Base64 encoded JAVA Implementation)

Import java. Io .*;

Public class mimebase64 {
/*
This is a simple base64 encoding program.
By ROC Chen rocanny@163.com.
Base64 uses 65 characters from a subset of the US-ASCII, each representing 6 Characters
Therefore, the base64 Value of "M" is 38, and the binary format is 100110.

For text strings, the encoding process is as follows. For example, "men ":

First convert to US-ASCII value.

"M": decimal 109
"E": decimal 101
"N" decimal 110

Binary:

M 01101101
E 01100101
N 01101110

Three 8-bit connections are 24-bit
011011010110010101101110

Then it is divided into 4 6 digits
011011 010110 010101 101110

Now we get four values in decimal format.
27 22 21 46

The corresponding base64 characters are:
B W v U

The encoding is always based on three characters, resulting in 4 base64 characters.
If only one or two characters are left, use the special character "=" to fill in the 4 characters of base64.
For example, encoding "me"

01101101 01100101
0110110101100101
011011 010110 0101
111111 (and, complement 6)
011011 010110 010100
B W u
B W u = ("=" complement 4 characters)

Therefore, "BWU =" is the base64 Value of "me.

Another example is encoding "M"

01101101
011011 01
111111
011011 010000
B q =
Therefore, "BQ =" is the base64 Value of "M.

It is worth noting that mime requires a maximum of 76 characters in a row.

*/

Static string basetable [] = {
"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", "+ ","/"
};

Public static void encode (string filename, bufferedwriter out ){
Try {
File F = new file (filename );
Fileinputstream fin = new fileinputstream (filename );

// Read the file to the byte array
Byte bytes [] = new byte [(INT) (F. Length ()];
Int n = fin. Read (bytes );

If (n <1) return; // NO content

Byte Buf [] = new byte [4]; // base64 character array

Int n3byt = N/3; // 3 bytes
Int nrest = n % 3; // The remaining bytes after the group
Int K = n3byt * 3 ;//
Int linelength = 0; // President
Int I = 0; // pointer

// 3-bytes group...
While (I <k ){
Buf [0] = (byte) (Bytes [I] & 0xfc)> 2 );
Buf [1] = (byte) (Bytes [I] & 0x03) <4) |
(Bytes [I + 1] & 0xf0)> 4 ));
Buf [2] = (byte) (Bytes [I + 1] & 0x0f) <2) |
(Bytes [I + 2] & 0xc0)> 6 ));
Buf [3] = (byte) (Bytes [I + 2] & 0x3f );
Send (Out, basetable [Buf [0]);
Send (Out, basetable [Buf [1]);
Send (Out, basetable [Buf [2]);
Send (Out, basetable [Buf [3]);
/*
The above code can be optimized, but it is hard to understand
Buf [0] = (byte) (B [I]> 2 );
Buf [1] = (byte) (B [I] & 0x03) <4) | (B [I + 1]> 4 ));
Buf [2] = (byte) (B [I + 1] & 0x0f) <2) | (B [I + 2]> 6 ));
Buf [3] = (byte) (B [I + 2] & 0x3f );
Send (Out, basetable [Buf [0] + basetable [Buf [1] +
Basetable [Buf [2] + basetable [Buf [3]);
*/

If (linelength + = 4)> = 76 ){
Send (Out ,"");
Linelength = 0;
}
I + = 3;
}

// Process the tail...
If (nrest = 2 ){
// 2 bytes left
Buf [0] = (byte) (Bytes [k] & 0xfc)> 2 );
Buf [1] = (byte) (Bytes [k] & 0x03) <4) |
(Bytes [k + 1] & 0xf0)> 4 ));
Buf [2] = (byte) (Bytes [k + 1] & 0x0f) <2 );
}
Else if (nrest = 1 ){
// 1 byte left
Buf [0] = (byte) (Bytes [k] & 0xfc)> 2 );
Buf [1] = (byte) (Bytes [k] & 0x03) <4 );
}
If (nrest> 0 ){
// Sending end
If (linelength + = 4)> = 76) Send (Out ,"");
Send (Out, basetable [Buf [0]);
Send (Out, basetable [Buf [1]);
//
If (nrest = 2 ){
Send (Out, basetable [Buf [2]);
}
Else {
Send (Out, "= ");
}
Send (Out, "= ");
}
Out. Flush ();
// The send method used here. Please write it as needed. You can output the result to the console or send an email.
}
Catch (exception e ){
E. printstacktrace ();
}
}
}