Daml Codegen for Java¶

Use the Daml Codegen for Java (daml codegen java) to generate Java classes representing all Daml data types defined in a Daml Archive (.dar) file. These classes simplify constructing the types required by the Java gRPC bindings for the gRPC Ledger API; for example, com.daml.ledger.api.v2.CreateCommand and com.daml.ledger.api.v2.ExerciseCommand. They also provide JSON decoding utilities, making it easier to work with JSON when using the JSON Ledger API.

See How to work with contracts and transactions in Java for details on how to use the generated classes. See the sections below for guidance on setting up and invoking the codegen.

Install¶

Install the Daml Codegen for Java by installing the Daml Assistant.

Configure¶

To configure the Daml Codegen, choose one of the two following methods:

Command line configuration: Specify all settings directly in the command line.
Project file configuration: Define all settings in the daml.yaml file.

Command line configuration¶

To view all available command line configuration options for Daml Codegen for Java, run daml codegen java --help in your terminal:

<DAR-file[=package-prefix]>...
                         DAR file to use as input of the codegen with an optional, but recommend, package prefix for the generated sources.
-o, --output-directory <value>
                         Output directory for the generated sources
-d, --decoderClass <value>
                         Fully Qualified Class Name of the optional Decoder utility
-V, --verbosity <value>  Verbosity between 0 (only show errors) and 4 (show all messages) -- defaults to 0
-r, --root <value>       Regular expression for fully-qualified names of templates to generate -- defaults to .*
--help                   This help text

Project file configuration¶

Specify the above settings in the codegen element of the Daml project file daml.yaml.

Here is an example:

sdk-version: 3.3.0-snapshot.20250507.0
name: quickstart
source: daml
init-script: Main:initialize
parties:
  - Alice
  - Bob
  - USD_Bank
  - EUR_Bank
version: 0.0.1
exposed-modules:
  - Main
dependencies:
  - daml-prim
  - daml-stdlib
codegen:
  java:
    package-prefix: com.daml.quickstart.iou
    output-directory: java-codegen/src/main/java
    verbosity: 2

Operate¶

Run the Daml Codegen using project file configuration with:

$ daml codegen java

or using command line configuration with:

$ daml codegen java ./.daml/dist/quickstart-0.0.1.dar=com.daml.quickstart.iou --output-directory=java-codegen/src/main/java --verbosity=2

References¶

Generated Java code¶

Daml primitives to Java types¶

Daml built-in types are translated to the following equivalent types in Java:

Daml type	Java type	Java Bindings Value type
`Int`	`java.lang.Long`	Int64
`Numeric`	`java.math.BigDecimal`	Numeric
`Text`	`java.lang.String`	Text
`Bool`	`java.util.Boolean`	Bool
`Party`	`java.lang.String`	Party
`Date`	`java.time.LocalDate`	Date
`Time`	`java.time.Instant`	Timestamp
`List` or `[]`	`java.util.List`	DamlList
`TextMap`	`java.util.Map` Restricted to using `String` keys.	DamlTextMap
`Optional`	`java.util.Optional`	DamlOptional
`()` (Unit)	None since the Java language does not have a direct equivalent of Daml’s Unit type `()`, the generated code uses the Java Bindings value type.	Unit
`ContractId`	Fields of type `ContractId X` refer to the generated `ContractId` class of the respective template `X`.	ContractId

Escaping rules¶

To avoid clashes with Java keywords, the Daml Codegen applies escaping rules to the following Daml identifiers:

Type names (except the already mapped built-in types)
Constructor names
Type parameters
Module names
Field names

If any of these identifiers match one of the Java reserved keywords, the Daml Codegen appends a dollar sign $ to the name. For example, a field with the name import will be generated as a Java field with the name import$.

Generated classes¶

Every user-defined data type in Daml (template, record, and variant) is represented by one or more Java classes as described in this section.

