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JavaでHello world

今回はJavaでhello Worldをしていきたいと思います！
JavascriptではなくJavaです！！

普段はフロントエンド業務をしているためほとんどクライアント側しか触らない自分ですが、
業務外で触れる機会があったので書き留めていきたいと思います！

環境準備

IDEをダウンロード

IntelliJ

IDEとは統合開発環境のことで、使用することでエディター上でクラスを実行できたり、コーディングを補助してくれたりと開発に使えるツールが詰め込まれたものです。

JDKをダウンロード

brew install openjdk

JDKとはvirtual machine(仮想環境)やコンパイラーの機能が備わっています。

Mavenをダウンロード

brew install maven

フロントの自分がいうところのnpmみたいなものになります。

Hello Worldしてみる

1,IntelliJを開く

先ほどダウンロードしたIDEを開いき、NEW Projectを押します。

2,Project SDKを指定

先ほどダウンロードしたJDKを指定します。

hoge

3,Projectの名前を指定

任意の名前を指定します。

hoge

4,pom.xml

pom.xmlはプロジェクト内で使用するプラグインや様々な情報を記載していくxmlファイルです。

<?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>

    <groupId>org.example</groupId>
    <artifactId>spring-boot-demo-app</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.3.2.RELEASE</version>
    </parent>

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

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>2.3.2.RELEASE</version>
            </plugin>
        </plugins>
    </build>
</project>

5,mavenをリロード

hoge

6,アプリケーションを作成

src/main/java/Example.java
を作成
hoge

import org.springframework.boot.*;
import org.springframework.boot.autoconfigure.*;
import org.springframework.web.bind.annotation.*;

