com.fasterxml.classmate
Class TypeResolver

java.lang.Object
  com.fasterxml.classmate.TypeResolver

All Implemented Interfaces:

Serializable

public class TypeResolver
extends Object
implements Serializable

Object that is used for resolving generic type information of a class so that it is accessible using simple API. Resolved types are also starting point for accessing resolved (generics aware) return and argument types of class members (methods, fields, constructors).

Note that resolver instances are stateful in that resolvers cache resolved types for efficiency. Since this is internal state and not directly visible to callers, access to state is fully synchronized so that access from multiple threads is safe.

See Also:

Serialized Form

Field Summary

protected static HashMap<ClassKey,ResolvedType>	_primitiveTypes Since number of primitive types is small, and they are frequently needed, let's actually pre-create them for efficient reuse.
protected ResolvedTypeCache	_resolvedTypes Simple cache of types resolved by this resolved; capped to last 200 resolved types.

Constructor Summary

TypeResolver()

Method Summary

ResolvedArrayType	arrayType(Type elementType) Factory method for constructing array type of given element type.
static boolean	isSelfReference(ResolvedType type) Helper method that can be used to checked whether given resolved type (with erased type of java.lang.Object) is a placeholder for "self-reference"; these are nasty recursive ("self") types needed with some interfaces
ResolvedType	resolve(TypeBindings typeBindings, Type jdkType) Factory method for resolving specified Java Type, given TypeBindings needed to resolve any type variables.
ResolvedType	resolve(Type type, Type... typeParameters) Factory method for resolving given base type using specified types as type parameters.
ResolvedType	resolveSubtype(ResolvedType supertype, Class<?> subtype) Factory method for constructing sub-classing specified type; class specified as sub-class must be compatible according to basic Java inheritance rules (subtype must propery extend or implement specified supertype).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

_primitiveTypes

protected static final HashMap<ClassKey,ResolvedType> _primitiveTypes

Since number of primitive types is small, and they are frequently needed, let's actually pre-create them for efficient reuse. Same goes for limited number of other "standard" types...

_resolvedTypes

protected final ResolvedTypeCache _resolvedTypes

Simple cache of types resolved by this resolved; capped to last 200 resolved types. Caching works because type instances themselves are mostly immutable; and properly synchronized in cases where transient data (raw members) are accessed.

Constructor Detail

TypeResolver

public TypeResolver()

Method Detail

resolve

public ResolvedType resolve(Type type,
                            Type... typeParameters)

Factory method for resolving given base type using specified types as type parameters. Sample usage would be:

  ResolvedType type = TypeResolver.resolve(List.class, Integer.class);

which would be equivalent to

  ResolvedType type = TypeResolver.resolve(new GenericType<List<Integer>>() { });

Note that you can mix different types of type parameters, whether already resolved (ResolvedType), type-erased (Class) or generic type reference (GenericType).

arrayType

public ResolvedArrayType arrayType(Type elementType)

Factory method for constructing array type of given element type.

resolve

public ResolvedType resolve(TypeBindings typeBindings,
                            Type jdkType)

Factory method for resolving specified Java Type, given TypeBindings needed to resolve any type variables.

Use of this method is discouraged (use if and only if you really know what you are doing!); but if used, type bindings passed should come from ResolvedType instance of declaring class (or interface).

NOTE: order of arguments was reversed for 0.8, to avoid problems with overload varargs method.

resolveSubtype

public ResolvedType resolveSubtype(ResolvedType supertype,
                                   Class<?> subtype)
                            throws IllegalArgumentException,
                                   UnsupportedOperationException

Factory method for constructing sub-classing specified type; class specified as sub-class must be compatible according to basic Java inheritance rules (subtype must propery extend or implement specified supertype).

A typical use case here is to refine a generic type; for example, given that we have generic type like List<Integer>, but we want a more specific implementation type like class ArrayList but with same parameterization (here just Integer), we could achieve it by:

  ResolvedType mapType = typeResolver.resolve(List.class, Integer.class);
  ResolveType concreteMapType = typeResolver.resolveSubType(mapType, ArrayList.class);

(in this case, it would have been simpler to resolve directly; but in some cases we are handled supertype and want to refine it, in which case steps would be the same but separated by other code)

Note that this method will fail if extension can not succeed; either because this type is not extendable (sub-classable) -- which is true for primitive and array types -- or because given class is not a subtype of this type. To check whether subtyping could succeed, you can call ResolvedType.canCreateSubtypes() to see if supertype can ever be extended.

Parameters:

supertype - Type to subtype (extend)

subtype - Type-erased sub-class or sub-interface

Returns:

Resolved subtype

Throws:

IllegalArgumentException - If this type can be extended in general, but not into specified sub-class

UnsupportedOperationException - If this type can not be sub-classed

isSelfReference

public static boolean isSelfReference(ResolvedType type)

Helper method that can be used to checked whether given resolved type (with erased type of java.lang.Object) is a placeholder for "self-reference"; these are nasty recursive ("self") types needed with some interfaces