判断设备是否有网络连接

1、利用ConnectivityManager取得系统的Context.CONNECTIVITY_SERVICE，需添加权限<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
 
 public boolean isConnect() {
  // 获取手机所有连接管理对象（包括对wi-fi,net等连接的管理）
  ConnectivityManager connectivity = (ConnectivityManager) this.getSystemService

   (Context.CONNECTIVITY_SERVICE);
  if (connectivity != null) {
   // 获取网络连接管理的对象
   NetworkInfo info = connectivity.getActiveNetworkInfo();
   if (info != null) {
    // 判断当前网络是否已经连接
    if (info.getState() == NetworkInfo.State.CONNECTED) {
     return true;
    }
   }
  }
  return false; 
 }
缺点：检测不够准确、及时

 

2、连接一个网址，判断是否连接上
   1〉socket

 public boolean isConnect() {
  boolean isConn = true;
  try {
    Socket socket = new Socket();
//    socket.connect(new InetSocketAddress("www.baidu.com",80),3000);//用域名会抱错，IP地址不会抱错
    socket.connect(new InetSocketAddress("202.108.22.5",80),3000);//设置连接地址、端口号、超时时间
    isConn = socket.isConnected();
  } catch (Exception e) {
   System.out.println(e.toString());
   isConn = false;
  }

  System.out.println(isConn);
  return isConn;
 }

 

2> http 不受域名限制
public boolean isConnect() {
  boolean isConn = true;
  try {
   //设置超时时间
   HttpParams httpParameters = new BasicHttpParams();// Set the timeout in milliseconds until a

connection is established.  
   HttpConnectionParams.setConnectionTimeout(httpParameters, 2000);// Set the default socket timeout

(SO_TIMEOUT) // in milliseconds which is the timeout for waiting for data.  
   HttpConnectionParams.setSoTimeout(httpParameters, 4000);  
   HttpClient httpClient = new DefaultHttpClient(httpParameters);  

   //检测网络
   String httpUrl = "http://www.baidu.com";
   HttpGet request = new HttpGet(httpUrl);
   HttpResponse response = httpClient.execute(request);
   if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
    isConn = true;
   } else {
    isConn = false;
   }

  } catch (Exception e) {
   System.out.println(e.toString());
   isConn = false;
  }

  System.out.println(isConn);
  return isConn;
 }