org.springframework.core.convert

Class TypeDescriptor

  • All Implemented Interfaces:
    Serializable

    public class TypeDescriptor
    extends Object
    implements Serializable
    Context about a type to convert from or to.
    Since:
    3.0
    Author:
    Keith Donald, Andy Clement, Juergen Hoeller, Phillip Webb, Sam Brannen
    See Also:
    Serialized Form
    • Constructor Detail

      • TypeDescriptor

        public TypeDescriptor(MethodParameter methodParameter)
        Create a new type descriptor from a MethodParameter.

        Use this constructor when a source or target conversion point is a constructor parameter, method parameter, or method return value.

        Parameters:
        methodParameter - the method parameter
      • TypeDescriptor

        public TypeDescriptor(Field field)
        Create a new type descriptor from a Field.

        Use this constructor when a source or target conversion point is a field.

        Parameters:
        field - the field
      • TypeDescriptor

        public TypeDescriptor(Property property)
        Create a new type descriptor from a Property.

        Use this constructor when a source or target conversion point is a property on a Java class.

        Parameters:
        property - the property
    • Method Detail

      • valueOf

        public static TypeDescriptor valueOf(Class<?> type)
        Create a new type descriptor from the given type.

        Use this to instruct the conversion system to convert an object to a specific target type, when no type location such as a method parameter or field is available to provide additional conversion context.

        Generally prefer use of forObject(Object) for constructing type descriptors from source objects, as it handles the null object case.

        Parameters:
        type - the class
        Returns:
        the type descriptor
      • collection

        public static TypeDescriptor collection(Class<?> collectionType,
                                TypeDescriptor elementTypeDescriptor)
        Create a new type descriptor from a Collection type.

        Useful for converting to typed Collections.

        For example, a List<String> could be converted to a List<EmailAddress> by converting to a targetType built with this method. The method call to construct such a TypeDescriptor would look something like: collection(List.class, TypeDescriptor.valueOf(EmailAddress.class));

        Parameters:
        collectionType - the collection type, which must implement Collection.
        elementTypeDescriptor - a descriptor for the collection's element type, used to convert collection elements
        Returns:
        the collection type descriptor
      • map

        public static TypeDescriptor map(Class<?> mapType,
                         TypeDescriptor keyTypeDescriptor,
                         TypeDescriptor valueTypeDescriptor)
        Create a new type descriptor from a Map type.

        Useful for converting to typed Maps.

        For example, a Map<String, String> could be converted to a Map<Id, EmailAddress> by converting to a targetType built with this method: The method call to construct such a TypeDescriptor would look something like: map(Map.class, TypeDescriptor.valueOf(Id.class), TypeDescriptor.valueOf(EmailAddress.class));

        Parameters:
        mapType - the map type, which must implement Map
        keyTypeDescriptor - a descriptor for the map's key type, used to convert map keys
        valueTypeDescriptor - the map's value type, used to convert map values
        Returns:
        the map type descriptor
      • array

        public static TypeDescriptor array(TypeDescriptor elementTypeDescriptor)
        Create a new type descriptor as an array of the specified type.

        For example to create a Map<String,String>[] use TypeDescriptor.array(TypeDescriptor.map(Map.class, TypeDescriptor.value(String.class), TypeDescriptor.value(String.class))).

        Parameters:
        elementTypeDescriptor - the TypeDescriptor of the array element or null
        Returns:
        an array TypeDescriptor or null if elementTypeDescriptor is null
        Since:
        3.2.1
      • nested

        public static TypeDescriptor nested(MethodParameter methodParameter,
                            int nestingLevel)
        Creates a type descriptor for a nested type declared within the method parameter.

        For example, if the methodParameter is a List<String> and the nesting level is 1, the nested type descriptor will be String.class.

        If the methodParameter is a List<List<String>> and the nesting level is 2, the nested type descriptor will also be a String.class.

        If the methodParameter is a Map<Integer, String> and the nesting level is 1, the nested type descriptor will be String, derived from the map value.

        If the methodParameter is a List<Map<Integer, String>> and the nesting level is 2, the nested type descriptor will be String, derived from the map value.

        Returns null if a nested type cannot be obtained because it was not declared. For example, if the method parameter is a List<?>, the nested type descriptor returned will be null.

        Parameters:
        methodParameter - the method parameter with a nestingLevel of 1
        nestingLevel - the nesting level of the collection/array element or map key/value declaration within the method parameter
        Returns:
        the nested type descriptor at the specified nesting level, or null if it could not be obtained
        Throws:
        IllegalArgumentException - if the nesting level of the input MethodParameter argument is not 1
        IllegalArgumentException - if the types up to the specified nesting level are not of collection, array, or map types
      • nested

        public static TypeDescriptor nested(Field field,
                            int nestingLevel)
        Creates a type descriptor for a nested type declared within the field.

