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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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