前几天无意中看到Java中有Base64编码，不解的我去百科了一下，了解了Base64的基本使用和实现原理，于是在空暇时自己手动写了一个，这个类可以完成对字母数字的编码和解码工作，但是对于中文，还没有仔细研究其编码的实现过程。至于什么是Base64，用它来干什么，请移步到：http://zh.wikipedia.org/zh-cn/Base64
下面贴出这个工具类的源代码，供朋友们参考，本人新手写得不好，请用力拍砖：
/************************Base64Util.java*****************************/
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package
util;
import
java.util.HashMap;
import
java.util.Map;
/**
* This class is a tool class to convert Base64 string and
* normal string to each other. <br><br>
* More information about base64, Please refer to:
* http://zh.wikipedia.org/zh-cn/Base64
* @author user
*/
public
class
Base64Util {
private
static
final
Map<Integer, Character> base64CharMap =
new
HashMap<>();
private
static
final
String base64CharString =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
;
static
{
// initialize base64 map
for
(
int
i=
0
;i<base64CharString.length();i++){
char
c = base64CharString.charAt(i);
base64CharMap.put(
new
Integer(i),
new
Character(c));
}
}
/**
* This method is used to encode a normal string to base64 string
* @param origin
* The String to be encoded
* @return
* The String after encoded.
*/
public
static
String encode (String origin) {
if
(origin ==
null
) {
return
null
;
}
if
(origin.length() ==
0
) {
return
""
;
}
int
length = origin.length();
String binaryString =
""
;
// to binary String
for
(
int
i=
0
;i<length;i++) {
int
ascii = origin.charAt(i);
String binaryCharString = Integer.toBinaryString(ascii);
while
(binaryCharString.length() <
8
) {
binaryCharString =
"0"
+ binaryCharString;
}
binaryString += binaryCharString;
}
// to base64 index
int
beginIndex =
0
;
int
endIndex = beginIndex +
6
;
String base64BinaryString =
""
;
String charString =
""
;
while
((base64BinaryString =
binaryString.substring(beginIndex, endIndex)).length() >
0
) {
//if length is less than 6, add "0".
while
(base64BinaryString.length() <
6
) {
base64BinaryString +=
"0"
;
}
int
index = Integer.parseInt(base64BinaryString,
2
);
char
base64Char = base64CharMap.get(index);
charString = charString + base64Char;
beginIndex +=
6
;
endIndex +=
6
;
if
(endIndex >= binaryString.length()) {
endIndex = binaryString.length();
}
if
(endIndex < beginIndex) {
break
;
}
}
if
(length %
3
==
2
) {
charString +=
"="
;
}
if
(length %
3
==
1
) {
charString +=
"=="
;
}
return
charString;
}
/**
* This method is used to decode from base64 string to a normal string.
* @param encodedString
* The string to be decoded.
* @return
* The string after decoded.
*/
public
static
String decode(String encodedString) {
if
(encodedString ==
null
) {
return
null
;
}
if
(encodedString.length() ==
0
) {
return
""
;
}
//get origin base64 String
String origin = encodedString.substring(
0
,encodedString.indexOf(
"="
));
String equals = encodedString.substring(encodedString.indexOf(
"="
));
String binaryString =
""
;
//convert base64 string to binary string
for
(
int
i=
0
;i<origin.length();i++) {
char
c = origin.charAt(i);
int
ascii = base64CharString.indexOf(c);
String binaryCharString = Integer.toBinaryString(ascii);
while
(binaryCharString.length() <
6
) {
binaryCharString =
"0"
+ binaryCharString;
}
binaryString += binaryCharString;
}
// the encoded string has 1 "=", means that the binary string has append 2 "0"
if
(equals.length() ==
1
) {
binaryString = binaryString.substring(
0
,binaryString.length()-
2
);
}
// the encoded string has 2 "=", means that the binary string has append 4 "0"
if
(equals.length() ==
2
) {
binaryString = binaryString.substring(
0
,binaryString.length()-
4
);
}
// convert to String
String charString =
""
;
String resultString =
""
;
int
beginIndex =
0
;
int
endIndex = beginIndex +
8
;
while
((charString =
binaryString.substring(beginIndex, endIndex)).length() ==
8
) {
int
ascii = Integer.parseInt(charString,
2
);
resultString += (
char
)ascii;
beginIndex +=
8
;
endIndex +=
8
;
if
(endIndex > binaryString.length()) {
break
;
}
}
return
resultString;
}
// Test methods here.
public
static
void
main(String[] args) {
String originString =
"Man is distinguished, not only by his reason, but by this singular passion from other animals, which is a lust of the mind, that by a perseverance of delight in the continued and indefatigable generation of knowledge, exceeds the short vehemence of any carnal pleasure."
;
String base64String =
"TWFuIGlzIGRpc3Rpbmd1aXNoZWQsIG5vdCBvbmx5IGJ5IGhpcyByZWFzb24sIGJ1dCBieSB0aGlz"
+
"IHNpbmd1bGFyIHBhc3Npb24gZnJvbSBvdGhlciBhbmltYWxzLCB3aGljaCBpcyBhIGx1c3Qgb2Yg"
+
"dGhlIG1pbmQsIHRoYXQgYnkgYSBwZXJzZXZlcmFuY2Ugb2YgZGVsaWdodCBpbiB0aGUgY29udGlu"
+
"dWVkIGFuZCBpbmRlZmF0aWdhYmxlIGdlbmVyYXRpb24gb2Yga25vd2xlZGdlLCBleGNlZWRzIHRo"
+
"ZSBzaG9ydCB2ZWhlbWVuY2Ugb2YgYW55IGNhcm5hbCBwbGVhc3VyZS4="
;
System.out.println(
"===============encode================="
);
String result = encode(originString);
System.out.println(result);
System.out.println(result.equals(base64String));
System.out.println(
"===============decode================="
);
String decodedString = decode(base64String);
System.out.println(decodedString);
System.out.println(originString.equals(decodedString));
System.out.println(decode(encode(
"abcdefg"
)));
}
}
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