[JAVA] Create a web api server with spring boot

Overview

--Create a web api that just returns a string with spring boot

environment

• macOS Mojave 10.14.6
• Java openjdk 12.0.1
• Spring Boot 2.1.7
• Intellij IDEA CE 2019.1

procedure

Create a template with spring initializr

--You can easily create a template of spring boot with spring initializr

1. Go to https://start.spring.io
2. Select as follows

• Project : Gradle Project
• Language : Java
• Spring Boot : 2.1.7
• Project Metadata : --Group: Root package name. This time com.example --Artifact: Project name. This time ʻapi--Options: No touch --Dependencies: Dependent libraries can be added tobuild.gradle` This time add the following --Spring Web Starter: Basic packages required for web api --Lombok: A library packed with useful features often used in java Reference: Notes when touching lombok

1. Select Generate the Project and download the zip
2. Unzip the zip and place the folder in a suitable location --The folder structure looks like this

.
├── HELP.md
├── README.md
├── build.gradle
├── gradle
│   └── wrapper
│       ├── gradle-wrapper.jar
│       └── gradle-wrapper.properties
├── gradlew
├── gradlew.bat
├── settings.gradle
└── src
    ├── main
    │   ├── java
    │   │   └── com
    │   │       └── example
    │   │           └── api
    │   │               └── ApiApplication.java
    │   └── resources
    │       ├── application.properties
    │       ├── static
    │       └── templates
    └── test
        └── java
            └── com
                └── example
                    └── api
                        └── ApiApplicationTests.java

Intellij IDEA Preferences

--Set up the IDE so that you can edit the zip you just created with Intellij IDEA.

1. After starting Intellij IDEA, select ʻimport project` and select the folder you just unzipped.
2. Select gradle from ʻImport project from external model`
3. Check ʻUse auto import`
4. Make sure the Gradle JVM is Java 12
5. Select Finish
6. In Preference-> Build, Execution, Deployment-> compiler-> annotation processor Check ʻEnable annotation processing` and save
7. Open the project settings with command +; and open the project settings Select 12 for each of Project SDK and Project language level and save

Check build.gradle

--Project dependencies are defined in build.gradle

build.gradle

plugins {
	id 'org.springframework.boot' version '2.1.7.RELEASE'
	id 'java'
}

apply plugin: 'io.spring.dependency-management'

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

repositories {
	mavenCentral()
}

dependencies {
	implementation 'org.springframework.boot:spring-boot-starter-web'
	testImplementation 'org.springframework.boot:spring-boot-starter-test'
}

--plugins, ʻapply plugin: Plugin settings -- java: You will be able to perform tasks such as compiling java source code and unit testing. --ʻOrg.springframework.boot: You will be able to perform spring boot tasks such as bootRun. --ʻIo.spring.dependency-management: Provides maven BOM functionality (which resolves dependent library versions) not found in gradle -- group, version: Project settings --suceCompatibility: Specify the version of the JDK used in the project --Change from 1.8 to 12 to use Java 12 this time. -- repositories: Specify the repository to get the dependent libraries --dependencies: Definition of external dependencies. The Spring Web Starter specified in initializr is reflected here. --ʻImplementation: Used at compile time and run time --testImplementation: Used at compile time and run time during testing

Launch application

--Right-click ʻApiApplication` and execute --The following log will be output and Spring boot will start.

23:07:15: Executing task 'ApiApplication.main()'...

> Task :compileJava
> Task :processResources
> Task :classes

> Task :ApiApplication.main()

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.1.7.RELEASE)

2019-08-06 23:07:32.447  INFO 20662 --- [           main] com.example.api.ApiApplication           : Starting ApiApplication on xxxnoMacBook-Air.local with PID 20662 (/Users/xxx/dev/spring-boot-api/build/classes/java/main started by xxx in /Users/xxx/dev/spring-boot-api)
2019-08-06 23:07:32.452  INFO 20662 --- [           main] com.example.api.ApiApplication           : No active profile set, falling back to default profiles: default
2019-08-06 23:07:35.060  INFO 20662 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2019-08-06 23:07:35.118  INFO 20662 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2019-08-06 23:07:35.119  INFO 20662 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.22]
2019-08-06 23:07:35.309  INFO 20662 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2019-08-06 23:07:35.309  INFO 20662 --- [           main] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 2746 ms
2019-08-06 23:07:35.680  INFO 20662 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2019-08-06 23:07:36.278  INFO 20662 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2019-08-06 23:07:36.292  INFO 20662 --- [           main] com.example.api.ApiApplication           : Started ApiApplication in 4.996 seconds (JVM running for 5.699)

--Access http: // localhost: 8080 with a browser, and if the following screen is displayed, it is OK.

Creating a Controller

--I created a package called controller and created a class called HelloWorldController under it. --String returns hello world! when a GET request comes in with the path / hello --The method name is getHello, but anything is fine.

HelloWorldController

package com.example.api.controller;

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 HelloWorldController {

    @RequestMapping(method = RequestMethod.GET)
    public String getHello() {
        return "hello world!";
    }
}

@RestController

--Annotation attached to Controller class that is the endpoint of REST web api ――The same effect as adding the following two annotations --@Controller: Indicates that it is a controller class of MVC --@ResponseBody: The return value of the method of the given class becomes the response body as it is.

@RequestMapping()

--Annotation that sets the path to access the REST web api --method = RequestMethod.XXX (XXX: GET, POST, etc.) can be assigned to each HTTP method.

Application restart

--Restart the application and access http: // localhost: 8080 / hello in your browser --If hello world! Is displayed on the white screen, it's OK!