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package com.sun.beans;

import java.lang.reflect.Array;
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.HashMap;
import java.util.Map;

import sun.reflect.generics.reflectiveObjects.GenericArrayTypeImpl;
import sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl;


This is utility class to resolve types.

Author:Eamonn McManus, Sergey Malenkov
Since:1.7
/**
 * This is utility class to resolve types.
 *
 * @since 1.7
 *
 * @author Eamonn McManus
 * @author Sergey Malenkov
 */
public final class TypeResolver {

    private static final WeakCache<Type, Map<Type, Type>> CACHE = new WeakCache<>();

    
Replaces the given type in an inherited method with the actual type it has in the given inClass. 
Although type parameters are not inherited by subclasses in the Java
language, they are effectively inherited when using reflection.
For example, if you declare an interface like this...


public interface StringToIntMap extends Map<String,Integer> {}



...then StringToIntMap.class.getMethods() will show that it has methods like put(K,V) even though StringToIntMap has no type parameters. The K and V variables are the ones declared by Map, so TypeVariable.getGenericDeclaration() will return Map.class.


The purpose of this method is to take a Type from a possibly-inherited
method and replace it with the correct Type for the inheriting class.
So given parameters of K and StringToIntMap.class in the above example,
this method will return String.


Params:
  • inClass –  the base class used to resolve
  • type –     the type to resolve
See Also:
Returns:a resolved type
/**
     * Replaces the given {@code type} in an inherited method
     * with the actual type it has in the given {@code inClass}.
     *
     * <p>Although type parameters are not inherited by subclasses in the Java
     * language, they <em>are</em> effectively inherited when using reflection.
     * For example, if you declare an interface like this...</p>
     *
     * <pre>
     * public interface StringToIntMap extends Map&lt;String,Integer> {}
     * </pre>
     *
     * <p>...then StringToIntMap.class.getMethods() will show that it has methods
     * like put(K,V) even though StringToIntMap has no type parameters.  The K
     * and V variables are the ones declared by Map, so
     * {@link TypeVariable#getGenericDeclaration()} will return Map.class.</p>
     *
     * <p>The purpose of this method is to take a Type from a possibly-inherited
     * method and replace it with the correct Type for the inheriting class.
     * So given parameters of K and StringToIntMap.class in the above example,
     * this method will return String.</p>
     *
     * @param inClass  the base class used to resolve
     * @param type     the type to resolve
     * @return a resolved type
     *
     * @see #getActualType(Class)
     * @see #resolve(Type,Type)
     */
    public static Type resolveInClass(Class<?> inClass, Type type) {
        return resolve(getActualType(inClass), type);
    }

    
Replaces all types in the given array with the actual types they have in the given inClass. 
Params:
  • inClass –  the base class used to resolve
  • types –    the array of types to resolve
See Also:
Returns:an array of resolved types
/**
     * Replaces all {@code types} in the given array
     * with the actual types they have in the given {@code inClass}.
     *
     * @param inClass  the base class used to resolve
     * @param types    the array of types to resolve
     * @return an array of resolved types
     *
     * @see #getActualType(Class)
     * @see #resolve(Type,Type[])
     */
    public static Type[] resolveInClass(Class<?> inClass, Type[] types) {
        return resolve(getActualType(inClass), types);
    }

    
Replaces type variables of the given formal type with the types they stand for in the given actual type. 
A ParameterizedType is a class with type parameters, and the values
of those parameters.  For example, Map<K,V> is a generic class, and
a corresponding ParameterizedType might look like
Map<K=String,V=Integer>.  Given such a ParameterizedType, this method
will replace K with String, or List<K> with List&ltString;, or
List<? super K> with List<? super String>.


The actual argument to this method can also be a Class. In this case, either it is equivalent to a ParameterizedType with no parameters (for example, Integer.class), or it is equivalent to a "raw" ParameterizedType (for example, Map.class). In the latter case, every type parameter declared or inherited by the class is replaced by its "erasure". For a type parameter declared as <T>, the erasure is Object. For a type parameter declared as <T extends Number>, the erasure is Number.


Although type parameters are not inherited by subclasses in the Java
language, they are effectively inherited when using reflection.
For example, if you declare an interface like this...


public interface StringToIntMap extends Map<String,Integer> {}



...then StringToIntMap.class.getMethods() will show that it has methods like put(K,V) even though StringToIntMap has no type parameters. The K and V variables are the ones declared by Map, so TypeVariable.getGenericDeclaration() will return Map.class.


