SpringBoot - ShortStarterDemo

Spring Boot?

• Spring Boot offers a fast way to build applications.
• It looks at your classpath and at the beans you have configured, makes reasonable assumptions about what you are missing, and adds those items.
• With Spring Boot, you can focus more on business features and less on infrastructure.

What it can do?

AUTO-CONFIG

Is Spring MVC on the classpath?

• Spring Boot adds them automatically.
• A Spring MVC application also needs a servlet container, so Spring Boot automatically configures embedded Tomcat.

Is Jetty on the classpath?

If so, you probably do NOT want Tomcat but instead want embedded Jetty. Spring Boot handles that for you.

Is Thymeleaf on the classpath?

If so, there are a few beans that must always be added to your application context. Spring Boot adds them for you.

Practice

1 Init

1 https://start.spring.io/
2 Chooose Grade || Maven
3 Dependency < Spring Web
4 Generate

2 Make Simple Web App

package com.example.springboot;

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

// Ready to handle Web request
// @RestController combines @Controller and @ResponseBody - When called returns data not view
@RestController
public class HelloController {
    // Maps / to index() method
	@GetMapping("/")
	public String index() {
		return "Greetings from Spring Boot!";
	}

}

3 Make Application Class

package com.example.springboot;

import java.util.Arrays;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;

/*
@SpringBootApplication Adds
- @Configuration :  Tags class as source of bean def. for application context
- @EnableAutoConfiguration : Add beans based on classpath settings
- @ComponentScan : Look for components in package to find controller
*/
@SpringBootApplication
public class Application {

  public static void main(String[] args) {
        //Launches App. (no web.xml) 
        SpringApplication.run(Application.class, args);
  }
  //Retrieves all the beans that were created by your application and runs them on start up
  @Bean 
  public CommandLineRunner commandLineRunner(ApplicationContext ctx) {
	return args -> {
		System.out.println("Let's inspect the beans provided by Spring Boot:");

		String[] beanNames = ctx.getBeanDefinitionNames();
		Arrays.sort(beanNames);
		for (String beanName : beanNames) {
		  System.out.println(beanName);
		}
	};
 }

}

4 Run App

# Gradle
./gradlew bootRun
# Maven
./mvnw spring-boot:run
# Check Server
$ curl localhost:8080
Greetings from Spring Boot!

5 Add Unit Test

Add unit test dependency to Gradle/Maven

package com.example.springboot;

import static org.hamcrest.Matchers.equalTo;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.http.MediaType;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.request.MockMvcRequestBuilders;

@SpringBootTest
@AutoConfigureMockMvc
public class HelloControllerTest {

    //MockMvc - import from SpringTest. Sends HTTPRequest into DispatcherServlet and make assertions about result.
	@Autowired
	private MockMvc mvc;

	@Test
	public void getHello() throws Exception {
		mvc.perform(MockMvcRequestBuilders.get("/").accept(MediaType.APPLICATION_JSON))
				.andExpect(status().isOk())
				.andExpect(content().string(equalTo("Greetings from Spring Boot!")));
	}
}

6 Add Production-grade service

Spring Boot provides - HTTP endpoints or with JMX. Auditing, health, and metrics gathering management services with actuator module.
Actuator : manufacturing term that refers to a mechanical device for moving or controlling something. Actuators can generate a large amount of motion from a small change.

# Startup server and check
$ curl localhost:8080/actuator/health
{"status":"UP"}

REF

https://spring.io/guides/gs/spring-boot/

https://docs.spring.io/spring-boot/docs/2.5.0/reference/htmlsingle/#getting-started