JDK8/Java8源码在线阅读
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*
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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.
*
* @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 {@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<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 {@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 {@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<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<String;, or
* List<? super K> with List<? 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 <T>, the erasure
* is Object. For a type parameter declared as <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<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<String,List<Integer>> {}
* public interface RawStringToIntListMap extends StringToIntListMap {}
* </pre>
*
* <p>...the V inherited from Map will show up as List<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 {@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 {@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 {@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 {@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 {@link GenericArrayType GenericArrayType}
* with plain array class where it is possible.
* Bug <a href="http://bugs.sun.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,
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