For this reason, this method replaces inherited type parameters too. Therefore if this method is called with actual being StringToIntMap.class and formal being the K from Map, it will return String.class.


In the case where actual is a "raw" ParameterizedType, the inherited type parameters will also be replaced by their erasures. The erasure of a Class is the Class itself, so a "raw" subinterface of StringToIntMap will still show the K from Map as String.class. But in a case like this... 
public interface StringToIntListMap extends Map<String,List<Integer>> {}
public interface RawStringToIntListMap extends StringToIntListMap {}



...the V inherited from Map will show up as List<Integer> in
StringToIntListMap, but as plain List in RawStringToIntListMap.


Params:
  • actual –  the type that supplies bindings for type variables
  • formal –  the type where occurrences of the variables in actual will be replaced by the corresponding bound values
Returns:a resolved type
/**
     * Replaces type variables of the given {@code formal} type
     * with the types they stand for in the given {@code actual} type.
     *
     * <p>A ParameterizedType is a class with type parameters, and the values
     * of those parameters.  For example, Map&lt;K,V> is a generic class, and
     * a corresponding ParameterizedType might look like
     * Map&lt;K=String,V=Integer>.  Given such a ParameterizedType, this method
     * will replace K with String, or List&lt;K> with List&ltString;, or
     * List&lt;? super K> with List&lt;? super String>.</p>
     *
     * <p>The {@code actual} argument to this method can also be a Class.
     * In this case, either it is equivalent to a ParameterizedType with
     * no parameters (for example, Integer.class), or it is equivalent to
     * a "raw" ParameterizedType (for example, Map.class).  In the latter
     * case, every type parameter declared or inherited by the class is replaced
     * by its "erasure".  For a type parameter declared as &lt;T>, the erasure
     * is Object.  For a type parameter declared as &lt;T extends Number>,
     * the erasure is Number.</p>
     *
     * <p>Although type parameters are not inherited by subclasses in the Java
     * language, they <em>are</em> effectively inherited when using reflection.
     * For example, if you declare an interface like this...</p>
     *
     * <pre>
     * public interface StringToIntMap extends Map&lt;String,Integer> {}
     * </pre>
     *
     * <p>...then StringToIntMap.class.getMethods() will show that it has methods
     * like put(K,V) even though StringToIntMap has no type parameters.  The K
     * and V variables are the ones declared by Map, so
     * {@link TypeVariable#getGenericDeclaration()} will return {@link Map Map.class}.</p>
     *
     * <p>For this reason, this method replaces inherited type parameters too.
     * Therefore if this method is called with {@code actual} being
     * StringToIntMap.class and {@code formal} being the K from Map,
     * it will return {@link String String.class}.</p>
     *
     * <p>In the case where {@code actual} is a "raw" ParameterizedType, the
     * inherited type parameters will also be replaced by their erasures.
     * The erasure of a Class is the Class itself, so a "raw" subinterface of
     * StringToIntMap will still show the K from Map as String.class.  But
     * in a case like this...
     *
     * <pre>
     * public interface StringToIntListMap extends Map&lt;String,List&lt;Integer>> {}
     * public interface RawStringToIntListMap extends StringToIntListMap {}
     * </pre>
     *
     * <p>...the V inherited from Map will show up as List&lt;Integer> in
     * StringToIntListMap, but as plain List in RawStringToIntListMap.</p>
     *
     * @param actual  the type that supplies bindings for type variables
     * @param formal  the type where occurrences of the variables
     *                in {@code actual} will be replaced by the corresponding bound values
     * @return a resolved type
     */
    public static Type resolve(Type actual, Type formal) {
        if (formal instanceof Class) {
            return formal;
        }
        if (formal instanceof GenericArrayType) {
            Type comp = ((GenericArrayType) formal).getGenericComponentType();
            comp = resolve(actual, comp);
            return (comp instanceof Class)
                    ? Array.newInstance((Class<?>) comp, 0).getClass()
                    : GenericArrayTypeImpl.make(comp);
        }
        if (formal instanceof ParameterizedType) {
            ParameterizedType fpt = (ParameterizedType) formal;
            Type[] actuals = resolve(actual, fpt.getActualTypeArguments());
            return ParameterizedTypeImpl.make(
                    (Class<?>) fpt.getRawType(), actuals, fpt.getOwnerType());
        }
        if (formal instanceof WildcardType) {
            WildcardType fwt = (WildcardType) formal;
            Type[] upper = resolve(actual, fwt.getUpperBounds());
            Type[] lower = resolve(actual, fwt.getLowerBounds());
            return new WildcardTypeImpl(upper, lower);
        }
        if (formal instanceof TypeVariable) {
            Map<Type, Type> map;
            synchronized (CACHE) {
                map = CACHE.get(actual);
                if (map == null) {
                    map = new HashMap<>();
                    prepare(map, actual);
                    CACHE.put(actual, map);
                }
            }
            Type result = map.get(formal);
            if (result == null || result.equals(formal)) {
                return formal;
            }
            result = fixGenericArray(result);
            // A variable can be bound to another variable that is itself bound
            // to something.  For example, given:
            // class Super<T> {...}
            // class Mid<X> extends Super<T> {...}
            // class Sub extends Mid<String>
            // the variable T is bound to X, which is in turn bound to String.
            // So if we have to resolve T, we need the tail recursion here.
            return resolve(actual, result);
        }
        throw new IllegalArgumentException("Bad Type kind: " + formal.getClass());
    }