The Java package for the generated classes is the equivalent of the lowercase Daml module name.

Daml¶

module Foo.Bar.Baz where

Java¶

package foo.bar.baz;

Records (a.k.a. product types)¶

A Daml record is represented by a Java class with fields that have the same name as the Daml record fields. A Daml field having the type of another record is represented as a field having the type of the generated class for that record.

Com/Acme/ProductTypes.daml¶

module Com.Acme.ProductTypes where

data Person = Person with name : Name; age : Decimal
data Name = Name with firstName : Text; lastName : Text

A Java file that defines the class for the type Person is generated:

com/acme/producttypes/Person.java¶

package com.acme.producttypes;

public class Person extends DamlRecord<Person> {
  public final Name name;
  public final BigDecimal age;

  public static Person fromValue(Value value$) { /* ... */ }

  public Person(Name name, BigDecimal age) { /* ... */ }
  public DamlRecord toValue() { /* ... */ }
}

A Java file that defines the class for the type Name is generated:

com/acme/producttypes/Name.java¶

package com.acme.producttypes;

public class Name extends DamlRecord<Name> {
  public final String firstName;
  public final String lastName;

  public static Person fromValue(Value value$) { /* ... */ }

  public Name(String firstName, String lastName) { /* ... */ }
  public DamlRecord toValue() { /* ... */ }
}

Templates¶

The Daml Codegen generates the following classes for a Daml template:

TemplateName
Represents the contract data or the template fields.

TemplateName.ContractId
Used whenever a contract ID of the corresponding template is used in another template or record, for example: data Foo = Foo (ContractId Bar). This class also provides methods to generate an ExerciseCommand for each choice that can be sent to the ledger with the Java Bindings.

TemplateName.Contract
Represents an actual contract on the ledger. It contains a field for the contract ID (of type TemplateName.ContractId) and a field for the template data (of type TemplateName). With the static method TemplateName.Contract.fromCreatedEvent, you can deserialize a CreatedEvent to an instance of TemplateName.Contract.
Com/Acme/Templates.daml¶
module Com.Acme.Templates where

data BarKey =
  BarKey
    with
      p : Party
      t : Text

template Bar
  with
    owner: Party
    name: Text
  where
    signatory owner

    key BarKey owner name : BarKey
    maintainer key.p

    choice Bar_SomeChoice: Bool
      with
        aName: Text
      controller owner
      do return True

In particular, the codegen generates a file that defines six Java classes and one interface:

Bar
Bar.ContractId
Bar.Contract
Bar.CreateAnd
Bar.JsonDecoder$
Bar.ByKey
Bar.Exercises

com/acme/templates/Bar.java¶

package com.acme.templates;

public class Bar extends Template {

  public static final Identifier TEMPLATE_ID = new Identifier("some-package-id", "Com.Acme.Templates", "Bar");

  public static final Choice<Bar, Archive, Unit> CHOICE_Archive =
    Choice.create(/* ... */);

  public static final ContractCompanion.WithKey<Contract, ContractId, Bar, BarKey> COMPANION =
      new ContractCompanion.WithKey<>("com.acme.templates.Bar",
        TEMPLATE_ID, ContractId::new, Bar::fromValue, Contract::new, e -> BarKey.fromValue(e), List.of(CHOICE_Archive));

  public final String owner;
  public final String name;

  public CreateAnd createAnd() { /* ... */ }

  public static ByKey byKey(BarKey key) { /* ... */ }

  public static class ContractId extends com.daml.ledger.javaapi.data.codegen.ContractId<Bar>
      implements Exercises<ExerciseCommand> {
    // inherited:
    public final String contractId;
  }

  public interface Exercises<Cmd> extends com.daml.ledger.javaapi.data.codegen.Exercises<Cmd> {
    default Cmd exerciseArchive(Unit arg) { /* ... */ }

