解释java实现的PING代码

Question

package keshe;
/*自从Java 1.5，java.net包中就实现了ICMP ping的功能。

• 见：Ping类的ping(String)函数。用Jdk1.5的InetAddresss方式 */ import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.net.InetAddress; //import java.net.UnknownHostException; import java.util.regex.Matcher; import java.util.regex.Pattern;

public class Ping3 {

public static boolean ping(String ipAddress) throws Exception {
    int timeOut = 3000; // 超时应该在3钞以上
    boolean status = InetAddress.getByName(ipAddress).isReachable(timeOut); 
    // 当返回值是true时，说明host是可用的，false则不可。
    return status;
}

public static void ping02(String ipAddress) throws Exception {
    String line = null;
    try {
        Process pro = Runtime.getRuntime().exec("ping " + ipAddress);
        BufferedReader buf = new BufferedReader(new InputStreamReader(
                pro.getInputStream()));
        while ((line = buf.readLine()) != null)
            System.out.println(line);
    } catch (Exception ex) {
        System.out.println(ex.getMessage());
    }
}

public static boolean ping(String ipAddress, int pingTimes, int timeOut) {
    BufferedReader in = null;
    Runtime r = Runtime.getRuntime(); // 将要执行的ping命令,此命令是windows格式的命令
    String pingCommand = "ping " + ipAddress + " -n " + pingTimes + " -w "
            + timeOut;
    try { // 执行命令并获取输出
        System.out.println(pingCommand);
        Process p = r.exec(pingCommand);
        if (p == null) {
            return false;
        }
        in = new BufferedReader(new InputStreamReader(p.getInputStream())); // 逐行检查输出,计算类似出现=23ms
                                                                            // TTL=62字样的次数
        int connectedCount = 0;
        String line = null;
        while ((line = in.readLine()) != null) {
            connectedCount += getCheckResult(line);
        } // 如果出现类似=23ms TTL=62这样的字样,出现的次数=测试次数则返回真
        return connectedCount == pingTimes;
    } catch (Exception ex) {
        ex.printStackTrace(); // 出现异常则返回假
        return false;
    } finally {
        try {
            in.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

// 若line含有=18ms TTL=16字样,说明已经ping通,返回1,否則返回0.
private static int getCheckResult(String line) { // System.out.println("控制台输出的结果为:"+line);
    Pattern pattern = Pattern.compile("(\\d+ms)(\\s+)(TTL=\\d+)",
            Pattern.CASE_INSENSITIVE);
    Matcher matcher = pattern.matcher(line);
    while (matcher.find()) {
        return 1;
    }
    return 0;
}

public static void main(String[] args) throws Exception {
    String ipAddress = "127.0.0.1";
    System.out.println(ping(ipAddress));
    ping02(ipAddress);
    System.out.println(ping(ipAddress, 5, 5000));
}

}

Answer 1

这些代码的本质其实就是调用操作系统的命令行的ping命令，并且获取命令的输出结果，对结果解析，然后再显示给用户。也就是这代码本身其实就是一个调用命令行得到输出的程序，而实际的功能是ping这个命令实现的。