33. 3つの比較と Spring Boot との関係

import java.util.List;
import java.util.Set;

// 「このプロジェクトは何でビルドするのか」は、ルートにあるファイル名で分かる、の模型。
// どれを使うかはプロジェクトが決めていて、読む側はファイルの有無で判断する。
// 判定の表は Ant / Maven / Gradle の文書と、手元の 3 プロジェクトの一覧に基づく(実装ではない)。
class Main {
    record Project(String name, Set<String> rootFiles) {}

    static String tool(Set<String> files) {
        if (files.contains("build.gradle") || files.contains("build.gradle.kts")) {
            String wrapper = files.contains("gradlew") ? "gradlew present" : "no wrapper: gradle must be installed";
            String dsl = files.contains("build.gradle.kts") ? "Kotlin DSL" : "Groovy DSL";
            return "Gradle (" + dsl + "; " + wrapper + ")";
        }
        if (files.contains("pom.xml")) {
            String wrapper = files.contains("mvnw") ? "mvnw present" : "no wrapper: mvn must be installed";
            return "Maven (" + wrapper + ")";
        }
        if (files.contains("build.xml")) {
            String deps = files.contains("ivy.xml") ? "ivy.xml present: Ivy fetches jars"
                                                    : "no ivy.xml: look for a lib/ directory";
            return "Ant (" + deps + ")";
        }
        return "none of the three: read the README";
    }

    public static void main(String[] args) {
        List<Project> projects = List.of(
            new Project("start.spring.io, Maven", Set.of("pom.xml", "mvnw", "mvnw.cmd", "src", "HELP.md")),
            new Project("start.spring.io, Gradle", Set.of("build.gradle", "settings.gradle", "gradlew", "gradlew.bat", "src")),
            new Project("start.spring.io, Gradle Kotlin", Set.of("build.gradle.kts", "settings.gradle.kts", "gradlew", "src")),
            new Project("Boot reference, Ant + Ivy", Set.of("build.xml", "ivy.xml", "src")),
            new Project("old Ant web app", Set.of("build.xml", "lib", "WebContent", "src")),
            new Project("a Node project", Set.of("package.json", "src")));

        for (Project p : projects) {
            System.out.printf("%-32s -> %s%n", p.name(), tool(p.rootFiles()));
        }
        System.out.println();
        System.out.println("The build tool is a decision the project already made; a reader only has to recognise it.");
    }
}

// 出力(JDK 22 で実行)
//   start.spring.io, Maven           -> Maven (mvnw present)
//   start.spring.io, Gradle          -> Gradle (Groovy DSL; gradlew present)
//   start.spring.io, Gradle Kotlin   -> Gradle (Kotlin DSL; gradlew present)
//   Boot reference, Ant + Ivy        -> Ant (ivy.xml present: Ivy fetches jars)
//   old Ant web app                  -> Ant (no ivy.xml: look for a lib/ directory)
//   a Node project                   -> none of the three: read the README