        For example, if the field is a List<String> and the nesting level is 1, the nested type descriptor will be String.class.

        If the field is a List<List<String>> and the nesting level is 2, the nested type descriptor will also be a String.class.

        If the field is a Map<Integer, String> and the nesting level is 1, the nested type descriptor will be String, derived from the map value.

        If the field is a List<Map<Integer, String>> and the nesting level is 2, the nested type descriptor will be String, derived from the map value.

        Returns null if a nested type cannot be obtained because it was not declared. For example, if the field is a List<?>, the nested type descriptor returned will be null.

        Parameters:
        field - the field
        nestingLevel - the nesting level of the collection/array element or map key/value declaration within the field
        Returns:
        the nested type descriptor at the specified nesting level, or null if it could not be obtained
        Throws:
        IllegalArgumentException - if the types up to the specified nesting level are not of collection, array, or map types
      • nested

        public static TypeDescriptor nested(Property property,
                            int nestingLevel)
        Creates a type descriptor for a nested type declared within the property.

        For example, if the property is a List<String> and the nesting level is 1, the nested type descriptor will be String.class.

        If the property is a List<List<String>> and the nesting level is 2, the nested type descriptor will also be a String.class.

        If the property is a Map<Integer, String> and the nesting level is 1, the nested type descriptor will be String, derived from the map value.

        If the property is a List<Map<Integer, String>> and the nesting level is 2, the nested type descriptor will be String, derived from the map value.

        Returns null if a nested type cannot be obtained because it was not declared. For example, if the property is a List<?>, the nested type descriptor returned will be null.

        Parameters:
        property - the property
        nestingLevel - the nesting level of the collection/array element or map key/value declaration within the property
        Returns:
        the nested type descriptor at the specified nesting level, or null if it could not be obtained
        Throws:
        IllegalArgumentException - if the types up to the specified nesting level are not of collection, array, or map types
      • forObject

        public static TypeDescriptor forObject(Object source)
        Create a new type descriptor for an object.

        Use this factory method to introspect a source object before asking the conversion system to convert it to some another type.

        If the provided object is null, returns null, else calls valueOf(Class) to build a TypeDescriptor from the object's class.

        Parameters:
        source - the source object
        Returns:
        the type descriptor
      • getType

        public Class<?> getType()
        The type of the backing class, method parameter, field, or property described by this TypeDescriptor.

        Returns primitive types as-is.

        See getObjectType() for a variation of this operation that resolves primitive types to their corresponding Object types if necessary.

        Returns:
        the type, or null
        See Also:
        getObjectType()
      • getObjectType

        public Class<?> getObjectType()
        Variation of getType() that accounts for a primitive type by returning its object wrapper type.

        This is useful for conversion service implementations that wish to normalize to object-based types and not work with primitive types directly.

      • narrow

        public TypeDescriptor narrow(Object value)
        Narrows this TypeDescriptor by setting its type to the class of the provided value.

        If the value is null, no narrowing is performed and this TypeDescriptor is returned unchanged.

        Designed to be called by binding frameworks when they read property, field, or method return values. Allows such frameworks to narrow a TypeDescriptor built from a declared property, field, or method return value type. For example, a field declared as java.lang.Object would be narrowed to java.util.HashMap if it was set to a java.util.HashMap value. The narrowed TypeDescriptor can then be used to convert the HashMap to some other type. Annotation and nested type context is preserved by the narrowed copy.

        Parameters:
        value - the value to use for narrowing this type descriptor
        Returns:
        this TypeDescriptor narrowed (returns a copy with its type updated to the class of the provided value)
      • upcast

        public TypeDescriptor upcast(Class<?> superType)
        Cast this TypeDescriptor to a superclass or implemented interface preserving annotations and nested type context.
        Parameters:
        superType - the super type to cast to (can be null
        Returns:
        a new TypeDescriptor for the up-cast type
        Throws:
        IllegalArgumentException - if this type is not assignable to the super-type
        Since:
        3.2
      • getName

        public String getName()
        Returns the name of this type: the fully qualified class name.
      • isPrimitive

        public boolean isPrimitive()
        Is this type a primitive type?
      • getAnnotations

        public Annotation[] getAnnotations()
        The annotations associated with this type descriptor, if any.
        Returns:
        the annotations, or an empty array if none
      • hasAnnotation

        public boolean hasAnnotation(Class<? extends Annotation> annotationType)
        Determine if this type descriptor has the specified annotation.
        Parameters:
        annotationType - the annotation type
        Returns:
        true if the annotation is present
      • getAnnotation

        public <T extends Annotation> T getAnnotation(Class<T> annotationType)
        Obtain the annotation associated with this type descriptor of the specified type.
        Parameters:
        annotationType - the annotation type
        Returns:
        the annotation, or null if no such annotation exists on this type descriptor
      • isAssignableTo

        public boolean isAssignableTo(TypeDescriptor typeDescriptor)
        Returns true if an object of this type descriptor can be assigned to the location described by the given type descriptor.

