method: Do the HTTP query according to hostURL with "post" method. */
    private Map<String, String> HTTPPostQuery(String hostURL) {
        // Declare a content string prepared for returning.
        String content = "";
        // Have an HTTP client to connect to the web service.
        HttpClient httpClient = new DefaultHttpClient();
        // Have an HTTP response container.
        HttpResponse httpResponse = null;
        // Have map container to store the information.
        Map<String, String> map = new HashMap<String, String>();
        
        // This try & catch is prepared for the IO exception in case.
        try {
            // Have a post method class with the query URL.
            HttpPost httpQuery = new HttpPost(hostURL);
            
            // Have a list of key-value pair container.
            List<NameValuePair> pairs = new ArrayList<NameValuePair>();
            // Add the HTTP post arguments into the list.
            pairs.add(new BasicNameValuePair("account", "青蛙"));
            pairs.add(new BasicNameValuePair("password", "frog"));
            // Assign the list as the arguments of post being UTF_8 encoding.
            httpQuery.setEntity(new UrlEncodedFormEntity(pairs, HTTP.UTF_8));
            
            // The HTTP client do the query and have the string type response.
            httpResponse = httpClient.execute(httpQuery);
            
            // Read the HTTP response content as an encoded string.
            content += EntityUtils.toString(httpResponse.getEntity());
        }
        // Catch the HTTP exception.
        catch(ClientProtocolException ex) {
            content = "ClientProtocolException:" + ex.getMessage();
        }
        // Catch the any IO exception.
        catch(IOException ex) {
            content = "IOException:" + ex.getMessage();
        }
        // The HTTP connection must be closed any way.
        finally    {
            httpClient.getConnectionManager().shutdown();
        }
        
        // Check the HTTP connection is executed or not.
        if (httpResponse != null) {
            // Put the status code with status key.
            map.put("status", Integer.toString(httpResponse.getStatusLine().getStatusCode()));
            // Put the response content with content key.
            map.put("content", content);
        }
        else {
            // Put the dummy with status key.
            map.put("status", "");
            // Put the dummy with content key.
            map.put("content", "");
        }
        
        // Return result.
        return map;
    }
}

因為用到HTTP client，這會需要用到網路IO，需要權限授權，

所以要改 res/AndroidManifest.xml

我在</APPLICATION>下加上：
    <uses-permission android:name="android.permission.INTERNET" />

參考：
Android 上的 HTTP 服務相關函式：
    http://ysl-paradise.blogspot.com/2008/09/android-http-i.html
    http://ysl-paradise.blogspot.com/2008/09/android-http-ii.html
    http://ysl-paradise.blogspot.com/2008/09/android-http-iii.html

HttpClient Examples：
    http://hc.apache.org/httpcomponents-client-ga/examples.html
    http://hc.apache.org/httpcomponents-client-ga/httpclient/examples/org/apache/http/examples/client/ClientWithResponseHandler.java

Permission denied error while call webservice using HTTP in android：
    http://stackoverflow.com/questions/3932129/permission-denied-error-while-call-webservice-using-http-in-android-application

本文取自 http://blog.xuite.net/zack_pan/blog/47887919