Typed Objects

The CBOR library contains support for creating type checked and automatically instantiated CBOR decoder classes. This scheme builds on that CBOR messages/documents are prepended by a COTX tag holding a specific object Id. See also CBORTypedObjectDecoder.enableCheckForUnread().

The following example shows how this scheme is to be used.

Sample program:

package cbor_api_demo;

import org.webpki.cbor.CBORInt;
import org.webpki.cbor.CBORMap;
import org.webpki.cbor.CBORObject;
import org.webpki.cbor.CBORString;
import org.webpki.cbor.CBORTag;
import org.webpki.cbor.CBORTypedObjectDecoder;
import org.webpki.cbor.CBORTypedObjectDecoderCache;

public class TypedObjectsDemo {

// Typed object decoder one.
public static class ObjectOne extends CBORTypedObjectDecoder {

int number;

static final String OBJECT_ID = "https://example.com/object-one";
static final CBORObject INT_KEY = new CBORInt(1);

@Override
protected void decode(CBORObject cborBody) {
number = cborBody.getMap().get(INT_KEY).getInt();
}

@Override
public String getObjectId() {
return OBJECT_ID;
}
}

// Typed object decoder two.
public static class ObjectTwo extends CBORTypedObjectDecoder {

static final String OBJECT_ID = "https://example.com/object-two";

String justAString;

@Override
protected void decode(CBORObject cborBody) {
justAString = cborBody.getString();
}

@Override
public String getObjectId() {
return OBJECT_ID;
}
}

// Register the object decoders.
static final CBORTypedObjectDecoderCache decoderCache = new CBORTypedObjectDecoderCache()
.addToCache(ObjectOne.class)
.addToCache(ObjectTwo.class);


public static void main(String[] args) {
// Create typed CBOR messages.
byte[] objectOne = new CBORTag(ObjectOne.OBJECT_ID,
new CBORMap().set(ObjectOne.INT_KEY, new CBORInt(-343)))
.encode();

byte[] objectTwo = new CBORTag(ObjectTwo.OBJECT_ID,
new CBORString("Hi there!"))
.encode();

// Decode and instantiate.
CBORTypedObjectDecoder decodedObject = decoderCache.decode(
CBORObject.decode(objectOne));

// Dispatch to the proper handler for the associated decoder.
switch (decodedObject.getObjectId()) {
case ObjectOne.OBJECT_ID:
System.out.println("Number=" + ((ObjectOne)decodedObject).number);
break;

default:
throw new RuntimeException("Unexpected");
}
}
}

Typed objectOne in diagnostic notation:

1010(["https://example.com/object-one", {
1: -343
}])