    default Cmd exerciseBar_SomeChoice(Bar_SomeChoice arg) { /* ... */ }

    default Cmd exerciseBar_SomeChoice(String aName) { /* ... */ }
  }

  public static class Contract extends ContractWithKey<ContractId, Bar, BarKey> {
    // inherited:
    public final ContractId id;
    public final Bar data;

    public static Contract fromCreatedEvent(CreatedEvent event) { /* ... */ }
  }

  public static final class CreateAnd
      extends com.daml.ledger.javaapi.data.codegen.CreateAnd
      implements Exercises<CreateAndExerciseCommand> { /* ... */ }

  public static class JsonDecoder$ { /* ... */ }

  public static final class ByKey
      extends com.daml.ledger.javaapi.data.codegen.ByKey
      implements Exercises<ExerciseByKeyCommand> { /* ... */ }
}

Note that byKey and ByKey will only be generated for templates that define a key.

Variants (a.k.a. sum types)¶

A variant or sum type is a type with multiple constructors, where each constructor wraps a value of another type. The generated code is comprised of an abstract class for the variant type itself and a subclass thereof for each constructor. Classes for variant constructors are similar to classes for records.

Com/Acme/Variants.daml¶

module Com.Acme.Variants where

data BookAttribute = Pages Int
                   | Authors [Text]
                   | Title Text
                   | Published with year: Int; publisher: Text

The Java code generated for this variant is:

com/acme/variants/BookAttribute.java¶

package com.acme.variants;

public class BookAttribute extends Variant<BookAttribute> {
  public static BookAttribute fromValue(Value value) { /* ... */ }

  public static BookAttribute fromValue(Value value) { /* ... */ }
  public abstract Variant toValue();
}

com/acme/variants/bookattribute/Pages.java¶

package com.acme.variants.bookattribute;

public class Pages extends BookAttribute {
  public final Long longValue;

  public static Pages fromValue(Value value) { /* ... */ }

  public Pages(Long longValue) { /* ... */ }
  public Variant toValue() { /* ... */ }
}

com/acme/variants/bookattribute/Authors.java¶

package com.acme.variants.bookattribute;

public class Authors extends BookAttribute {
  public final List<String> listValue;

  public static Authors fromValue(Value value) { /* ... */ }

  public Author(List<String> listValue) { /* ... */ }
  public Variant toValue() { /* ... */ }

}

com/acme/variants/bookattribute/Title.java¶

package com.acme.variants.bookattribute;

public class Title extends BookAttribute {
  public final String stringValue;

  public static Title fromValue(Value value) { /* ... */ }

  public Title(String stringValue) { /* ... */ }
  public Variant toValue() { /* ... */ }
}

com/acme/variants/bookattribute/Published.java¶

package com.acme.variants.bookattribute;

public class Published extends BookAttribute {
  public final Long year;
  public final String publisher;

  public static Published fromValue(Value value) { /* ... */ }

  public Published(Long year, String publisher) { /* ... */ }
  public Variant toValue() { /* ... */ }
}

Enums¶

An enum type is a simplified sum type with multiple constructors but without argument nor type parameters. The generated code is standard java Enum whose constants map enum type constructors.

Com/Acme/Enum.daml¶

module Com.Acme.Enum where

data Color = Red | Blue | Green

The Java code generated for this variant is:

com/acme/enum/Color.java¶

package com.acme.enum;

public enum Color implements DamlEnum<Color> {
  RED,
  GREEN,
  BLUE;

  /* ... */
  public static final Color fromValue(Value value$) { /* ... */ }
  public final DamlEnum toValue() { /* ... */ }
}

Parameterized types¶

Note

This section is only included for completeness. The fromValue and toValue methods would typically come from a template that does not have any unbound type parameters.

The Daml Codegen uses Java Generic types to represent Daml parameterized types.

