Convert and Append string into existing byte array

Question

I am working on converting and existing C# project over to Java/Android. I am looking for the Java equivalent to UTF8Encoding.GetBytes(String, Int32, Int32, Byte[], Int32). Take a look at the C# code below, how do I add the string packet into the data byte array? I have looked at the String.getBytes() method but it is not the same.

int length = packet.Length;

byte[] data = new byte[6 + length + 1];
data[0] = (byte)VAR1;
data[1] = 1;

**Encoding.UTF8.GetBytes(packet, 0, length, data, 6);**

data[6 + length] = (byte)VAR2;

data[5] = (byte)(length % 256);
length /= 256;
data[4] = (byte)(length % 256);
length /= 256;
data[3] = (byte)(length % 256);
length /= 256;
data[2] = (byte)(length % 256);

You seem to be assuming that you can get all of the UTF-8-encoded data into the same number of bytes as there are characters. That's simply not true, unless all the characters are ASCII. — Jon Skeet
– Jon Skeet, Commented May 1, 2014 at 12:56
@JonSkeet, they are all ASCII. All characters that can be found in the string "packet" are "predefined". — user1017477
– user1017477, Commented May 1, 2014 at 13:03
In that case, why specify UTF-8? Why not use Encoding.ASCII, which is a lot clearer in intent? — Jon Skeet
– Jon Skeet, Commented May 1, 2014 at 13:04

Jon Skeet · Accepted Answer · 2014-05-01 13:08:56Z

1

Okay, given that you mean ASCII rather than UTF-8, there are two immediate options:

Intermediate byte array

byte[] encodedText = text.getBytes(StandardCharsets.US_ASCII);
System.arraycopy(encodedText, 0, data, 6, encodedText.length);

This is inefficient, but simple.

Charset directly

CharsetEncoder encoder = StandardCharsets.US_ASCII.newEncoder();
CharBuffer charBuffer = CharBuffer.wrap(text);
ByteBuffer byteBuffer = ByteBuffer.wrap(data, 6, data.length - 6);
encoder.encode(charBuffer, byteBuffer, true);

This is possibly more efficient, but more complicated to understand.

answered May 1, 2014 at 13:08

Jon Skeet

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6 Comments

user1017477 Over a year ago

Thanks Jon Skeet, that worked a charm. The System.arraycopy was what I needed. Honestly, for my proposes the encoding specification is irrelevant.

Jon Skeet Over a year ago

@user1017477: It's really not - because if you specify something like EBCDIC or UTF-16, you won't get the bytes you expect. Encodings are never irrelevant.

user1017477 Over a year ago

I understand what you're saying however, in this case all of the text that is to be converted is essentially "hard coded". I have run your suggestion through a handful of possible scenarios without specifying the encoding type of getBytes() and everything is functioning as it should.

Jon Skeet Over a year ago

@user1017477: That just means you haven't run it on a system where the default encoding is inhospitable to you. It doesn't mean such code isn't broken.

user1017477 Over a year ago

you are correct again. I guess by working on apps that only target a small subset of users within a controlled environment, one can overlook the ramifications of running the same app on a larger scale?

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