org.springframework.core.ReactiveAdapterRegistry Maven / Gradle / Ivy
/*
* Copyright 2002-2018 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.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.CompletableFuture;
import java.util.function.Function;
import io.reactivex.BackpressureStrategy;
import io.reactivex.Flowable;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import rx.RxReactiveStreams;
import org.springframework.lang.Nullable;
import org.springframework.util.ClassUtils;
import org.springframework.util.ReflectionUtils;
/**
* A registry of adapters to adapt Reactive Streams {@link Publisher} to/from
* various async/reactive types such as {@code CompletableFuture}, RxJava
* {@code Observable}, and others.
*
* By default, depending on classpath availability, adapters are registered
* for Reactor, RxJava 1, RxJava 2 types, {@link CompletableFuture}, and Java 9+
* Flow.Publisher.
*
* @author Rossen Stoyanchev
* @author Sebastien Deleuze
* @since 5.0
*/
public class ReactiveAdapterRegistry {
@Nullable
private static volatile ReactiveAdapterRegistry sharedInstance;
private final boolean reactorPresent;
private final List adapters = new ArrayList<>(32);
/**
* Create a registry and auto-register default adapters.
* @see #getSharedInstance()
*/
public ReactiveAdapterRegistry() {
// Reactor
boolean reactorRegistered = false;
try {
new ReactorRegistrar().registerAdapters(this);
reactorRegistered = true;
}
catch (Throwable ex) {
// Ignore
}
this.reactorPresent = reactorRegistered;
// RxJava1
try {
new RxJava1Registrar().registerAdapters(this);
}
catch (Throwable ex) {
// Ignore
}
// RxJava2
try {
new RxJava2Registrar().registerAdapters(this);
}
catch (Throwable ex) {
// Ignore
}
// Java 9+ Flow.Publisher
try {
new ReactorJdkFlowAdapterRegistrar().registerAdapter(this);
}
catch (Throwable ex) {
// Ignore for the time being...
// We can fall back on "reactive-streams-flow-bridge" (once released)
}
}
/**
* Whether the registry has any adapters which would be the case if any of
* Reactor, RxJava 2, or RxJava 1 (+ RxJava Reactive Streams bridge) are
* present on the classpath.
*/
public boolean hasAdapters() {
return !this.adapters.isEmpty();
}
/**
* Register a reactive type along with functions to adapt to and from a
* Reactive Streams {@link Publisher}. The functions can assume their
* input is never be {@code null} nor {@link Optional}.
*/
public void registerReactiveType(ReactiveTypeDescriptor descriptor,
Function> toAdapter, Function, Object> fromAdapter) {
if (reactorPresent) {
this.adapters.add(new ReactorAdapter(descriptor, toAdapter, fromAdapter));
}
else {
this.adapters.add(new ReactiveAdapter(descriptor, toAdapter, fromAdapter));
}
}
/**
* Get the adapter for the given reactive type.
*/
@Nullable
public ReactiveAdapter getAdapter(Class reactiveType) {
return getAdapter(reactiveType, null);
}
/**
* Get the adapter for the given reactive type. Or if a "source" object is
* provided, its actual type is used instead.
* @param reactiveType the reactive type
* (may be {@code null} if a concrete source object is given)
* @param source an instance of the reactive type
* (i.e. to adapt from; may be {@code null} if the reactive type is specified)
*/
@Nullable
public ReactiveAdapter getAdapter(@Nullable Class reactiveType, @Nullable Object source) {
Object sourceToUse = (source instanceof Optional ? ((Optional) source).orElse(null) : source);
Class clazz = (sourceToUse != null ? sourceToUse.getClass() : reactiveType);
if (clazz == null) {
return null;
}
return this.adapters.stream()
.filter(adapter -> adapter.getReactiveType() == clazz)
.findFirst()
.orElseGet(() ->
this.adapters.stream()
.filter(adapter -> adapter.getReactiveType().isAssignableFrom(clazz))
.findFirst()
.orElse(null));
}
/**
* Return a shared default {@code ReactiveAdapterRegistry} instance, lazily
* building it once needed.
* NOTE: We highly recommend passing a long-lived, pre-configured
* {@code ReactiveAdapterRegistry} instance for customization purposes.
* This accessor is only meant as a fallback for code paths that want to
* fall back on a default instance if one isn't provided.
