不，仅使用JDK 5.0是不可能的.

No, it's not possible based on just using JDK 5.0.

您需要推出自己的实现(这并不难)，或者***使用其中一种开源实现.有很多包括提供 Base64 的 Commons Codec http://commons.apache.org/codec/api-release/org/apache/commons/codec/binary/Base64.html

You'll need to roll your own implementation (it isn't that hard) or preferably use one of the open source implementations. There are lots including Commons Codec which provides Base64 http://commons.apache.org/codec/api-release/org/apache/commons/codec/binary/Base64.html

JavaMail 还通过 MimeUtility 提供 Base64 编码/解码，它还提供引用的可打印编码等...

JavaMail also provides Base64 encoding/decoding via MimeUtility which also does quoted printable encoding etc...

http://java.sun.com/产品/javamail/javadocs/javax/mail/internet/MimeUtility.html