The other answers that use ConnectivityManager are wrong because having a network connection doesn't mean you have internet access. For example, the user might be connected to a coffee shop's WiFi portal but can't get to the internet. To check that the internet is accessible you have to try to connect to an actual server. Normally when you want to do this you have a specific server in mind that you want to connect to, so go ahead and check if you can connect to that server. Here's a simple method for checking connectivity to a server.

private boolean isOnTheInternet() {
    try {
        URLConnection urlConnection = new URL("http://yourserver").openConnection();
        urlConnection.setConnectTimeout(400);
        urlConnection.connect();
        return true;
    } catch (Exception e) {
        return false;
    }
}

设置ConnectTimeout的原因是，否则它默认为TCP超时，可以有很多秒长。

还要注意的是，Android不允许你在主线程上运行这个程序。

如果你需要检查网络连接，使用ping到服务器的方法:

public boolean checkIntCON() {
    try {
        Process ipProcess = Runtime.getRuntime().exec("/system/bin/ping -c 1 8.8.8.8");
        return (ipProcess.waitFor() == 0);
    }
    catch (IOException e)          { e.printStackTrace(); }
    catch (InterruptedException e) { e.printStackTrace(); }
    return false;
}

您可以使用端口进行检查

public boolean checkIntCON() {
    try {
        Socket sock = new Socket();
        SocketAddress sockaddr = new InetSocketAddress("8.8.8.8", 80); 
        // port will change according to protocols

        sock.connect(sockaddr, 1250);
        sock.close();

        return true;
    } catch (IOException e) { return false; }
}

public boolean isNetworkAvailable(Context context) {
    ConnectivityManager connectivityManager
            = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();
    return activeNetworkInfo != null && activeNetworkInfo.isConnected();
}

以下是您需要的许可:

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

看一下ConnectivityManager类。您可以使用这个类来获取主机上活动连接的信息。http://developer.android.com/reference/android/net/ConnectivityManager.html

编辑:你可以使用

Context.getSystemService(Context.CONNECTIVITY_SERVICE)
    .getNetworkInfo(ConnectivityManager.TYPE_MOBILE) 

or

Context.getSystemService(Context.CONNECTIVITY_SERVICE)
    .getNetworkInfo(ConnectivityManager.TYPE_WIFI) 

并解析返回NetworkInfo对象的DetailedState枚举

EDIT EDIT:查看是否可以访问主机

Context.getSystemService(Context.CONNECTIVITY_SERVICE)
    .requestRouteToHost(TYPE_WIFI, int hostAddress)

显然，我使用Context.getSystemService(Context.CONNECTIVITY_SERVICE)作为代理来表示

ConnectivityManager cm = Context.getSystemService(Context.CONNECTIVITY_SERVICE);
cm.yourMethodCallHere();

如果您正在使用API 23或更高版本，您现在可以使用NetworkCapabilities检查internet是否处于活动状态。net_capacity_validated，由谷歌自己的ping服务支持。

ConnectivityManager.NetworkCallback networkCallback = new ConnectivityManager.NetworkCallback() {
    @Override
    public void onLost(Network network) {
        // handle network lost
    }

    @Override
    public void onAvailable(Network network) {
        ConnectivityManager cm = (ConnectivityManager) getApplicationContext().getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo info = cm.getNetworkInfo(network);
        boolean isConnected = (info != null && info.isConnectedOrConnecting());

        if (isConnected) {
            NetworkCapabilities nc = cm.getNetworkCapabilities(network);
            if (nc != null) {
                boolean isInternetValid = nc.hasCapability(NetworkCapabilities.NET_CAPABILITY_VALIDATED);
                if (isInternetValid) {
                    // internet is valid
                }
            }
        }
    }
};

NetworkRequest request = new NetworkRequest.Builder().addCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET).build();
ConnectivityManager connectivityManager = (ConnectivityManager) getApplicationContext().getSystemService(Context.CONNECTIVITY_SERVICE);
connectivityManager.registerNetworkCallback(request, networkCallback);

最简单的解决办法是

在大多数情况下，如果他/她想连接到远程服务器，只会检查互联网连接，所以简单和最好的解决方案是ping你的服务器，如下所示。

public boolean isConnected() {
    final String command = "ping -c 1 yourExmapleDomain.com";
    boolean isConnected = false;
    try {
        isConnected = Runtime.getRuntime().exec(command).waitFor() == 0;
    } catch (InterruptedException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return isConnected;
}