Test Timestamp and TimestampTZ data types of PostgreSQL

TimestampTest.java

package com.test.time;

import com.zaxxer.hikari.HikariConfig;
import com.zaxxer.hikari.HikariDataSource;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.core.PreparedStatementCallback;

import java.sql.Timestamp;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.util.Calendar;
import java.util.TimeZone;

public class TimestampTest {
    private static final Logger log = LoggerFactory.getLogger(TimestampTest.class);
  
    /*
    SET timezone = 'Asia/Dhaka';
    CREATE TABLE timestamp_demo (
      ts TIMESTAMP,
      tstz TIMESTAMPTZ
    );
    */

    public static void main(String[] args) throws Exception {

        HikariConfig config = new HikariConfig();
        config.setJdbcUrl("jdbc:postgresql://localhost:5432/****");
        config.setUsername("***");
        config.setPassword("***");
        config.setDriverClassName("org.postgresql.Driver");
        config.setMaximumPoolSize(40);
        config.setMinimumIdle(2);


        JdbcTemplate jt = new JdbcTemplate(new HikariDataSource(config));

        // System variables
        log.info("Timezone: {}", jt.queryForObject("SHOW TIMEZONE;", String.class));
        log.info("Now: {}", jt.queryForObject("SELECT NOW();", String.class));

        // Insert a new value
        jt.execute("INSERT INTO timestamp_demo (ts, tstz) VALUES(?,?);", (PreparedStatementCallback<?>) ps -> {
            ZonedDateTime saveMe = ZonedDateTime.now();

            ps.setTimestamp(
                    1,
                    new Timestamp(saveMe.toInstant().toEpochMilli())
            );

            ps.setTimestamp(
                    2,
                    new Timestamp(saveMe.toInstant().toEpochMilli()),
                    Calendar.getInstance(TimeZone.getTimeZone(saveMe.getZone()))
            );
            return ps.execute();
        });

        // Query a value
        jt.query("SELECT * FROM timestamp_demo", rs -> {
            Timestamp ts = rs.getTimestamp("ts");
            ZonedDateTime gotTs = ZonedDateTime.ofInstant(ts.toInstant(), ZoneId.of("UTC"));
            log.info("Timestamp without zone: {}", gotTs);

            Timestamp tstz = rs.getTimestamp("tstz");
            ZonedDateTime gotTsTz = ZonedDateTime.ofInstant(tstz.toInstant(), ZoneId.of("UTC"));
            log.info("Timestamp with zone: {}", gotTsTz);
        });
    }
}