笔者最近在做产品,其中一个环节用到ping测试主机是否在线。
开发环境：Windows 7 64bit+JDK1.8 x64
以下是检测主机是否在线,开发环境中测试通过
public static boolean hostAvailabilityCheck(String host,int timeout){
try {
InetAddress inet = InetAddress.getByName(host);
System.out.println("Sending Ping Request to " + inet);
if(inet.isReachable(timeout)){
System.out.println("Host is reachable");
return true;
}
} catch (IOException e) {
System.out.println("Host is NOT reachable");
e.printStackTrace();
}
return false;
}
正常运行结果
当在windows XP下就运行不正常了，inet.isReachable处始终返回false。Google了一番(java inetaddress isreachable windows xp did not work)，
确定这是个bug，有可能是因为Microsoft放弃了Windows XP等不再维护的操作系统，Oracle公司也不再向后兼容这些系统了。网上反馈bug的比比皆是。
JDK-5061568 : java.net.InetAddress.isReachable() kills Windows networking文章说这个bug会一直重现(This bug can be reproduced always.)
JDK-5061571 : InetAddress#isReachable does not send PINGs but only TCP echos
JDK-6595834 : InetAddress.isReachable is not thread safe when using ICMP ECHO.
以上三篇文章就指出了这个方法存在的一些问题：非线程安全、只发送TCP ECHO，对于框架设计人员来说，作为客户端编程人员我们关注的是api是否
能够达到预期目的，可是jdk1.8.0_144仍旧没有解决这个问题。
笔者最终通过网络搜索，在*上找到了解决方法。
解决方法一（推荐）:
出处：Why does InetAddress.isReachable return false, when I can ping the IP address?
// in case of Linux change the 'n' to 'c' 如果是Linux系统,请将n改成c
Process p1 = java.lang.Runtime.getRuntime().exec("ping -n 1 www.google.com");
int returnVal = p1.waitFor();
boolean reachable = (returnVal==0);
windows系统批处理返回值非0即失败。所以，如果以上返回为0说明ping的通，如果返回2则失败。
解决方法二：
出处：Odd InetAddress.isReachable() issue
说明：需要第三方库JNA支持,需要一定的操作系统知识。此方法将会通过JNA调用COM组件来调用Windows API函数，
相关DLL是IPHLPAPI.DLL和 WSOCK32.DLL
public interface InetAddr extends StdCallLibrary {
InetAddr INSTANCE = (InetAddr)
Native.loadLibrary("wsock32.dll", InetAddr.class);
ULONG inet_addr(String cp); //in_addr creator. Creates the in_addr C struct used below
}
public interface IcmpEcho extends StdCallLibrary {
IcmpEcho INSTANCE = (IcmpEcho)
Native.loadLibrary("iphlpapi.dll", IcmpEcho.class);
int IcmpSendEcho(
HANDLE IcmpHandle, //Handle to the ICMP
ULONG DestinationAddress, //Destination address, in the form of an in_addr C Struct defaulted to ULONG
Pointer RequestData, //Pointer to the buffer where my Message to be sent is
short RequestSize, //size of the above buffer. sizeof(Message)
byte[] RequestOptions, //OPTIONAL!! Can set this to NULL
Pointer ReplyBuffer, //Pointer to the buffer where the replied echo is written to
int ReplySize, //size of the above buffer. Normally its set to the sizeof(ICMP_ECHO_REPLY), but arbitrarily set it to 256 bytes
int Timeout); //time, as int, for timeout
HANDLE IcmpCreateFile(); //win32 ICMP Handle creator
boolean IcmpCloseHandle(HANDLE IcmpHandle); //win32 ICMP Handle destroyer
}
public void SendReply(String ipAddress) {
final IcmpEcho icmpecho = IcmpEcho.INSTANCE;
final InetAddr inetAddr = InetAddr.INSTANCE;
HANDLE icmpHandle = icmpecho.IcmpCreateFile();
byte[] message = new String("thisIsMyMessage!".toCharArray()).getBytes();
Memory messageData = new Memory(32); //In C/C++ this would be: void *messageData = (void*) malloc(message.length);
messageData.write(0, message, 0, message.length); //but ignored the length and set it to 32 bytes instead for now
Pointer requestData = messageData;
Pointer replyBuffer = new Memory(256);
replyBuffer.clear(256);
// HERE IS THE NATIVE CALL!!
reply = icmpecho.IcmpSendEcho(icmpHandle,
inetAddr.inet_addr(ipAddress),
requestData,
(short) 32,
null,
replyBuffer,
256,
timeout);
// NATIVE CALL DONE, CHECK REPLY!!
icmpecho.IcmpCloseHandle(icmpHandle);
}
public boolean IsReachable () {
return (reply > 0);
}
笔者简单封装了一下代码
class IcmpEchoPatch{
int reply;
public void SendReply(String host,int timeout) {
final IcmpEcho icmpecho = IcmpEcho.INSTANCE;
final InetAddr inetAddr = InetAddr.INSTANCE;
HANDLE icmpHandle = icmpecho.IcmpCreateFile();
byte[] message = new String("thisIsMyMessage!".toCharArray()).getBytes();
Memory messageData = new Memory(32); //In C/C++ this would be: void *messageData = (void*) malloc(message.length);
messageData.write(0, message, 0, message.length); //but ignored the length and set it to 32 bytes instead for now
Pointer requestData = messageData;
Pointer replyBuffer = new Memory(256);
replyBuffer.clear(256);
// HERE IS THE NATIVE CALL!!
reply = icmpecho.IcmpSendEcho(icmpHandle,
inetAddr.inet_addr(host),
requestData,
(short) 32,
null,
replyBuffer,
256,
timeout);
// NATIVE CALL DONE, CHECK REPLY!!
icmpecho.IcmpCloseHandle(icmpHandle);
}
public boolean IsReachable () {
return (reply > 0);
}
}
最终hostAvailabilityCheck方法代码如下：
public static boolean hostAvailabilityCheck(String host,int timeout){
try {
HardWareIdentifier resolver = HardWareIdentifier.getDefault(); //替换为你的方法
if(resolver.isMinSupportPlat()){ //替换为你的方法判断操作系统
IcmpEchoPatch ping = new IcmpEchoPatch();
ping.SendReply(host, timeout);
if(ping.IsReachable()){
System.out.println("Host is reachable");
return true;
}
}else{
InetAddress inet = InetAddress.getByName(host);
System.out.println("Sending Ping Request to " + inet);
if(inet.isReachable(timeout)){
System.out.println("Host is reachable");
return true;
}
}
} catch (IOException e) {
System.out.println("Host is NOT reachable");
e.printStackTrace();
}
return false;
}