Let's use Spring Initializr (https://start.spring.io) to get started with Microservice A. Choose GroupId, ArtifactId, and the frameworks, as shown in the following screenshot:

We will create a service to expose a set of random numbers:

    @RestController
    public class RandomNumberController {
      private Log log =
        LogFactory.getLog(RandomNumberController.class);
      @RequestMapping("/random")
      public List<Integer> random() {
        List<Integer> numbers = new ArrayList<Integer>();
        for (int i = 1; i <= 5; i++) {
          numbers.add(generateRandomNumber());
        }
        log.warn("Returning " + numbers);
        return numbers;
      }
      private int generateRandomNumber() {
        return (int) (Math.random() * 1000);
      }
    }

Important things to note are as follows:

• @RequestMapping("/random") public List<Integer> random(): Random service returns a list of random numbers
• private int generateRandomNumber() {: Generates random numbers between 0 and 1000

The following snippet shows a sample response from the service at http://localhost:8080/random:

    [666,257,306,204,992]

Next, we would want to create a service to return a simple message from the application configuration in application.properties.

Let's define a simple application configuration with one property--message:

    @Component
    @ConfigurationProperties("application")
    public class ApplicationConfiguration {
      private String message;
      public String getMessage() {
        return message;
      }
      public void setMessage(String message) {
        this.message = message;
      }
    }

A few important things to note are as follows:

• @ConfigurationProperties("application"): Defines a class defining application.properties.
• private String message: Defines one property--message. The value can be configured in application.properties with application.message as the key.

Let's configure application.properties, as shown in the following snippet:

    spring.application.name=microservice-a
    application.message=Default Message

A couple of important things to note are as follows:

• spring.application.name=microservice-a: spring.application.name is used to give a name to the application
• application.message=Default Message: Configures a default message for application.message

Let's create a controller to read the message and return it, as shown in the following snippet:

    @RestController
    public class MessageController {
      @Autowired
      private ApplicationConfiguration configuration;
      @RequestMapping("/message")
      public Map<String, String> welcome() {
        Map<String, String> map = new HashMap<String, String>();
        map.put("message", configuration.getMessage());
        return map;
      }
    }

Important things to note are as follows:

• @Autowired private ApplicationConfiguration configuration: Autowires ApplicationConfiguration to enable reading the configured message value.
• @RequestMapping("/message") public Map<String, String> welcome(): Exposes a simple service at the URI/message.
• map.put("message", configuration.getMessage()): The service returns a map with one entry. It has a key message and the value is picked up from the ApplicationConfiguration.

When the service is executed at http://localhost:8080/message, we get the following response:

    {"message":"Default Message"}