Introduction to Currency Conversion and Currency Exchange Service
In this section, we will create a couple of microservices: CurrencyCalculationService and CurrencyExchangeService.
Note: In this tutorial, we have quoted currency conversion service as a currency calculation service. Both the services have the same meaning, so don't be confused.
Let's understand the functionality of these services.
In the above figure, the CurrencyExchangeService uses JPA to talk to the database and returns the exchange value of the specific currency. For example, USD to INR conversion.
When we invoke CurrencyExchangeService, we need to pass two parameters: from(convert from), and to (convert to). For example, if we want to convert currency from USD to INR.
Consider the URL http://localhost:8000/currency-exchange/from/USD/to/INR. It retunes the following response:
The currency exchange service will return what the conversion multiple is. The conversion multiple means 1 USD is equal to 72 INR. The currency converter service uses a currency exchange service. Suppose the currency converter service wants to convert 100 USD to INR. So it will call the currency exchange service and will convert the specified amount that we have provided in the path parameter. For example:
We will implement these two services in our example using Spring Cloud.
Setting up a currency-exchange-service
Step 1: Open the spring initializer http://start.spring.io.
Step 2: Select the Project: Maven Project, Language: Java, and Spring Boot version 2.2.0 M6 or above. Provide the Group name and Artifact ID. We have provided com.javatpoint.microservices and currency-exchange-service, for group name and Artifact id respectively.
Step 3: Add the dependencies Web, DevTools, Actuator, and Config Client.
Step 4: Click on the Generate Project button. It will download the zip file of the project.
Step 5: Extract it in the local disk.
Step 6: Import the project.
Click on File menu-> Import -> Existing Maven Projects -> Next -> Browse ->Select the project ->Finish
It takes some time to import. When the project import is done, it shows the following project directory. Do not consider the data.sql file in the directory, because we will create it later.
Step 7: Open the application.properties file and configure the application name and port number.
When we run the currency-exchange-service, it runs but does not perform any service. In the next step, we will implement code in the currency-exchange-service.
Hardcoded the currency-exchange-service
Now we will create a service that converts the currency from USD to INR.
Step 1: Create a class file (REST Controller) with the name CurrencyExchangeController in the package com.javatpoint.microservices.currencyexchangeservice.
Step 2: Create a class file with the name ExchangeValue.
Step 3: Run the CurrencyExchangeServiceApplication.java. It runs on the port 8000 that we have configured in the application.properties file.
We get the following response on the browser:
Setting up Dynamic port in the Response
The CurrencyExchangeService determines the exchange value of the currency. The CurrencyCalculationService uses the CurrencyExchangeService to determine the value of one currency in other currency. We will create multiple instances of the CurrencyExchangeService later in next topic.
At present, the service is running on port 8000. Later we will run it on port 8001, 8002, and so on. In the next step, we will set a port to the currency-exchange-service.
Step 1: Open the ExchangeValue.java file and add a port variable. Generate getters and setters for the port variable only.
We have already configured the application name and port number in the application.properties file, so need not to configure again.
Now pick up port number from the environment.
Step 3: Open the CurrencyExchangeController.java and get the property of the environment.
When we refresh the browser, the URL changes to: http://localhost:8000/currency-exchange/from/USD/to/INR.
At present CurrencyExchangeServiceApplication is running on port 8000.
Now we will run CurrencyExchangeServiceApplication on a different port number. For this, we have to change the port in the application.properties file from 8000 to 8001, 8002, etc. whichever we want.
Suppose we want to create two instances of the CurrencyExchangeServiceApplication. For this, we have to set port externally.
Let's create an instance of the CurrencyExchangeServiceApplication that runs on the port 8001.
Step 1: Right-click on the project -> Run As -> Run Configurations.
Or click on the highlighted symbol -> Run Configurations.
Step 2: Rename the CurrencyExchangeServiceAppication to CurrencyExchangeServiceAppication8000 and click on the Apply button.
Step 3: Right-click on the CurrencyExchangeServiceApplication8000 -> Duplicate.
It generates the duplicate file of CurrencyExchangeServiceApplication8000. We will run it on port 8001.
Step 4: Click on the Arguments tab and write –Dserver.port=8001 in the VM arguments text box. Click on the Apply and Run button, respectively.
Note: Whatever value we are passing in the VM arguments, it overwrites the configuration of the application.properties file.
After clicking on the Run button, it starts running on port 8001.
Step 5: Change the port number in the URL http://localhost:8001/currency-exchange/from/USD/to/INR and press enter key. We get the following response:
Now we have two instances of CurrencyExchangeServiceApplication that are running on two different ports 8000 and 8001.