    
Replaces type variables of all formal types in the given array with the types they stand for in the given actual type. 
Params:
  • actual –   the type that supplies bindings for type variables
  • formals –  the array of types to resolve
Returns:an array of resolved types
/**
     * Replaces type variables of all formal types in the given array
     * with the types they stand for in the given {@code actual} type.
     *
     * @param actual   the type that supplies bindings for type variables
     * @param formals  the array of types to resolve
     * @return an array of resolved types
     */
    public static Type[] resolve(Type actual, Type[] formals) {
        int length = formals.length;
        Type[] actuals = new Type[length];
        for (int i = 0; i < length; i++) {
            actuals[i] = resolve(actual, formals[i]);
        }
        return actuals;
    }

    
Converts the given type to the corresponding class. This method implements the concept of type erasure, that is described in section 4.6 of The Java Language Specification.

Params:
  • type –  the array of types to convert
Returns:a corresponding class
/**
     * Converts the given {@code type} to the corresponding class.
     * This method implements the concept of type erasure,
     * that is described in section 4.6 of
     * <cite>The Java Language Specification</cite>.
     *
     * @param type  the array of types to convert
     * @return a corresponding class
     */
    public static Class<?> erase(Type type) {
        if (type instanceof Class) {
            return (Class<?>) type;
        }
        if (type instanceof ParameterizedType) {
            ParameterizedType pt = (ParameterizedType) type;
            return (Class<?>) pt.getRawType();
        }
        if (type instanceof TypeVariable) {
            TypeVariable<?> tv = (TypeVariable<?>)type;
            Type[] bounds = tv.getBounds();
            return (0 < bounds.length)
                    ? erase(bounds[0])
                    : Object.class;
        }
        if (type instanceof WildcardType) {
            WildcardType wt = (WildcardType)type;
            Type[] bounds = wt.getUpperBounds();
            return (0 < bounds.length)
                    ? erase(bounds[0])
                    : Object.class;
        }
        if (type instanceof GenericArrayType) {
            GenericArrayType gat = (GenericArrayType)type;
            return Array.newInstance(erase(gat.getGenericComponentType()), 0).getClass();
        }
        throw new IllegalArgumentException("Unknown Type kind: " + type.getClass());
    }

    
Converts all types in the given array to the corresponding classes. 
Params:
  • types –  the array of types to convert
See Also:
Returns:an array of corresponding classes
/**
     * Converts all {@code types} in the given array
     * to the corresponding classes.
     *
     * @param types  the array of types to convert
     * @return an array of corresponding classes
     *
     * @see #erase(Type)
     */
    public static Class<?>[] erase(Type[] types) {
        int length = types.length;
        Class<?>[] classes = new Class<?>[length];
        for (int i = 0; i < length; i++) {
            classes[i] = TypeResolver.erase(types[i]);
        }
        return classes;
    }

    
Fills the map from type parameters to types as seen by the given type. The method is recursive because the type inherits mappings from its parent classes and interfaces. The type can be either a Class or a ParameterizedType. If it is a Class, it is either equivalent to a ParameterizedType with no parameters, or it represents the erasure of a ParameterizedType. 
Params:
  • map –   the mappings of all type variables
  • type –  the next type in the hierarchy
/**
     * Fills the map from type parameters
     * to types as seen by the given {@code type}.
     * The method is recursive because the {@code type}
     * inherits mappings from its parent classes and interfaces.
     * The {@code type} can be either a {@link Class Class}
     * or a {@link ParameterizedType ParameterizedType}.
     * If it is a {@link Class Class}, it is either equivalent
     * to a {@link ParameterizedType ParameterizedType} with no parameters,
     * or it represents the erasure of a {@link ParameterizedType ParameterizedType}.
     *
     * @param map   the mappings of all type variables
     * @param type  the next type in the hierarchy
     */
    private static void prepare(Map<Type, Type> map, Type type) {
        Class<?> raw = (Class<?>)((type instanceof Class<?>)
                ? type
                : ((ParameterizedType)type).getRawType());