* @return the shared {@code ReactiveAdapterRegistry} instance (never {@code null})
* @since 5.0.2
*/
public static ReactiveAdapterRegistry getSharedInstance() {
ReactiveAdapterRegistry registry = sharedInstance;
if (registry == null) {
synchronized (ReactiveAdapterRegistry.class) {
registry = sharedInstance;
if (registry == null) {
registry = new ReactiveAdapterRegistry();
sharedInstance = registry;
}
}
}
return registry;
}
private static class ReactorRegistrar {
void registerAdapters(ReactiveAdapterRegistry registry) {
// Register Flux and Mono before Publisher...
registry.registerReactiveType(
ReactiveTypeDescriptor.singleOptionalValue(Mono.class, Mono::empty),
source -> (Mono) source,
Mono::from
);
registry.registerReactiveType(
ReactiveTypeDescriptor.multiValue(Flux.class, Flux::empty),
source -> (Flux) source,
Flux::from);
registry.registerReactiveType(
ReactiveTypeDescriptor.multiValue(Publisher.class, Flux::empty),
source -> (Publisher) source,
source -> source);
registry.registerReactiveType(
ReactiveTypeDescriptor.singleOptionalValue(CompletableFuture.class, () -> {
CompletableFuture empty = new CompletableFuture<>();
empty.complete(null);
return empty;
}),
source -> Mono.fromFuture((CompletableFuture) source),
source -> Mono.from(source).toFuture()
);
}
}
private static class RxJava1Registrar {
void registerAdapters(ReactiveAdapterRegistry registry) {
registry.registerReactiveType(
ReactiveTypeDescriptor.multiValue(rx.Observable.class, rx.Observable::empty),
source -> RxReactiveStreams.toPublisher((rx.Observable) source),
RxReactiveStreams::toObservable
);
registry.registerReactiveType(
ReactiveTypeDescriptor.singleRequiredValue(rx.Single.class),
source -> RxReactiveStreams.toPublisher((rx.Single) source),
RxReactiveStreams::toSingle
);
registry.registerReactiveType(
ReactiveTypeDescriptor.noValue(rx.Completable.class, rx.Completable::complete),
source -> RxReactiveStreams.toPublisher((rx.Completable) source),
RxReactiveStreams::toCompletable
);
}
}
private static class RxJava2Registrar {
void registerAdapters(ReactiveAdapterRegistry registry) {
registry.registerReactiveType(
ReactiveTypeDescriptor.multiValue(io.reactivex.Flowable.class, io.reactivex.Flowable::empty),
source -> (io.reactivex.Flowable) source,
Flowable::fromPublisher
);
registry.registerReactiveType(
ReactiveTypeDescriptor.multiValue(io.reactivex.Observable.class, io.reactivex.Observable::empty),
source -> ((io.reactivex.Observable) source).toFlowable(BackpressureStrategy.BUFFER),
source -> io.reactivex.Flowable.fromPublisher(source).toObservable()
);
registry.registerReactiveType(
ReactiveTypeDescriptor.singleRequiredValue(io.reactivex.Single.class),
source -> ((io.reactivex.Single) source).toFlowable(),
source -> io.reactivex.Flowable.fromPublisher(source).toObservable().singleElement().toSingle()
);
registry.registerReactiveType(
ReactiveTypeDescriptor.singleOptionalValue(io.reactivex.Maybe.class, io.reactivex.Maybe::empty),
source -> ((io.reactivex.Maybe) source).toFlowable(),
source -> io.reactivex.Flowable.fromPublisher(source).toObservable().singleElement()
);
registry.registerReactiveType(
ReactiveTypeDescriptor.noValue(io.reactivex.Completable.class, io.reactivex.Completable::complete),
source -> ((io.reactivex.Completable) source).toFlowable(),
source -> io.reactivex.Flowable.fromPublisher(source).toObservable().ignoreElements()
);
}
}
private static class ReactorJdkFlowAdapterRegistrar {
void registerAdapter(ReactiveAdapterRegistry registry) throws Exception {
// TODO: remove reflection when build requires JDK 9+
String publisherName = "java.util.concurrent.Flow.Publisher";
Class publisherClass = ClassUtils.forName(publisherName, getClass().getClassLoader());
String adapterName = "reactor.adapter.JdkFlowAdapter";
Class flowAdapterClass = ClassUtils.forName(adapterName, getClass().getClassLoader());
Method toFluxMethod = flowAdapterClass.getMethod("flowPublisherToFlux", publisherClass);
Method toFlowMethod = flowAdapterClass.getMethod("publisherToFlowPublisher", Publisher.class);
Object emptyFlow = ReflectionUtils.invokeMethod(toFlowMethod, null, Flux.empty());
registry.registerReactiveType(
ReactiveTypeDescriptor.multiValue(publisherClass, () -> emptyFlow),
source -> (Publisher) ReflectionUtils.invokeMethod(toFluxMethod, null, source),
publisher -> ReflectionUtils.invokeMethod(toFlowMethod, null, publisher)
);
}
}
/**
* ReactiveAdapter variant that wraps adapted Publishers as {@link Flux} or
* {@link Mono} depending on {@link ReactiveTypeDescriptor#isMultiValue()}.
* This is important in places where only the stream and stream element type
* information is available like encoders and decoders.
*/
private static class ReactorAdapter extends ReactiveAdapter {
ReactorAdapter(ReactiveTypeDescriptor descriptor,
Function> toPublisherFunction,
Function, Object> fromPublisherFunction) {
super(descriptor, toPublisherFunction, fromPublisherFunction);
}
@Override
public Publisher toPublisher(@Nullable Object source) {
Publisher publisher = super.toPublisher(source);
return (isMultiValue() ? Flux.from(publisher) : Mono.from(publisher));
}
}
}