Decodieren Sie Base64-Daten in Java

Ich habe ein Bild, das Base64-codiert ist. Was ist der beste Weg, um das in Java zu dekodieren? Hoffentlich werden nur die in Sun Java 6 enthaltenen Bibliotheken verwendet.

Ab Version 6 wird Java SE mit JAXB ausgeliefert. javax.xml.bind.DatatypeConverterhat statische Methoden, die dies einfach machen. Siehe parseBase64Binary()und printBase64Binary().

Ab Java 8 gibt es eine offiziell unterstützte API für die Base64-Codierung und -Decodierung. Mit der Zeit wird dies wahrscheinlich die Standardauswahl sein.

Die API enthält die Klasse java.util.Base64und ihre verschachtelten Klassen. Es werden drei verschiedene Varianten unterstützt: Basic, URL Safe und MIME.

Beispielcode mit der "grundlegenden" Codierung:

import java.util.Base64;

byte[] bytes = "Hello, World!".getBytes("UTF-8");
String encoded = Base64.getEncoder().encodeToString(bytes);
byte[] decoded = Base64.getDecoder().decode(encoded);

Die Dokumentation fürjava.util.Base64 enthält mehrere weitere Methoden zum Konfigurieren von Encodern und Decodern sowie zum Verwenden verschiedener Klassen als Ein- und Ausgänge (Byte-Arrays, Strings, ByteBuffers, java.io-Streams).

Keine Notwendigkeit, Commons zu verwenden - Sun liefert einen Base64-Encoder mit Java aus. Sie können es als solches importieren:

import sun.misc.BASE64Decoder;

Und dann benutze es so:

BASE64Decoder decoder = new BASE64Decoder();
byte[] decodedBytes = decoder.decodeBuffer(encodedBytes);

Wo encodedBytesist entweder ein java.lang.Stringoder ein java.io.InputStream. Beachten Sie nur, dass die sun.*Klassen von Sun nicht "offiziell unterstützt" werden.

EDIT: Wer wusste, dass dies die umstrittenste Antwort sein würde, die ich jemals posten würde? Ich weiß, dass sun. * -Pakete nicht unterstützt werden oder garantiert weiterhin existieren, und ich kenne Commons und verwende sie ständig. Das Poster fragte jedoch nach einer Klasse, die "in Sun Java 6 enthalten" war, und das versuchte ich zu beantworten. Ich stimme zu, dass Commons der beste Weg im Allgemeinen ist.

EDIT 2: Wie amir75 weiter unten ausführt, wird Java 6+ mit JAXB ausgeliefert, das unterstützten Code zum Codieren / Decodieren von Base64 enthält. Bitte sehen Sie die Antwort von Jeremy Ross unten.

Speziell im Commons Codec : Klasse Base64zu decode(byte[] array)oderencode(byte[] array)

In Guava ist jetzt die Base64-Dekodierung integriert.

Verwenden Sie BaseEncoding.base64 (). Decode ()

Bezüglich des Umgangs mit möglichen Leerzeichen bei der Verwendung von Eingaben

BaseEncoding.base64().decode(CharMatcher.WHITESPACE.removeFrom(...));

Weitere Informationen finden Sie in dieser Diskussion

Meine Lösung ist am schnellsten und einfachsten.

public class MyBase64 {

    private final static char[] ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();

    private static int[]  toInt   = new int[128];

    static {
        for(int i=0; i< ALPHABET.length; i++){
            toInt[ALPHABET[i]]= i;
        }
    }

