Creating REST API

We are going to create a simple REST API web application using Spring 5.

Lets first create build.gradle file in the project root directory.

buildscript {
  ext {
    springBootVersion = '2.0.0.M7'
  }
  repositories {
    mavenCentral()
    maven { url "https://repo.spring.io/snapshot" }
    maven { url "https://repo.spring.io/milestone" }
  }
  dependencies {
    classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
  }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'

group = 'com.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = 1.8

repositories {
  mavenCentral()
  maven { url "https://repo.spring.io/snapshot" }
  maven { url "https://repo.spring.io/milestone" }
}


dependencies {
  compile('org.springframework.boot:spring-boot-starter-web')
  testCompile('org.springframework.boot:spring-boot-starter-test')
}

Now lets create the application that will be used to start up our server.

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {

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

The last step is to create REST API controller that will respond to user requests.

package com.example.demo;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

   @GetMapping("/hello")
   public String sayHello() {
      return "Hello";
   }
}

Now we can build the code. Run this command in the project root, where the build.gradle file is located.

➜ gradle clean build
Starting a Gradle Daemon (subsequent builds will be faster)

> Task :test
2018-01-10 09:14:09.499  INFO 78584 --- [       Thread-5] o.s.w.c.s.GenericWebApplicationContext   : Closing org.springframework.web.context.support.GenericWebApplicationContext@7baa7756: startup date [Wed Jan 10 09:14:07 PST 2018]; root of context hierarchy


BUILD SUCCESSFUL in 16s
6 actionable tasks: 5 executed, 1 up-to-date

Then we have couple of ways to run the application. If we want to run the application for development, we can use Gradle task bootRun.

gradle bootRun

If we want to see all the tasks available, run gradle tasks --all

If we want to run the application without Gradle, we can use java -jar from the command line.

java -jar build/libs/demo-0.0.1-SNAPSHOT.jar

Check Docker Handbook to see how to run Java application in Docker.

After the application is started up, we can try to call the api from the command line.

➜ curl localhost:8080/hello
Hello

Test the application is able to start

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class ApplicationTest {

    @Test
    public void contextLoads() throws Exception {
    }

}