This Daml fragment defines the parameterized type Attribute, used by the BookAttribute type for modeling the characteristics of the book:

Com/Acme/ParameterizedTypes.daml¶

module Com.Acme.ParameterizedTypes where

data Attribute a = Attribute
    with v : a

data BookAttributes = BookAttributes with
   pages : (Attribute Int)
   authors : (Attribute [Text])
   title : (Attribute Text)

The Daml Codegen generates a Java file with a generic class for the Attribute a data type:

com/acme/parameterizedtypes/Attribute.java¶

package com.acme.parameterizedtypes;

public class Attribute<a> {
  public final a value;

  public Attribute(a value) { /* ... */  }

  public DamlRecord toValue(Function<a, Value> toValuea) { /* ... */ }

  public static <a> Attribute<a> fromValue(Value value$, Function<Value, a> fromValuea) { /* ... */ }
}

Convert a value of a generated type to a Java Bindings Value¶

To convert an instance of the generic type Attribute<a> to a Java Bindings Value, call the toValue method and pass a function as the toValuea argument for converting the field of type a to the respective Java Bindings Value. The name of the parameter consists of toValue and the name of the type parameter, in this case a, to form the name toValuea.

Below is a Java fragment that converts an attribute with a java.lang.Long value to the Java Bindings representation using the method reference Int64::new.

Attribute<Long> pagesAttribute = new Attributes<>(42L);

Value serializedPages = pagesAttribute.toValue(Int64::new);

See Daml To Java Type Mapping for an overview of the Java Bindings Value types.

Note

If the Daml type is a record or variant with more than one type parameter, you need to pass a conversion function to the toValue method for each type parameter.

Create a Value of a generated type from a Java Bindings Value¶

Analogous to the toValue method, to create a value of a generated type, call the method fromValue and pass conversion functions from a Java Bindings Value type to the expected Java type.

Attribute<Long> pagesAttribute = Attribute.<Long>fromValue(serializedPages,
    f -> f.asInt64().getOrElseThrow(() -> throw new IllegalArgumentException("Expected Int field").getValue());

See Java Bindings Value class for the methods to transform the Java Bindings types into corresponding Java types.

Non-exposed parameterized types¶

If the parameterized type is contained in a type where the actual type is specified (as in the BookAttributes type above), then the conversion methods of the enclosing type provides the required conversion function parameters automatically.

Convert optional values¶

The conversion of the Java Optional requires two steps. The Optional must be mapped in order to convert its contains before to be passed to DamlOptional::of function.

Attribute<Optional<Long>> idAttribute = new Attribute<List<Long>>(Optional.of(42));

val serializedId = DamlOptional.of(idAttribute.map(Int64::new));

To convert back DamlOptional to Java Optional, one must use the containers method toOptional. This method expects a function to convert back the value possibly contains in the container.

Attribute<Optional<Long>> idAttribute2 =
  serializedId.toOptional(v -> v.asInt64().orElseThrow(() -> new IllegalArgumentException("Expected Int64 element")));

Convert collection values¶

DamlCollectors provides collectors to converted Java collection containers such as List and Map to DamlValues in one pass. The builders for those collectors require functions to convert the element of the container.

Attribute<List<String>> authorsAttribute =
    new Attribute<List<String>>(Arrays.asList("Homer", "Ovid", "Vergil"));

Value serializedAuthors =
    authorsAttribute.toValue(f -> f.stream().collect(DamlCollector.toList(Text::new));

To convert back Daml containers to Java ones, one must use the containers methods toList or toMap. Those methods expect functions to convert back the container’s entries.