    /**
     * Translates the specified byte array into Base64 string.
     *
     * @param buf the byte array (not null)
     * @return the translated Base64 string (not null)
     */
    public static String encode(byte[] buf){
        int size = buf.length;
        char[] ar = new char[((size + 2) / 3) * 4];
        int a = 0;
        int i=0;
        while(i < size){
            byte b0 = buf[i++];
            byte b1 = (i < size) ? buf[i++] : 0;
            byte b2 = (i < size) ? buf[i++] : 0;

            int mask = 0x3F;
            ar[a++] = ALPHABET[(b0 >> 2) & mask];
            ar[a++] = ALPHABET[((b0 << 4) | ((b1 & 0xFF) >> 4)) & mask];
            ar[a++] = ALPHABET[((b1 << 2) | ((b2 & 0xFF) >> 6)) & mask];
            ar[a++] = ALPHABET[b2 & mask];
        }
        switch(size % 3){
            case 1: ar[--a]  = '=';
            case 2: ar[--a]  = '=';
        }
        return new String(ar);
    }

    /**
     * Translates the specified Base64 string into a byte array.
     *
     * @param s the Base64 string (not null)
     * @return the byte array (not null)
     */
    public static byte[] decode(String s){
        int delta = s.endsWith( "==" ) ? 2 : s.endsWith( "=" ) ? 1 : 0;
        byte[] buffer = new byte[s.length()*3/4 - delta];
        int mask = 0xFF;
        int index = 0;
        for(int i=0; i< s.length(); i+=4){
            int c0 = toInt[s.charAt( i )];
            int c1 = toInt[s.charAt( i + 1)];
            buffer[index++]= (byte)(((c0 << 2) | (c1 >> 4)) & mask);
            if(index >= buffer.length){
                return buffer;
            }
            int c2 = toInt[s.charAt( i + 2)];
            buffer[index++]= (byte)(((c1 << 4) | (c2 >> 2)) & mask);
            if(index >= buffer.length){
                return buffer;
            }
            int c3 = toInt[s.charAt( i + 3 )];
            buffer[index++]= (byte)(((c2 << 6) | c3) & mask);
        }
        return buffer;
    } 

}

Hier ist meine eigene Implementierung, wenn sie für jemanden nützlich sein könnte:

public class Base64Coder {

    // The line separator string of the operating system.
    private static final String systemLineSeparator = System.getProperty("line.separator");

    // Mapping table from 6-bit nibbles to Base64 characters.
    private static final char[] map1 = new char[64];
       static {
          int i=0;
          for (char c='A'; c<='Z'; c++) map1[i++] = c;
          for (char c='a'; c<='z'; c++) map1[i++] = c;
          for (char c='0'; c<='9'; c++) map1[i++] = c;
          map1[i++] = '+'; map1[i++] = '/'; }

    // Mapping table from Base64 characters to 6-bit nibbles.
    private static final byte[] map2 = new byte[128];
       static {
          for (int i=0; i<map2.length; i++) map2[i] = -1;
          for (int i=0; i<64; i++) map2[map1[i]] = (byte)i; }

    /**
    * Encodes a string into Base64 format.
    * No blanks or line breaks are inserted.
    * @param s  A String to be encoded.
    * @return   A String containing the Base64 encoded data.
    */
    public static String encodeString (String s) {
       return new String(encode(s.getBytes())); }

    /**
    * Encodes a byte array into Base 64 format and breaks the output into lines of 76 characters.
    * This method is compatible with <code>sun.misc.BASE64Encoder.encodeBuffer(byte[])</code>.
    * @param in  An array containing the data bytes to be encoded.
    * @return    A String containing the Base64 encoded data, broken into lines.
    */
    public static String encodeLines (byte[] in) {
       return encodeLines(in, 0, in.length, 76, systemLineSeparator); }

