Spring Boot - Intro

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Spring Boot makes it easy to create production ready Spring-based applications.

Getting Start

Visit Spring initializr - https://start.spring.io/. add ‘Web’ dependency. and click ‘Generate Project’ to generate Spring Boot project

You can use curl to download the project from https://start.spring.io/ too.

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curl https://start.spring.io/starter.tgz \
-d dependencies=web,actuator \
-d language=java \
-d type=maven-project \
-d baseDir=demo-project | tar -xzvf -

For more information on Spring Initializr, see Spring Initializr Repo

The project can now be imported to IDE.

Adding Maven Dependency

Add web dependency to pom.xml

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<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-web</artifactId>
</dependency>

The complete pom.xml should look like this

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<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.1.4.RELEASE</version>
		<relativePath /> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>hello-world</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>demo</name>
	<description>Demo project for Spring Boot</description>

	<properties>
		<java.version>1.8</java.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-devtools</artifactId>
			<scope>runtime</scope>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
				<configuration>
					<fork>true</fork>
				</configuration>
			</plugin>
		</plugins>
	</build>

</project>

Adding Controller

Add controller to handle http request.

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package com.example.demo.controller;

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

@RestController
    public class HelloController {
    @RequestMapping("/hello")
    public String sayHello(){
        return "Hello World";
    }
}

Running Application

The main method calls SpringApplication class’s run method to bootstrap our application.

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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);
	}
}

Now run the application using the main method. go to http://localhost:8080/hello to see the output.

Alternatively, you can run as maven project

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./mvnw spring-boot:run

If you are a gradle user, execute bootRun task instead

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./gradlew bootRun

Go to http://localhost:8080/hello and the result page will show text

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Hello World

Adding Junit Test

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package com.example.demo.controller;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.servlet.MockMvc;

import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

@RunWith(SpringRunner.class)
@WebMvcTest(HelloController.class)
public class HelloControllerTest {
    @Autowired
    private MockMvc mockMvc;

    @Test
    public void shouldReturnMessage() throws Exception{
        this.mockMvc.perform(get("/hello")).andExpect(status().isOk())
                .andExpect(content().string("Hello World"));
    }
}

see source code at github

Creating Executable Jar

To create an executable jar(fat jar)
, we need to have spring-boot-maven-plugin in our pom.xml file. The project generated by Spring initializr adds spring-boot-maven-plugin in pom.xml already.

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<plugin>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-maven-plugin</artifactId>
	<configuration>
		<fork>true</fork>
	</configuration>
</plugin>

Run mvn package will generate the executable jar file. use java -jar command to run the jar. The executable jar is ready for production deployment.

Online Tutorials

Reference