Package groovy.transform

Annotation Type MapConstructor

@Documented @Retention(SOURCE) @Target(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:

  • Optional Element Summary

    Optional Elements
    Modifier and Type
    Optional Element
    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 Details

    • excludes

      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

      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

      boolean includeProperties
      Include properties in the constructor.
      Default:
      true

    • includeFields

      boolean includeFields
      Include fields in the constructor. Fields come after any properties.
      Default:
      false

    • includeSuperProperties

      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

      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

      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

      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

      boolean includeStatic
      Whether to include static properties in the constructor.
      Default:
      false

    • allNames

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

    • noArg

      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

      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

      String visibilityId
      If specified, must match the "id" attribute in a VisibilityOptions annotation to enable a custom visibility.
      Default:
      "<DummyUndefinedMarkerString-DoNotUse>"

    • pre

      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

      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