org.hildan.generics.MentionedClassesExplorer Maven / Gradle / Ivy

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A way to recursively build something out of a generic type declaration

There is a newer version: 1.2.0

package org.hildan.generics;

import java.lang.reflect.GenericArrayType;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import org.jetbrains.annotations.NotNull;

/**
 * An implementation of {@link GenericTypeHandler} that lists all classes appearing in a generic type declaration.
 */
public class MentionedClassesExplorer implements GenericTypeHandler>> {

    /**
     * Returns all classes/interfaces appearing in the given type declaration. This method recursively explores type
     * parameters and array components to find the involved types.
     * 
     * For instance, for the type {@code Map[]>}, we get [Map, Custom, List, Integer].
     *
     * @param type
     *         the type to explore
     *
     * @return a non-null set of all classes involved in the given type declaration
     */
    @NotNull
    public static Set> getClassesInDeclaration(@NotNull Type type) {
        return GenericDeclarationExplorer.explore(type, new MentionedClassesExplorer());
    }

    @Override
    public Set> handleVoid() {
        return Collections.emptySet();
    }

    @Override
    public Set> handleSimpleClass(@NotNull Class clazz) {
        return Collections.singleton(clazz);
    }

    @Override
    public Set> handleEnumClass(@NotNull Class clazz) {
        return handleSimpleClass(clazz);
    }

    @Override
    public Set> handleArrayClass(@NotNull Class arrayClass, Set> handledComponentClass) {
        return handledComponentClass;
    }

    @Override
    public Set> handleGenericArray(@NotNull GenericArrayType type, Set> handledComponentClass) {
        return handledComponentClass;
    }

    @Override
    public Set> handleParameterizedType(@NotNull ParameterizedType type, Set> handledRawType,
            @NotNull List>> handledTypeParameters) {
        Set> result = new HashSet<>(handledRawType);
        handledTypeParameters.forEach(result::addAll);
        return result;
    }

    @Override
    public Set> handleTypeVariable(@NotNull TypeVariable type, @NotNull List>> handledBounds) {
        return handledBounds.stream().flatMap(Collection::stream).collect(Collectors.toSet());
    }

    @Override
    public Set> handleWildcardType(@NotNull WildcardType type, @NotNull List>> handledUpperBounds,
            @NotNull List>> handledLowerBounds) {
        Stream>> upperBoundsStream = handledUpperBounds.stream();
        Stream>> lowerBoundsStream = handledLowerBounds.stream();
        return Stream.concat(upperBoundsStream, lowerBoundsStream)
                     .flatMap(Collection::stream)
                     .collect(Collectors.toSet());
    }
}