        For example, valueOf(String.class).isAssignableTo(valueOf(CharSequence.class)) returns true because a String value can be assigned to a CharSequence variable. On the other hand, valueOf(Number.class).isAssignableTo(valueOf(Integer.class)) returns false because, while all Integers are Numbers, not all Numbers are Integers.

        For arrays, collections, and maps, element and key/value types are checked if declared. For example, a List<String> field value is assignable to a Collection<CharSequence> field, but List<Number> is not assignable to List<Integer>.

        Returns:
        true if this type is assignable to the type represented by the provided type descriptor
        See Also:
        getObjectType()
      • isCollection

        public boolean isCollection()
        Is this type a Collection type?
      • isArray

        public boolean isArray()
        Is this type an array type?
      • getElementTypeDescriptor

        public TypeDescriptor getElementTypeDescriptor()
        If this type is an array, returns the array's component type. If this type is a Collection and it is parameterized, returns the Collection's element type. If the Collection is not parameterized, returns null indicating the element type is not declared.
        Returns:
        the array component type or Collection element type, or null if this type is a Collection but its element type is not parameterized
        Throws:
        IllegalStateException - if this type is not a java.util.Collection or Array type
      • elementTypeDescriptor

        public TypeDescriptor elementTypeDescriptor(Object element)
        If this type is a Collection or an Array, creates a element TypeDescriptor from the provided collection or array element.

        Narrows the elementType property to the class of the provided collection or array element. For example, if this describes a java.util.List<java.lang.Number< and the element argument is a java.lang.Integer, the returned TypeDescriptor will be java.lang.Integer. If this describes a java.util.List<?> and the element argument is a java.lang.Integer, the returned TypeDescriptor will be java.lang.Integer as well.

        Annotation and nested type context will be preserved in the narrowed TypeDescriptor that is returned.

        Parameters:
        element - the collection or array element
        Returns:
        a element type descriptor, narrowed to the type of the provided element
        Throws:
        IllegalStateException - if this type is not a java.util.Collection or Array type
        See Also:
        narrow(Object)
      • isMap

        public boolean isMap()
        Is this type a Map type?
      • getMapKeyTypeDescriptor

        public TypeDescriptor getMapKeyTypeDescriptor()
        If this type is a Map and its key type is parameterized, returns the map's key type. If the Map's key type is not parameterized, returns null indicating the key type is not declared.
        Returns:
        the Map key type, or null if this type is a Map but its key type is not parameterized
        Throws:
        IllegalStateException - if this type is not a java.util.Map
      • getMapKeyTypeDescriptor

        public TypeDescriptor getMapKeyTypeDescriptor(Object mapKey)
        If this type is a Map, creates a mapKey TypeDescriptor from the provided map key.

        Narrows the mapKeyType property to the class of the provided map key. For example, if this describes a java.util.Map<java.lang.Number, java.lang.String< and the key argument is a java.lang.Integer, the returned TypeDescriptor will be java.lang.Integer.

        If this describes a java.util.Map<?, ?> and the key argument is a java.lang.Integer, the returned TypeDescriptor will be java.lang.Integer as well.

        Annotation and nested type context will be preserved in the narrowed TypeDescriptor that is returned.

        Parameters:
        mapKey - the map key
        Returns:
        the map key type descriptor
        Throws:
        IllegalStateException - if this type is not a java.util.Map
        See Also:
        narrow(Object)
      • getMapValueTypeDescriptor

        public TypeDescriptor getMapValueTypeDescriptor()
        If this type is a Map and its value type is parameterized, returns the map's value type.

        If the Map's value type is not parameterized, returns null indicating the value type is not declared.

        Returns:
        the Map value type, or null if this type is a Map but its value type is not parameterized
        Throws:
        IllegalStateException - if this type is not a java.util.Map
      • getMapValueTypeDescriptor

        public TypeDescriptor getMapValueTypeDescriptor(Object mapValue)
        If this type is a Map, creates a mapValue TypeDescriptor from the provided map value.

        Narrows the mapValueType property to the class of the provided map value. For example, if this describes a java.util.Map<java.lang.String, java.lang.Number< and the value argument is a java.lang.Integer, the returned TypeDescriptor will be java.lang.Integer. If this describes a java.util.Map<?, ?> and the value argument is a java.lang.Integer, the returned TypeDescriptor will be java.lang.Integer as well.

        Annotation and nested type context will be preserved in the narrowed TypeDescriptor that is returned.

        Parameters:
        mapValue - the map value
        Returns:
        the map value type descriptor
        Throws:
        IllegalStateException - if this type is not a java.util.Map
      • hashCode

        public int hashCode()
        Overrides:
        hashCode in class  Object