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/*
 * Copyright 2020 Google LLC
 *
 * 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.auto.value.extension.serializable.serializer.impl;

import com.google.auto.common.MoreTypes;
import com.google.auto.service.AutoService;
import com.google.auto.value.extension.serializable.serializer.interfaces.Serializer;
import com.google.auto.value.extension.serializable.serializer.interfaces.SerializerExtension;
import com.google.auto.value.extension.serializable.serializer.interfaces.SerializerFactory;
import com.squareup.javapoet.CodeBlock;
import java.util.Optional;
import javax.annotation.processing.ProcessingEnvironment;
import javax.lang.model.type.TypeKind;
import javax.lang.model.type.TypeMirror;

/**
 * A {@link SerializerExtension} that enables {@link Optional} types to be serialized.
 *
 * 

The type argument {@code T} of {@code Optional} is queried against the {@link * SerializerFactory}. */ @AutoService(SerializerExtension.class) public final class OptionalSerializerExtension implements SerializerExtension { public OptionalSerializerExtension() {} /** Creates a {@link Serializer} that supports {@link Optional} types. */ @Override public Optional getSerializer( TypeMirror typeMirror, SerializerFactory factory, ProcessingEnvironment processingEnv) { if (!isOptional(typeMirror)) { return Optional.empty(); } // Extract the T of Optional. TypeMirror containedType = getContainedType(typeMirror); Serializer containedTypeSerializer = factory.getSerializer(containedType); return Optional.of(new OptionalSerializer(containedTypeSerializer)); } private static class OptionalSerializer implements Serializer { private final Serializer containedTypeSerializer; OptionalSerializer(Serializer containedTypeSerializer) { this.containedTypeSerializer = containedTypeSerializer; } @Override public TypeMirror proxyFieldType() { // If this is an Optional then the proxy field type is String. // If this is an Optional, and the proxy field type for Foo is Bar, then the proxy field // type for Optional is Bar. return containedTypeSerializer.proxyFieldType(); } @Override public CodeBlock toProxy(CodeBlock expression) { return CodeBlock.of( "$L.isPresent() ? $L : null", expression, containedTypeSerializer.toProxy(CodeBlock.of("$L.get()", expression))); } @Override public CodeBlock fromProxy(CodeBlock expression) { return CodeBlock.of( "$T.ofNullable($L == null ? null : $L)", Optional.class, expression, containedTypeSerializer.fromProxy(expression)); } } /** Checks if the given type is an {@link Optional}. */ private static boolean isOptional(TypeMirror type) { if (type.getKind() != TypeKind.DECLARED) { return false; } return MoreTypes.asTypeElement(type).getQualifiedName().contentEquals("java.util.Optional"); } /** * Gets the given type's first type argument. * *

Returns the {@code T} in {@code Optional}. */ private static TypeMirror getContainedType(TypeMirror type) { return MoreTypes.asDeclared(type).getTypeArguments().get(0); } }





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