Java Spring Boot Microservices Sample Project

Microservices are more popular nowadays. They can be written in any language. In this article, let us see Spring Boot Microservices. in this article let us see a base project "currency-exchange-sample-service" which has a business logic and which can be invoked in another project "currency-conversion-sample-service". Both are Maven projects and let us see them one by one

Microservice 1: currency-exchange-sample-service

Project Structure

👁 Project structure

pom.xml

Let us see the important files 

CurrencyExchangeServiceSampleApplication.java

CurrencyExchangeSampleController.java

@GetMapping("/currency-exchange-sample/fromCurrency/{fromCurrency}/toCurrency/{toCurrency}") 
// where {fromCurrency} and {toCurrency} are path variable
// fromCurrency can be USD,EUR,AUD,INR and toCurrency can be the opposite of any fromCurrency

ExchangeValue.java

application.properties

spring.application.name=currency-exchange-sample-service
server.port=8000 #Representation of the port number . We can set different port number in run configuration also
spring.jpa.show-sql=true #To display the SQL
spring.h2.console.enabled=true 
spring.datasource.platform=h2 #As we are using h2 datasource 
spring.datasource.url=jdbc:h2:mem:gfg 

data.sql

insert into exchange_value(id,currency_from,currency_to,conversion_multiple,port) 
values(10001,'USD', 'INR' ,65,0); 
insert into exchange_value(id,currency_from,currency_to,conversion_multiple,port) 
values(10002,'EUR', 'INR' ,82,0); 
insert into exchange_value(id,currency_from,currency_to,conversion_multiple,port) 
values(10003,'AUD', 'INR' ,53,0);

By default, it has been set to run on port 8000. We can create another instance and can make the project run on port 8001 in the below ways

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As this is the spring boot application, it can be normally run as Java application

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If we set to run the application on two different ports, we will get the below options

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Let us select the first one. On running the application, in the console, we see as

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From the console, we can see that it used default Tomcat and the project is running on port 8080. As we have used 3 insert scripts, automatically table is created and the data is inserted. We can able to do the following 

http://localhost:8000/currency-exchange-sample/fromCurrency/USD/toCurrency/INR

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When this URL is hit, it will be redirected to the controller, and fromCurrency is taken as "USD" and toCurrency is taken as "INR"

Because of this,

// Below set of code is executed and hence we are seeing the result like above
if (fromCurrency != null && toCurrency != null) {
 if (fromCurrency.equalsIgnoreCase("USD") && toCurrency.equalsIgnoreCase("INR")) {
 conversionMultiple = BigDecimal.valueOf(78);
 }

Similarly, we can able to execute the below following URLs

http://localhost:8000/currency-exchange-sample/fromCurrency/EUR/toCurrency/INR

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http://localhost:8000/currency-exchange-sample/fromCurrency/AUD/toCurrency/INR

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Hence according to our business needs, we can add business logic to the controller file. Let us see how the above service is getting called in the currency-conversion project

Microservice 2:currency-conversion-sample-service

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This is also a maven project

pom.xml

Main important java files

CurrencyConversionSampleServiceApplication.java

CurrencyConversionSampleBean.java

CurrencyConversionSampleController.java

@GetMapping("/currency-converter-sample/fromCurrency/{fromCurrency}/toCurrency/{toCurrency}/quantity/{quantity}")

That is this project is started on port 8100. Now we can able to execute the following URLS

http://localhost:8100/currency-converter-sample/fromCurrency/USD/toCurrency/INR/quantity/1000

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When this service is called, it will in turn invoke.

Assumption: currency-exchange-sample is running in port 8000 and it produces the required response

http://localhost:8000/currency-exchange-sample/fromCurrency/USD/toCurrency/INR

And then as the logic is written as

ResponseEntity<CurrencyConversionSampleBean>responseEntity=new RestTemplate().getForEntity("http://localhost:8000/currency-exchange-sample/fromCurrency/{fromCurrency}/toCurrency/{toCurrency}",CurrencyConversionSampleBean.class, uriVariables);
 CurrencyConversionSampleBean response=responseEntity.getBody(); 
 // creating a new response bean and getting the response back and taking it into Bean
 // Hence the output bean should have all the fields that is received from the response
 return new CurrencyConversionSampleBean(response.getId(), fromCurrency,toCurrency,response.getConversionMultiple(), quantity,quantity.multiply(response.getConversionMultiple()),response.getPort()); 

We are seeing the totalCalculatedAmount as 78 * 1000  i.e. 78000. We are getting "conversionMultiple" from the first URL and it is multiplied with the quantity value here. It is very ideal that, we no need to carry exchange service logic into this application i.e. part 1 project can be separate and part 2 project can invoke part 1 URLs here. So microservices can run separately and other services can use them. Rest of the URLs that can be checked

Example

http://localhost:8100/currency-converter-sample/fromCurrency/EUR/toCurrency/INR/quantity/5000

This will call in turn

http://localhost:8000/currency-exchange-sample/fromCurrency/EUR/toCurrency/INR

And the output will be 

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Example

http://localhost:8100/currency-converter-sample/fromCurrency/AUD/toCurrency/INR/quantity/2000

This will call in turn

http://localhost:8000/currency-exchange-sample/fromCurrency/AUD/toCurrency/INR

And the output will be

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