Android的网络通信机制

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HttpClient接口

在Android6.0中，HttpClient库已经被移除

Android SDK附带的Apache的HttpClient，使用步骤如下：

1. 使用DefaultHttpClient类实例化HttpClient对象；
2. 创建HttpGet或HttpPost对象，将要请求的URL通过构造方法传入HttpGet或HttpPost对象；
3. 调用execute方法发送HTTP GET或HTTP　POST请求，并返回HttpResponse对象；
4. 通过HttpResponse接口的getEntity方法返回响应信息，并进行相应的处理。

HttpGet示例代码如下：

public void sendGetRequest(String Url) throws Exception {
    //创建HttpClient对象，设置默认参数
    HttpClient mHttpClient = new DefaultHttpClient();
    //创建HttpGet对象
    HttpGet mHttpGet = new HttpGet(Url);
    //添加Header
    mHttpGet.addHeader("Connection", "Keep-Alive");
    //执行Http请求
    HttpResponse mResponse = new mHttpClient.execute(mHttpGet );
    HttpEntity mHttpEntity = new mResponse().getEntity();
    if (mHttpEntity != null) {
        InputStream mInputStream = mHttpEntity.getContent();
        BufferedReader mBufferedReader = new BufferedReader(new InputStreamReader(mInputStream));
        StringBuilder mStringBuilder = new StringBuilder();
        String line = null;
        try{
             while((line = mBufferedReader.readLine()) != null ) {
                 mStringBuilder.append(line );
             }
        } catch (IOException e) {
              e.printStackTrace();
        } finally {
            mInputStream.close();
      }
      Log.e("","###请求结果：" + mStringBuilder.toString());
    }
}

HttpPost示例代码如下：

public void sendPostRequest(String Url) throws Exception {
    //创建HttpClient对象，设置默认参数
    HttpClient mHttpClient = new DefaultHttpClient();
    //创建HttpGet对象
    HttpGet mHttpPost = new HttpPost(Url);
    //添加Header
    mHttpGet.addHeader("Connection", "Keep-Alive");
    //使用NameValuePair>来保存要传递的Post参数
    List postParameters = new ArrayList();
    //添加要传递的参数，BasicNameValuePair是存储键值对的类
    postParameters.add(new BasicNameValuePair("username", "myname"));
    postParameters.add(new BasicNameValuePair("password", "mypwd"));
    //实例化UrlEndecodedFormEntity对象
    UrlEncodedFormEntity mUrlEncodedFormEntity = new UrlEncodedFormEntity(postParameters);
     //使用HttpPost对象来设置UrlEncodedFormEntity的Entity
     mHttpPost.setEntity(mUrlEncodedFormEntity );
    //执行Http请求
    HttpResponse mResponse = new mHttpClient.execute(mHttpPost );
    HttpEntity mHttpEntity = new mResponse().getEntity();
    if (mHttpEntity != null) {
        InputStream mInputStream = mHttpEntity.getContent();
        BufferedReader mBufferedReader = new BufferedReader(new InputStreamReader(mInputStream));
        StringBuilder mStringBuilder = new StringBuilder();
        String line = null;
        try{
             while((line = mBufferedReader.readLine()) != null ) {
                 mStringBuilder.append(line );
             }
        } catch (IOException e) {
              e.printStackTrace();
        } finally {
            mInputStream.close();
      }
      Log.e("","###请求结果：" + mStringBuilder.toString());
    }
}

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HttpURLConnection接口---Google官方推荐

HttpURLConnection的压缩和缓存机制可以有效地减少网络访问的流量，提升速度和省电。

HttpURLConnection默认使用Get请求：

public void sendRequest(String url) throws IOException {
    String line = null;.
    String result = null;
    //使用HttpURLConnection 打开链接
    try{
        Url mUrl = new Url(url);
        HttpURLConnection mHttpURLConnection = (HttpURLConnection ) mUrl.openConnection();
        //读取响应的内容(流)
        InputStreamReader mInputStreamReader = new InputStreamReader(new InputStream(mHttpURLConnection.getInputStream()));
        BufferedReader mBufferedReader = new BufferedReader(mInputStreamReader );
        if ((line = mBufferedReader.readLine())) {
            result = line + “\n”;
        }
        Log.e("", "请求结果：" + result);
     } catch ((MalformedURLException e)    
        {    
            Log.e(DEBUG_TAG, "MalformedURLException");    
        } finally {
        mInputStreamReader.close();
        mHttpURLConnection.disconnect();
     }

} 

HttpURLConnection的Post请求

public void sendRequest(String url) throws IOException {
    String line = null;.
    String result = null;
      try{
        Url mUrl = new Url(url);
        HttpURLConnection mHttpURLConnection = (HttpURLConnection ) mUrl.openConnection();
        //设置读取超时为10秒
        mHttpURLConnection.setReadTimeout(10000);
        //设置链接超时为15秒
        mHttpURLConnection.setConnectionTimeout(15000);
        //设置请求方式
        mHttpURLConnection.setRequestMethod("Post");
        //接收输入流
        mHttpURLConnection.setDoInput(true);
        //启动输出流，当需要传递参数时需要开启
        mHttpURLConnection.setDoOutput(true);
        //添加Header
        mHttpURLConnection.setRequestProperty("Connection", "Keep-Alive");
        //添加请求参数
        List paramsList = new ArrayList();
        paramsList .add(new BasicNameValuePair("username", "myname"));
        paramsList .add(new BasicNameValuePair("password", "mypwd"));
        //将参数写入到输出流
        wriParams(mHttpURLConnection.getOutputStream(), paramsList);
        
        //发起请求
        mHttpURLConnection.connect();
        BufferedReader mBufferedReader = new BufferedReader(new InputStreamReader(mHttpURLConnection.getInputStream()));
        StringBuilder sb = new StringBuilder();
        while((line = mBufferedReader.readLine()) != null) {
            sb.append(line + "\n");
        }
        result = sb.toString();
         } catch ((MalformedURLException e)    
        {    
            Log.e(DEBUG_TAG, "MalformedURLException");    
        } finally {
        mHttpURLConnection.disconnect();
     }

}

private void writeParams(OutputStream mOutputStream, List paramsList){
      StringBuilder paramStr = new StringBuilder();
      for (NameValuePair pair : paramsList) {
          if (!TextUtils.isEmpty(paramStr)) {
              paramStr.append("&"):
          }
          paramStr.append(URLEncoder.encode(pair.getName(), "UTF-8"));
          paramStr.append("=");
          paramStr.append(URLEncoder.encode(pair.getValue(), "UTF-8"));
      }
      BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(mOutputStream, "UTF-8"));
      //将参数写入输出流
      writer.write(paramStr.toString());
      writer.flush();
      writer.close();
}

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注：任何输出流都是有缓冲区的,Bufferedxxx这种输出流提供可配置缓冲区大小，其他输出流都是有默认大小的缓冲区的,FileWriter的flush()方法是从OutputStreamWriter中继承来的,其作用就是 清空缓冲区并完成文件写入操作的。