devkuma – Spring Boot

Spring Boot

kc@example.com (kc kim) — Tue, 15 Aug 2017 22:34:03 +0900

Spring Boot

Spring Boot Overview

kc@example.com (kc kim) — Tue, 15 Aug 2017 22:34:03 +0900

What Is Spring Boot?

It is a framework that lets you quickly use various libraries and frameworks provided by the Spring project.
It is something like the Spring version of Dropwizard.
When you build it, a single jar file is created.
- For web applications, it starts the embedded Tomcat server. You can switch to Jetty or Undertow.
- It can also run as a normal Java program rather than a web application.
It uses build tools such as Maven or Gradle. Ant is not supported.
If you add the components you want to use as dependencies, the settings required for integration are configured automatically.
You can write, build, and run Spring applications independently, and because embedded Tomcat or Jetty can be used, there is no need to package and deploy them as WAR files.
Because Tomcat or Jetty is embedded, the project can be deployed easily as a .jar file.
Complex XML settings are simplified and replaced with annotation-based Java config, making server configuration easier.
It allows you to build web projects quickly, similar to Django or Ruby on Rails.

Spring Boot Auto-configuration

@SpringBootApplication
- Means that @Configuration, @EnableAutoConfiguration, and @ComponentScan are used together by default.
@Configuration
- Declared on a class.
- Provides one or more @Bean methods in the class and lets the Spring container create and manage those beans.
@EnableAutoConfiguration
- Performs various default configuration tasks, such as embedded Tomcat server setup and automatic registration of Spring MVC’s DispatcherServlet.
@ComponentScan
- Automatically scans classes annotated with @Component, @Service, @Repository, and @Controller, and registers them as beans.

Creating an Initial Spring Project

kc@example.com (kc kim) — Sat, 13 Aug 2022 09:49:00 +0900

Spring Initializr

Spring Initializr is a web service that creates an initial Spring Boot project according to the selected conditions. If you specify project settings and the Spring projects to use in the web UI, you can easily start developing a Spring Boot project.

Spring Initializr with curl

When you need to scaffold or build projects repeatedly for Spring verification and similar work, using the web UI can be cumbersome. Therefore, this section uses curl to access the Spring Initializr API and create an initial project.

% curl https://start.spring.io/
  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
:: Spring Initializr ::  https://start.spring.io

This service generates quickstart projects that can be easily customized.
Possible customizations include a project's dependencies, Java version, and
build system or build structure. See below for further details.

The services uses a HAL based hypermedia format to expose a set of resources
to interact with. If you access this root resource requesting application/json
as media type the response will contain the following links:
+-----------------+------------------------------------------+
| Rel             | Description                              |
+-----------------+------------------------------------------+
| gradle-build    | Generate a Gradle build file.            |
| gradle-project  | Generate a Gradle based project archive. |
| maven-build     | Generate a Maven pom.xml.                |
| maven-project * | Generate a Maven based project archive. |
+-----------------+------------------------------------------+


The URI templates take a set of parameters to customize the result of a request
to the linked resource.
+-----------------+------------------------------------------+------------------------------+
| Parameter       | Description                              | Default value                |
+-----------------+------------------------------------------+------------------------------+
| applicationName | application name                         | DemoApplication              |
| artifactId      | project coordinates (infer archive name) | demo                         |
| baseDir         | base directory to create in the archive  | no base dir                  |
| bootVersion     | spring boot version                      | 2.7.2                        |
| dependencies    | dependency identifiers (comma-separated) | none                         |
| description     | project description                      | Demo project for Spring Boot |
| groupId         | project coordinates                      | com.example                  |
| javaVersion     | language level                           | 17                           |
| language        | programming language                     | java                         |
| name            | project name (infer application name)    | demo                         |
| packageName     | root package                             | com.example.demo             |
| packaging       | project packaging                        | jar                          |
| type            | project type                             | maven-project                |
| version         | project version                          | 0.0.1-SNAPSHOT               |
+-----------------+------------------------------------------+------------------------------+

... omitted ...

Examples:

To create a default demo.zip:
	$ curl -G https://start.spring.io/starter.zip -o demo.zip

To create a web project using Java 11:
	$ curl -G https://start.spring.io/starter.zip -d dependencies=web \
			-d javaVersion=11 -o demo.zip

To create a web/data-jpa gradle project unpacked:
	$ curl -G https://start.spring.io/starter.tgz -d dependencies=web,data-jpa \
		   -d type=gradle-project -d baseDir=my-dir | tar -xzvf -

To generate a Maven POM with war packaging:
	$ curl -G https://start.spring.io/pom.xml -d packaging=war -o pom.xml

Starting a Spring Boot Web Application

kc@example.com (kc kim) — Tue, 15 Aug 2017 22:34:03 +0900

Starting a Web Application

Here, we will modify Spring Boot - Hello World.

Changing Dependencies for a Web Application

build.gradle

dependencies {
-   compile 'org.springframework.boot:spring-boot-starter'
+   compile 'org.springframework.boot:spring-boot-starter-web'
}

When creating a web application, use the spring-boot-starter-web module.
By default, it creates a web application using Spring MVC.

Changing the Startup Method

Because the container exits after the server starts, change the code so it does not use a try-with-resources statement.

src/main/java/sample/springboot/Main.java

package sample.springboot;

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

@SpringBootApplication
public class Main {

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

Spring MVC Controller Class

When creating a class that becomes the entry point of a Web API, add @RestController to the class.
If you want a controller that corresponds to the C in MVC instead of a Web API, add the @Controller annotation.
Use @RequestMapping to map paths and HTTP methods. It feels roughly similar to JAX-RS.

src/main/java/sample/springboot/web/HelloController.java

package sample.springboot.web;

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

@RestController
@RequestMapping("/hello")
public class HelloController {

    @RequestMapping(method=RequestMethod.GET)
    public String hello() {
        return "Hello Spring MVC";
    }
}

Running the Application

Run with Gradle

$ gradle bootRun
(omitted)
> :bootRun

Test with curl

$ curl http://localhost:8080/hello
Hello Spring MVC

Source Code

https://github.com/devkuma/tutorial/tree/master/spring-boot-hello-world-2

Changing the Spring Boot Server Port Number

kc@example.com (kc kim) — Tue, 15 Aug 2017 22:34:03 +0900

Changing the Server Port Number

You can specify the port number with server.port in the application.properties configuration file.

Change the configuration file as follows. application.properties

server.port=1598

Run the Application

$ gradle bootRun
(omitted)
2017-08-17 22:30:13.211  INFO 14485 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 1598 (http)
(omitted)

Description

For an explanation of application.properties, see here.
Other changes are also possible, such as the following.
- server.address: Server address. If set to localhost, access is restricted to local access only.
- server.sessionTimeout: Session timeout duration.