https://github.com/spring-projects/spring-framework: Spring Core (Spring IO)
  • Juergen Hoeller 
/*
 * Copyright 2002-2020 the original author or 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
 *
 *      https://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 org.springframework.core;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.lang.reflect.Field;
import java.lang.reflect.GenericArrayType;
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 org.springframework.lang.Nullable;
import org.springframework.util.ConcurrentReferenceHashMap;
import org.springframework.util.ObjectUtils;
import org.springframework.util.ReflectionUtils;


Internal utility class that can be used to obtain wrapped Serializable variants of java.lang.reflect.Types. 
Fields or 
MethodParameters can be used as the root source for a serializable type. Alternatively, a regular Class can also be used as source. 
The returned type will either be a Class or a serializable proxy of GenericArrayType, ParameterizedType, TypeVariable or WildcardType. With the exception of Class (which is final) calls to methods that return further Types (for example GenericArrayType.getGenericComponentType()) will be automatically wrapped. 
Author:Phillip Webb, Juergen Hoeller, Sam Brannen
Since:4.0
/**
 * Internal utility class that can be used to obtain wrapped {@link Serializable}
 * variants of {@link java.lang.reflect.Type java.lang.reflect.Types}.
 *
 * <p>{@link #forField(Field) Fields} or {@link #forMethodParameter(MethodParameter)
 * MethodParameters} can be used as the root source for a serializable type.
 * Alternatively, a regular {@link Class} can also be used as source.
 *
 * <p>The returned type will either be a {@link Class} or a serializable proxy of
 * {@link GenericArrayType}, {@link ParameterizedType}, {@link TypeVariable} or
 * {@link WildcardType}. With the exception of {@link Class} (which is final) calls
 * to methods that return further {@link Type Types} (for example
 * {@link GenericArrayType#getGenericComponentType()}) will be automatically wrapped.
 *
 * @author Phillip Webb
 * @author Juergen Hoeller
 * @author Sam Brannen
 * @since 4.0
 */
final class SerializableTypeWrapper {

	private static final Class<?>[] SUPPORTED_SERIALIZABLE_TYPES = {
			GenericArrayType.class, ParameterizedType.class, TypeVariable.class, WildcardType.class};

	
Whether this environment lives within a native image. Exposed as a private static field rather than in a NativeImageDetector.inNativeImage() static method due to https://github.com/oracle/graal/issues/2594. 
See Also:
/**
	 * Whether this environment lives within a native image.
	 * Exposed as a private static field rather than in a {@code NativeImageDetector.inNativeImage()} static method due to https://github.com/oracle/graal/issues/2594.
	 * @see <a href="https://github.com/oracle/graal/blob/master/sdk/src/org.graalvm.nativeimage/src/org/graalvm/nativeimage/ImageInfo.java">ImageInfo.java</a>
	 */
	private static final boolean IN_NATIVE_IMAGE = (System.getProperty("org.graalvm.nativeimage.imagecode") != null);

	static final ConcurrentReferenceHashMap<Type, Type> cache = new ConcurrentReferenceHashMap<>(256);


	private SerializableTypeWrapper() {
	}


	
Return a Serializable variant of Field.getGenericType(). 
/**
	 * Return a {@link Serializable} variant of {@link Field#getGenericType()}.
	 */
	@Nullable
	public static Type forField(Field field) {
		return forTypeProvider(new FieldTypeProvider(field));
	}

	/**
	 * Return a {@link Serializable} variant of
	 * {@link MethodParameter#getGenericParameterType()}.
	 */
	@Nullable
	public static Type forMethodParameter(MethodParameter methodParameter) {
		return forTypeProvider(new MethodParameterTypeProvider(methodParameter));
	}

	
Unwrap the given type, effectively returning the original non-serializable type.

