How to Build Microservices in Java using Spring, Eureka (step by step Procedure)

We would build a Microservices in Java Step by step. Find the Source Codes here

This microservice is based on a simple hypothetical Hospital Information System shown below:

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1. Create 3 Spring Applications in start.spring.io (add the Web dependency)

   • Admissions (list of patients)
   • HR (list of employee)
   • Pathology (list of diseases)

2. Open the three applications in Spring Tool Suite

3. Set the ports and application name in the application.properties file

4. Build the  addmissions-service

   • Create the AdmissionsResource class(controller) in a resources package
   • Annotate the class with @RestController
   • Create a method getPatients() that return list of patients
   • Create a method getPatientById that takes an Id and returns a single Patient
   • Annotate the Id parameter with @PathVariable annotation
   • Create a class called Patient in the models package
   • Add some hardcoded patients to the getPatients method
   • Annotate the AdmissionsResource with RequestMapping of /admissions
   • Annotate the getPatients method with the RequestMapping of /patients
   • Annotate the getPatientById method with RequestMapping of /patients/{id}
   • Move the hardcoded patients outside the method
   • Test the addmissions-service

5. Build the hr-service

   • Create a HrResource class in the resources package
   • Annotate the class with the @RestController
   • Annotate the class with @RequestMapping of /hr
   • Add some hardcoded list of patients
   • Create the Employee class in the models folder
   • Create the getEmployees method to return list of employees
   • Annotate the getEmployees method with RequestMapping of /employees
   • Create the getEmployeeById method that take an Id to return a single employee
   • Annotate the Id parameter with @PathVariable annotation
   • Annotate the getEmployeeById method with @RequestMapping of /employees/{id}
   • Test the hr-service(remember the port!)

6. Build  the pathology service

   • Create the PathologyResource class in the resources model
   • Annotate this class with the @RestController annotation
   • Annotate this class with the @RequestMapping annotation of /pathology
   • Create a hardcoded list of diseases
   • Create the Disease class in the models package
   • Create the getDiseases method to return list of diseases
   • Annotate the getDiseases method with RequestMapping of /diseases
   • Create the getDiseaseById method to return a single disease
   • Annotate the getDiseaseById method with RequestMapping of /diseases/{Id}
   • Annotate the Id parameter with the @PathVariable annotation
   • Test the pathology-service

7. Call the hr-service from the admissions-service using RestTemplate

   • Add a getRestTemplate method to the AdmissionsServiceApplication file. This method returns a new RestTemplate (this is a bean)
   • Annotate this method with the @Bean annotation
   • Create a RestTemplate private variable in the AdmissionsResource class
   • Annotate this with the @Autowired annotation
   • Create a getPhysicians method in the AdmissionsResource class. This method uses restTemplate to get list of employees from the hr-service. It returns this list of employees as EmployeesList object
   • Modify the getEmployees method in the HrResource class in the hr-service to return EmployeesList object instead of List<Employees>
   • Create the EmployeesList class in the hr-service model package
   • Copy the EmployeesList and the Employee class to the admissions-service
   • Test the services

8. Call the pathology-service from the admissions-services using RestTemplate

   • Create a method getDiseases in the AdminssionsResource class. This method uses restTemplate to get the list of diseases. This method returns a list of diseases as DiseasesList object
   • Annotate the getDiseases method with RequestMapping of /diseases
   • Modify the getDiseases method in the pathology-service to return DiseasesList object instead of List<Diseases> object
   • Create a DiseasesList class
   • Copy the DiseasesList class and the Disease class to the admissions-service
   • Test the services

9. Create the Discovery Server (Eureka) and make the service Eureka Client

   • Create a spring boot application using spring initializr (add the Eureka Server dependency)
   • Add the @EnableEurekaServer annotation to the DiscoveryServerApplication
   • Ensure that the spring cloud dependency is in the pom.xml
   • Update the application.properties file with register-with-eureka and fetch-registry to false
   • Test the Eureka Server

10. Publish the three services to the Eureka Server

    • For the admissions-service, Open the pom.xml and add the spring cloud client dependency (check the pom of the discovery server)
    • Provide the spring cloud version as a property
    • Copy over the dependencyManagement section from the discovery-server pom.xml to the admissions-service pom.xml
    • Copy over the repositories section from the discovery-server pom.xml to the admissions-service.xml (spring-milestones repository)

11. Repeat the procedure in 10 for the hr-service and the pathology-service

12. Start all the services

13. Test the Eureka server and make sure all the services are registered

14. 

    If you followed the steps correctly, then you will have the window below

15. Make the admissions-service consume the hr-service and the pathology service

    • Add @LoadBalanced Annotation to the RestTemplate bean in the admissions-service class
    • Open the AdmissionsResource class
    • Replace the urls with the name of the services (replace only the http://localhost:port section of the url)

More Tutorials on Microservices

• How to Make two Microservices Communicate

• How to Build Microservices in Java using Spring, Eureka (Source Codes)

• How to Build Microservices in Java using Spring, Eureka (step by step Procedure)

• Dockers, Containers and Kubernetes – A Simple Explanation

• What are Microservices? – A Simple Explanation