iOS Base64URL编码 等同于java中的Base64.

一. iOS Base64URL编码：
java中，在进行base64编码时会看到类似如下代码：

    String result = Base64.encodeToString(bytedata, Base64.URL_SAFE | Base64.NO_WRAP |  Base64.NO_PADDING)；

其中参数的含义是：

    URL_SAFE：安全的URL编码，base64转码过程中会生成“+”，“/”，“=”这些会被URL进行转码的特殊字符，导致前后台数据不同，所以需要将这些字符替代为URL不会进行转码的字符，保证数据同步；
        "-" -> "+"
        "_" -> "/"
    NO_WRAP：不换行
    NO_PADDING："="号补齐去除，base64会对字符进行串长度余4的"="的补位，需去除"="。

这些功能都是android.utils.Base64中自带的
在iOS中没有，所以我们只能自己动手了～

Swift代码：

//MARK: Data转Base64URL加密
internal class func convertByte(bytedata:Data?) -> String {
    guard let bytedata = bytedata else {
        return ""
    }
    // data数据进行base64加密
    guard let result = bytedata.base64EncodedString() else {
        return ""
    }
    // %替换为_
    let result4 = result.replacingOccurrences(of: "%", with: "_")
    // =替换为空
    let result1 = result4.replacingOccurrences(of: "=", with: "")
    // +替换为—
    let result2 = result1.replacingOccurrences(of: "+", with: "-")
    // /替换为_
    let result3 = result2.replacingOccurrences(of: "/", with: "_")
    return result3
}
//MARK: 后台反回的base64字符串转为data
internal class func convertBase64URL(base64:String?) -> Data? {
    guard let base64 = base64 else {
        return nil
    }
    // -替换为+
    let base64Str = base64.replacingOccurrences(of: "-", with: "+")
    // _替换为/
    let base64Str2 = base64Str.replacingOccurrences(of: "_", with: "/")
    var base64Str3 = ""
    // =号补全
    let mod4 = base64Str.count % 4
    if mod4 > 0 {
        let appStr = ("====" as NSString).substring(to: (4 - mod4))
        base64Str3 = base64Str2 + appStr
    }
    // base64Str转data并进行Base64Decoding
    return Data(base64Encoded: base64Str3, options: Data.Base64DecodingOptions.init(rawValue: 0))
}

OC:

//MARK: 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 % 4;
            if(mod4 > 0)
                    [base64Str appendString:[@"====" substringToIndex:(4-mod4)]];
            NSLog(@"Base64原文：%@", base64Str);
            return [GTMBase64 decodeData:[base64Str dataUsingEncoding:NSUTF8StringEncoding]];
            
}

//MARK: 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;
}