    /**
    * Encodes a byte array into Base 64 format and breaks the output into lines.
    * @param in            An array containing the data bytes to be encoded.
    * @param iOff          Offset of the first byte in <code>in</code> to be processed.
    * @param iLen          Number of bytes to be processed in <code>in</code>, starting at <code>iOff</code>.
    * @param lineLen       Line length for the output data. Should be a multiple of 4.
    * @param lineSeparator The line separator to be used to separate the output lines.
    * @return              A String containing the Base64 encoded data, broken into lines.
    */
    public static String encodeLines (byte[] in, int iOff, int iLen, int lineLen, String lineSeparator) {
       int blockLen = (lineLen*3) / 4;
       if (blockLen <= 0) throw new IllegalArgumentException();
       int lines = (iLen+blockLen-1) / blockLen;
       int bufLen = ((iLen+2)/3)*4 + lines*lineSeparator.length();
       StringBuilder buf = new StringBuilder(bufLen);
       int ip = 0;
       while (ip < iLen) {
          int l = Math.min(iLen-ip, blockLen);
          buf.append (encode(in, iOff+ip, l));
          buf.append (lineSeparator);
          ip += l; }
       return buf.toString(); }

    /**
    * Encodes a byte array into Base64 format.
    * No blanks or line breaks are inserted in the output.
    * @param in  An array containing the data bytes to be encoded.
    * @return    A character array containing the Base64 encoded data.
    */
    public static char[] encode (byte[] in) {
       return encode(in, 0, in.length); }

    /**
    * Encodes a byte array into Base64 format.
    * No blanks or line breaks are inserted in the output.
    * @param in    An array containing the data bytes to be encoded.
    * @param iLen  Number of bytes to process in <code>in</code>.
    * @return      A character array containing the Base64 encoded data.
    */
    public static char[] encode (byte[] in, int iLen) {
       return encode(in, 0, iLen); }

    /**
    * Encodes a byte array into Base64 format.
    * No blanks or line breaks are inserted in the output.
    * @param in    An array containing the data bytes to be encoded.
    * @param iOff  Offset of the first byte in <code>in</code> to be processed.
    * @param iLen  Number of bytes to process in <code>in</code>, starting at <code>iOff</code>.
    * @return      A character array containing the Base64 encoded data.
    */
    public static char[] encode (byte[] in, int iOff, int iLen) {
       int oDataLen = (iLen*4+2)/3;       // output length without padding
       int oLen = ((iLen+2)/3)*4;         // output length including padding
       char[] out = new char[oLen];
       int ip = iOff;
       int iEnd = iOff + iLen;
       int op = 0;
       while (ip < iEnd) {
          int i0 = in[ip++] & 0xff;
          int i1 = ip < iEnd ? in[ip++] & 0xff : 0;
          int i2 = ip < iEnd ? in[ip++] & 0xff : 0;
          int o0 = i0 >>> 2;
          int o1 = ((i0 &   3) << 4) | (i1 >>> 4);
          int o2 = ((i1 & 0xf) << 2) | (i2 >>> 6);
          int o3 = i2 & 0x3F;
          out[op++] = map1[o0];
          out[op++] = map1[o1];
          out[op] = op < oDataLen ? map1[o2] : '='; op++;
          out[op] = op < oDataLen ? map1[o3] : '='; op++; }
       return out; }

    /**
    * 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 and ignores line separators, tabs and blanks.
    * CR, LF, Tab and Space characters are ignored in the input data.
    * This method is compatible with <code>sun.misc.BASE64Decoder.decodeBuffer(String)</code>.
    * @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[] decodeLines (String s) {
       char[] buf = new char[s.length()];
       int p = 0;
       for (int ip = 0; ip < s.length(); ip++) {
          char c = s.charAt(ip);
          if (c != ' ' && c != '\r' && c != '\n' && c != '\t')
             buf[p++] = c; }
       return decode(buf, 0, p); }

    /**
    * 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; }

    // Dummy constructor.
    private Base64Coder() {}
}

sun.misc.BASE64DecoderSchauen Sie sich als Alternative zu oder als Nicht-Kernbibliotheken an javax.mail.internet.MimeUtility.decode().