@RestController
@EnableAutoConfiguration
public class Example {

    @RequestMapping("/")
    String home() {
        return "Hello World!";
    }

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

}

7,クラスを実行

hoge

実行後下記が表示されれば成功です！

/Library/Java/JavaVirtualMachines/jdk-14.0.2.jdk/Contents/Home/bin/java -javaagent:/Applications/IntelliJ IDEA CE.app/Contents/lib/idea_rt.jar=52512:/Applications/IntelliJ IDEA CE.app/Contents/bin -Dfile.encoding=UTF-8 -classpath /Users/masayuki/Documents/program/spring-boot-demo-app/target/classes:/Users/masayuki/.m2/repository/org/springframework/boot/spring-boot-starter-web/2.3.2.RELEASE/spring-boot-starter-web-2.3.2.RELEASE.jar:/Users/masayuki/.m2/repository/org/springframework/boot/spring-boot-starter/2.3.2.RELEASE/spring-boot-starter-2.3.2.RELEASE.jar:/Users/masayuki/.m2/repository/org/springframework/boot/spring-boot/2.3.2.RELEASE/spring-boot-2.3.2.RELEASE.jar:/Users/masayuki/.m2/repository/org/springframework/boot/spring-boot-autoconfigure/2.3.2.RELEASE/spring-boot-autoconfigure-2.3.2.RELEASE.jar:/Users/masayuki/.m2/repository/org/springframework/boot/spring-boot-starter-logging/2.3.2.RELEASE/spring-boot-starter-logging-2.3.2.RELEASE.jar:/Users/masayuki/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar:/Users/masayuki/.m2/repository/ch/qos/logback/logback-core/1.2.3/logback-core-1.2.3.jar:/Users/masayuki/.m2/repository/org/slf4j/slf4j-api/1.7.30/slf4j-api-1.7.30.jar:/Users/masayuki/.m2/repository/org/apache/logging/log4j/log4j-to-slf4j/2.13.3/log4j-to-slf4j-2.13.3.jar:/Users/masayuki/.m2/repository/org/apache/logging/log4j/log4j-api/2.13.3/log4j-api-2.13.3.jar:/Users/masayuki/.m2/repository/org/slf4j/jul-to-slf4j/1.7.30/jul-to-slf4j-1.7.30.jar:/Users/masayuki/.m2/repository/jakarta/annotation/jakarta.annotation-api/1.3.5/jakarta.annotation-api-1.3.5.jar:/Users/masayuki/.m2/repository/org/springframework/spring-core/5.2.8.RELEASE/spring-core-5.2.8.RELEASE.jar:/Users/masayuki/.m2/repository/org/springframework/spring-jcl/5.2.8.RELEASE/spring-jcl-5.2.8.RELEASE.jar:/Users/masayuki/.m2/repository/org/yaml/snakeyaml/1.26/snakeyaml-1.26.jar:/Users/masayuki/.m2/repository/org/springframework/boot/spring-boot-starter-json/2.3.2.RELEASE/spring-boot-starter-json-2.3.2.RELEASE.jar:/Users/masayuki/.m2/repository/com/fasterxml/jackson/core/jackson-databind/2.11.1/jackson-databind-2.11.1.jar:/Users/masayuki/.m2/repository/com/fasterxml/jackson/core/jackson-annotations/2.11.1/jackson-annotations-2.11.1.jar:/Users/masayuki/.m2/repository/com/fasterxml/jackson/core/jackson-core/2.11.1/jackson-core-2.11.1.jar:/Users/masayuki/.m2/repository/com/fasterxml/jackson/datatype/jackson-datatype-jdk8/2.11.1/jackson-datatype-jdk8-2.11.1.jar:/Users/masayuki/.m2/repository/com/fasterxml/jackson/datatype/jackson-datatype-jsr310/2.11.1/jackson-datatype-jsr310-2.11.1.jar:/Users/masayuki/.m2/repository/com/fasterxml/jackson/module/jackson-module-parameter-names/2.11.1/jackson-module-parameter-names-2.11.1.jar:/Users/masayuki/.m2/repository/org/springframework/boot/spring-boot-starter-tomcat/2.3.2.RELEASE/spring-boot-starter-tomcat-2.3.2.RELEASE.jar:/Users/masayuki/.m2/repository/org/apache/tomcat/embed/tomcat-embed-core/9.0.37/tomcat-embed-core-9.0.37.jar:/Users/masayuki/.m2/repository/org/glassfish/jakarta.el/3.0.3/jakarta.el-3.0.3.jar:/Users/masayuki/.m2/repository/org/apache/tomcat/embed/tomcat-embed-websocket/9.0.37/tomcat-embed-websocket-9.0.37.jar:/Users/masayuki/.m2/repository/org/springframework/spring-web/5.2.8.RELEASE/spring-web-5.2.8.RELEASE.jar:/Users/masayuki/.m2/repository/org/springframework/spring-beans/5.2.8.RELEASE/spring-beans-5.2.8.RELEASE.jar:/Users/masayuki/.m2/repository/org/springframework/spring-webmvc/5.2.8.RELEASE/spring-webmvc-5.2.8.RELEASE.jar:/Users/masayuki/.m2/repository/org/springframework/spring-aop/5.2.8.RELEASE/spring-aop-5.2.8.RELEASE.jar:/Users/masayuki/.m2/repository/org/springframework/spring-context/5.2.8.RELEASE/spring-context-5.2.8.RELEASE.jar:/Users/masayuki/.m2/repository/org/springframework/spring-expression/5.2.8.RELEASE/spring-expression-5.2.8.RELEASE.jar Example

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.3.2.RELEASE)

2020-08-02 14:26:02.276  INFO 35892 --- [           main] Example                                  : Starting Example on maa with PID 35892 (/Users/masayuki/Documents/program/spring-boot-demo-app/target/classes started by masayuki in /Users/masayuki/Documents/program/spring-boot-demo-app)
2020-08-02 14:26:02.280  INFO 35892 --- [           main] Example                                  : No active profile set, falling back to default profiles: default
2020-08-02 14:26:04.567  INFO 35892 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2020-08-02 14:26:04.624  INFO 35892 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2020-08-02 14:26:04.625  INFO 35892 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.37]
2020-08-02 14:26:04.847  INFO 35892 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2020-08-02 14:26:04.848  INFO 35892 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 2435 ms
2020-08-02 14:26:05.231  INFO 35892 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2020-08-02 14:26:05.676  INFO 35892 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2020-08-02 14:26:05.703  INFO 35892 --- [           main] Example                                  : Started Example in 4.953 seconds (JVM running for 6.18)

http://localhost:8080へアクセスしてHello Worldが表示されているか確認してみましょう