Modifying our microservice

Now, let's navigate in our code so we can edit it for adding some changes.

1. In the Project window that is on the top-left side of the screen, expand src | main | Kotlin to view our source files
2. Then we can open our packages until we see our application: Chapter2Application.kt

package com.microservices.chapter2

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class Chapter2Application

fun main(args: Array<String>) {
    runApplication<Chapter2Application>(*args)
}

This code will create and run a Spring Boot application, that will launch a microservice listening on port 8080.

We can see that, in the gutter area of the Edit Window, there is a Kotlin symbol in the same line that our main function is. If we click on it, we can run this function and it will launch our microservice and a Run window will appear that allows us to view the log, stop, or restart the process.

Now, let's modify the example code:

package com.microservices.chapter2

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication
import org.springframework.stereotype.Controller
import org.springframework.web.bind.annotation.RequestMapping
import org.springframework.web.bind.annotation.RequestMethod
import org.springframework.web.bind.annotation.ResponseBody

@SpringBootApplication
class Chapter2Application

@Controller
class FirstController {
  @RequestMapping(value = "/user", method = arrayOf(RequestMethod.GET))
  @ResponseBody
  fun hello() = "hello world"
}

fun main(args: Array<String>) {
    runApplication<Chapter2Application>(*args)
}

If we run the application now and go to the browser to the URL http://localhost:8080/user/, we will see the following:

hello world

This small change adds a controller, basically a class that will handle requests to our microservice, and then we add a mapping for a particular path, in this example /user, then it will output hello world to any request.

Now, let's create a new class, in the project window, right-click on our package, and then choose New | Kotlin File / Class.

A new window will appear asking us for the name, let's type ExampleService and choose Class in the Kind dropdown.

Then, we will add this code:

package com.microservices.chapter2

import org.springframework.stereotype.Service

@Service
class ExampleService {
  fun getHello(name : String) = "hello $name"
}

Finally, we can modify our controller to use this newly created service:

package com.microservices.chapter2

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication
import org.springframework.stereotype.Controller
import org.springframework.web.bind.annotation.PathVariable
import org.springframework.web.bind.annotation.RequestMapping
import org.springframework.web.bind.annotation.RequestMethod
import org.springframework.web.bind.annotation.ResponseBody

@SpringBootApplication
class Chapter2Application

@Controller
class FirstController(val exampleService: ExampleService) {
  @RequestMapping(value = "/user/{name}", method = arrayOf(RequestMethod.GET))
  @ResponseBody
  fun hello(@PathVariable name: String) = exampleService.getHello(name)
}

fun main(args: Array<String>) {
    runApplication<Chapter2Application>(*args)
}

We set an exampleService instance as an attribute of our controller; then, to create our output, we will get the name of the user that we greet as a path variable and we will call the service to get the result.

Executing the service and going to the URL http://localhost:8080/user/Kotlin, will output the following:

hello Kotlin