Decodes a string from Base64 format. - Java java.lang

Java examples for java.lang:String Base64

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Description

Decodes a string from Base64 format.

Demo Code


//package com.java2s;

public class Main {
    public static void main(String[] argv) throws Exception {
        String s = "java2s.com";
        System.out.println(decodeString(s));
    }/*from   w w  w  .  j a va  2  s .c om*/

    private static final byte[] map2 = new byte[128];

    /**
     * Decodes a string from Base64 format.
     * No blanks or line breaks are allowed within the Base64 encoded input data.
     *
     * @param s A Base64 String to be decoded.
     * @return A String containing the decoded data.
     * @throws IllegalArgumentException If the input is not valid Base64 encoded data.
     */
    public static String decodeString(String s) {
        return new String(decode(s));
    }

    /**
     * Decodes a byte array from Base64 format.
     * No blanks or line breaks are allowed within the Base64 encoded input data.
     *
     * @param s A Base64 String to be decoded.
     * @return An array containing the decoded data bytes.
     * @throws IllegalArgumentException If the input is not valid Base64 encoded data.
     */
    public static byte[] decode(String s) {
        return decode(s.toCharArray());
    }

    /**
     * Decodes a byte array from Base64 format.
     * No blanks or line breaks are allowed within the Base64 encoded input data.
     *
     * @param in A character array containing the Base64 encoded data.
     * @return An array containing the decoded data bytes.
     * @throws IllegalArgumentException If the input is not valid Base64 encoded data.
     */
    public static byte[] decode(char[] in) {
        return decode(in, 0, in.length);
    }

    /**
     * Decodes a byte array from Base64 format.
     * No blanks or line breaks are allowed within the Base64 encoded input data.
     *
     * @param in   A character array containing the Base64 encoded data.
     * @param iOff Offset of the first character in <code>in</code> to be processed.
     * @param iLen Number of characters to process in <code>in</code>, starting at <code>iOff</code>.
     * @return An array containing the decoded data bytes.
     * @throws IllegalArgumentException If the input is not valid Base64 encoded data.
     */
    public static byte[] decode(char[] in, int iOff, int iLen) {
        if (iLen % 4 != 0)
            throw new IllegalArgumentException(
                    "Length of Base64 encoded input string is not a multiple of 4.");
        while (iLen > 0 && in[iOff + iLen - 1] == '=')
            iLen--;
        int oLen = (iLen * 3) / 4;
        byte[] out = new byte[oLen];
        int ip = iOff;
        int iEnd = iOff + iLen;
        int op = 0;
        while (ip < iEnd) {
            int i0 = in[ip++];
            int i1 = in[ip++];
            int i2 = ip < iEnd ? in[ip++] : 'A';
            int i3 = ip < iEnd ? in[ip++] : 'A';
            if (i0 > 127 || i1 > 127 || i2 > 127 || i3 > 127)
                throw new IllegalArgumentException(
                        "Illegal character in Base64 encoded data.");
            int b0 = map2[i0];
            int b1 = map2[i1];
            int b2 = map2[i2];
            int b3 = map2[i3];
            if (b0 < 0 || b1 < 0 || b2 < 0 || b3 < 0)
                throw new IllegalArgumentException(
                        "Illegal character in Base64 encoded data.");
            int o0 = (b0 << 2) | (b1 >>> 4);
            int o1 = ((b1 & 0xf) << 4) | (b2 >>> 2);
            int o2 = ((b2 & 3) << 6) | b3;
            out[op++] = (byte) o0;
            if (op < oLen)
                out[op++] = (byte) o1;
            if (op < oLen)
                out[op++] = (byte) o2;
        }
        return out;
    }
}

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