在实践项目中。常常要处理网络异常等问题。为此，专门设计一个类，随时能够使用。
import java.io.IOException;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.net.UnknownHostException;
import java.util.Enumeration; /**
* @author administrator
*
*/
public class NetworkMonitor implements Runnable {
private String m_strUrl = "192.168.1.27";
private static boolean m_bNetworkAvailable = false; /**
*
*/
public NetworkMonitor() {
// TODO:
} /**
* @param strUrl
*/
public NetworkMonitor(String strUrl) {
this.m_strUrl = strUrl;
} /**
* @return
*/
public static boolean isNetworkAvailable() {
return m_bNetworkAvailable;
} /* (non-Javadoc)
* @see java.lang.Runnable#run()
*/
@Override
public void run() {
while (true) {
try {
InetAddress inetAddress = InetAddress.getByName(m_strUrl);
m_bNetworkAvailable = inetAddress.isReachable(5000); //測试能否够达到该地址 Thread.sleep(2000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
// e.printStackTrace();
m_bNetworkAvailable = false;
} catch(UnknownHostException e) {
// System.err.println("连接失败");
m_bNetworkAvailable = false;
} catch (IOException e) {
// TODO Auto-generated catch block
// e.printStackTrace();
m_bNetworkAvailable = false;
}
}
} public void isAddressAvailable(String ip) {
try {
InetAddress address = InetAddress.getByName(ip); //ping this IP
if (address instanceof java.net.Inet4Address) {
System.out.println(ip + " is ipv4 address");
} else if (address instanceof java.net.Inet6Address) {
System.out.println(ip + " is ipv6 address");
} else {
System.out.println(ip + " is unrecongized");
} if (address.isReachable(5000)) {
System.out.println("SUCCESS - ping " + ip + " with no interface specified");
} else {
System.out.println("FAILURE - ping " + ip + " with no interface specified");
} System.out.println("\n-------Trying different interfaces--------");
Enumeration<NetworkInterface> netInterfaces = NetworkInterface.getNetworkInterfaces();
while (netInterfaces.hasMoreElements()) {
NetworkInterface ni = netInterfaces.nextElement();
System.out.println( "Checking interface, DisplayName:" + ni.getDisplayName() + ", Name:" + ni.getName());
if(address.isReachable(ni, 0, 5000)){
System.out.println("SUCCESS - ping " + ip);
} else {
System.out.println("FAILURE - ping " + ip);
}
Enumeration<InetAddress> ips = ni.getInetAddresses();
while(ips.hasMoreElements()) {
System.out.println("IP: " + ips.nextElement().getHostAddress());
}
System.out.println("-------------------------------------------"); }
} catch (Exception e) {
System.out.println("error occurs.");
e.printStackTrace();
}
}
}
实际中须要知道网络状态的时候，不必专门去再检查。由于那样可能会堵塞，导致调用者挂起，在这里直接调用isNetworkAvailable方法能够马上知道网络状态，所以性能不会受到不论什么影响。
这个类以下实现的线程run方法中，检查网络也是2秒钟检查一次，不会影响整个程序的性能。假设有更高的要求，能够改成1秒或者0.5秒。我的意见是2秒够了。
由于网络断开非常快，可是要恢复也是须要点时间的，所以不必重复检查。那样会影响性能。
调用演示样例：
public class Startup {
/**
* @see 应用程序入口
* @param args
*/
public static void main(String[] args) {
Startup startup = new Startup();
startup.startNetworkMonitor();
for (int i = 0; i < 60; i++) {
System.out.println("network[" + i + 1 +"]: " + NetworkMonitor.isNetworkAvailable());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public void startNetworkMonitor() {
NetworkMonitor networkMonitor = new NetworkMonitor();
networkMonitor.isAddressAvailable("192.168.1.1");
Thread thread = new Thread(networkMonitor);
thread.start();
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
试执行就能够知道。 这一句
System.out.println("network[" + i + 1 +"]: " + NetworkMonitor.isNetworkAvailable());
全然就是毫秒级返回。各方面表现很理想。