Attribute<List<String>> authorsAttribute2 =
    Attribute.<List<String>>fromValue(
        serializedAuthors,
        f0 -> f0.asList().orElseThrow(() -> new IllegalArgumentException("Expected DamlList field"))
             .toList(
                 f1 -> f1.asText().orElseThrow(() -> new IllegalArgumentException("Expected Text element"))
                      .getValue()
             )
    );

Daml interfaces¶

From this Daml definition:

Interfaces.daml¶

module Interfaces where

data TIfView = TIfView { name : Text }

interface TIf where
  viewtype TIfView
  getOwner: Party
  dup: Update (ContractId TIf)
  choice Ham: ContractId TIf with
    controller getOwner this
    do dup this
  choice Useless: ContractId TIf with
      interfacely: ContractId TIf
    controller getOwner this
    do
      dup this

template Child
    with
    party: Party
  where
    signatory party
    choice Bar: () with
      controller party
      do
        return ()

    interface instance TIf for Child where
      view = TIfView "Child"
      getOwner = party
      dup = toInterfaceContractId <$> create this

The generated file for the interface definition can be seen below. Effectively it is a class that contains only the inner type ContractId because one will always only be able to deal with Interfaces via their ContractId.

interfaces/TIf.java¶

package interfaces

/* imports */

public final class TIf {
  public static final Identifier TEMPLATE_ID = new Identifier("94fb4fa48cef1ec7d474ff3d6883a00b2f337666c302ec5e2b87e986da5c27a3", "Interfaces", "TIf");

  public static final Choice<TIf, Transfer, ContractId> CHOICE_Transfer =
    Choice.create(/* ... */);

  public static final Choice<TIf, Archive, Unit> CHOICE_Archive =
    Choice.create(/* ... */);

  public static final INTERFACE INTERFACE = new INTERFACE();

  public static final class ContractId extends com.daml.ledger.javaapi.data.codegen.ContractId<TIf>
      implements Exercises<ExerciseCommand> {
    public ContractId(String contractId) { /* ... */ }
  }

  public interface Exercises<Cmd> extends com.daml.ledger.javaapi.data.codegen.Exercises<Cmd> {
    default Cmd exerciseUseless(Useless arg) { /* ... */ }

    default Cmd exerciseHam(Ham arg) { /* ... */ }
  }

  public static final class CreateAnd
      extends com.daml.ledger.javaapi.data.codegen.CreateAnd.ToInterface
      implements Exercises<CreateAndExerciseCommand> { /* ... */ }

  public static final class ByKey
      extends com.daml.ledger.javaapi.data.codegen.ByKey.ToInterface
      implements Exercises<ExerciseByKeyCommand> { /* ... */ }

  public static final class INTERFACE extends InterfaceCompanion<TIf> { /* ... */}
}

For templates the code generation will be slightly different if a template implements interfaces. To allow converting the ContractId of a template to an interface ContractId, an additional conversion method called toInterface is generated. An unsafeFromInterface is also generated to make the unchecked conversion in the other direction.

interfaces/Child.java¶

package interfaces

/* ... */

public final class Child extends Template {

  /* ... */

  public static final class ContractId extends com.daml.ledger.javaapi.data.codegen.ContractId<Child>
      implements Exercises<ExerciseCommand> {

    /* ... */

    public TIf.ContractId toInterface(TIf.INTERFACE interfaceCompanion) { /* ... */ }

    public static ContractId unsafeFromInterface(TIf.ContractId interfaceContractId) { /* ... */ }

  }

  public interface Exercises<Cmd> extends com.daml.ledger.javaapi.data.codegen.Exercises<Cmd> {
    default Cmd exerciseBar(Bar arg) { /* ... */ }

    default Cmd exerciseBar() { /* ... */ }
  }

  /* ... */

}

Daml Codegen for Java¶

Install¶

Configure¶

Command line configuration¶

Project file configuration¶

Operate¶

References¶

Generated Java code¶

Daml primitives to Java types¶

Escaping rules¶

Generated classes¶

Records (a.k.a. product types)¶

Templates¶

Variants (a.k.a. sum types)¶

Enums¶

Parameterized types¶

Convert a value of a generated type to a Java Bindings Value¶

Create a Value of a generated type from a Java Bindings Value¶

Non-exposed parameterized types¶

Convert optional values¶

Convert collection values¶

Daml interfaces¶

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