public static byte[] encode(byte[] b) throws Exception {
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    OutputStream b64os = MimeUtility.encode(baos, "base64");
    b64os.write(b);
    b64os.close();
    return baos.toByteArray();
}
public static byte[] decode(byte[] b) throws Exception {
    ByteArrayInputStream bais = new ByteArrayInputStream(b);
    InputStream b64is = MimeUtility.decode(bais, "base64");
    byte[] tmp = new byte[b.length];
    int n = b64is.read(tmp);
    byte[] res = new byte[n];
    System.arraycopy(tmp, 0, res, 0, n);
    return res;
}

Link mit vollständigem Code: Codieren / Decodieren zu / von Base64

Eine weitere späte Antwort, aber mein Benchmarking zeigt, dass Jettys Implementierung des Base64- Encoders ziemlich schnell ist. Nicht so schnell wie MiGBase64, aber schneller als iHarder Base64 .

import org.eclipse.jetty.util.B64Code;

final String decoded = B64Code.decode(encoded, "UTF-8");

Ich habe auch einige Benchmarks gemacht:

      library     |    encode    |    decode   
------------------+--------------+-------------
 'MiGBase64'      |  10146001.00 |  6426446.00
 'Jetty B64Code'  |   8846191.00 |  3101361.75
 'iHarder Base64' |   3259590.50 |  2505280.00
 'Commons-Codec'  |    241318.04 |   255179.96

Dies sind Läufe / Sek., Daher ist höher besser.

Bei einem Test Encoder / Decoder Beispiel javax.xml.bind.DatatypeConverter unter Verwendung von Methoden parseBase64Binary () und printBase64Binary () mit Bezug auf @ jeremy-ross und @nightfirecat Antwort.

@Test
public void EncodeDecode() {
    //ENCODE
    String hello = "Hello World";
    byte[] helloBytes = hello.getBytes(StandardCharsets.UTF_8);
    String encodedHello = DatatypeConverter.printBase64Binary(helloBytes);
    LOGGER.info(hello + " encoded=> " + encodedHello);

    //DECODE
    byte[] encodedHelloBytes = DatatypeConverter.parseBase64Binary(encodedHello);
    String helloAgain = new String(encodedHelloBytes, StandardCharsets.UTF_8) ;
    LOGGER.info(encodedHello + " decoded=> " + helloAgain);

    Assert.assertEquals(hello, helloAgain);
}

Ergebnis:

INFO - Hello World encoded=> SGVsbG8gV29ybGQ=
INFO - SGVsbG8gV29ybGQ= decoded=> Hello World

Wenn Sie eine leistungsbasierte Lösung bevorzugen, können Sie "MiGBase64" verwenden.

http://migbase64.sourceforge.net/

public class Base64Test {
    public static void main(String[] args) {
    String encodeToString = Base64.encodeToString("JavaTips.net".getBytes(), true);
    System.out.println("encodeToString " + encodeToString);
    byte[] decodedBytes = Base64.decode(encodeToString.getBytes());
    System.out.println("decodedBytes " + new String(decodedBytes));
    }
}

Dies ist eine späte Antwort, aber Joshua Bloch hat seine Base64Klasse (als er für Sun, ahem, Oracle arbeitete) unter derjava.util.prefs Paket verpflichtet. Diese Klasse existiert seit JDK 1.4.

Z.B

String currentString = "Hello World";
String base64String = java.util.prefs.Base64.byteArrayToBase64(currentString.getBytes("UTF-8"));

Hoffe das hilft dir:

import com.sun.org.apache.xml.internal.security.utils.Base64;
String str="Hello World";
String base64_str=Base64.encode(str.getBytes("UTF-8"));

Oder:

String str="Hello World";
String base64_str="";
try
   {base64_str=(String)Class.forName("java.util.prefs.Base64").getDeclaredMethod("byteArrayToBase64", new Class[]{byte[].class}).invoke(null, new Object[]{str.getBytes("UTF-8")});
   }
catch (Exception ee) {}

java.util.prefs.Base64 arbeitet auf lokal rt.jar ,

Aber es ist nicht in der weißen Liste der JRE-Klasse

und nicht in Verfügbare Klassen, die nicht in der GAE / J-Whitelist aufgeführt sind

Was für eine Schande!

