Java Base64 Convert to fromBase64Impl(String data)

Description

Decode a base64 string into a byte array.

License

Apache License

Parameter

Parameter	Description
data	the encoded data.

Return

a byte array.

Declaration

private static byte[] fromBase64Impl(String data) 

Method Source Code

//package com.java2s;
/*//w ww. j av a2 s.  c om
 * Copyright 2009 Google Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

public class Main {
    /**
     * An array mapping legal base 64 characters [a-zA-Z0-9$_] to their associated 6-bit values.
     * The source indicies will be given by 7-bit ASCII characters, thus the array size needs to
     * be 128 (actually 123 would suffice for the given set of characters in use).
     */
    private static final byte[] base64Values = new byte[128];

    /**
     * Decode a base64 string into a byte array.
     * 
     * @param data the encoded data.
     * @return a byte array.
     * @see #fromBase64(String)
     */
    private static byte[] fromBase64Impl(String data) {
        if (data == null) {
            return null;
        }

        int len = data.length();
        assert (len % 4) == 0;

        if (len == 0) {
            return new byte[0];
        }

        char[] chars = new char[len];
        data.getChars(0, len, chars, 0);

        int olen = 3 * (len / 4);
        if (chars[len - 2] == '=') {
            --olen;
        }
        if (chars[len - 1] == '=') {
            --olen;
        }

        byte[] bytes = new byte[olen];

        int iidx = 0;
        int oidx = 0;
        while (iidx < len) {
            int c0 = base64Values[chars[iidx++] & 0xff];
            int c1 = base64Values[chars[iidx++] & 0xff];
            int c2 = base64Values[chars[iidx++] & 0xff];
            int c3 = base64Values[chars[iidx++] & 0xff];
            int c24 = (c0 << 18) | (c1 << 12) | (c2 << 6) | c3;

            bytes[oidx++] = (byte) (c24 >> 16);
            if (oidx == olen) {
                break;
            }
            bytes[oidx++] = (byte) (c24 >> 8);
            if (oidx == olen) {
                break;
            }
            bytes[oidx++] = (byte) c24;
        }

        return bytes;
    }
}

Related

1. fromBase64(String base64Text)
2. fromBase64(String data)
3. fromBase64(String s)
4. fromBase64(String str)
5. fromBase64decodedImageToByte(String base64encoded)
6. fromBase64String(String base64)
7. fromBase64String(String encoded)
8. fromBase64Url(String data)