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Interservice Communication
===========================

=> If one service is communicating with another service then it is called as Interservice communication.

=> To establish interservice communication we have 3 options

		1) RestTemplate
		2) WebClient
		3) FeignClient

=> If we use RestTemplate or WebClient then we need to configure service URL to send HTTP request. 

Note: If service URL is modified or if service is running with multiple instances then our code will not work as expected.

=> To overcome this problem we will use "FeignClient" for interservice communication. 

Note: feign-client will use "service-name" for communication. 

=> FeignClient will get "service-urls" from service-registry based on given service-name for communication.

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Interserivice communication usecases
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# Scenario-1 : "orders-api" will communicate with "customer-api" to create customer account or get customer account based on given email id when new order got placed.

# Scenario-2 : "customer-api" will communicate with "orders-api" to get logged in customer orders to display in dashboard.

"Scenario-3" : "admin-api" will communicate with "orders-api" to get all orders based on filters for reports generation.

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FeignClient implementation
===========================

# Step-1 : Write @EnableFeignClients annotation at orders-api start class.

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@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
public class PaymentGatewayAppApplication {

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

}
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# Step-2 : Create FeignClient interface to communicate with customer-api.

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@FeignClient(name = "customer-api")
public interface CustomerFeignClient {

	@PostMapping("/api/customer/register")
	public ResponseEntity<Customer> createCustomerAcc(@RequestBody CustomerDTO customer);

}
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# Step-3 : Inject FeignClient into OrderService and call feignclient method as part of "createOrder" method.

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//invoke customer api

CustomerDTO customerDTO = new CustomerDTO();
customerDTO.setName(purchaseDto.getCustomer().getName());
customerDTO.setEmail(purchaseDto.getCustomer().getEmail());
customerDTO.setPhno(purchaseDto.getCustomer().getPhno());

ResponseEntity<Customer> res = 
		customerFeignClient.createCustomerAcc(customerDTO);

Customer customer = null;

if(res.getStatusCode().is2xxSuccessful()) {
	customer = res.getBody();
}else {
	throw new Exception("Customer Not Found");
}

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