CloudflareDDNSUpdate Java and Jbang based script. See https://javastreets.com/blog/java-jbang-cloudflare-ddns.html

cf_example.properties

zoneId=
fqdn=
cfApiToken=

CloudflareDDNSUpdate.java

//usr/bin/env jbang "$0" "$@" ; exit $?
//DEPS com.konghq:unirest-java:3.4.00:standalone
//DEPS info.picocli:picocli:4.1.4

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.Properties;
import java.util.concurrent.Callable;

import kong.unirest.Unirest;
import kong.unirest.json.JSONObject;
import picocli.CommandLine;
import picocli.CommandLine.Command;
import picocli.CommandLine.Parameters;

/**
 * This class updates the DNS in Cloudflare with public IP address for current network.
 * 
 * cfConfigPath must point to a properties file containing three property values - 
 * zoneId: Cloudflare DNS Zone Id
 * fqdn: Fully qualified domain name to update with public IP. eg. test.example.com
 * cfApiToken: An API Token for interacting with Cloudflare apis.
 * 
 * @author manikmagar
 */
@Command(name = "CloudflareDDNSUpdate", mixinStandardHelpOptions = true, version = "CloudflareDDNSUpdate 1.0",
        description = "Dynamic DNS update for Cloudflare")
class CloudflareDDNSUpdate implements Callable<Integer> {

    @Parameters(index = "0", description = "Cloudflare configuration properties file path")
    private File cfConfigPath;

    public static void main(String[] args) {
        Integer exit = new CommandLine(new CloudflareDDNSUpdate()).execute(args);
        System.exit(exit);
    }

    public Integer call() throws Exception {
        System.out.println("Initiating DNS update for cloudflare ...");
        final String zoneId, fqdn, cfApiToken;
        // Load properties file
        Properties props = new Properties();
        try {
            props.load(new FileInputStream(cfConfigPath));
        } catch (IOException e) {
            System.err.println("Unable to load configuration file - " + e.getMessage());
            return 1;
        }
        zoneId = props.getProperty("zoneId");
        fqdn =  props.getProperty("fqdn");
        cfApiToken =  props.getProperty("cfApiToken");
        
        String publicIP = Unirest.post("https://beta.ipinfo.in").asString().getBody();
        System.out.println("Public IP is - " + publicIP);
        JSONObject dnsRecord = Unirest.get("https://api.cloudflare.com/client/v4/zones/{zone_id}/dns_records")
                .routeParam("zone_id", zoneId).queryString("type", "A").queryString("name", fqdn)
                .header("Authorization", "Bearer " + cfApiToken).asJson().getBody().getObject().getJSONArray("result")
                .optJSONObject(0);

        if (dnsRecord == null) {
            System.err.println("DNS Record " + fqdn + " does not exist in zone id " + zoneId);
            return 1;
        }

        if (dnsRecord.getString("content").equals(publicIP)) {
            System.out.println("Public IP has not changed. Skipping DNS update.");
            return 0;
        }

        final String dnsRecordId = dnsRecord.getString("id");
        System.out.println("DNS Record Id - " + dnsRecordId);

        Map<String, Object> dnsData = new HashMap<>();
        dnsData.put("type", "A");
        dnsData.put("name", fqdn);
        dnsData.put("content", publicIP);
	dnsData.put("ttl",1);
        JSONObject dns = new JSONObject(dnsData);

        JSONObject putResponse = Unirest
                .put("https://api.cloudflare.com/client/v4/zones/" + zoneId + "/dns_records/" + dnsRecordId).body(dns)
                .header("Authorization", "Bearer " + cfApiToken).header("Content-Type", "application/json").asJson()
                .getBody().getObject();

        if (!putResponse.getBoolean("success")) {
            System.err.println("DNS Update failed with error - " + putResponse.getJSONArray("errors").join(","));
            return 1;
        } else {
            System.out.println("DNS Updated successfully with new ip address - " + publicIP);
            return 0;
        }
    }
}