Params:
  • type – the type to unwrap
Returns:the original non-serializable type
/**
	 * Unwrap the given type, effectively returning the original non-serializable type.
	 * @param type the type to unwrap
	 * @return the original non-serializable type
	 */
	@SuppressWarnings("unchecked")
	public static <T extends Type> T unwrap(T type) {
		Type unwrapped = null;
		if (type instanceof SerializableTypeProxy) {
			unwrapped = ((SerializableTypeProxy) type).getTypeProvider().getType();
		}
		return (unwrapped != null ? (T) unwrapped : type);
	}

	
Return a Serializable Type backed by a TypeProvider . 
If type artifacts are generally not serializable in the current runtime environment, this delegate will simply return the original Type as-is. 
/**
	 * Return a {@link Serializable} {@link Type} backed by a {@link TypeProvider} .
	 * <p>If type artifacts are generally not serializable in the current runtime
	 * environment, this delegate will simply return the original {@code Type} as-is.
	 */
	@Nullable
	static Type forTypeProvider(TypeProvider provider) {
		Type providedType = provider.getType();
		if (providedType == null || providedType instanceof Serializable) {
			// No serializable type wrapping necessary (e.g. for java.lang.Class)
			return providedType;
		}
		if (IN_NATIVE_IMAGE || !Serializable.class.isAssignableFrom(Class.class)) {
			// Let's skip any wrapping attempts if types are generally not serializable in
			// the current runtime environment (even java.lang.Class itself, e.g. on GraalVM native images)
			return providedType;
		}

		// Obtain a serializable type proxy for the given provider...
		Type cached = cache.get(providedType);
		if (cached != null) {
			return cached;
		}
		for (Class<?> type : SUPPORTED_SERIALIZABLE_TYPES) {
			if (type.isInstance(providedType)) {
				ClassLoader classLoader = provider.getClass().getClassLoader();
				Class<?>[] interfaces = new Class<?>[] {type, SerializableTypeProxy.class, Serializable.class};
				InvocationHandler handler = new TypeProxyInvocationHandler(provider);
				cached = (Type) Proxy.newProxyInstance(classLoader, interfaces, handler);
				cache.put(providedType, cached);
				return cached;
			}
		}
		throw new IllegalArgumentException("Unsupported Type class: " + providedType.getClass().getName());
	}


	
Additional interface implemented by the type proxy.

/**
	 * Additional interface implemented by the type proxy.
	 */
	interface SerializableTypeProxy {

		
Return the underlying type provider.

/**
		 * Return the underlying type provider.
		 */
		TypeProvider getTypeProvider();
	}


	
A Serializable interface providing access to a Type. 
/**
	 * A {@link Serializable} interface providing access to a {@link Type}.
	 */
	@SuppressWarnings("serial")
	interface TypeProvider extends Serializable {

		
Return the (possibly non Serializable) Type. 
/**
		 * Return the (possibly non {@link Serializable}) {@link Type}.
		 */
		@Nullable
		Type getType();

		
Return the source of the type, or null if not known. 
The default implementations returns null. 
/**
		 * Return the source of the type, or {@code null} if not known.
		 * <p>The default implementations returns {@code null}.
		 */
		@Nullable
		default Object getSource() {
			return null;
		}
	}


	
Serializable InvocationHandler used by the proxied Type. Provides serialization support and enhances any methods that return Type or Type[]. 
/**
	 * {@link Serializable} {@link InvocationHandler} used by the proxied {@link Type}.
	 * Provides serialization support and enhances any methods that return {@code Type}
	 * or {@code Type[]}.
	 */
	@SuppressWarnings("serial")
	private static class TypeProxyInvocationHandler implements InvocationHandler, Serializable {

		private final TypeProvider provider;

		public TypeProxyInvocationHandler(TypeProvider provider) {
			this.provider = provider;
		}

		@Override
		@Nullable
		public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
			switch (method.getName()) {
				case "equals":
					Object other = args[0];
					// Unwrap proxies for speed
					if (other instanceof Type) {
						other = unwrap((Type) other);
					}
					return ObjectUtils.nullSafeEquals(this.provider.getType(), other);
				case "hashCode":
					return ObjectUtils.nullSafeHashCode(this.provider.getType());
				case "getTypeProvider":
					return this.provider;
			}

			if (Type.class == method.getReturnType() && ObjectUtils.isEmpty(args)) {
				return forTypeProvider(new MethodInvokeTypeProvider(this.provider, method, -1));
			}
			else if (Type[].class == method.getReturnType() && ObjectUtils.isEmpty(args)) {
				Type[] result = new Type[((Type[]) method.invoke(this.provider.getType())).length];
				for (int i = 0; i < result.length; i++) {
					result[i] = forTypeProvider(new MethodInvokeTypeProvider(this.provider, method, i));
				}
				return result;
			}

			try {
				return method.invoke(this.provider.getType(), args);
			}
			catch (InvocationTargetException ex) {
				throw ex.getTargetException();
			}
		}
	}


