How to convert a Java String to an ASCII byte array?

How to convert a Java String to an ASCII byte array?

Solution 1:

Using the getBytes method, giving it the appropriate Charset (or Charset name).

Example:

String s = "Hello, there.";
byte[] b = s.getBytes(StandardCharsets.US_ASCII);

If more control is required (such as throwing an exception when a character outside the 7 bit US-ASCII is encountered) then CharsetDecoder can be used:

private static byte[] strictStringToBytes(String s, Charset charset) throws CharacterCodingException {
    ByteBuffer x  = charset.newEncoder().onMalformedInput(CodingErrorAction.REPORT).encode(CharBuffer.wrap(s));
    byte[] b = new byte[x.remaining()];
    x.get(b);
    return b;
 }

Before Java 7 it is possible to use: byte[] b = s.getBytes("US-ASCII");. The enum StandardCharsets, the encoder as well as the specialized getBytes(Charset) methods have been introduced in Java 7.

Solution 2:

If you are a guava user there is a handy Charsets class:

String s = "Hello, world!";
byte[] b = s.getBytes(Charsets.US_ASCII);

Apart from not hard-coding arbitrary charset name in your source code it has a much bigger advantage: Charsets.US_ASCII is of Charset type (not String) so you avoid checked UnsupportedEncodingException thrown only from String.getBytes(String), but not from String.getBytes(Charset).

In Java 7 there is equivalent StandardCharsets class.

Solution 3:

There is only one character wrong in the code you tried:

Charset characterSet = Charset.forName("US-ASCII");
String string = "Wazzup";
byte[] bytes = String.getBytes(characterSet);
               ^

Notice the upper case "String". This tries to invoke a static method on the string class, which does not exist. Instead you need to invoke the method on your string instance:

byte[] bytes = string.getBytes(characterSet);