Moving common spring-cloud-circuitbreaker code to commons

docs/src/main/asciidoc/spring-cloud-circuitbreaker.adoc

@@ -0,0 +1,82 @@
+== Introduction
+
+Spring Cloud Circuit breaker provides an abstraction across different circuit breaker implementations.
+It provides a consistent API to use in your applications allowing you the developer to choose the circuit breaker implementation that best fits your needs for your app.
+
+=== Supported Implementations
+
+* https://github.com/Netflix/Hystrix[Netfix Hystrix]
+* https://github.com/resilience4j/resilience4j[Resilience4J]
+* https://github.com/alibaba/Sentinel[Sentinel]
+* https://github.com/spring-projects/spring-retry[Spring Retry]
+
+== Core Concepts
+
+To create a circuit breaker in your code you can use the `CircuitBreakerFactory` API. When you include a Spring Cloud Circuit Breaker starter on your classpath a bean implementing this API will automatically be created for you.
+A very simple example of using this API is given below
+
+====
+[source,java]
+----
+@Service
+public static class DemoControllerService {
+	private RestTemplate rest;
+	private CircuitBreakerFactory cbFactory;
+
+	public DemoControllerService(RestTemplate rest, CircuitBreakerFactory cbFactory) {
+		this.rest = rest;
+		this.cbFactory = cbFactory;
+	}
+
+	public String slow() {
+		return cbFactory.create("slow").run(() -> rest.getForObject("/slow", String.class), throwable -> "fallback");
+	}
+
+}
+----
+====
+
+The `CircuitBreakerFactory.create` API will create an instance of a class called `CircuitBreaker`.
+The `run` method takes a `Supplier` and a `Function`.
+The `Supplier` is the code that you are going to wrap in a circuit breaker.
+The `Function` is the fallback that will be executed if the circuit breaker is tripped.
+The function will be passed the `Throwable` that caused the fallback to be triggered.
+You can optionally exclude the fallback if you do not want to provide one.
+
+=== Circuit Breakers In Reactive Code
+
+If Project Reactor is on the class path then you can also use `ReactiveCircuitBreakerFactory` for your reactive code.
+
+====
+[source,java]
+----
+@Service
+public static class DemoControllerService {
+	private ReactiveCircuitBreakerFactory cbFactory;
+	private WebClient webClient;
+
+
+	public DemoControllerService(WebClient webClient, ReactiveCircuitBreakerFactory cbFactory) {
+		this.webClient = webClient;
+		this.cbFactory = cbFactory;
+	}
+
+	public Mono<String> slow() {
+		return webClient.get().uri("/slow").retrieve().bodyToMono(String.class).transform(
+		it -> cbFactory.create("slow").run(it, throwable -> return Mono.just("fallback")));
+	}
+}
+----
+====
+
+The `ReactiveCircuitBreakerFactory.create` API will create an instance of a class called `ReactiveCircuitBreaker`.
+The `run` method takes with a `Mono` or `Flux` and wraps it in a circuit breaker.
+You can optionally profile a fallback `Function` which will be called if the circuit breaker is tripped and will be passed the `Throwable`
+that caused the failure.
+
+== Configuration
+
+You can configure your circuit breakers using by creating beans of type `Customizer`.
+The `Customizer` interface has a single method called `customize` that takes in the `Object` to customize.
+
+// TODO link to implementation docs

docs/src/main/asciidoc/spring-cloud-commons.adoc

@@ -767,4 +767,8 @@ If you want to learn more about the Spring Cloud Release train compatibility, yo
 In order to disable this feature, set `spring.cloud.compatibility-verifier.enabled` to `false`.
 If you want to override the compatible Spring Boot versions, just set the
 `spring.cloud.compatibility-verifier.compatible-boot-versions` property with a comma separated list
-of compatible Spring Boot versions.
+of compatible Spring Boot versions.
+
+== Spring Cloud Circuit Breaker
+
+include::spring-cloud-circuitbreaker.adoc[]

spring-cloud-commons/src/main/java/org/springframework/cloud/client/circuitbreaker/AbstractCircuitBreakerFactory.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2013-2018 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.cloud.client.circuitbreaker;
+
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Consumer;
+import java.util.function.Function;
+
+/**
+ * Base class for factories which produce circuit breakers.
+ *
+ * @author Ryan Baxter
+ */
+public abstract class AbstractCircuitBreakerFactory<CONF, CONFB extends ConfigBuilder<CONF>> {
+
+	private final ConcurrentHashMap<String, CONF> configurations = new ConcurrentHashMap<>();
+
+	/**
+	 * Adds configurations for circuit breakers.
+	 * @param ids The id of the circuit breaker
+	 * @param consumer A configuration builder consumer, allows consumers to customize the
+	 * builder before the configuration is built
+	 */
+	public void configure(Consumer<CONFB> consumer, String... ids) {
+		for (String id : ids) {
+			CONFB builder = configBuilder(id);
+			consumer.accept(builder);
+			CONF conf = builder.build();
+			getConfigurations().put(id, conf);
+		}
+	}
+
+	/**
+	 * Gets the configurations for the circuit breakers.
+	 * @return The configurations
+	 */
+	protected ConcurrentHashMap<String, CONF> getConfigurations() {
+		return configurations;
+	}
+
+	/**
+	 * Creates a configuration builder for the given id.
+	 * @param id The id of the circuit breaker
+	 * @return The configuration builder
+	 */
+	protected abstract CONFB configBuilder(String id);
+
+	/**
+	 * Sets the default configuration for circuit breakers.
+	 * @param defaultConfiguration A function that returns the default configuration
+	 */
+	public abstract void configureDefault(Function<String, CONF> defaultConfiguration);
+
+}

