Android String Decode decode(String source)

Description

Returns the plaintext equivalent of a base 64-encoded string.

License

Open Source License

Parameter

Parameter	Description
source	a base 64 string (which must have a multiple of 4 characters)

Declaration

public static String decode(String source) 

Method Source Code

//package com.java2s;
/********************************************************************************************************************
 * $Id: Base64.java,v 1.4 2002/12/24 15:17:17 russgold Exp $
 *
 * Copyright (c) 2000-2002 by Russell Gold
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated 
 * documentation files (the "Software"), to deal in the Software without restriction, including without limitation 
 * the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and
 * to permit persons to whom the Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or substantial portions 
 * of the Software./*from w  w  w  .ja  v  a 2s.co  m*/
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO
 * THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
 * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 *
 *******************************************************************************************************************/

public class Main {
    final static String encodingChar = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

    /**
     * Returns the plaintext equivalent of a base 64-encoded string.
     * 
     * @param source
     *            a base 64 string (which must have a multiple of 4 characters)
     */
    public static String decode(String source) {
        if (source.length() % 4 != 0)
            throw new RuntimeException(
                    "valid Base64 codes have a multiple of 4 characters");
        int numGroups = source.length() / 4;
        int numExtraBytes = source.endsWith("==") ? 2 : (source
                .endsWith("=") ? 1 : 0);
        byte[] targetBytes = new byte[3 * numGroups];
        byte[] sourceBytes = new byte[4];
        for (int group = 0; group < numGroups; group++) {
            for (int i = 0; i < sourceBytes.length; i++) {
                sourceBytes[i] = (byte) Math.max(0,
                        encodingChar.indexOf(source.charAt(4 * group + i)));
            }
            convert4To3(sourceBytes, targetBytes, group * 3);
        }
        return new String(targetBytes, 0, targetBytes.length
                - numExtraBytes);
    }

    private static void convert4To3(byte[] source, byte[] target,
            int targetIndex) {
        target[targetIndex] = (byte) ((source[0] << 2) | (source[1] >>> 4));
        target[targetIndex + 1] = (byte) (((source[1] & 0x0f) << 4) | (source[2] >>> 2));
        target[targetIndex + 2] = (byte) (((source[2] & 0x03) << 6) | (source[3]));
    }
}

Related

1. decode(String sourceStr, String compareStr, String returnStr)
2. decode(String sourceStr, String compareStr, String returnStr, String defaultStr)
3. decode(String str)
4. decode(String str)
5. decode(String base64)
6. decode(String str)
7. decode(String str)
8. decode(String s)
9. decode(String str)