Spring Boot Hystrix

As Simply hystrix is using circuit breaker design pattern. In here I have Used three services called appointment, payment, email. Appointment service uses payment, email services. which both services are required to complete the transaction. If some service goes down, generally, it should return an error, but see what happens.

Basically, You have to add spring-cloud-starter-netflix-hystrix dependency.

<dependency>
         <groupId>org.springframework.cloud</groupId>
         <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
      </dependency>

Let's create appointment service

appointment-service

pom.xml

<?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>2.3.2.RELEASE</version>
      <relativePath/> <!-- lookup parent from repository -->
   </parent>
   <groupId>com.easyittech</groupId>
   <artifactId>appointment-service</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <name>appointment-service</name>
   <description>Demo project for Spring Boot</description>

   <properties>
      <java.version>1.8</java.version>
      <spring-cloud.version>Hoxton.SR7</spring-cloud.version>
   </properties>

   <dependencies>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-web</artifactId>
      </dependency>
      <dependency>
         <groupId>org.springframework.cloud</groupId>
         <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
      </dependency>
      <dependency>
         <groupId>org.springframework.cloud</groupId>
         <artifactId>spring-cloud-starter-netflix-hystrix-dashboard</artifactId>
      </dependency>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-actuator</artifactId>
      </dependency>

      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-test</artifactId>
         <scope>test</scope>
         <exclusions>
            <exclusion>
               <groupId>org.junit.vintage</groupId>
               <artifactId>junit-vintage-engine</artifactId>
            </exclusion>
         </exclusions>
      </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>

AppointmentServiceApplication.java

In the relevant method, we use @HystrixCommand annotation. That annotation has an attribute called fallbackMethod. Which called the method mentioned in fallbackMethod attribute, If there is any failure on calling other services.

package com.easyittech.appointmentservice;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.hystrix.EnableHystrix;
import org.springframework.cloud.netflix.hystrix.dashboard.EnableHystrixDashboard;
import org.springframework.context.annotation.Bean;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
@RestController
@EnableHystrix
@EnableHystrixDashboard
public class AppointmentServiceApplication {

    @Autowired
    private RestTemplate restTemplate;

    @HystrixCommand(groupKey = "easyittech", commandKey = "easyittech", fallbackMethod = "errorFallBack")
    @GetMapping("/appointment")
    public String makeAppointment() {
        String pay = restTemplate.getForObject("http://localhost:8081/payment", String.class);
        String email = restTemplate.getForObject("http://localhost:8082/email", String.class);
        return pay + " - " + email;
    }

    public String errorFallBack() {
        return "operation is failed";
    }

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

    @Bean
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

Other two services (email and payment), which not included the hystrix.

email-service

pom.xml

<?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>2.3.2.RELEASE</version>
      <relativePath/> <!-- lookup parent from repository -->
   </parent>
   <groupId>com.easyittech</groupId>
   <artifactId>email-service</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <name>email-service</name>
   <description>Demo project for Spring Boot</description>

   <properties>
      <java.version>1.8</java.version>
   </properties>

   <dependencies>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-web</artifactId>
      </dependency>

      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-test</artifactId>
         <scope>test</scope>
         <exclusions>
            <exclusion>
               <groupId>org.junit.vintage</groupId>
               <artifactId>junit-vintage-engine</artifactId>
            </exclusion>
         </exclusions>
      </dependency>
   </dependencies>

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

</project>

EmailServiceApplication.java

package com.easyittech.emailservice;

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

@SpringBootApplication
@RestController
public class EmailServiceApplication {

   public static void main(String[] args) {
      SpringApplication.run(EmailServiceApplication.class, args);
   }
   @GetMapping("/email")
   public String sendEmail() {
      return "send EMail success";
   }
}

payment-service

pom.xml

<?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>2.3.2.RELEASE</version>
      <relativePath/> <!-- lookup parent from repository -->
   </parent>
   <groupId>com.easyittech</groupId>
   <artifactId>payment-service</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <name>payment-service</name>
   <description>Demo project for Spring Boot</description>

   <properties>
      <java.version>1.8</java.version>
   </properties>

   <dependencies>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-web</artifactId>
      </dependency>

      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-test</artifactId>
         <scope>test</scope>
         <exclusions>
            <exclusion>
               <groupId>org.junit.vintage</groupId>
               <artifactId>junit-vintage-engine</artifactId>
            </exclusion>
         </exclusions>
      </dependency>
   </dependencies>

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

</project>

PaymentServiceApplication.java

package com.easyittech.paymentservice;

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

@SpringBootApplication
@RestController
public class PaymentServiceApplication {

   public static void main(String[] args) {
      SpringApplication.run(PaymentServiceApplication.class, args);
   }
   @GetMapping("/payment")
   public String makePayment() {
      return "payment success";
   }

}

The result is given below after running the three services without any issue.

The result is given below after the email service is down or disconnected.

KavinduGayan/spring-boot-hystrix