HOWTO Use Encoding

The Encoding class in POJava is for the type of encoding used to represent binary data in a more portable format. It currently includes Base64 and Hexadecimal encoding and decoding. Hexadecimal is familiar even to new programmers, while Base64 is only a little less so. Both encoding methods use a fixed set of characters to represent a sequence of bits. The main difference between the two is that Hexadecimal characters each represent 4 bits, and Base64 characters each represent 6 bits.

Encoding and decoding data in either format using POJava is simple. Here is an example.

// Encoding
String str="This is the data I wish to encode.";
char[] encoded=EncodingTool.base64Encode(str.getBytes());

// Decoding
String decoded=EncodingTool.base64Decode(encoded);
assertEquals(str, decoded);

If your encoded Base64 content contains spaces and carriage returns, you can pass it as a String to the base64Decode method and it will ignore the whitespace in the String. Passing in a byte array will prompt a more strict interpretation of allowed characters.

String encodedString=new String(encoded);
String decoded=EncodingTool.base64Decode(encoded);

Reversibility

Both Base64 and Hexadecimal encodings are reversible without any loss of data. Both represent an exact sequence of ones and zeros.

Portability

The notion of portability implies that there are places where pure binary data can't go without some sort of conversion. Where might this happen? I've seen Hexadecimal encoding used most frequently on a computer screen. Some byte values of a character set represent unviewable values like null, backspace, clear or down, so displaying a memory or packet dump of raw data often uses hexadecimal instead. Base64 is frequently associated with printable documents, like MIME-encoded e-mails or with binary data stored in an XML or HTML document.

Hexadecimal Encoding

Hexadecimal encoding takes a series of bytes, and represents each sequence of 4 bits with an individual character. The ASCII characters '0' through '9' map to the first ten bit combinations, and the characters 'A' - 'F' represent the last six, adding up to all 16 possible combinations.

Bits	Dec	Hex
0000	0	0
0001	1	1
0010	2	2
0011	3	3
0100	4	4
0101	5	5
0110	6	6
0111	7	7

Bits	Dec	Hex
1000	8	8
1001	9	9
1010	10	A
1011	11	B
1100	12	C
1101	13	D
1110	14	E
1111	15	F

Base64 Encoding

Base64 converts a sequence of bytes into a sequence of characters, each representing six bits. Each sequence of three unencoded bytes will fall neatly into a sequence of four encoded characters, each representing the same twenty-four bits.

If the sequence of bytes to encode doesn't fall evenly into three bytes at a time, the remaining bytes are still sequenced into four encoded characters. Equals signs are used to represent the filler portion that will not be decoded into the original data. Depending on the length of the original data, the encoded characters may end in zero, one or two equals signs.

Bits	Dec	Base64
000000	0	A
000001	1	B
000010	2	C
000011	3	D
000100	4	E
000101	5	F
000110	6	G
000111	7	H
001000	8	I
001001	9	J
001010	10	K
001011	11	L
001100	12	M
001101	13	N
001110	14	O
001111	15	P

Bits	Dec	Base64
010000	16	Q
010001	17	R
010010	18	S
010011	19	T
010100	20	U
010101	21	V
010110	22	W
010111	23	X
011000	24	Y
011001	25	Z
011010	26	a
011011	27	b
011100	28	c
011101	29	d
011110	30	e
011111	31	f

Bits	Dec	Base64
100000	32	g
100001	33	h
100010	34	i
100011	35	j
100100	36	k
100101	37	l
100110	38	m
100111	39	n
101000	40	o
101001	41	p
101010	42	q
101011	43	r
101100	44	s
101101	45	t
101110	46	u
101111	47	v

Bits	Dec	Base64
110000	48	w
110001	49	x
110010	50	y
110011	51	z
110100	52	0
110101	53	1
110110	54	2
110111	55	3
111000	56	4
111001	57	5
111010	58	6
111011	59	7
111100	60	8
111101	61	9
111110	62	+
111111	63	/

Encoding is not Encryption

Even though a person cannot easily interpret Base64 encoded content without the aid of a computer, one should not confuse it with encryption. Base64 offers no privacy. It is not weak encryption-- it is simply a representation of data in a more portable format.