URL安全的Base64编码，解码

Base64 可以将二进制转码成可见字符方便进行http传输，但是base64转码时会生成“+”，“/”，“=”这些被URL进行转码的特殊字符，导致两方面数据不一致。

我们可以在发送前将“+”，“/”，“=”替换成URL不会转码的字符，接收到数据后，再将这些字符替换回去，再进行解码。

Base64加密转换原理与代码实现 :http://www.cnblogs.com/jxust-jiege666/p/8590116.html

PHP：

     /**

      * URL base64解码

      * '-' -> '+'

      * '_' -> '/'

      * 字符串长度%4的余数，补'='

      * @param unknown $string

      */

     public static function urlsafe_b64decode($string) {

         $data = str_replace(array('-','_'),array('+','/'),$string);

         $mod4 = strlen($data) % 4;

         if ($mod4) {

             $data .= substr('====', $mod4);

         }

         return base64_decode($data);

     }

     /**

      * URL base64编码

      * '+' -> '-'

      * '/' -> '_'

      * '=' -> ''

      * @param unknown $string

      */

     function urlsafe_b64encode($string) {

         $data = base64_encode($string);

         $data = str_replace(array('+','/','='),array('-','_',''),$data);

         return $data;

     }

OC:

 #pragma - 将saveBase64编码中的"-"，"_"字符串转换成"+"，"/"，字符串长度余4倍的位补"="

 +(NSData*)safeUrlBase64Decode:(NSString*)safeUrlbase64Str

 {

     // '-' -> '+'

     // '_' -> '/'

     // 不足4倍长度，补'='

     NSMutableString * base64Str = [[NSMutableString alloc]initWithString:safeUrlbase64Str];

     base64Str = (NSMutableString * )[base64Str stringByReplacingOccurrencesOfString:@"-" withString:@"+"];

     base64Str = (NSMutableString * )[base64Str stringByReplacingOccurrencesOfString:@"_" withString:@"/"];

     NSInteger mod4 = base64Str.length % ;

     if(mod4 > )

         [base64Str appendString:[@"====" substringToIndex:(-mod4)]];

     NSLog(@"Base64原文：%@", base64Str);

     return [GTMBase64 decodeData:[base64Str dataUsingEncoding:NSUTF8StringEncoding]];

 }

 #pragma - 因为Base64编码中包含有+,/,=这些不安全的URL字符串，所以要进行换字符

 +(NSString*)safeUrlBase64Encode:(NSData*)data

 {

     // '+' -> '-'

     // '/' -> '_'

     // '=' -> ''

     NSString * base64Str = [GTMBase64 stringByEncodingData:data];

     NSMutableString * safeBase64Str = [[NSMutableString alloc]initWithString:base64Str];

     safeBase64Str = (NSMutableString * )[safeBase64Str stringByReplacingOccurrencesOfString:@"+" withString:@"-"];

     safeBase64Str = (NSMutableString * )[safeBase64Str stringByReplacingOccurrencesOfString:@"/" withString:@"_"];

     safeBase64Str = (NSMutableString * )[safeBase64Str stringByReplacingOccurrencesOfString:@"=" withString:@""];

     NSLog(@"safeBase64编码：%@", safeBase64Str);

     return safeBase64Str;

 }

Java：

 public static String safeUrlBase64Encode(byte[] data){

 String encodeBase64 = new BASE64Encoder().encode(data);

 String safeBase64Str = encodeBase64.replace('+', '-');

 safeBase64Str = safeBase64Str.replace('/', '_');

 safeBase64Str = safeBase64Str.replaceAll("=", "");

 return safeBase64Str;

 }

 public static byte[] safeUrlBase64Decode(final String safeBase64Str){

 String base64Str = safeBase64Str.replace('-', '+');

 base64Str = base64Str.replace('_', '/');

 int mod4 = base64Str.length()%4;

 if(mod4 > 0){

 base64Str = base64Str + "====".substring(mod4);

 }

 return new BASE64Decoder().decodeBuffer(base64Str);

 }

如果是Android的话，android.utils.Base64自带该功能：

 Base64.encodeToString(encrypted, Base64.URL_SAFE|Base64.NO_WRAP)
 Base64.decode(data, Base64.URL_SAFE);