Spring Cloud サーキットブレーカーガイド

package hello;

import reactor.core.publisher.Mono;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.RequestMapping;

@RestController
@SpringBootApplication
public class BookstoreApplication {

  @RequestMapping(value = "/recommended")
  public Mono<String> readingList(){
    return Mono.just("Spring in Action (Manning), Cloud Native Java (O'Reilly), Learning Spring Boot (Packt)");
  }

  public static void main(String[] args) {
    SpringApplication.run(BookstoreApplication.class, args);
  }
}

server.port=8090

package hello;

import reactor.core.publisher.Mono;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.reactive.function.client.WebClient;

@RestController
@SpringBootApplication
public class ReadingApplication {

  @RequestMapping("/to-read")
    public Mono<String> toRead() {
      return WebClient.builder().build()
      .get().uri("http://localhost:8090/recommended").retrieve()
      .bodyToMono(String.class);
  }

  public static void main(String[] args) {
    SpringApplication.run(ReadingApplication.class, args);
  }
}

server.port=8080

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>3.5.0</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>spring-cloud-circuit-breaker-reading</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>spring-cloud-circuit-breaker-reading</name>
	<description>Demo project for Spring Boot</description>
	<properties>
		<java.version>17</java.version>
		<spring-cloud.version>2025.0.0</spring-cloud.version>
	</properties>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-webflux</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-circuitbreaker-reactor-resilience4j</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>io.projectreactor</groupId>
			<artifactId>reactor-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>
	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>org.springframework.cloud</groupId>
				<artifactId>spring-cloud-dependencies</artifactId>
				<version>${spring-cloud.version}</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

plugins {
	id 'java'
	id 'org.springframework.boot' version '3.5.0'
	id 'io.spring.dependency-management' version '1.1.5'
}

group = 'com.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '17'

repositories {
	mavenCentral()
}

ext {
	springCloudVersion = '2025.0.0'
}

dependencies {
	implementation 'org.springframework.boot:spring-boot-starter-webflux'
	implementation 'org.springframework.cloud:spring-cloud-starter-circuitbreaker-reactor-resilience4j'
	testImplementation 'org.springframework.boot:spring-boot-starter-test'
	testImplementation 'io.projectreactor:reactor-test'
}

dependencyManagement {
	imports {
		mavenBom "org.springframework.cloud:spring-cloud-dependencies:${springCloudVersion}"
	}
}

tasks.named('test') {
	useJUnitPlatform()
}

package hello;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import reactor.core.publisher.Mono;

import org.springframework.cloud.client.circuitbreaker.ReactiveCircuitBreaker;
import org.springframework.cloud.client.circuitbreaker.ReactiveCircuitBreakerFactory;
import org.springframework.stereotype.Service;
import org.springframework.web.reactive.function.client.WebClient;

@Service
public class BookService {

  private static final Logger LOG = LoggerFactory.getLogger(BookService.class);


  private final WebClient webClient;
  private final ReactiveCircuitBreaker readingListCircuitBreaker;

  public BookService(ReactiveCircuitBreakerFactory circuitBreakerFactory) {
    this.webClient = WebClient.builder().baseUrl("http://localhost:8090").build();
    this.readingListCircuitBreaker = circuitBreakerFactory.create("recommended");
  }

  public Mono<String> readingList() {
    return readingListCircuitBreaker.run(webClient.get().uri("/recommended").retrieve().bodyToMono(String.class), throwable -> {
      LOG.warn("Error making request to book service", throwable);
      return Mono.just("Cloud Native Java (O'Reilly)");
    });
  }
}

package hello;

import reactor.core.publisher.Mono;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.reactive.function.client.WebClient;

@RestController
@SpringBootApplication
public class ReadingApplication {

  @Autowired
  private BookService bookService;

  @RequestMapping("/to-read")
  public Mono<String> toRead() {
    return bookService.readingList();
  }

  public static void main(String[] args) {
    SpringApplication.run(ReadingApplication.class, args);
  }
}

Spring in Action (Manning), Cloud Native Java (O'Reilly), Learning Spring Boot (Packt)

Cloud Native Java (O'Reilly)