Package groovy.transform
Annotation Type MapConstructor
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@Documented @Retention(SOURCE) @Target(TYPE) public @interface MapConstructorClass 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.*
The@TupleConstructorclass 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)'@MapConstructorannotation 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
@MapConstructorannotation generates a public constructor unless an applicableVisibilityOptionsannotation 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@CompileStaticin conjunction with such an approach since dynamic Groovy currently gives the ability to access even private constructors.) - An optional
visibilityIdattribute can be specified. If present, it must match the optionalidattribute of an applicableVisibilityOptionsannotation. This can be useful if multipleVisibilityOptionsannotations are needed.
Custom property handling:
- The
@MapConstructorannotation supports customization using@PropertyOptionswhich allows a custom property handler to be defined. This is most typically used behind the scenes by the@Immutablemeta-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:
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The generated map constructor will have an argument of type
Mapunless 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 typeLinkedHashMap. 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
- The
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Optional Element Summary
Optional Elements Modifier and Type Optional Element Description booleanallNamesWhether to include all fields and/or properties within the constructor, including those with names that are considered internal.booleanallPropertiesWhether to include all properties (as per the JavaBean spec) in the generated constructor.java.lang.String[]excludesList of field and/or property names to exclude from the constructor.booleanincludeFieldsInclude fields in the constructor.booleanincludePropertiesInclude properties in the constructor.java.lang.String[]includesList of field and/or property names to include within the constructor.booleanincludeStaticWhether to include static properties in the constructor.booleanincludeSuperFieldsInclude fields from super classes in the constructor.booleanincludeSuperPropertiesInclude properties from super classes in the constructor.booleannoArgIn addition to the map constructor, provide a no-arg constructor which calls the map constructor with an empty map.java.lang.ClasspostA Closure containing statements which will be appended to the end of the generated constructor.java.lang.ClasspreA Closure containing statements which will be prepended to the generated constructor.booleanspecialNamedArgHandlingIf 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.booleanuseSettersBy default, Groovy properties are set directly using their respective field.java.lang.StringvisibilityIdIf specified, must match the "id" attribute in a VisibilityOptions annotation to enable a custom visibility.
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Element Detail
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excludes
java.lang.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:
- {}
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includes
java.lang.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>"}
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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
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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
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useSetters
boolean useSetters
By default, Groovy properties are set directly using their respective field. By settinguseSetters=truethen 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
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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
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