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The Types.java Java example source code
/*
* Copyright (C) 2011 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
* in compliance with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License
* is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
* or implied. See the License for the specific language governing permissions and limitations under
* the License.
*/
package com.google.common.reflect;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.Iterables.transform;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Function;
import com.google.common.base.Joiner;
import com.google.common.base.Objects;
import com.google.common.base.Predicates;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Iterables;
import java.io.Serializable;
import java.lang.reflect.AnnotatedElement;
import java.lang.reflect.Array;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.GenericDeclaration;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Proxy;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;
import java.security.AccessControlException;
import java.util.Arrays;
import java.util.Collection;
import java.util.concurrent.atomic.AtomicReference;
import javax.annotation.Nullable;
/**
* Utilities for working with {@link Type}.
*
* @author Ben Yu
*/
final class Types {
/** Class#toString without the "class " and "interface " prefixes */
private static final Function<Type, String> TYPE_NAME =
new Function<Type, String>() {
@Override
public String apply(Type from) {
return JavaVersion.CURRENT.typeName(from);
}
};
private static final Joiner COMMA_JOINER = Joiner.on(", ").useForNull("null");
/** Returns the array type of {@code componentType}. */
static Type newArrayType(Type componentType) {
if (componentType instanceof WildcardType) {
WildcardType wildcard = (WildcardType) componentType;
Type[] lowerBounds = wildcard.getLowerBounds();
checkArgument(lowerBounds.length <= 1, "Wildcard cannot have more than one lower bounds.");
if (lowerBounds.length == 1) {
return supertypeOf(newArrayType(lowerBounds[0]));
} else {
Type[] upperBounds = wildcard.getUpperBounds();
checkArgument(upperBounds.length == 1, "Wildcard should have only one upper bound.");
return subtypeOf(newArrayType(upperBounds[0]));
}
}
return JavaVersion.CURRENT.newArrayType(componentType);
}
/**
* Returns a type where {@code rawType} is parameterized by {@code arguments} and is owned by
* {@code ownerType}.
*/
static ParameterizedType newParameterizedTypeWithOwner(
@Nullable Type ownerType, Class<?> rawType, Type... arguments) {
if (ownerType == null) {
return newParameterizedType(rawType, arguments);
}
// ParameterizedTypeImpl constructor already checks, but we want to throw NPE before IAE
checkNotNull(arguments);
checkArgument(rawType.getEnclosingClass() != null, "Owner type for unenclosed %s", rawType);
return new ParameterizedTypeImpl(ownerType, rawType, arguments);
}
/**
* Returns a type where {@code rawType} is parameterized by {@code arguments}.
*/
static ParameterizedType newParameterizedType(Class<?> rawType, Type... arguments) {
return new ParameterizedTypeImpl(
ClassOwnership.JVM_BEHAVIOR.getOwnerType(rawType), rawType, arguments);
}
/** Decides what owner type to use for constructing {@link ParameterizedType} from a raw class. */
private enum ClassOwnership {
OWNED_BY_ENCLOSING_CLASS {
@Nullable
@Override
Class<?> getOwnerType(Class rawType) {
return rawType.getEnclosingClass();
}
},
LOCAL_CLASS_HAS_NO_OWNER {
@Nullable
@Override
Class<?> getOwnerType(Class rawType) {
if (rawType.isLocalClass()) {
return null;
} else {
return rawType.getEnclosingClass();
}
}
};
@Nullable
abstract Class<?> getOwnerType(Class rawType);
static final ClassOwnership JVM_BEHAVIOR = detectJvmBehavior();
private static ClassOwnership detectJvmBehavior() {
class LocalClass<T> {}
Class<?> subclass = new LocalClass() {}.getClass();
ParameterizedType parameterizedType = (ParameterizedType) subclass.getGenericSuperclass();
for (ClassOwnership behavior : ClassOwnership.values()) {
if (behavior.getOwnerType(LocalClass.class) == parameterizedType.getOwnerType()) {
return behavior;
}
}
throw new AssertionError();
}
}
/**
* Returns a new {@link TypeVariable} that belongs to {@code declaration} with {@code name} and
* {@code bounds}.
