[轉] How To: ICMP Ping in Java (JDK 1.5 and above)

Programatically using ICMP Ping is a great way to establish that a server is up and running. Previously you couldn’t do ICMP ping (what ping command does in Linux/Unix & Windows) in java without using JNI or exec calls. Here is a simple and reliable method to do ICMP pings in Java without using JNI or NIO.


String host = "172.16.0.2"
int timeOut = 3000; // I recommend 3 seconds at least
boolean status = InetAddress.getByName(host).isReachable(timeOut)

status is true if the machine is reachable by ping; false otherwise. Best effort is made to try to reach the host, but firewalls and server configuration may block requests resulting in a unreachable status while some specific ports may be accessible. A typical implementation will use ICMP ECHO REQUESTs if the privilege can be obtained, otherwise it will try to establish a TCP connection on port 7 (Echo) of the destination host.

In Linux/Unix you may have to suid the java executable to get ICMP Ping working, ECHO REQUESTs will be fine even without suid. However on Windows you can get ICMP Ping without any issues whatsoever.

PS: Linux 版必須該 JVM 使用者有 root 權限發 ICMP

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