PS. In Android ist es einfach, weil das android.util.Base64seit Android API Level 8 enthalten ist.

Sie können eine Datei aus einer codierten Base64-Zeichenfolge schreiben oder herunterladen:

Base64 base64 = new Base64(); 
String encodedFile="JVBERi0xLjUKJeLjz9MKMSAwIG9iago8PCAKICAgL1R5cGUgL0NhdGFsb2cKICAgL1BhZ2VzIDIgMCBSCiAgIC9QYWdlTGF5b3V0IC9TaW5"; 
              byte[] dd=encodedFile.getBytes();
            byte[] bytes = Base64.decodeBase64(dd);

 response.setHeader("Content-disposition", "attachment; filename=\""+filename+"\"");
            response.setHeader("Cache-Control", "no-cache");
            response.setHeader("Expires", "-1");

            // actually send result bytes
            response.getOutputStream().write(bytes);

Arbeitete für mich und hoffentlich auch für dich ...

Die Java 8-Implementierung von java.util.Base64 hat keine Abhängigkeiten von anderen Java 8-spezifischen Klassen.

Ich bin nicht sicher, ob dies für Java 6-Projekte funktioniert, aber es ist möglich, die Base64.javaDatei zu kopieren, in ein Java 7-Projekt einzufügen und sie ohne andere Änderungen als das Importieren von java.util.Arrays und zu kompilierenjava.util.Objects .

Beachten Sie, dass die Base64.java-Datei von der GNU GPL2 abgedeckt wird

Ich habe das benutzt android.util.base64, das ohne Abhängigkeiten ziemlich gut funktioniert:

Verwendungszweck:

byte[] decodedKey = Base64.decode(encodedPublicKey, Base64.DEFAULT);

Paket com.test;

import java.io.UnsupportedEncodingException;

/**
 * Utilities for encoding and decoding the Base64 representation of
 * binary data.  See RFCs <a
 * href="http://www.ietf.org/rfc/rfc2045.txt">2045</a> and <a
 * href="http://www.ietf.org/rfc/rfc3548.txt">3548</a>.
 */
public class Base64 {

    public static final int DEFAULT = 0;


    public static final int NO_PADDING = 1;


    public static final int NO_WRAP = 2;


    public static final int CRLF = 4;


    public static final int URL_SAFE = 8;


    public static final int NO_CLOSE = 16;

    //  --------------------------------------------------------
    //  shared code
    //  --------------------------------------------------------

    /* package */ static abstract class Coder {
        public byte[] output;
        public int op;

        public abstract boolean process(byte[] input, int offset, int len, boolean finish);


        public abstract int maxOutputSize(int len);
    }

    //  --------------------------------------------------------
    //  decoding
    //  --------------------------------------------------------


    public static byte[] decode(String str, int flags) {
        return decode(str.getBytes(), flags);
    }

    public static byte[] decode(byte[] input, int flags) {
        return decode(input, 0, input.length, flags);
    }


    public static byte[] decode(byte[] input, int offset, int len, int flags) {
        // Allocate space for the most data the input could represent.
        // (It could contain less if it contains whitespace, etc.)
        Decoder decoder = new Decoder(flags, new byte[len*3/4]);

        if (!decoder.process(input, offset, len, true)) {
            throw new IllegalArgumentException("bad base-64");
        }

        // Maybe we got lucky and allocated exactly enough output space.
        if (decoder.op == decoder.output.length) {
            return decoder.output;
        }

        // Need to shorten the array, so allocate a new one of the
        // right size and copy.
        byte[] temp = new byte[decoder.op];
        System.arraycopy(decoder.output, 0, temp, 0, decoder.op);
        return temp;
    }

   static class Decoder extends Coder {       
        private static final int DECODE[] = {
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
            52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1,
            -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
            15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
            -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
            41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        };

