// 将 s 进行 BASE64 编码
public static String getBASE64(String s) {
if (s == null) return null;
return (new sun.misc.BASE64Encoder()).encode( s.getBytes() );
}

// 将 BASE64 编码的字符串 s 进行解码
public static String getFromBASE64(String s) {
if (s == null) return null;
BASE64Decoder decoder = new BASE64Decoder();
try {
byte[] b = decoder.decodeBuffer(s);
return new String(b);
} catch (Exception e) {
return null;
}
}

或者apache的包

import java.io.UnsupportedEncodingException;

import org.apache.commons.codec.binary.Base64;
public class Base64Util {


	/**
	 * 将二进制数据编码为BASE64字符串
	 * @param binaryData
	 * @return
	 */
	public static String encode(byte[] binaryData) {
		try {
			return new String(Base64.encodeBase64(binaryData), "UTF-8");
		} catch (UnsupportedEncodingException e) {
			return null;
		}
	}
	
	/**
	 * 将BASE64字符串恢复为二进制数据
	 * @param base64String
	 * @return
	 */
	public static byte[] decode(String base64String) {
		try {
			return Base64.decodeBase64(base64String.getBytes("UTF-8"));
		} catch (UnsupportedEncodingException e) {
			return null;
		}
	}

}