How to convert Base64 encode binary String to bina

How can i convert the following Base64 encode binary string into a binary in java. I have seen people doing the same in php using the following code. How to achieve this in java?

In PHP:

$byteArr = "AAAAAEAA";
$maparray = array();
$map = "";
foreach(str_split($byteArr) as $c)
    $maparray [] = sprintf("%08b", ord($c));
$map = implode("", $maparray );

Output is $map -> "000000000000000000000000000000000100000000000000";

But when i try this in java:

String input = "AAAAAEAA";
String mapArray = "";
for(int b=0;b<input.length();b++){
   int asciValueOfChar =(int)toByte.charAt(b);
   String binaryInt = Integer.toBinaryString(asciValueOfChar);
   String paddedBinaryInt = String.format("%8s", binaryInt);
   paddedBinaryInt = paddedBinaryInt.replace(' ', '0');
   System.out.println("ASCII Code::"+asciValueOfChar);
   System.out.println("Binary of Char::"+binaryInt);
   System.out.println("Binary of Padded Char::"+binaryInt);
   mapArray = mapArray + paddedBinaryInt ;
}
System.out.println("Binary Array::"+mapArray);

Output is mapArray -> "0100000101000001010000010100000101000001010001010100000101000001"

The output varies.

How can i achieve the same output?

Thanks,

回答1:

First of all, I don't believe PHP gives you above mentioned string (000000000000000000000000000000000100000000000000) as an output!

The code in your question enumerate each character in input string (AAAAAEAA), retrieves ASCII value of each character and post it in output. If you execute PHP code you mentioned, you will give exact the same output, as running JAVA code you mentioned (0100000101000001010000010100000101000001010001010100000101000001).

For example,

ord("A") = 65

65 in turn has 01000001 binary representation.

Second, correct your question to get correct answer. It seems, guys, answered earlier, didn't understand your question at all.

Third, if you want to get binary represenation of a given string, use getBytes() method to retrieve bytes representation of entire string. Use or adapt this code snippet to get binary representation of a given bytes-array.

回答2:

To decode base64, the simplest is to use the Apache commons Decoder.

import org.apache.commons.codec.binary.Base64;

byte[] decodedBytes = Base64.decodeBase64(input);

Do you really need the binary as a string made of "0" and "1" chars ?

回答3:

I expect people to recommend apache commons but I do not know if it's portable or not...

you can use this one:

public class Base64Coder
{

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


/**
 * 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;
}

/**
 * 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 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 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));
}

/**
 * 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;
}

/**
 * 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 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()));
}

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

Usage:

String message = "blahblah";
byte[] encoded = Base64Coder.encode(message.getBytes("UTF-8"));
byte[] decoded = Base64Coder.decode(encoded);
String msg2 = new String(decoded, "UTF-8");
if(message.equals(msg2)) System.out.println("yaay");

It's also compatible with Sun's code...

回答4:

Android includes its own Base64 encoder and decoder. All you need to decode a Base64 string is this:

byte[] decoded = Base64.decode( string, Base64.DEFAULT );

The second parameter is a flag. See here: Base64