groovy.transform.builder

Annotation Type Builder

@Documented
@Retention(value=RUNTIME)
@Target(value={TYPE,CONSTRUCTOR,METHOD})
public @interface Builder

The @Builder AST transformation is used to help write classes that can be created using fluent api calls. The transform supports multiple building strategies to cover a range of cases and there are a number of configuration options to customize the building process. In addition, a number of annotation attributes let you customise the building process. Not all annotation attributes are supported by all strategies. See the individual strategy documentation for more details. If you're an AST hacker, you can also define your own strategy class. The following strategies are bundled with Groovy:

• SimpleStrategy for creating chained setters
• ExternalStrategy where you annotate an explicit builder class while leaving some buildee class being built untouched
• DefaultStrategy which creates a nested helper class for instance creation
• InitializerStrategy which creates a nested helper class for instance creation which when used with @CompileStatic allows type-safe object creation

Note that Groovy provides other built-in mechanisms for easy creation of objects, e.g. the named-args constructor:

 new Person(firstName: "Robert", lastName: "Lewandowski", age: 21)
 

or the with statement:

 new Person().with {
     firstName = "Robert"
     lastName = "Lewandowski"
     age = 21
 }
 

so you might not find value in using the builder transform at all. But if you need Java integration or in some cases improved type safety, the @Builder transform might prove very useful.

Author:

Marcin Grzejszczak, Paul King

See Also:

SimpleStrategy, ExternalStrategy, DefaultStrategy, InitializerStrategy

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
String	builderClassName For strategies which create a builder helper class, the class name to use for the helper class.
String	builderMethodName The method name to use for a builder factory method in the source class for easy access of the builder helper class for strategies which create such a helper class.
Class<? extends BuilderASTTransformation.BuilderStrategy>	builderStrategy A class capturing the builder strategy
String	buildMethodName For strategies which create a builder helper class that creates the instance, the method name to call to create the instance.
String[]	excludes List of field and/or property names to exclude from generated builder methods.
Class	forClass A class for which builder methods should be created.
String[]	includes List of field and/or property names to include within the generated builder methods.
String	prefix The prefix to use when creating the setter methods.

Element Detail

forClass

public abstract Class forClass

A class for which builder methods should be created. It will be an error to leave this attribute with its default value for some strategies.

Default:

groovy.transform.Undefined.CLASS.class

builderStrategy

public abstract Class<? extends BuilderASTTransformation.BuilderStrategy> builderStrategy

A class capturing the builder strategy

Default:

groovy.transform.builder.DefaultStrategy.class

prefix

public abstract String prefix

The prefix to use when creating the setter methods. Default is determined by the strategy which might use "" or "set" but you can choose your own, e.g. "with". If non-empty the first letter of the property will be capitalized before being appended to the prefix.

Default:

"<DummyUndefinedMarkerString-DoNotUse>"

builderClassName

public abstract String builderClassName

For strategies which create a builder helper class, the class name to use for the helper class. Not used if using forClass since in such cases the builder class is explicitly supplied. Default is determined by the strategy, e.g. TargetClass + "Builder" or TargetClass + "Initializer".

Default:

"<DummyUndefinedMarkerString-DoNotUse>"

buildMethodName

public abstract String buildMethodName

For strategies which create a builder helper class that creates the instance, the method name to call to create the instance. Default is determined by the strategy, e.g. build or create.

Default:

"<DummyUndefinedMarkerString-DoNotUse>"

builderMethodName

public abstract String builderMethodName

The method name to use for a builder factory method in the source class for easy access of the builder helper class for strategies which create such a helper class. Must not be used if using forClass. Default is determined by the strategy, e.g. builder or createInitializer.

Default:

"<DummyUndefinedMarkerString-DoNotUse>"

excludes

public abstract String[] excludes

List of field and/or property names to exclude from generated builder methods. Must not be used if 'includes' is used. For convenience, a String with comma separated names can be used in addition to an array (using Groovy's literal list notation) of String values.

Default:

{}

includes

public abstract String[] includes

List of field and/or property names to include within the generated builder methods. Must not be used if 'excludes' is used. For convenience, a String with comma separated names can be used in addition to an array (using Groovy's literal list notation) of String values.

Default:

{}