解决InetAddress.isReachable(timeout)在windows xp始终返回false的bug

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stackoverflow上找到了解决方法。

// 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;
    }