如何JAVA编程判断局域网中的某个IP地址是否已经被使用？

import java.io.*;import java.net.*;import java.nio.*;import java.nio.channels.*;import java.nio.charset.*;import java.util.*;import java.util.regex.*;public class Ping { // The default daytime port static int DAYTIME_PORT = 13; // The port we'll actually use static int port = DAYTIME_PORT; // Representation of a ping target // static class Target { InetSocketAddress address; SocketChannel channel; Exception failure; long connectStart; long connectFinish = 0; boolean shown = false; Target(String host) { try { address = new InetSocketAddress(InetAddress.getByName(host), port); } catch (IOException x) { failure = x; } } void show() { String result; if (connectFinish != 0) result = Long.toString(connectFinish - connectStart) + "ms"; else if (failure != null) result = failure.toString(); else result = "Timed out"; System.out.println(address + " : " + result); shown = true; } } // Thread for printing targets as they're heard from // static class Printer extends Thread { LinkedList pending = new LinkedList(); Printer() { setName("Printer"); setDaemon(true); } void add(Target t) { synchronized (pending) { pending.add(t); pending.notify(); } } public void run() { try { for (;;) { Target t = null; synchronized (pending) { while (pending.size() == 0) pending.wait(); t = (Target)pending.removeFirst(); } t.show(); } } catch (InterruptedException x) { return; } } } // Thread for connecting to all targets in parallel via a single selector // static class Connector extends Thread { Selector sel; Printer printer; // List of pending targets. We use this list because if we try to // register a channel with the selector while the connector thread is // blocked in the selector then we will block. // LinkedList pending = new LinkedList(); Connector(Printer pr) throws IOException { printer = pr; sel = Selector.open(); setName("Connector"); } // Initiate a connection sequence to the given target and add the // target to the pending-target list // void add(Target t) { SocketChannel sc = null; try { // Open the channel, set it to non-blocking, initiate connect sc = SocketChannel.open(); sc.configureBlocking(false); sc.connect(t.address); // Record the time we started t.channel = sc; t.connectStart = System.currentTimeMillis(); // Add the new channel to the pending list synchronized (pending) { pending.add(t); } // Nudge the selector so that it will process the pending list sel.wakeup(); } catch (IOException x) { if (sc != null) { try { sc.close(); } catch (IOException xx) { } } t.failure = x; printer.add(t); } } // Process any targets in the pending list // void processPendingTargets() throws IOException { synchronized (pending) { while (pending.size() > 0) { Target t = (Target)pending.removeFirst(); try { // Register the channel with the selector, indicating // interest in connection completion and attaching the // target object so that we can get the target back // after the key is added to the selector's // selected-key set t.channel.register(sel, SelectionKey.OP_CONNECT, t); } catch (IOException x) { // Something went wrong, so close the channel and // record the failure t.channel.close(); t.failure = x; printer.add(t); } } } } // Process keys that have become selected // void processSelectedKeys() throws IOException { for (Iterator i = sel.selectedKeys().iterator(); i.hasNext();) { // Retrieve the next key and remove it from the set SelectionKey sk = (SelectionKey)i.next(); i.remove(); // Retrieve the target and the channel Target t = (Target)sk.attachment(); SocketChannel sc = (SocketChannel)sk.channel(); // Attempt to complete the connection sequence try { if (sc.finishConnect()) { sk.cancel(); t.connectFinish = System.currentTimeMillis(); sc.close(); printer.add(t); } } catch (IOException x) { sc.close(); t.failure = x; printer.add(t); } } } volatile boolean shutdown = false; // Invoked by the main thread when it's time to shut down // void shutdown() { shutdown = true; sel.wakeup(); } // Connector loop // public void run() { for (;;) { try { int n = sel.select(); if (n > 0) processSelectedKeys(); processPendingTargets(); if (shutdown) { sel.close(); return; } } catch (IOException x) { x.printStackTrace(); } } } } public static void main(String[] args) throws InterruptedException, IOException { if (args.length < 1) { System.err.println("Usage: java Ping [port] host..."); return; } int firstArg = 0; // If the first argument is a string of digits then we take that // to be the port number to use if (Pattern.matches("[0-9]+", args[0])) { port = Integer.parseInt(args[0]); firstArg = 1; } // Create the threads and start them up Printer printer = new Printer(); printer.start(); Connector connector = new Connector(printer); connector.start(); // Create the targets and add them to the connector LinkedList targets = new LinkedList(); for (int i = firstArg; i < args.length; i++) { Target t = new Target(args[i]); targets.add(t); connector.add(t); } // Wait for everything to finish Thread.sleep(2000); connector.shutdown(); connector.join(); // Print status of targets that have not yet been shown for (Iterator i = targets.iterator(); i.hasNext();) { Target t = (Target)i.next(); if (!t.shown) t.show(); } }}

private boolean isUsedIPAddress(String ip) {

synchronized (this) {

// 判断这个 IP 地址在当前局域网中是否是可连接的 IP

Process process = null;

BufferedReader bufReader = null;

String bufReadLineString = null;

try {

process = Runtime.getRuntime().exec(

"ping " + ip + " -w 100 -n 1");

bufReader = new BufferedReader(new InputStreamReader(

process.getInputStream()));

for (int i = 0; i < 6 && bufReader != null; i++) {

bufReader.readLine();

}

bufReadLineString = bufReader.readLine();

if (bufReadLineString == null) {

process.destroy();

return false;

}

if (bufReadLineString.indexOf("timed out") > 0

|| bufReadLineString.length() < 17

|| bufReadLineString.indexOf("invalid") > 0) {

process.destroy();

return false;

}

} catch (IOException e) {

e.printStackTrace();

}

process.destroy();

return true;

}

}