*/
static <D extends GenericDeclaration> TypeVariable newArtificialTypeVariable(
D declaration, String name, Type... bounds) {
return newTypeVariableImpl(
declaration, name, (bounds.length == 0) ? new Type[] {Object.class} : bounds);
}
/** Returns a new {@link WildcardType} with {@code upperBound}. */
@VisibleForTesting
static WildcardType subtypeOf(Type upperBound) {
return new WildcardTypeImpl(new Type[0], new Type[] {upperBound});
}
/** Returns a new {@link WildcardType} with {@code lowerBound}. */
@VisibleForTesting
static WildcardType supertypeOf(Type lowerBound) {
return new WildcardTypeImpl(new Type[] {lowerBound}, new Type[] {Object.class});
}
/**
* Returns human readable string representation of {@code type}.
* <ul>
* <li>For array type {@code Foo[]}, {@code "com.mypackage.Foo[]"} are returned.
* <li>For any class, {@code theClass.getName()} are returned.
* <li>For all other types, {@code type.toString()} are returned.
* </ul>
*/
static String toString(Type type) {
return (type instanceof Class) ? ((Class<?>) type).getName() : type.toString();
}
@Nullable
static Type getComponentType(Type type) {
checkNotNull(type);
final AtomicReference<Type> result = new AtomicReference();
new TypeVisitor() {
@Override
void visitTypeVariable(TypeVariable<?> t) {
result.set(subtypeOfComponentType(t.getBounds()));
}
@Override
void visitWildcardType(WildcardType t) {
result.set(subtypeOfComponentType(t.getUpperBounds()));
}
@Override
void visitGenericArrayType(GenericArrayType t) {
result.set(t.getGenericComponentType());
}
@Override
void visitClass(Class<?> t) {
result.set(t.getComponentType());
}
}.visit(type);
return result.get();
}
/**
* Returns {@code ? extends X} if any of {@code bounds} is a subtype of {@code X[]}; or null
* otherwise.
*/
@Nullable
private static Type subtypeOfComponentType(Type[] bounds) {
for (Type bound : bounds) {
Type componentType = getComponentType(bound);
if (componentType != null) {
// Only the first bound can be a class or array.
// Bounds after the first can only be interfaces.
if (componentType instanceof Class) {
Class<?> componentClass = (Class) componentType;
if (componentClass.isPrimitive()) {
return componentClass;
}
}
return subtypeOf(componentType);
}
}
return null;
}
private static final class GenericArrayTypeImpl implements GenericArrayType, Serializable {
private final Type componentType;
GenericArrayTypeImpl(Type componentType) {
this.componentType = JavaVersion.CURRENT.usedInGenericType(componentType);
}
@Override
public Type getGenericComponentType() {
return componentType;
}
@Override
public String toString() {
return Types.toString(componentType) + "[]";
}
@Override
public int hashCode() {
return componentType.hashCode();
}
@Override
public boolean equals(Object obj) {
if (obj instanceof GenericArrayType) {
GenericArrayType that = (GenericArrayType) obj;
return Objects.equal(getGenericComponentType(), that.getGenericComponentType());
}
return false;
}
private static final long serialVersionUID = 0;
}
private static final class ParameterizedTypeImpl implements ParameterizedType, Serializable {
private final Type ownerType;
private final ImmutableList<Type> argumentsList;
private final Class<?> rawType;
ParameterizedTypeImpl(@Nullable Type ownerType, Class<?> rawType, Type[] typeArguments) {
checkNotNull(rawType);
checkArgument(typeArguments.length == rawType.getTypeParameters().length);
disallowPrimitiveType(typeArguments, "type parameter");
this.ownerType = ownerType;
this.rawType = rawType;
