Converts a base64 encoded string of four chars to the corresponding bytes - Java java.lang

Java examples for java.lang:String Base64

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Description

Converts a base64 encoded string of four chars to the corresponding bytes

Demo Code

/**/*from   w  w  w  . j  av a 2  s .  c  o  m*/
 * 
 * Copyright (C) 2004-2008 FhG Fokus
 *
 * This file is part of the FhG Fokus UPnP stack - an open source UPnP implementation
 * with some additional features
 *
 * You can redistribute the FhG Fokus UPnP stack and/or modify it
 * under the terms of the GNU General Public License Version 3 as published by
 * the Free Software Foundation.
 *
 * For a license to use the FhG Fokus UPnP stack software under conditions
 * other than those described here, or to purchase support for this
 * software, please contact Fraunhofer FOKUS by e-mail at the following
 * addresses:
 *   upnpstack@fokus.fraunhofer.de
 *
 * The FhG Fokus UPnP stack is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>
 * or write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
 */
//package com.java2s;

public class Main {
    public static void main(String[] argv) throws Exception {
        String value = "java2s.com";
        System.out.println(java.util.Arrays.toString(base64ToBytes(value)));
    }

    /** Converts a base64 encoded string of four chars to the corresponding bytes */
    private static byte[] base64ToBytes(String value) {
        // catch wrong size
        if (value.length() != 4) {
            return null;
        }

        // process padding
        int paddingOffset = value.indexOf("=");
        // no padding
        if (paddingOffset == -1) {
            byte[] result = new byte[3];
            result[0] = (byte) (base64ToBits(value.charAt(0)) << 2 | base64ToBits(value
                    .charAt(1)) >> 4);
            result[1] = (byte) (base64ToBits(value.charAt(1)) << 4 | base64ToBits(value
                    .charAt(2)) >> 2);
            result[2] = (byte) (base64ToBits(value.charAt(2)) << 6 | base64ToBits(value
                    .charAt(3)));
            return result;
        }
        // 1 padded byte
        if (paddingOffset == 3) {
            byte[] result = new byte[2];
            result[0] = (byte) (base64ToBits(value.charAt(0)) << 2 | base64ToBits(value
                    .charAt(1)) >> 4);
            result[1] = (byte) (base64ToBits(value.charAt(1)) << 4 | base64ToBits(value
                    .charAt(2)) >> 2);
            return result;
        }
        // 2 padded bytes
        if (paddingOffset == 2) {
            byte[] result = new byte[1];
            result[0] = (byte) (base64ToBits(value.charAt(0)) << 2 | base64ToBits(value
                    .charAt(1)) >> 4);
            return result;
        }
        // error
        return null;
    }

    /** Converts a Base64 char to to corresponding 6-bit value */
    private static byte base64ToBits(char data) {
        if (data >= 'A' && data <= 'Z') {
            return (byte) (data - 'A');
        }
        if (data >= 'a' && data <= 'z') {
            return (byte) (data - 'a' + 26);
        }
        if (data >= '0' && data <= '9') {
            return (byte) (data - '0' + 52);
        }
        if (data == '+') {
            return (byte) 62;
        }
        return (byte) 63;
    }
}

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