Java Base64 Decode base64Decode(String b64)

Description

Decode a Base-64 string into a byte array.

License

Open Source License

Parameter

Parameter	Description
b64	The Base-64 encoded string.

Exception

Parameter	Description

Return

The decoded bytes.

Declaration

public static byte[] base64Decode(String b64) throws IOException 

Method Source Code

//package com.java2s;
// under the terms of the GNU General Public License as published by the Free

import java.io.ByteArrayOutputStream;
import java.io.IOException;

public class Main {
    /** Base-64 characters. */
    private static final String BASE_64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    /** Base-64 padding character. */
    private static final char BASE_64_PAD = '=';

    /**//from   ww  w  .ja  v  a 2  s .  c o  m
     * Decode a Base-64 string into a byte array.
     *
     * @param b64 The Base-64 encoded string.
     * @return The decoded bytes.
     * @throws java.io.IOException If the argument is not a valid Base-64
     *    encoding.
     */
    public static byte[] base64Decode(String b64) throws IOException {
        ByteArrayOutputStream result = new ByteArrayOutputStream();
        int state = 0, i;
        byte temp = 0;

        for (i = 0; i < b64.length(); i++) {
            if (Character.isWhitespace(b64.charAt(i))) {
                continue;
            }
            if (b64.charAt(i) == BASE_64_PAD) {
                break;
            }

            int pos = BASE_64.indexOf(b64.charAt(i));
            if (pos < 0) {
                throw new IOException("non-Base64 character " + b64.charAt(i));
            }
            switch (state) {
            case 0:
                temp = (byte) (pos - BASE_64.indexOf('A') << 2);
                state = 1;
                break;

            case 1:
                temp |= (byte) (pos - BASE_64.indexOf('A') >>> 4);
                result.write(temp);
                temp = (byte) ((pos - BASE_64.indexOf('A') & 0x0f) << 4);
                state = 2;
                break;

            case 2:
                temp |= (byte) ((pos - BASE_64.indexOf('A') & 0x7f) >>> 2);
                result.write(temp);
                temp = (byte) ((pos - BASE_64.indexOf('A') & 0x03) << 6);
                state = 3;
                break;

            case 3:
                temp |= (byte) (pos - BASE_64.indexOf('A') & 0xff);
                result.write(temp);
                state = 0;
                break;

            default:
                throw new Error("this statement should be unreachable");
            }
        }

        if (i < b64.length() && b64.charAt(i) == BASE_64_PAD) {
            switch (state) {
            case 0:
            case 1:
                throw new IOException("malformed Base64 sequence");

            case 2:
                for (; i < b64.length(); i++) {
                    if (!Character.isWhitespace(b64.charAt(i))) {
                        break;
                    }
                }
                // We must see a second pad character here.
                if (b64.charAt(i) != BASE_64_PAD) {
                    throw new IOException("malformed Base64 sequence");
                }
                i++;
                // Fall-through.

            case 3:
                i++;
                for (; i < b64.length(); i++) {
                    // We should only see whitespace after this.
                    if (!Character.isWhitespace(b64.charAt(i))) {
                        System.err.println(b64.charAt(i));
                        throw new IOException("malformed Base64 sequence");
                    }
                }
            }
        } else {
            if (state != 0) {
                throw new IOException("malformed Base64 sequence");
            }
        }

        return result.toByteArray();
    }
}

Related

1. base64Decode(byte[] textBytes)
2. base64Decode(char[] a_data)
3. base64Decode(final String data)
4. base64Decode(final String s)
5. base64Decode(String _s, String _enc)
6. base64Decode(String base64Str)
7. base64Decode(String data)
8. base64Decode(String input)
9. base64Decode(String s)