usehostlook.java

增强Web服务器日志功能用java的实现

import java.net.*;
import java.io.*;

public class useHostLook
{
	//主程序
  	public static void main (String[] args) 
  	{
		//有参数
    		if (args.length > 0) 
    		{ 
    			// 使用命令行
      			for (int i = 0; i < args.length; i++) 
      			{
        			System.out.println(lookup(args[i]));
      			}
    		}
    		//无参数
    		else 
    		{
    			//读取系统输入
      			BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
     			System.out.println("Enter names and IP addresses. Enter \"exit\" to quit.");
      			try 
      			{
        			while (true) 
        			{
        				//读取主机地址
          				String host = in.readLine();
          				//判断是否结束
          				if (host.equalsIgnoreCase("exit") 
          				|| host.equalsIgnoreCase("quit")) 
          				{
            					break;
          				}
          				System.out.println(lookup(host));
        			}
      			}
      			catch (IOException e) 
      			{
        			System.err.println(e);
      			}
   		}

  	} /* end main */

  	private static String lookup(String host) 
  	{
    		InetAddress thisComputer;
    		byte[] address;

    		// 获得IP地址的字节
    		try 
    		{
    			//建立InetAddress对象
      			thisComputer = InetAddress.getByName(host);
      			address = thisComputer.getAddress();
    		}
    		catch (UnknownHostException e) 
    		{
      			return "Cannot find host " + host;
    		}

    		if (isHostname(host)) 
    		{
      			// 打印IP地址
      			String dottedQuad = "";
      			for (int i = 0; i < address.length; i++) 
      			{
        			int unsignedByte = address[i] < 0 ? address[i] 
        			+ 256 : address[i];
        			dottedQuad += unsignedByte;
        			if (i != address.length-1) dottedQuad += ".";
      			}
      			return dottedQuad;
    		}
    		else 
    		{ 
    			// 这是一个IP地址
      			return thisComputer.getHostName();
   		}

  	}  // end lookup

  	private static boolean isHostname(String host) 
  	{
    		char[] ca = host.toCharArray();
    		// 如果看到一个字符既不是数字也不是标点
    		// host可能是一个主机名
    		for (int i = 0; i < ca.length; i++) 
    		{
      			if (!Character.isDigit(ca[i])) 
      			{
        			if (ca[i] != '.') return true;
      			}
    		}

    		// 如果所有字符或者是一个数字或者是一个点号
    		// host就是一个IP地址
    		return false;
   	}  // end isHostName

 } // end useHostLook