	
TypeProvider for Types obtained from a Field. 
/**
	 * {@link TypeProvider} for {@link Type Types} obtained from a {@link Field}.
	 */
	@SuppressWarnings("serial")
	static class FieldTypeProvider implements TypeProvider {

		private final String fieldName;

		private final Class<?> declaringClass;

		private transient Field field;

		public FieldTypeProvider(Field field) {
			this.fieldName = field.getName();
			this.declaringClass = field.getDeclaringClass();
			this.field = field;
		}

		@Override
		public Type getType() {
			return this.field.getGenericType();
		}

		@Override
		public Object getSource() {
			return this.field;
		}

		private void readObject(ObjectInputStream inputStream) throws IOException, ClassNotFoundException {
			inputStream.defaultReadObject();
			try {
				this.field = this.declaringClass.getDeclaredField(this.fieldName);
			}
			catch (Throwable ex) {
				throw new IllegalStateException("Could not find original class structure", ex);
			}
		}
	}


	
TypeProvider for Types obtained from a MethodParameter. 
/**
	 * {@link TypeProvider} for {@link Type Types} obtained from a {@link MethodParameter}.
	 */
	@SuppressWarnings("serial")
	static class MethodParameterTypeProvider implements TypeProvider {

		@Nullable
		private final String methodName;

		private final Class<?>[] parameterTypes;

		private final Class<?> declaringClass;

		private final int parameterIndex;

		private transient MethodParameter methodParameter;

		public MethodParameterTypeProvider(MethodParameter methodParameter) {
			this.methodName = (methodParameter.getMethod() != null ? methodParameter.getMethod().getName() : null);
			this.parameterTypes = methodParameter.getExecutable().getParameterTypes();
			this.declaringClass = methodParameter.getDeclaringClass();
			this.parameterIndex = methodParameter.getParameterIndex();
			this.methodParameter = methodParameter;
		}

		@Override
		public Type getType() {
			return this.methodParameter.getGenericParameterType();
		}

		@Override
		public Object getSource() {
			return this.methodParameter;
		}

		private void readObject(ObjectInputStream inputStream) throws IOException, ClassNotFoundException {
			inputStream.defaultReadObject();
			try {
				if (this.methodName != null) {
					this.methodParameter = new MethodParameter(
							this.declaringClass.getDeclaredMethod(this.methodName, this.parameterTypes), this.parameterIndex);
				}
				else {
					this.methodParameter = new MethodParameter(
							this.declaringClass.getDeclaredConstructor(this.parameterTypes), this.parameterIndex);
				}
			}
			catch (Throwable ex) {
				throw new IllegalStateException("Could not find original class structure", ex);
			}
		}
	}


	
TypeProvider for Types obtained by invoking a no-arg method. 
/**
	 * {@link TypeProvider} for {@link Type Types} obtained by invoking a no-arg method.
	 */
	@SuppressWarnings("serial")
	static class MethodInvokeTypeProvider implements TypeProvider {

		private final TypeProvider provider;

		private final String methodName;

		private final Class<?> declaringClass;

		private final int index;

		private transient Method method;

		@Nullable
		private transient volatile Object result;

		public MethodInvokeTypeProvider(TypeProvider provider, Method method, int index) {
			this.provider = provider;
			this.methodName = method.getName();
			this.declaringClass = method.getDeclaringClass();
			this.index = index;
			this.method = method;
		}

		@Override
		@Nullable
		public Type getType() {
			Object result = this.result;
			if (result == null) {
				// Lazy invocation of the target method on the provided type
				result = ReflectionUtils.invokeMethod(this.method, this.provider.getType());
				// Cache the result for further calls to getType()
				this.result = result;
			}
			return (result instanceof Type[] ? ((Type[]) result)[this.index] : (Type) result);
		}

		@Override
		@Nullable
		public Object getSource() {
			return null;
		}

		private void readObject(ObjectInputStream inputStream) throws IOException, ClassNotFoundException {
			inputStream.defaultReadObject();
			Method method = ReflectionUtils.findMethod(this.declaringClass, this.methodName);
			if (method == null) {
				throw new IllegalStateException("Cannot find method on deserialization: " + this.methodName);
			}
			if (method.getReturnType() != Type.class && method.getReturnType() != Type[].class) {
				throw new IllegalStateException(
						"Invalid return type on deserialized method - needs to be Type or Type[]: " + method);
			}
			this.method = method;
		}
	}

}