Simple DB utility prototype on Java8

console.log

$ javac -version
javac 1.8.0
$ javac DB.java
$ java DB
Query: 'select name from members' with connection: DB$Connection@23fc625e
closed
Alice
Bob

DB.java

import java.util.function.Function;
import java.util.*;

public class DB {
  static void println(String s) { System.out.println(s); }

  // java.sql.Connection
  static class Connection implements AutoCloseable {
    @Override public void close() { println("closed"); }
  }
  static class ConnectionPool {
    static Connection borrow() { return new Connection(); }
  }

  public static <R> R transaction(Function<Connection, R> f) {
    try (Connection conn = ConnectionPool.borrow();) {
      return f.apply(conn);
    }
  }

  // sample DAO
  static class MemberDao {
    private Connection conn;
    MemberDao(Connection conn) { this.conn = conn; }
    List<String> findAllNames() {
      println("Query: 'select name from members' with connection: " + conn);
      return Arrays.asList("Alice", "Bob");
    }
  }

  public static void main(String[] args) {
    List<String> names = DB.transaction((tx) -> {
      return new MemberDao(tx).findAllNames();
    });
    names.forEach(n -> println(n));
  }

}