Android客户端使用HTTP通信

1. 注意
2. 代码

Android作为客户端（client）对服务器（server）进行request操作，并从服务器中得到response。

这里主要使用HTTP来进行数据传输，request有GET和POST两种方式。

完整的项目：https://github.com/lijiancheng0614/android-NetworkConnect

注意

以下代码可以检测网络是否连接，但不包括hotspot的连接。

/**
 * Check network connection.
 *
 * @return true if connected.
 */
private boolean isNetworkConnected() {
    ConnectivityManager mConnectivityManager = (ConnectivityManager) mContext
            .getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo mNetworkInfo = mConnectivityManager.getActiveNetworkInfo();
    return mNetworkInfo != null && mNetworkInfo.isConnected();
}

代码

RequestTask类封装了AsyncTask，实现了异步通信等细节。

• RequestTask.java

  package com.example.android.networkconnect;
  
  import android.os.AsyncTask;
  
  import java.io.DataOutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.net.HttpURLConnection;
  import java.net.URL;
  
  /**
   * Implementation of AsyncTask, to fetch the data in the background away from the UI thread.
   */
  public class RequestTask extends AsyncTask<String, Void, String> {
  
      public static final String TAG = "RequestTask";
      private static final int CONNECT_TIMEOUT = 15000 /* milliseconds */;
      private static final int BUFFER_SIZE = 32;
      private boolean isPost = false;
  
      /**
       * Set POST method.
       *
       * @param isPost true if post.
       */
      public void setPost(boolean isPost) {
          this.isPost = isPost;
      }
  
      @Override
      protected String doInBackground(String... strings) {
          try {
              String result = "";
  
              HttpURLConnection conn;
              if (isPost) {
                  conn = doPost(strings[0], strings[1]);
              } else {
                  conn = doGet(strings[0]);
              }
              // Success HTTP Status Code
              if (conn.getResponseCode() / 100 != 2)
                  return result;
              result = getStringFromStream(conn.getInputStream());
              return result;
          } catch (IOException e) {
              return e.getLocalizedMessage();
          }
      }
  
      /**
       * Given a string representation of a URL, sets up a connection for GET request.
       *
       * @param urlString A string representation of a URL.
       * @return A HttpURLConnection.
       * @throws java.io.IOException
       */
      private HttpURLConnection doGet(String urlString) throws IOException {
          URL url = new URL(urlString);
          HttpURLConnection conn = (HttpURLConnection) url.openConnection();
          conn.setConnectTimeout(15000 /* milliseconds */);
          conn.setRequestMethod("GET");
          conn.setDoInput(true);
          conn.connect();
          return conn;
      }
  
      /**
       * Given a string representation of a URL, sets up a connection for POST request.
       *
       * @param urlString A string representation of a URL.
       * @param postData  Post data.
       * @return A HttpURLConnection.
       * @throws java.io.IOException
       */
      private HttpURLConnection doPost(String urlString, String postData) throws IOException {
          URL url = new URL(urlString);
          HttpURLConnection conn = (HttpURLConnection) url.openConnection();
          conn.setConnectTimeout(CONNECT_TIMEOUT);
          conn.setRequestMethod("POST");
          conn.setDoOutput(true);
          conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
          conn.setRequestProperty("Content-Length", Integer.toString(postData.length()));
          DataOutputStream dataOutputStream = null;
          try {
              dataOutputStream = new DataOutputStream(conn.getOutputStream());
              dataOutputStream.writeBytes(postData);
          } finally {
              if (dataOutputStream != null)
                  dataOutputStream.close();
          }
          return conn;
      }
  
      /**
       * Reads an InputStream and converts it to a String.
       *
       * @param inputStream InputStream.
       * @return String from inputStream.
       * @throws java.io.IOException
       */
      private String getStringFromStream(InputStream inputStream) throws IOException {
          InputStreamReader isr = new InputStreamReader(inputStream, "UTF-8");
          StringBuilder sb = new StringBuilder(BUFFER_SIZE);
          char[] buffer = new char[BUFFER_SIZE];
          int length;
          while ((length = isr.read(buffer, 0, BUFFER_SIZE)) != -1) {
              sb.append(buffer, 0, length);
              if (isCancelled())
                  return null;
          }
          inputStream.close();
          isr.close();
          return sb.toString();
      }
  }