        /**
         * Decode lookup table for the "web safe" variant (RFC 3548
         * sec. 4) where - and _ replace + and /.
         */
        private static final int DECODE_WEBSAFE[] = {
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1,
            52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1,
            -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
            15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, 63,
            -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
            41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        };

        /** Non-data values in the DECODE arrays. */
        private static final int SKIP = -1;
        private static final int EQUALS = -2;


        private int state;   // state number (0 to 6)
        private int value;

        final private int[] alphabet;

        public Decoder(int flags, byte[] output) {
            this.output = output;

            alphabet = ((flags & URL_SAFE) == 0) ? DECODE : DECODE_WEBSAFE;
            state = 0;
            value = 0;
        }


        public int maxOutputSize(int len) {
            return len * 3/4 + 10;
        }

        /**
         * Decode another block of input data.
         *
         * @return true if the state machine is still healthy.  false if
         *         bad base-64 data has been detected in the input stream.
         */
        public boolean process(byte[] input, int offset, int len, boolean finish) {
            if (this.state == 6) return false;

            int p = offset;
            len += offset;

            int state = this.state;
            int value = this.value;
            int op = 0;
            final byte[] output = this.output;
            final int[] alphabet = this.alphabet;

            while (p < len) {                
                if (state == 0) {
                    while (p+4 <= len &&
                           (value = ((alphabet[input[p] & 0xff] << 18) |
                                     (alphabet[input[p+1] & 0xff] << 12) |
                                     (alphabet[input[p+2] & 0xff] << 6) |
                                     (alphabet[input[p+3] & 0xff]))) >= 0) {
                        output[op+2] = (byte) value;
                        output[op+1] = (byte) (value >> 8);
                        output[op] = (byte) (value >> 16);
                        op += 3;
                        p += 4;
                    }
                    if (p >= len) break;
                }

                int d = alphabet[input[p++] & 0xff];

                switch (state) {
                case 0:
                    if (d >= 0) {
                        value = d;
                        ++state;
                    } else if (d != SKIP) {
                        this.state = 6;
                        return false;
                    }
                    break;

                case 1:
                    if (d >= 0) {
                        value = (value << 6) | d;
                        ++state;
                    } else if (d != SKIP) {
                        this.state = 6;
                        return false;
                    }
                    break;

                case 2:
                    if (d >= 0) {
                        value = (value << 6) | d;
                        ++state;
                    } else if (d == EQUALS) {
                        // Emit the last (partial) output tuple;
                        // expect exactly one more padding character.
                        output[op++] = (byte) (value >> 4);
                        state = 4;
                    } else if (d != SKIP) {
                        this.state = 6;
                        return false;
                    }
                    break;

                case 3:
                    if (d >= 0) {
                        // Emit the output triple and return to state 0.
                        value = (value << 6) | d;
                        output[op+2] = (byte) value;
                        output[op+1] = (byte) (value >> 8);
                        output[op] = (byte) (value >> 16);
                        op += 3;
                        state = 0;
                    } else if (d == EQUALS) {
                        // Emit the last (partial) output tuple;
                        // expect no further data or padding characters.
                        output[op+1] = (byte) (value >> 2);
                        output[op] = (byte) (value >> 10);
                        op += 2;
                        state = 5;
                    } else if (d != SKIP) {
                        this.state = 6;
                        return false;
                    }
                    break;

                case 4:
                    if (d == EQUALS) {
                        ++state;
                    } else if (d != SKIP) {
                        this.state = 6;
                        return false;
                    }
                    break;

                case 5:
                    if (d != SKIP) {
                        this.state = 6;
                        return false;
                    }
                    break;
                }
            }

            if (!finish) {
                // We're out of input, but a future call could provide
                // more.
                this.state = state;
                this.value = value;
                this.op = op;
                return true;
            }


            switch (state) {
            case 0:
                break;
            case 1:
                this.state = 6;
                return false;
            case 2:
                output[op++] = (byte) (value >> 4);
                break;
            case 3:
               output[op++] = (byte) (value >> 10);
                output[op++] = (byte) (value >> 2);
                break;
            case 4:
                this.state = 6;
                return false;
            case 5:
                break;
            }

            this.state = state;
            this.op = op;
            return true;
        }
    }