spring-cloud-commons/src/main/java/org/springframework/cloud/client/circuitbreaker/CircuitBreaker.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2013-2019 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.cloud.client.circuitbreaker;
+
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+/**
+ * Spring Cloud circuit breaker.
+ *
+ * @author Ryan Baxter
+ */
+public interface CircuitBreaker {
+
+	default <T> T run(Supplier<T> toRun) {
+		return run(toRun, throwable -> {
+			throw new NoFallbackAvailableException("No fallback available.", throwable);
+		});
+	};
+
+	<T> T run(Supplier<T> toRun, Function<Throwable, T> fallback);
+
+}

spring-cloud-commons/src/main/java/org/springframework/cloud/client/circuitbreaker/CircuitBreakerFactory.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2013-2019 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.cloud.client.circuitbreaker;
+
+/**
+ * Creates circuit breakers based on the underlying implementation.
+ *
+ * @author Ryan Baxter
+ */
+public abstract class CircuitBreakerFactory<CONF, CONFB extends ConfigBuilder<CONF>>
+		extends AbstractCircuitBreakerFactory<CONF, CONFB> {
+
+	public abstract CircuitBreaker create(String id);
+
+}

spring-cloud-commons/src/main/java/org/springframework/cloud/client/circuitbreaker/ConfigBuilder.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2013-2019 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.cloud.client.circuitbreaker;
+
+/**
+ * A builder for circuit breaker configurations.
+ *
+ * @author Ryan Baxter
+ */
+public interface ConfigBuilder<CONF> {
+
+	CONF build();
+
+}

spring-cloud-commons/src/main/java/org/springframework/cloud/client/circuitbreaker/Customizer.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2013-2019 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.cloud.client.circuitbreaker;
+
+/**
+ * Customizes the parameterized class.
+ *
+ * @author Ryan Baxter
+ */
+public interface Customizer<TOCUSTOMIZE> {
+
+	void customize(TOCUSTOMIZE tocustomize);
+
+}

spring-cloud-commons/src/main/java/org/springframework/cloud/client/circuitbreaker/NoFallbackAvailableException.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2013-2019 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.cloud.client.circuitbreaker;
+
+/**
+ * A runtime exception that tells no fallback is available for the circuit breaker.
+ *
+ * @author Toshiaki Maki
+ */
+public class NoFallbackAvailableException extends RuntimeException {
+
+	public NoFallbackAvailableException(String message, Throwable cause) {
+		super(message, cause);
+	}
+
+}

spring-cloud-commons/src/main/java/org/springframework/cloud/client/circuitbreaker/ReactiveCircuitBreaker.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2013-2019 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.cloud.client.circuitbreaker;
+
+import java.util.function.Function;
+
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+/**
+ * Spring Cloud reactive circuit breaker API.
+ *
+ * @author Ryan Baxter
+ */
+public interface ReactiveCircuitBreaker {
+
+	default <T> Mono<T> run(Mono<T> toRun) {
+		return run(toRun, throwable -> {
+			throw new NoFallbackAvailableException("No fallback available.", throwable);
+		});
+	}
+
+	<T> Mono<T> run(Mono<T> toRun, Function<Throwable, Mono<T>> fallback);
+
+	default <T> Flux<T> run(Flux<T> toRun) {
+		return run(toRun, throwable -> {
+			throw new NoFallbackAvailableException("No fallback available.", throwable);
+		});
+	}
+
+	<T> Flux<T> run(Flux<T> toRun, Function<Throwable, Flux<T>> fallback);
+
+}

spring-cloud-commons/src/main/java/org/springframework/cloud/client/circuitbreaker/ReactiveCircuitBreakerFactory.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2013-2018 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.cloud.client.circuitbreaker;
+
+/**
+ * Creates reactive circuit breakers.
+ *
+ * @author Ryan Baxter
+ */
+public abstract class ReactiveCircuitBreakerFactory<CONF, CONFB extends ConfigBuilder<CONF>>
+		extends AbstractCircuitBreakerFactory<CONF, CONFB> {
+
+	public abstract ReactiveCircuitBreaker create(String id);
+
+}