base64.java

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/****************************************************************************
 * Package		: com.ecSolutions.ecAppServer.util
 * File			: Base64.java
 * Create Date  : 2007-7-27
 * Author		: Steven Chen
 * 
 * Copyright(C) 2006 ecSolutions(shanghai) Co.,Limited.All Rights Reserved.
 *			
 ***************************************************************************/
package com.ecSolutions.ecAppServer.util;

/**
 * 
 * @author Steven Chen
 * @version $Id$
 *
 */
public class Base64 {
	/**
	 * 使用Base64算法加密字符串，使用系统字符集取byte数组，
	 * 如要加密中文字符串，请使用方法bytesToBase64(byte[] b)。
	 *
	 * @param 原字符串
	 * @return Base64加密的字符串
	 */
	    public static String encode(String s) throws Exception {
	        
	        return bytesToBase64(s.getBytes());
	        
	    }

	/**
	 * 解密使用Base64算法加密的字符串
	 *
	 * @param Base64加密的字符串
	 * @return 原字符串
	 */
	    public static String decode(String s) throws Exception {
	        byte encodechar[] = base64ToBytes(s);
	        return new String(encodechar);
	    }

		/**
		 * 解密使用Base64算法加密的字符串
		 *
		 * @param Base64加密的字符串
		 * @return 原字符串的byte数组
		 */
		    public static final byte[] base64ToBytes(String s) {
		        int k = 0;
		        char c[] = s.toCharArray();
		        int i = c.length;
		        int j = 0;
		        if (c[i - 1] == '=') {
		            j++;
		        }
		        if (c[i - 2] == '=') {
		            j++;
		        }
		        i = (i / 4) * 3 - j;
		        byte[] bt = new byte[i];
		        int l = 0;
		        int m = 0;
		        while(l + 3 < c.length) {
		            k = base64Int(c[l + 0]) << 18 | base64Int(c[l + 1]) << 12 | base64Int(c[l + 2]) << 6 
		                    | base64Int(c[l + 3]);
		            l += 4;
		            if(m >= i - 2)
		                break;
		            bt[m++] = (byte)(k >> 16 & 0xff);
		            bt[m++] = (byte)(k >> 8 & 0xff);
		            bt[m++] = (byte)(k & 0xff);
		        }
		        if (m < bt.length) {
		            bt[m++] = (byte)(k >> 16 & 0xff);
		        }
		        if (m < bt.length) {
		            bt[m++] = (byte)(k >> 8 & 0xff);
		        }
		        return bt;
		    }
		    
		    
			/**
			 * 使用Base64算法加密原byte数组
			 *
			 * @param 原byte数组
			 * @return 加密字符串
			 */
			    public static final String bytesToBase64(byte[] b) {
			        int m = 0;
			        int n = 0;
			        int i = (((b.length + 3) - 1) / 3) * 4;
			        char c[] = new char[i];
			        for (int j = b.length - 2; m < j;) {
			            int k = (b[m + 0] & 0xff) << 16 | (b[m + 1] & 0xff) << 8 | b[m + 2] & 0xff;
			            m += 3;
			            c[n++] = base64Char(k >> 18 & 0x3f);
			            c[n++] = base64Char(k >> 12 & 0x3f);
			            c[n++] = base64Char(k >> 6 & 0x3f);
			            c[n++] = base64Char(k & 0x3f);
			        }

			        if (m < b.length - 1) {
			            int l = (b[m + 0] & 0xff) << 16 | (b[m + 1] & 0xff) << 8;
			            c[n++] = base64Char(l >> 18 & 0x3f);
			            c[n++] = base64Char(l >> 12 & 0x3f);
			            c[n++] = base64Char(l >> 6 & 0x3f);
			            c[n++] = '=';
			        } else if (m < b.length) {
			            int o = (b[m + 0] & 0xff) << 16;
			            c[n++] = base64Char(o >> 18 & 0x3f);
			            c[n++] = base64Char(o >> 12 & 0x3f);
			            c[n++] = '=';
			            c[n++] = '=';
			        }
			        return new String(c, 0, n);
			    }

			    private static final char base64Char(int i) {
			        if (i >= 52) {
			            if (i < 62) {
			                return (char)((i - 52) + 48);
			            }
			            if (i == 62) {
			                return '+';
			            }
			            return i != 63 ? '?' : '/';
			        }
			        if (i >= 26) {
			            return (char)((i - 26) + 97);
			        }
			        if (i >= 0) {
			            return (char)((i - 0) + 65);
			        } else {
			            return '?';
			        }
			    }

			    private static final int base64Int(char c) {
			        if (c >= 'a') {
			            if (c <= 'z') {
			                return (c - 97) + 26;
			            } else {
			                return -1;
			            }
			        }
			        if (c >= 'A') {
			            if (c <= 'Z') {
			                return (c - 65) + 0;
			            } else {
			                return -1;
			            }
			        }
			        if (c >= '0') {
			            if (c <= '9') {
			                return (c - 48) + 52;
			            }
			            return c != '=' ? -1 : 0;
			        }
			        if (c == '+') {
			            return 62;
			        }
			        return c != '/' ? -1 : 63;
			    }		    
}