urldecoder.java

基于人工免疫原理的入侵检测系统框架

/*=================
 * Copyright (C) 2001  The University of New Mexico. All Rights Reserved. 
 *
 * Lisys is a program that monitors TCP SYN packets to detect network
 * traffic anomalies.
 *
 * Licensed under the GNU General Public License (GPL), version 2 or
 * higher.  Please see the COPYING and PATENT files included with the
 * Lisys distribution, which can be found at:
 *
 *   http://www.cs.unm.edu/~judd/lisys/
 *
 * Also, the current text of the GPL can be found at: 
 *
 *   http://www.gnu.org/copyleft/gpl.html
 * 
 * Note that Lisys has NO WARRANTY!
 *=================*/

package edu.unm.cs.lisys.net;

/**==========
 * URLDecoder.java
 *   Since java 1.1 doesn't have the URLDecoder (this appears in java
 *   1.2), we have written an equivalent.
 *
 *   The class contains one static function, used to decode URLs encoded
 *   by java.net.URLEncoder.
 *   @see java.net.URLEncoder
 *
 * Here are the people who have worked on this code in the order they
 * have worked on it:
 *   @author Hajime Inoue <[e-mail]>
 *   @author Justin Balthrop <[e-mail]>
 *==========*/

public class URLDecoder
{
    /**==========
     * decode:
     *   When given an encoded URL as a string, it decodes it.
     * 
     * @param url the URL to be decoded
     * @return the decoded URL
     *==========*/
    public static String decode(String url)
    {
	StringBuffer sb = new StringBuffer();
	
	for(int i=0; i < url.length(); i++) {
	    int val = (int)url.charAt(i);
	    if ( (val >= 'a' && val <= 'z') ||
		 (val >= 'A' && val <= 'Z') ||
		 (val >= '0' && val <= '9') ||
		 (val == '&') || (val == '.') ||
		 (val == '/') || (val == '_') ||
		 (val == '?') ) {
		sb.append((char)val);
	    }
	    else if ( val == '+') {
		sb.append(' ');
	    }
	    else if ( val == '%') {
		char first = url.charAt(i+1);
		char second = url.charAt(i+2);
		
		val = hex(first, second);
		sb.append((char)val);
		i = i+2;
	    }
	}
	return sb.toString();
    }
	
    /**==========
     * hex:
     *	 Utility function used to calculate hex values from two
     *	 characters.  For instance, if you have the value 20 in HEX,
     *	 it will return the value 32 in DECIMAL.
     *
     * @param first the first char in hex representation
     * @param second the second char in hex representation
     * @return the decimal value of the two chars as an integer 
     *==========*/	
    protected static int hex(char first, char second)
    {
	int x, y;
	
	x = (int)first;
	y = (int)second;
	
	// To upper case
	if ( x > 71 ) x = x - 32;
	if ( y > 71 ) y = y - 32;
	
	if ( x > 57 ) x = 16 * ( x - 55);
	else x = 16 * ( x - 48);

	if ( y > 57 ) y = y - 55;
	else y = y - 48;
	
	return x + y;
    }
}