How to encode a long into base64 and get it back?

Hi!

I want to encode a long into base64 and decode it back. I have:

But I am not getting it to be the same value. Can someone help?

Thanks.

What are you getting? What's the for loop supposed to do? Have you tried "new String(epochtime1)" instead?

Tim probably means new String(receivedEpoch) in combination with parseLong, and I think he's right.
There are at least two ways of converting a long into a byte[] and vice versa, and you've mixed the two. Instead you should match the long to byte[] conversion and the byte[] to long conversion. With the new String fix you'll do that. Alternatively, and this would be my preferred way, is to change the long into a byte[] in a similar way as your original byte[] to long conversion. Right now, your byte[] will contain about 13 elements, whereas you only need 8 (64 bits / 8 bits).

Alan Blass wrote:I want to encode a long into base64 and decode it back. I have:
...
But I am not getting it to be the same value. Can someone help?

The others are right, the problem is in your
byte [] epochtime1 = Base64.encodeBase64(String.valueOf(t).getBytes());
line.

Base64 is a binary, not a String, encoding. Therefore, as Rob said, you need to convert your long to an array of bytes containing it's binary representation.
One possibility is to use BigInteger, viz:
byte [] epochtime1 = Base64.encodeBase64( BigInteger.valueOf(t).toByteArray() );
but you may run into problems with that method if you use it on more than 1 value, because it does NOT pad the returned array to the correct length. I leave that for you as an exercise.

HIH

Winston

Hi!

Thanks for your replies.

Strange thing is when I print out the encoded base 64 from 1328175927236, I get [B@7b582c6f. But if I use an online base64 encoder to encode 1328175927236, I get: MTMyODE3NTkyNzIzNg==

Below is my code:

In addition, what if the received epochtime is a String? Should I use:

byte[] receivedEpoch = Base64.decodeBase64(epochtime1.getBytes());

Please help. Thanks

Alan Blass wrote:Strange thing is when I print out the encoded base 64 from 1328175927236, I get [B@7b582c6f.

That's because arrays don't override toString() and therefore use the implementation provided by java.lang.Object: the class name ([B for byte arrays) followed by @ and the hexadecimal hash code. Use Arrays.toString(epochtime1) instead.

Hi!

I get this:

received base64: [65, 84, 85, 57, 100, 69, 47, 69].

I have also looked up the ASCII table 65 is A in decimal. It is suppose to be M. How do I get the encoded Base64?
My code:

What should I use if the encoded epochtime is a string instead of byte array?

Thanks.

Alan Blass wrote:I have also looked up the ASCII table 65 is A in decimal. It is suppose to be M. How do I get the encoded Base64?

Well, first, as I said, look at the number of bytes you're getting back from BigInteger.toByteArray(). If it isn't 8 (although it looks like it should be), you may well end up with a different base64 result.

Second, "MTMyODE3NTkyNzIzNg==" looks like the result of a complete file to me, which I wouldn't expect from a Java method (there may be more values to append); so you need to find out what it's padding philosophy is (the two '=' at the end are padding, but I can't remember the exact algorithm). Also, when encoding a complete value, the number of bytes is often put at the front. Certainly, what you're seeing is way more than just a long.

There is a lot to know about base64, and I suspect you need to do some reading, rather than just "expecting" your encoded value to be the same as what you see from an outside source.

Another suggestion: go through the exercise yourself, and work out what you would expect from your long value. It's tedious, but at least you'll be a bit further on.

What should I use if the encoded epochtime is a string instead of byte array?

If it is, you're in big trouble, and whoever provided you with the data should have nasty things done to their reproductive organs.

Winston

PS: Just one other thing. You may also need to check the "endian" that the class uses. BigInteger.toByteArray() returns its bytes in big-endian "digit" order, which goes along with Java's philosophy of all binary numbers being 'big-endian'. If that's not what the method is expecting you could get garbage.

As I said above - lots of reading.

"MTMyODE3NTkyNzIzNg==" decodes to [49, 51, 50, 56, 49, 55, 53, 57, 50, 55, 50, 51, 54] which is in String form "1328175927236". That looks like a time stamp to me.
[65, 84, 85, 57, 100, 69, 47, 69] is the byte representation of String "ATU9dE/E". If I instead convert that byte[] into a long I either get 4707481215492763461 or 4985279609283368001, depending on the endianness.

Now I think I haven't got my message through last time. If you convert the long into a String, then turn the String into a byte[] for encoding, you must convert the decoded byte[] back into a String which you then parse into a long. If you want to convert the decoded byte[] using your long calculation, then you must create the byte[] for encoding using a similar long calculation. In other words, the method for converting a long into a byte[] must be the inverse of converting a byte[] into a long.

Rob Spoor wrote:"MTMyODE3NTkyNzIzNg==" decodes to [49, 51, 50, 56, 49, 55, 53, 57, 50, 55, 50, 51, 54] which is in String form "1328175927236". That looks like a time stamp to me.

Well spotted that man.

My question: Why would anyone encode a string in base64, which
(a) is designed for encoding binary data.
(b) produces a string that is longer than the original one (well, longer than an ASCII string anyway

).
???

Winston

Ok. I got it. Thanks everyone.