this.argumentsList = JavaVersion.CURRENT.usedInGenericType(typeArguments);
}
@Override
public Type[] getActualTypeArguments() {
return toArray(argumentsList);
}
@Override
public Type getRawType() {
return rawType;
}
@Override
public Type getOwnerType() {
return ownerType;
}
@Override
public String toString() {
StringBuilder builder = new StringBuilder();
if (ownerType != null) {
builder.append(JavaVersion.CURRENT.typeName(ownerType)).append('.');
}
return builder
.append(rawType.getName())
.append('<')
.append(COMMA_JOINER.join(transform(argumentsList, TYPE_NAME)))
.append('>')
.toString();
}
@Override
public int hashCode() {
return (ownerType == null ? 0 : ownerType.hashCode())
^ argumentsList.hashCode()
^ rawType.hashCode();
}
@Override
public boolean equals(Object other) {
if (!(other instanceof ParameterizedType)) {
return false;
}
ParameterizedType that = (ParameterizedType) other;
return getRawType().equals(that.getRawType())
&& Objects.equal(getOwnerType(), that.getOwnerType())
&& Arrays.equals(getActualTypeArguments(), that.getActualTypeArguments());
}
private static final long serialVersionUID = 0;
}
private static <D extends GenericDeclaration> TypeVariable newTypeVariableImpl(
D genericDeclaration, String name, Type[] bounds) {
TypeVariableImpl<D> typeVariableImpl =
new TypeVariableImpl<D>(genericDeclaration, name, bounds);
@SuppressWarnings("unchecked")
TypeVariable<D> typeVariable =
Reflection.newProxy(
TypeVariable.class, new TypeVariableInvocationHandler(typeVariableImpl));
return typeVariable;
}
/**
* Invocation handler to work around a compatibility problem between Java 7 and Java 8.
*
* <p>Java 8 introduced a new method {@code getAnnotatedBounds()} in the {@link TypeVariable}
* interface, whose return type {@code AnnotatedType[]} is also new in Java 8. That means that we
* cannot implement that interface in source code in a way that will compile on both Java 7 and
* Java 8. If we include the {@code getAnnotatedBounds()} method then its return type means it
* won't compile on Java 7, while if we don't include the method then the compiler will complain
* that an abstract method is unimplemented. So instead we use a dynamic proxy to get an
* implementation. If the method being called on the {@code TypeVariable} instance has the same
* name as one of the public methods of {@link TypeVariableImpl}, the proxy calls the same method
* on its instance of {@code TypeVariableImpl}. Otherwise it throws
* {@link UnsupportedOperationException}; this should only apply to {@code getAnnotatedBounds()}.
* This does mean that users on Java 8 who obtain an instance of {@code TypeVariable} from
* {@link TypeResolver#resolveType} will not be able to call {@code getAnnotatedBounds()} on it,
* but that should hopefully be rare.
*
* <p>This workaround should be removed at a distant future time when we no longer support Java
* versions earlier than 8.
*/
private static final class TypeVariableInvocationHandler implements InvocationHandler {
private static final ImmutableMap<String, Method> typeVariableMethods;
static {
ImmutableMap.Builder<String, Method> builder = ImmutableMap.builder();
for (Method method : TypeVariableImpl.class.getMethods()) {
if (method.getDeclaringClass().equals(TypeVariableImpl.class)) {
try {
method.setAccessible(true);
} catch (AccessControlException e) {
// OK: the method is accessible to us anyway. The setAccessible call is only for
// unusual execution environments where that might not be true.
