Package dev.enola.common.io.resource

Interface ChangeToken

public interface ChangeToken

Change Token ("Tag") for ReadableResource.changeToken().

This is named a "change token" and not "version" (or "revision") because that might imply something “numeric” - but this is explicitly NOT intended to be used for “is it newer or older” comparison, only “has it changed”. It's also not called a "fingerprint" because that might imply it's derived only from the content itself (like a hash), whereas this may be based on more than that, e.g. additional metadata.

Field Summary

Fields

Modifier and Type	Field	Description
static final ChangeToken	NOT_AVAILABLE	Constant (singleton) for "not available" change tokens.

Method Summary

Modifier and Type	Method	Description
boolean	isDifferent(ChangeToken other)	Check is this ChangeToken is different from that other ChangeToken.
ByteSeq	toBytes()
String	toString()	String representation of this ChangeToken, (only) for ReadableResource.isDifferent(String).

Field Details

NOT_AVAILABLE

static final ChangeToken NOT_AVAILABLE

Constant (singleton) for "not available" change tokens.

Returned by ReadableResource.changeToken() when it's impossible to obtain a ChangeToken e.g. due to internal technical errors, including because the URI points to a non-existing resource. Its isDifferent(ChangeToken) always returns true.

Method Details

isDifferent

boolean isDifferent(ChangeToken other)

Check is this ChangeToken is different from that other ChangeToken.

If it's not sure, prefer "erring on the side of caution" by returning true instead of false. That's why two NOT_AVAILABLE are considered representing (possibly) different resource contents (returns true).

toString

String toString()

String representation of this ChangeToken, (only) for ReadableResource.isDifferent(String).

Do not interpret the content of this String. It's intended to be used completely "opaque", and only for before & after comparison, on a Resource from the same URI. Implementations are encouraged to return strings which do not (directly) "look like something familiar", to avoid users relying on implementation details.

Overrides:

toString in class Object

toBytes

ByteSeq toBytes()