groovy.transform

Annotation Type MapConstructor

@Documented
 @Retention(value=SOURCE)
 @Target(value=TYPE)
public @interface MapConstructor

Class annotation used to assist in the creation of map constructors in classes. If the class is also annotated with @ImmutableBase, then the generated constructor will contain additional code needed for immutable classes.

It allows you to write classes in this shortened form:

 import groovy.transform.*

 @TupleConstructor
 class Person {
     String first, last
 }

 @CompileStatic // optional
 @ToString(includeSuperProperties=true)
 @MapConstructor(pre={ super(args?.first, args?.last); args = args ?: [:] }, post = { first = first?.toUpperCase() })
 class Author extends Person {
     String bookName
 }

 assert new Author(first: 'Dierk', last: 'Koenig', bookName: 'ReGinA').toString() == 'Author(ReGinA, DIERK, Koenig)'
 assert new Author().toString() == 'Author(null, null, null)'
 

The @MapConstructor annotation instructs the compiler to execute an AST transformation which adds the necessary constructor method to your class.

A map constructor is created which sets properties, and optionally fields and super properties if the property/field name is a key within the map.

For the above example, the generated constructor will be something like:

 public Author(java.util.Map args) {
     super(args?.first, args?.last)
     args = args ? args : [:]
     if (args.containsKey('bookName')) {
         this.bookName = args['bookName']
     }
     first = first?.toUpperCase()
 }
 

Custom visibility:

• The @MapConstructor annotation generates a public constructor unless an applicable VisibilityOptions annotation is also present. It can be useful to change the visibility if you want to also create a builder or provide your own static factory method for object creation. You can make the constructor private and access it from the builder or your factory method. (Note: you'll probably want to use @CompileStatic in conjunction with such an approach since dynamic Groovy currently gives the ability to access even private constructors.)
• An optional visibilityId attribute can be specified. If present, it must match the optional id attribute of an applicable VisibilityOptions annotation. This can be useful if multiple VisibilityOptions annotations are needed.

Custom property handling:

• The @MapConstructor annotation supports customization using @PropertyOptions which allows a custom property handler to be defined. This is most typically used behind the scenes by the @Immutable meta-annotation but you can also define your own handler. If a custom handler is present, it will determine the code generated when initializing any property (or field).

Known limitations/special cases:

• The generated map constructor will have an argument of type Map unless a single property (or field) is included and the type of that property (or field) is Object, AbstractMap, Map or HashMap. In this case, the generated constructor will be of type LinkedHashMap. This allows the possibility of also adding a tuple constructor without conflict, although no such constructor is added automatically. You can disable this behavior by setting the specialNamedArgHandling annotation attribute to false. This means that for the special case mentioned above, you will not be able to also add a tuple constructor with a single Map argument but you can supply any kind of map as your argument. We'd also recommend not having both a map constructor and a tuple constructor with a single Object, AbstractMap or HashMap since it can cause confusion as to which will be called.

Since:

2.5.0

See Also:

PropertyOptions, VisibilityOptions

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
boolean	allNames Whether to include all fields and/or properties within the constructor, including those with names that are considered internal.
boolean	allProperties Whether to include all properties (as per the JavaBean spec) in the generated constructor.
String[]	excludes List of field and/or property names to exclude from the constructor.
boolean	includeFields Include fields in the constructor.
boolean	includeProperties Include properties in the constructor.
String[]	includes List of field and/or property names to include within the constructor.
boolean	includeStatic Whether to include static properties in the constructor.
boolean	includeSuperFields Include fields from super classes in the constructor.
boolean	includeSuperProperties Include properties from super classes in the constructor.
boolean	noArg In addition to the map constructor, provide a no-arg constructor which calls the map constructor with an empty map.
Class	post A Closure containing statements which will be appended to the end of the generated constructor.
Class	pre A Closure containing statements which will be prepended to the generated constructor.
boolean	specialNamedArgHandling If true, change the type of the map constructor argument from Map to LinkedHashMap only for the case where the class has a single property (or field) with a Map-like type.
boolean	useSetters By default, Groovy properties are set directly using their respective field.
String	visibilityId If specified, must match the "id" attribute in a VisibilityOptions annotation to enable a custom visibility.

Element Detail

excludes

public abstract String[] excludes

List of field and/or property names to exclude from the constructor. 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 constructor. 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. The default value is a special marker value indicating that no includes are defined; all fields and/or properties are included if 'includes' remains undefined and 'excludes' is explicitly or implicitly an empty list.

Default:

"<DummyUndefinedMarkerString-DoNotUse>"

includeProperties

public abstract boolean includeProperties

Include properties in the constructor.

Default:

true

includeFields

public abstract boolean includeFields

Include fields in the constructor. Fields come after any properties.

Default:

false

includeSuperProperties

public abstract boolean includeSuperProperties

Include properties from super classes in the constructor. Groovy properties, JavaBean properties and fields (in that order) from superclasses come before the members from a subclass (unless 'includes' is used to determine the order).

Default:

false

includeSuperFields

public abstract boolean includeSuperFields

Include fields from super classes in the constructor. Groovy properties, JavaBean properties and fields (in that order) from superclasses come before the members from a subclass (unless 'includes' is used to determine the order).

Default:

false

allProperties

public abstract boolean allProperties

Whether to include all properties (as per the JavaBean spec) in the generated constructor. When true, Groovy treats any explicitly created setXxx() methods as property setters as per the JavaBean specification. JavaBean properties come after any Groovy properties but before any fields for a given class (unless 'includes' is used to determine the order).

Default:

false

useSetters

public abstract boolean useSetters

By default, Groovy properties are set directly using their respective field. By setting useSetters=true then a writable property will be set using its setter. If turning on this flag we recommend that setters that might be called are made null-safe wrt the parameter.

Default:

false

includeStatic

public abstract boolean includeStatic

Whether to include static properties in the constructor.

Default:

false

allNames

public abstract boolean allNames

Whether to include all fields and/or properties within the constructor, including those with names that are considered internal.

Default:

false

noArg

public abstract boolean noArg

In addition to the map constructor, provide a no-arg constructor which calls the map constructor with an empty map.

Default:

false

specialNamedArgHandling

public abstract boolean specialNamedArgHandling

If true, change the type of the map constructor argument from Map to LinkedHashMap only for the case where the class has a single property (or field) with a Map-like type. This allows both a map and a tuple constructor to be used side-by-side so long as care is taken about the types used when calling.

Default:

true

visibilityId

public abstract String visibilityId

If specified, must match the "id" attribute in a VisibilityOptions annotation to enable a custom visibility.

Default:

"<DummyUndefinedMarkerString-DoNotUse>"

pre

public abstract Class pre

A Closure containing statements which will be prepended to the generated constructor. The first statement within the Closure may be "super(someArgs)" in which case the no-arg super constructor won't be called.

Default:

groovy.transform.Undefined.CLASS.class

post

public abstract Class post

A Closure containing statements which will be appended to the end of the generated constructor. Useful for validation steps or tweaking the populated fields/properties.

Default:

groovy.transform.Undefined.CLASS.class