Android学习笔记：利用httpclient和AsyncTask 发起网络http post操作

1、在android4中，发起网络http操作，不能在Activity的事件（即主线程）中进行，必须在单独的线程中操作。

另外进行网络操作，需要在manifest文件中增加如下的权限：

<uses-permission android:name="android.permission.INTERNET" />

2、下面给出代码事例

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public void loadData() {         new AsyncTask<String, Void, String>() {             @Override             protected String doInBackground(String... paramsInput) {                 String url = "http://10.0.0.5:8080/examples/action";                 List<NameValuePair> params = new ArrayList<NameValuePair>();                 params.add(new BasicNameValuePair("type", paramsInput[0]));                 params.add(new BasicNameValuePair("id", paramsInput[1]));                 /* 建立HTTPPost对象 */                 HttpPost httpRequest = new HttpPost(url);                   String strResult = "doPostError";                 try {                     HttpClient httpClient = getHttpClient();                     /* 添加请求参数到请求对象 */                     httpRequest.setEntity(new UrlEncodedFormEntity(params,                             HTTP.UTF_8));                     /* 发送请求并等待响应 */                     HttpResponse httpResponse = httpClient.execute(httpRequest);                     /* 若状态码为200 ok */                     if (httpResponse.getStatusLine().getStatusCode() == 200) {                         /* 读返回数据 */                         strResult = EntityUtils.toString(httpResponse                                 .getEntity());                       } else {                         strResult = "Error Response: "                                 + httpResponse.getStatusLine().toString();                     }                 } catch (ClientProtocolException e) {                     strResult = "Error Response: " + e.getMessage().toString();                     e.printStackTrace();                 } catch (IOException e) {                     strResult = "Error Response: " + e.getMessage().toString();                     e.printStackTrace();                 } catch (Exception e) {                     strResult = "Error Response: " + e.getMessage().toString();                     e.printStackTrace();                 }                 return strResult;             }               @Override             protected void onPostExecute(String result) {                 TextView view = (TextView) findViewById(R.id.resultText);                 view.setText(result);                 super.onPostExecute(result);             }           }.execute("query","1");     }   private HttpClient getHttpClient() {           // 创建 HttpParams 以用来设置 HTTP 参数（这一部分不是必需的）           HttpParams httpParams = new BasicHttpParams();           // 设置连接超时和 Socket 超时，以及 Socket 缓存大小           HttpConnectionParams.setConnectionTimeout(httpParams, 20 * 1000);           HttpConnectionParams.setSoTimeout(httpParams, 20 * 1000);           HttpConnectionParams.setSocketBufferSize(httpParams, 8192);           // 设置重定向，缺省为 true           HttpClientParams.setRedirecting(httpParams, true);           // 设置 user agent           String userAgent = "Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9.2) Gecko/20100115 Firefox/3.6";         HttpProtocolParams.setUserAgent(httpParams, userAgent);           // 创建一个 HttpClient 实例           // 注意 HttpClient httpClient = new HttpClient(); 是Commons HttpClient           // 中的用法，在 Android 1.5 中我们需要使用 Apache 的缺省实现 DefaultHttpClient           HttpClient httpClient = new DefaultHttpClient(httpParams);           return httpClient;     }

　上述代码的loadData方法中，创建一个AsyncTask对象，在对象的doInBackground方法中发起网络操作，获取到操作结果。然后在onPostExecute方法中，利用前面获取到的结果更新界面。

   这里的网络操作主要是利用了HttpClient等相关api，位于org.apache.http.client.HttpClient下。