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小編給大家分享一下怎么用Java語言實現(xiàn)Base64編碼，希望大家閱讀完這篇文章之后都有所收獲，下面讓我們一起去探討吧！
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import java.io.*;
public class MIMEBase64 {
/*
這是個簡單的Base64編碼程序
作者：Roc Chen [email protected]
Base64 使用US-ASCII子集的65個字符, 每個字符用6位表示
因此"m"的Base64值為38, 二進制形式是 100110.
對于文本串，編碼過程如下。例如"men":
先轉(zhuǎn)成US-ASCII值.
"m"十進制 109
"e"十進制 101
"n"十進制 110
二進制 :
m 01101101
e 01100101
n 01101110
三個8位連起來是24位
011011010110010101101110
然后分成4個6位
011011
010110 010101 101110
現(xiàn)在得到4個值，十進制為
27 22 21 46
對應的 Base64 字符是
:
b W V u
編碼總是基于3個字符，從而產(chǎn)生4個Base64字符。
如果只剩1或2個字符，使用特殊字符"="補齊Base64的4字。
如，編碼"me"
01101101 01100101
0110110101100101
011011 010110 0101
111111 (與，補足6位)
011011
010110 010100
b W U
b W U = ("=" 補足4字符)
于是 "bWU="
就是"me"的Base64值.
再如編碼 "m"
01101101
011011 01
111111
011011 010000
b Q = =
于是 "bQ==" 就是"m"的Base64值.
值得注意的是，MIME規(guī)定一行最多76個字符.
*/
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);
// 讀文件到BYTE數(shù)組
byte bytes[] = new
byte[(int)(f.length())];
int n = fin.read(bytes);
if (n < 1)
return; // 沒有內(nèi)容
byte buf[] = new byte[4]; // base64 字符數(shù)組
int
n3byt = n / 3; // 3 bytes 組數(shù)
int nrest = n % 3; // 分組后剩余 bytes
int k =
n3byt * 3; //
int linelength = 0; // 行長
int i = 0; // 指針
//
3-bytes 分組 ...
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]]);
/*
以上代碼可以優(yōu)化，但會難以理解
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;
}
// 處理尾部 ...
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) {
// 發(fā)送尾部
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();
//這里用到的send方法，請大家根據(jù)需要，自己寫?？梢允前呀Y(jié)果輸出到控制臺，或發(fā)送郵件。
}
catch (Exception e)
{
e.printStackTrace();
}
}
}
看完了這篇文章，相信你對“怎么用Java語言實現(xiàn)Base64編碼”有了一定的了解，如果想了解更多相關(guān)知識，歡迎關(guān)注創(chuàng)新互聯(lián)行業(yè)資訊頻道，感謝各位的閱讀！
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