Efficient way to calculate byte length of a character, depending on the encoding

Question

What\'s the most efficient way to calculate the byte length of a character, taking the character encoding into account? The encoding would be only known during runtime. In UTF-8

Answer 1

Use a CharsetEncoder and reuse a CharBuffer as input and a ByteBuffer as output.

On my system, the following code takes 25 seconds to encode 100,000 single characters:

Charset utf8 = Charset.forName("UTF-8");
char[] array = new char[1];
for (int reps = 0; reps < 10000; reps++) {
    for (array[0] = 0; array[0] < 10000; array[0]++) {
        int len = new String(array).getBytes(utf8).length;
    }
}

However, the following code does the same thing in under 4 seconds:

Charset utf8 = Charset.forName("UTF-8");
CharsetEncoder encoder = utf8.newEncoder();
char[] array = new char[1];
CharBuffer input = CharBuffer.wrap(array);
ByteBuffer output = ByteBuffer.allocate(10);
for (int reps = 0; reps < 10000; reps++) {
    for (array[0] = 0; array[0] < 10000; array[0]++) {
        output.clear();
        input.clear();
        encoder.encode(input, output, false);
        int len = output.position();
    }
}

Edit: Why do haters gotta hate?

Here's a solution that reads from a CharBuffer and keeps track of surrogate pairs:

Charset utf8 = Charset.forName("UTF-8");
CharsetEncoder encoder = utf8.newEncoder();
CharBuffer input = //allocate in some way, or pass as parameter
ByteBuffer output = ByteBuffer.allocate(10);

int limit = input.limit();
while(input.position() < limit) {
    output.clear();
    input.mark();
    input.limit(Math.max(input.position() + 2, input.capacity()));
    if (Character.isHighSurrogate(input.get()) && !Character.isLowSurrogate(input.get())) {
        //Malformed surrogate pair; do something!
    }
    input.limit(input.position());
    input.reset();
    encoder.encode(input, output, false);
    int encodedLen = output.position();
}