}
builder.put(method.getName(), method);
}
}
typeVariableMethods = builder.build();
}
private final TypeVariableImpl<?> typeVariableImpl;
TypeVariableInvocationHandler(TypeVariableImpl<?> typeVariableImpl) {
this.typeVariableImpl = typeVariableImpl;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
String methodName = method.getName();
Method typeVariableMethod = typeVariableMethods.get(methodName);
if (typeVariableMethod == null) {
throw new UnsupportedOperationException(methodName);
} else {
try {
return typeVariableMethod.invoke(typeVariableImpl, args);
} catch (InvocationTargetException e) {
throw e.getCause();
}
}
}
}
private static final class TypeVariableImpl<D extends GenericDeclaration> {
private final D genericDeclaration;
private final String name;
private final ImmutableList<Type> bounds;
TypeVariableImpl(D genericDeclaration, String name, Type[] bounds) {
disallowPrimitiveType(bounds, "bound for type variable");
this.genericDeclaration = checkNotNull(genericDeclaration);
this.name = checkNotNull(name);
this.bounds = ImmutableList.copyOf(bounds);
}
public Type[] getBounds() {
return toArray(bounds);
}
public D getGenericDeclaration() {
return genericDeclaration;
}
public String getName() {
return name;
}
public String getTypeName() {
return name;
}
@Override
public String toString() {
return name;
}
@Override
public int hashCode() {
return genericDeclaration.hashCode() ^ name.hashCode();
}
@Override
public boolean equals(Object obj) {
if (NativeTypeVariableEquals.NATIVE_TYPE_VARIABLE_ONLY) {
// equal only to our TypeVariable implementation with identical bounds
if (obj != null
&& Proxy.isProxyClass(obj.getClass())
&& Proxy.getInvocationHandler(obj) instanceof TypeVariableInvocationHandler) {
TypeVariableInvocationHandler typeVariableInvocationHandler =
(TypeVariableInvocationHandler) Proxy.getInvocationHandler(obj);
TypeVariableImpl<?> that = typeVariableInvocationHandler.typeVariableImpl;
return name.equals(that.getName())
&& genericDeclaration.equals(that.getGenericDeclaration())
&& bounds.equals(that.bounds);
}
return false;
} else {
// equal to any TypeVariable implementation regardless of bounds
if (obj instanceof TypeVariable) {
TypeVariable<?> that = (TypeVariable) obj;
return name.equals(that.getName())
&& genericDeclaration.equals(that.getGenericDeclaration());
}
return false;
}
}
}
static final class WildcardTypeImpl implements WildcardType, Serializable {
private final ImmutableList<Type> lowerBounds;
private final ImmutableList<Type> upperBounds;
WildcardTypeImpl(Type[] lowerBounds, Type[] upperBounds) {
disallowPrimitiveType(lowerBounds, "lower bound for wildcard");
disallowPrimitiveType(upperBounds, "upper bound for wildcard");
this.lowerBounds = JavaVersion.CURRENT.usedInGenericType(lowerBounds);
this.upperBounds = JavaVersion.CURRENT.usedInGenericType(upperBounds);
}
@Override
public Type[] getLowerBounds() {
return toArray(lowerBounds);
}
@Override
public Type[] getUpperBounds() {
return toArray(upperBounds);
}
@Override
public boolean equals(Object obj) {
if (obj instanceof WildcardType) {
WildcardType that = (WildcardType) obj;
return lowerBounds.equals(Arrays.asList(that.getLowerBounds()))
&& upperBounds.equals(Arrays.asList(that.getUpperBounds()));
}
return false;
}
@Override
public int hashCode() {
return lowerBounds.hashCode() ^ upperBounds.hashCode();
}
@Override
public String toString() {
StringBuilder builder = new StringBuilder("?");
for (Type lowerBound : lowerBounds) {
builder.append(" super ").append(JavaVersion.CURRENT.typeName(lowerBound));
}
for (Type upperBound : filterUpperBounds(upperBounds)) {
builder.append(" extends ").append(JavaVersion.CURRENT.typeName(upperBound));
}
return builder.toString();
}
private static final long serialVersionUID = 0;
}
private static Type[] toArray(Collection<Type> types) {
return types.toArray(new Type[types.size()]);
}
private static Iterable<Type> filterUpperBounds(Iterable bounds) {
return Iterables.filter(bounds, Predicates.not(Predicates.<Type>equalTo(Object.class)));
}
private static void disallowPrimitiveType(Type[] types, String usedAs) {
for (Type type : types) {
if (type instanceof Class) {
Class<?> cls = (Class) type;
checkArgument(!cls.isPrimitive(), "Primitive type '%s' used as %s", cls, usedAs);
}
}
}
/** Returns the {@code Class} object of arrays with {@code componentType}. */
static Class<?> getArrayClass(Class componentType) {
// TODO(user): This is not the most efficient way to handle generic
// arrays, but is there another way to extract the array class in a
// non-hacky way (i.e. using String value class names- "[L...")?
