Path·Files와 텍스트 파일 저장소

import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;

public final class FirstTextFile {
    public static void main(String[] args) throws Exception {
        Path directory = Path.of("data");
        Path file = directory.resolve("hello.txt");

        Files.createDirectories(directory);
        Files.writeString(file, "안녕하세요, 파일!", StandardCharsets.UTF_8);

        String text = Files.readString(file, StandardCharsets.UTF_8);
        System.out.println(text);
        System.out.println(file.toAbsolutePath());
    }
}

javac --release 25 -d out src/FirstTextFile.java
java -cp out FirstTextFile

import java.util.Arrays;

public final class NaiveDelimitedMember {
    record Member(String id, String name, int age) {}

    static String encode(Member member) {
        return member.id() + "," + member.name() + "," + member.age();
    }

    static Member decode(String line) {
        String[] fields = line.split(",");
        return new Member(fields[0], fields[1], Integer.parseInt(fields[2]));
    }

    public static void main(String[] args) {
        String line = encode(new Member("u1", "Kim, Mina", 31));
        System.out.println(line);
        System.out.println(Arrays.toString(line.split(",")));
        System.out.println(decode(line));
    }
}

import java.util.ArrayList;
import java.util.List;

public final class MemoryMemberRepository {
    public record Member(String id, String name, int age) {
        public Member {
            if (id == null || id.isBlank()) throw new IllegalArgumentException("id");
            if (name == null || name.isBlank()) throw new IllegalArgumentException("name");
            if (age < 0) throw new IllegalArgumentException("age");
        }
    }

    private final List<Member> members = new ArrayList<>();

    public synchronized void add(Member member) {
        if (members.stream().anyMatch(existing -> existing.id().equals(member.id()))) {
            throw new IllegalArgumentException("duplicate id: " + member.id());
        }
        members.add(member);
    }

    public synchronized List<Member> findAll() {
        return List.copyOf(members);
    }

    public static void main(String[] args) {
        var repository = new MemoryMemberRepository();
        repository.add(new Member("u1", "Mina", 31));
        System.out.println(repository.findAll());
    }
}

import java.nio.charset.StandardCharsets;
import java.util.Base64;

public final class MemberTextCodec {
    record Member(String id, String name, int age) {}

    private static String text(String value) {
        return Base64.getUrlEncoder().withoutPadding()
                .encodeToString(value.getBytes(StandardCharsets.UTF_8));
    }

    private static String value(String encoded) {
        return new String(Base64.getUrlDecoder().decode(encoded), StandardCharsets.UTF_8);
    }

    static String encode(Member member) {
        return text(member.id()) + "\t" + text(member.name()) + "\t" + member.age();
    }

    static Member decode(String line) {
        String[] fields = line.split("\t", -1);
        if (fields.length != 3) throw new IllegalArgumentException("field count");
        int age = Integer.parseInt(fields[2]);
        if (age < 0) throw new IllegalArgumentException("negative age");
        return new Member(value(fields[0]), value(fields[1]), age);
    }

    public static void main(String[] args) {
        Member source = new Member("id\t1", "Kim, Mina\n팀장", 31);
        String row = encode(source);
        System.out.println(row);
        System.out.println(source.equals(decode(row)));
    }
}

import java.nio.charset.StandardCharsets;
import java.nio.file.AtomicMoveNotSupportedException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardCopyOption;
import java.util.List;

public final class AtomicTextSnapshot {
    static void replace(Path target, List<String> rows) throws Exception {
        Path parent = target.toAbsolutePath().getParent();
        Files.createDirectories(parent);
        Path temp = Files.createTempFile(parent, target.getFileName().toString(), ".tmp");
        boolean moved = false;
        try {
            Files.write(temp, rows, StandardCharsets.UTF_8);
            try {
                Files.move(temp, target, StandardCopyOption.ATOMIC_MOVE,
                        StandardCopyOption.REPLACE_EXISTING);
            } catch (AtomicMoveNotSupportedException unsupported) {
                Files.move(temp, target, StandardCopyOption.REPLACE_EXISTING);
            }
            moved = true;
        } finally {
            if (!moved) Files.deleteIfExists(temp);
        }
    }

    public static void main(String[] args) throws Exception {
        Path directory = Files.createTempDirectory("members-");
        Path file = directory.resolve("members.txt");
        try {
            replace(file, List.of("v1", "row-a", "row-b"));
            System.out.println(Files.readAllLines(file, StandardCharsets.UTF_8));
        } finally {
            Files.deleteIfExists(file);
            Files.deleteIfExists(directory);
        }
    }
}