        TypeVariable<?>[] formals = raw.getTypeParameters();

        Type[] actuals = (type instanceof Class<?>)
                ? formals
                : ((ParameterizedType)type).getActualTypeArguments();

        assert formals.length == actuals.length;
        for (int i = 0; i < formals.length; i++) {
            map.put(formals[i], actuals[i]);
        }
        Type gSuperclass = raw.getGenericSuperclass();
        if (gSuperclass != null) {
            prepare(map, gSuperclass);
        }
        for (Type gInterface : raw.getGenericInterfaces()) {
            prepare(map, gInterface);
        }
        // If type is the raw version of a parameterized class, we type-erase
        // all of its type variables, including inherited ones.
        if (type instanceof Class<?> && formals.length > 0) {
            for (Map.Entry<Type, Type> entry : map.entrySet()) {
                entry.setValue(erase(entry.getValue()));
            }
        }
    }

    
Replaces a GenericArrayType with plain array class where it is possible. Bug 5041784 is that arrays of non-generic type sometimes show up as GenericArrayType when using reflection. For example, a String[] might show up as a GenericArrayType where getGenericComponentType is String.class. This violates the specification, which says that GenericArrayType is used when the component type is a type variable or parameterized type. We fit the specification here. 
Params:
  • type –  the type to fix
Returns:a corresponding type for the generic array type, or the same type as type
/**
     * Replaces a {@link GenericArrayType GenericArrayType}
     * with plain array class where it is possible.
     * Bug <a href="https://bugs.java.com/view_bug.do?bug_id=5041784">5041784</a>
     * is that arrays of non-generic type sometimes show up
     * as {@link GenericArrayType GenericArrayType} when using reflection.
     * For example, a {@code String[]} might show up
     * as a {@link GenericArrayType GenericArrayType}
     * where {@link GenericArrayType#getGenericComponentType getGenericComponentType}
     * is {@code String.class}.  This violates the specification,
     * which says that {@link GenericArrayType GenericArrayType}
     * is used when the component type is a type variable or parameterized type.
     * We fit the specification here.
     *
     * @param type  the type to fix
     * @return a corresponding type for the generic array type,
     *         or the same type as {@code type}
     */
    private static Type fixGenericArray(Type type) {
        if (type instanceof GenericArrayType) {
            Type comp = ((GenericArrayType)type).getGenericComponentType();
            comp = fixGenericArray(comp);
            if (comp instanceof Class) {
                return Array.newInstance((Class<?>)comp, 0).getClass();
            }
        }
        return type;
    }

    
Replaces a Class with type parameters with a ParameterizedType where every parameter is bound to itself. When calling resolveInClass in the context of inClass, we can't just pass inClass as the actual parameter, because if inClass has type parameters that would be interpreted as accessing the raw type, so we would get unwanted erasure. This is why we bind each parameter to itself. If inClass does have type parameters and has methods where those parameters appear in the return type or argument types, we will correctly leave those types alone. 
Params:
  • inClass –  the base class used to resolve
Returns:a parameterized type for the class, or the same class as inClass
/**
     * Replaces a {@link Class Class} with type parameters
     * with a {@link ParameterizedType ParameterizedType}
     * where every parameter is bound to itself.
     * When calling {@link #resolveInClass} in the context of {@code inClass},
     * we can't just pass {@code inClass} as the {@code actual} parameter,
     * because if {@code inClass} has type parameters
     * that would be interpreted as accessing the raw type,
     * so we would get unwanted erasure.
     * This is why we bind each parameter to itself.
     * If {@code inClass} does have type parameters and has methods
     * where those parameters appear in the return type or argument types,
     * we will correctly leave those types alone.
     *
     * @param inClass  the base class used to resolve
     * @return a parameterized type for the class,
     *         or the same class as {@code inClass}
     */
    private static Type getActualType(Class<?> inClass) {
        Type[] params = inClass.getTypeParameters();
        return (params.length == 0)
                ? inClass
                : ParameterizedTypeImpl.make(
                        inClass, params, inClass.getEnclosingClass());
    }
}