    //  --------------------------------------------------------
    //  encoding
    //  --------------------------------------------------------    
    public static String encodeToString(byte[] input, int flags) {
        try {
            return new String(encode(input, flags), "US-ASCII");
        } catch (UnsupportedEncodingException e) {
            // US-ASCII is guaranteed to be available.
            throw new AssertionError(e);
        }
    }


    public static String encodeToString(byte[] input, int offset, int len, int flags) {
        try {
            return new String(encode(input, offset, len, flags), "US-ASCII");
        } catch (UnsupportedEncodingException e) {
            // US-ASCII is guaranteed to be available.
            throw new AssertionError(e);
        }
    }


    public static byte[] encode(byte[] input, int flags) {
        return encode(input, 0, input.length, flags);
    }


    public static byte[] encode(byte[] input, int offset, int len, int flags) {
        Encoder encoder = new Encoder(flags, null);

        // Compute the exact length of the array we will produce.
        int output_len = len / 3 * 4;

        // Account for the tail of the data and the padding bytes, if any.
        if (encoder.do_padding) {
            if (len % 3 > 0) {
                output_len += 4;
            }
        } else {
            switch (len % 3) {
                case 0: break;
                case 1: output_len += 2; break;
                case 2: output_len += 3; break;
            }
        }

        // Account for the newlines, if any.
        if (encoder.do_newline && len > 0) {
            output_len += (((len-1) / (3 * Encoder.LINE_GROUPS)) + 1) *
                (encoder.do_cr ? 2 : 1);
        }

        encoder.output = new byte[output_len];
        encoder.process(input, offset, len, true);

        assert encoder.op == output_len;

        return encoder.output;
    }

    /* package */ static class Encoder extends Coder {
        /**
         * Emit a new line every this many output tuples.  Corresponds to
         * a 76-character line length (the maximum allowable according to
         * <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>).
         */
        public static final int LINE_GROUPS = 19;

        /**
         * Lookup table for turning Base64 alphabet positions (6 bits)
         * into output bytes.
         */
        private static final byte ENCODE[] = {
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
            'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
            'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/',
        };

        /**
         * Lookup table for turning Base64 alphabet positions (6 bits)
         * into output bytes.
         */
        private static final byte ENCODE_WEBSAFE[] = {
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
            'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
            'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-', '_',
        };

        final private byte[] tail;
        /* package */ int tailLen;
        private int count;

        final public boolean do_padding;
        final public boolean do_newline;
        final public boolean do_cr;
        final private byte[] alphabet;

        public Encoder(int flags, byte[] output) {
            this.output = output;

            do_padding = (flags & NO_PADDING) == 0;
            do_newline = (flags & NO_WRAP) == 0;
            do_cr = (flags & CRLF) != 0;
            alphabet = ((flags & URL_SAFE) == 0) ? ENCODE : ENCODE_WEBSAFE;

            tail = new byte[2];
            tailLen = 0;

            count = do_newline ? LINE_GROUPS : -1;
        }

        /**
         * @return an overestimate for the number of bytes {@code
         * len} bytes could encode to.
         */
        public int maxOutputSize(int len) {
            return len * 8/5 + 10;
        }

        public boolean process(byte[] input, int offset, int len, boolean finish) {
            // Using local variables makes the encoder about 9% faster.
            final byte[] alphabet = this.alphabet;
            final byte[] output = this.output;
            int op = 0;
            int count = this.count;

            int p = offset;
            len += offset;
            int v = -1;