return Array.newInstance(componentType, 0).getClass();
}
// TODO(benyu): Once we are on Java 8, delete this abstraction
enum JavaVersion {
JAVA6 {
@Override
GenericArrayType newArrayType(Type componentType) {
return new GenericArrayTypeImpl(componentType);
}
@Override
Type usedInGenericType(Type type) {
checkNotNull(type);
if (type instanceof Class) {
Class<?> cls = (Class) type;
if (cls.isArray()) {
return new GenericArrayTypeImpl(cls.getComponentType());
}
}
return type;
}
},
JAVA7 {
@Override
Type newArrayType(Type componentType) {
if (componentType instanceof Class) {
return getArrayClass((Class<?>) componentType);
} else {
return new GenericArrayTypeImpl(componentType);
}
}
@Override
Type usedInGenericType(Type type) {
return checkNotNull(type);
}
},
JAVA8 {
@Override
Type newArrayType(Type componentType) {
return JAVA7.newArrayType(componentType);
}
@Override
Type usedInGenericType(Type type) {
return JAVA7.usedInGenericType(type);
}
@Override
String typeName(Type type) {
try {
Method getTypeName = Type.class.getMethod("getTypeName");
return (String) getTypeName.invoke(type);
} catch (NoSuchMethodException e) {
throw new AssertionError("Type.getTypeName should be available in Java 8");
} catch (InvocationTargetException e) {
throw new RuntimeException(e);
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
}
}
};
static final JavaVersion CURRENT;
static {
if (AnnotatedElement.class.isAssignableFrom(TypeVariable.class)) {
CURRENT = JAVA8;
} else if (new TypeCapture<int[]>() {}.capture() instanceof Class) {
CURRENT = JAVA7;
} else {
CURRENT = JAVA6;
}
}
abstract Type newArrayType(Type componentType);
abstract Type usedInGenericType(Type type);
String typeName(Type type) {
return Types.toString(type);
}
final ImmutableList<Type> usedInGenericType(Type[] types) {
ImmutableList.Builder<Type> builder = ImmutableList.builder();
for (Type type : types) {
builder.add(usedInGenericType(type));
}
return builder.build();
}
}
/**
* Per https://code.google.com/p/guava-libraries/issues/detail?id=1635, In JDK 1.7.0_51-b13,
* TypeVariableImpl.equals() is changed to no longer be equal to custom TypeVariable
* implementations. As a result, we need to make sure our TypeVariable implementation respects
* symmetry. Moreover, we don't want to reconstruct a native type variable <A> using our
* implementation unless some of its bounds have changed in resolution. This avoids creating
* unequal TypeVariable implementation unnecessarily. When the bounds do change, however, it's
* fine for the synthetic TypeVariable to be unequal to any native TypeVariable anyway.
*/
static final class NativeTypeVariableEquals<X> {
static final boolean NATIVE_TYPE_VARIABLE_ONLY =
!NativeTypeVariableEquals.class.getTypeParameters()[0]
.equals(newArtificialTypeVariable(NativeTypeVariableEquals.class, "X"));
}
private Types() {}
}
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