JSON Jackson Serializer and Deserializer

Use JacksonSerializer and JacksonDeserializer to serialize and deserialize Java Jackson JSON object to and from the Candid payload of type RECORD.

A fully functional example using JacksonSerializer and JacksonDeserializer can be found here.

This example uses Motoko to call the canister main.mo. The canister uses 2 complex types, LoanApplication and LoanOffer.

main.mo

// Loan Application
public type LoanApplication = {
    id: Nat;
    firstname: Text;
    lastname: Text;
    zipcode: Text;
    ssn: Text;
    amount: Float;
    term: Nat16;
    created: Int;
 };

// Loan Offer
public type LoanOffer = {
    providerid: Principal;
    providername: Text;
    applicationid: Nat;
    apr: Float;
    created: Int;
};

The canister has 2 methods: apply and getOffers.

main.mo

public shared (msg) func apply(input : LoanApplication) : async LoanOffer { 
       counter += 1;
        Debug.print("Loan Application for user " #Principal.toText(msg.caller));
        
        let offer  : LoanOffer = {
            providerid = Principal.fromActor(this);
            providername = "Loan Provider";
            applicationid = counter;
            apr = 3.14;
            created = Time.now();
        };

        var userOffers :  ?Offers<LoanOffer> = offers.get(msg.caller);

        switch userOffers {
            case (null) { var userOffer : Offers<LoanOffer> = Buffer.Buffer(0); userOffer.add(offer);  offers.put(msg.caller, userOffer)};
            case (?userOffer) { userOffer.add(offer); };
        };
        return offer;
};

public query (msg) func getOffers() : async [LoanOffer] {
        var userOffers :  ?Offers<LoanOffer> = offers.get(msg.caller);

        switch userOffers {
            case (null) { return [] };
            case (?userOffer) { return userOffer.toArray() };
        };
};

The example uses the file with JSON LoanApplication payload as an input.

LoanApplication.json

{
"id" : 0,
"firstname" : "John",
"lastname" : "Doe",
"zipcode" : "99999",
"ssn" : "111-11-1111",
"amount" : 2000.00,
"term" : 24,
"created" : 0
}

To be able to properly map JSON names and values to Candid name types declare the IDLType structure as follows:

Main.java

Map<Label,IDLType> applicationRecord = new TreeMap<Label,IDLType>();
applicationRecord.put(Label.createNamedLabel("id"), IDLType.createType(Type.NAT));
applicationRecord.put(Label.createNamedLabel("firstname"), IDLType.createType(Type.TEXT));
applicationRecord.put(Label.createNamedLabel("lastname"), IDLType.createType(Type.TEXT));
applicationRecord.put(Label.createNamedLabel("zipcode"), IDLType.createType(Type.TEXT));
applicationRecord.put(Label.createNamedLabel("ssn"), IDLType.createType(Type.TEXT));		
applicationRecord.put(Label.createNamedLabel("amount"), IDLType.createType(Type.FLOAT64));
applicationRecord.put(Label.createNamedLabel("term"), IDLType.createType(Type.NAT16));
applicationRecord.put(Label.createNamedLabel("created"), IDLType.createType(Type.INT));
		
IDLType idlType =  IDLType.createType(Type.RECORD, applicationRecord);
		
Map<Label,IDLType> offerRecord = new TreeMap<Label,IDLType>();
offerRecord.put(Label.createNamedLabel("providerid"), IDLType.createType(Type.PRINCIPAL));
offerRecord.put(Label.createNamedLabel("providername"), IDLType.createType(Type.TEXT));
offerRecord.put(Label.createNamedLabel("applicationid"), IDLType.createType(Type.NAT));	
offerRecord.put(Label.createNamedLabel("apr"), IDLType.createType(Type.FLOAT64));		
offerRecord.put(Label.createNamedLabel("created"), IDLType.createType(Type.INT));
		
IDLType resultIdlType =  IDLType.createType(Type.RECORD, offerRecord);	

Next, create IDLValue using the JacksonSerializer create method.

The Serializer input is the variable type JsonNode.

Main.java

JsonNode jsonValue = readNode(LOAN_APPLICATION_FILE);
		
IDLValue idlValue = IDLValue.create(jsonValue, JacksonSerializer.create(idlType));
List<IDLValue> idlArgs = new ArrayList<IDLValue>();
idlArgs.add(idlValue);

byte[] buf = IDLArgs.create(idlArgs).toBytes();

Use UpdateBuilder, QueryBuilder or Raw Methods to call the Canister and deserialize output to JsonNode.

Main.java

CompletableFuture<byte[]> response = UpdateBuilder.create(agent,Principal.fromString(icCanister), "apply").arg(buf).callAndWait(Waiter.create(60, 5));
		
byte[] output = response.get();
JsonNode jsonResult = IDLArgs.fromBytes(output).getArgs().get(0)
			.getValue(JacksonDeserializer.create(resultIdlType), JsonNode.class);