How to convert Strings to and from UTF8 byte arrays in Java

In Java, I have a String and I want to encode it as a byte array (in UTF8, or some other encoding). Alternately, I have a byte array (in some known encoding) and I want to convert it into a Java String. How do I do these conversions?

Convert from String to byte[]:

String s = "some text here";
byte[] b = s.getBytes(StandardCharsets.UTF_8);

Convert from byte[] to String:

byte[] b = {(byte) 99, (byte)97, (byte)116};
String s = new String(b, StandardCharsets.US_ASCII);

You should, of course, use the correct encoding name. My examples used US-ASCII and UTF-8, the two most common encodings.

Here's a solution that avoids performing the Charset lookup for every conversion:

import java.nio.charset.Charset;

private final Charset UTF8_CHARSET = Charset.forName("UTF-8");

String decodeUTF8(byte[] bytes) {
    return new String(bytes, UTF8_CHARSET);
}

byte[] encodeUTF8(String string) {
    return string.getBytes(UTF8_CHARSET);
}

String original = "hello world";
byte[] utf8Bytes = original.getBytes("UTF-8");

You can convert directly via the String(byte[], String) constructor and getBytes(String) method. Java exposes available character sets via the Charset class. The JDK documentation lists supported encodings.

90% of the time, such conversions are performed on streams, so you'd use the Reader/Writer classes. You would not incrementally decode using the String methods on arbitrary byte streams - you would leave yourself open to bugs involving multibyte characters.