Java garbled and transcoding problems

In a project, encountered an interesting problem, after invoking a third-party interface callback local code, the encrypted request parameter decryption and transcoding, one of the decoding method is invalid, another decoding method valid, what solution? ：

1. Encrypt a string when invoking a third-party interface:

String str = "AKDFJLKSJFDLJSDLFSLFLD";

(New Base64encoder ()). Encodebuffer (Str.getbytes ());

2, synchronous callback local code when decrypting and transcoding the string, using the following transcoding scheme is not a problem, while the asynchronous callback local code when decrypting and transcoding the string, using the following transcoding scheme has the problem:

String Merpriv = Request ("Merpriv");

String newmerpriv = new String ((New Base64decoder ()). Decodebuffer (Merpriv));

Newmerpriv = Urldecoder.decode (Newmerpriv, "UTF-8"). Trim ();

3, the asynchronous callback local code when decrypting and transcoding the string, using the following transcoding scheme no problem:

String Merpriv = Request ("Merpriv");

String newmerpriv = new String ((New Base64decoder ()). Decodebuffer (Merpriv));

Newmerpriv = new String (newmerpriv.getbytes ("iso-8859-1"), "UTF-8");

Java garbled and transcoding problems