            // First we need to concatenate the tail of the previous call
            // with any input bytes available now and see if we can empty
            // the tail.

            switch (tailLen) {
                case 0:
                    // There was no tail.
                    break;

                case 1:
                    if (p+2 <= len) {
                        // A 1-byte tail with at least 2 bytes of
                        // input available now.
                        v = ((tail[0] & 0xff) << 16) |
                            ((input[p++] & 0xff) << 8) |
                            (input[p++] & 0xff);
                        tailLen = 0;
                    };
                    break;

                case 2:
                    if (p+1 <= len) {
                        // A 2-byte tail with at least 1 byte of input.
                        v = ((tail[0] & 0xff) << 16) |
                            ((tail[1] & 0xff) << 8) |
                            (input[p++] & 0xff);
                        tailLen = 0;
                    }
                    break;
            }

            if (v != -1) {
                output[op++] = alphabet[(v >> 18) & 0x3f];
                output[op++] = alphabet[(v >> 12) & 0x3f];
                output[op++] = alphabet[(v >> 6) & 0x3f];
                output[op++] = alphabet[v & 0x3f];
                if (--count == 0) {
                    if (do_cr) output[op++] = '\r';
                    output[op++] = '\n';
                    count = LINE_GROUPS;
                }
            }

            // At this point either there is no tail, or there are fewer
            // than 3 bytes of input available.

            // The main loop, turning 3 input bytes into 4 output bytes on
            // each iteration.
            while (p+3 <= len) {
                v = ((input[p] & 0xff) << 16) |
                    ((input[p+1] & 0xff) << 8) |
                    (input[p+2] & 0xff);
                output[op] = alphabet[(v >> 18) & 0x3f];
                output[op+1] = alphabet[(v >> 12) & 0x3f];
                output[op+2] = alphabet[(v >> 6) & 0x3f];
                output[op+3] = alphabet[v & 0x3f];
                p += 3;
                op += 4;
                if (--count == 0) {
                    if (do_cr) output[op++] = '\r';
                    output[op++] = '\n';
                    count = LINE_GROUPS;
                }
            }

            if (finish) {

                if (p-tailLen == len-1) {
                    int t = 0;
                    v = ((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 4;
                    tailLen -= t;
                    output[op++] = alphabet[(v >> 6) & 0x3f];
                    output[op++] = alphabet[v & 0x3f];
                    if (do_padding) {
                        output[op++] = '=';
                        output[op++] = '=';
                    }
                    if (do_newline) {
                        if (do_cr) output[op++] = '\r';
                        output[op++] = '\n';
                    }
                } else if (p-tailLen == len-2) {
                    int t = 0;
                    v = (((tailLen > 1 ? tail[t++] : input[p++]) & 0xff) << 10) |
                        (((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 2);
                    tailLen -= t;
                    output[op++] = alphabet[(v >> 12) & 0x3f];
                    output[op++] = alphabet[(v >> 6) & 0x3f];
                    output[op++] = alphabet[v & 0x3f];
                    if (do_padding) {
                        output[op++] = '=';
                    }
                    if (do_newline) {
                        if (do_cr) output[op++] = '\r';
                        output[op++] = '\n';
                    }
                } else if (do_newline && op > 0 && count != LINE_GROUPS) {
                    if (do_cr) output[op++] = '\r';
                    output[op++] = '\n';
                }

                assert tailLen == 0;
                assert p == len;
            } else {
                // Save the leftovers in tail to be consumed on the next
                // call to encodeInternal.

                if (p == len-1) {
                    tail[tailLen++] = input[p];
                } else if (p == len-2) {
                    tail[tailLen++] = input[p];
                    tail[tailLen++] = input[p+1];
                }
            }

            this.op = op;
            this.count = count;

            return true;
        }
    }

    private Base64() { }   // don't instantiate
}