rdap-java

Lightweight RDAP client library to check if a domain is registered.

Supports all TLDs via IANA bootstrap data + built-in fallback for TLDs not yet registered with IANA.

Features

• Check domain registration status (registered / available)
• Supports all TLDs (including IDN TLDs) via IANA bootstrap + curated fallback
• Automatic RDAP server discovery per TLD
• Fallback across multiple RDAP servers per TLD
• Custom server registration for unsupported TLDs
• IDN/Punycode support
• Nameserver extraction from RDAP responses
• Thread-safe, cached IANA bootstrap
• Zero heavy frameworks – just Java 11+ and org.json
• ~5 KB library code

Requirements

• Java 11+

Installation

Gradle

repositories {
    mavenCentral()
}

dependencies {
    implementation 'com.slxca:rdap-java:1.0.0'
}

Maven

<dependency>
    <groupId>com.slxca</groupId>
    <artifactId>rdap-java</artifactId>
    <version>1.0.0</version>
</dependency>

Manual

Download the JAR from Releases.

Usage

Basic check

import com.slxca.rdap.RDAPClient;
import com.slxca.rdap.RDAPResult;

RDAPClient client = new RDAPClient();
RDAPResult result = client.checkDomain("google.com");

if (result.isRegistered()) {
    System.out.println(result.getDomain() + " is registered");
} else {
    System.out.println(result.getDomain() + " is available");
}

Output:

google.com is registered

Nameservers

RDAPResult result = client.checkDomain("google.com");
for (String ns : result.getNameservers()) {
    System.out.println("NS: " + ns);
}

Custom RDAP server

client.registerServer("io", "https://rdap.afilias.net/rdap/");
RDAPResult result = client.checkDomain("example.io");

Command line

java -jar rdap-java.jar google.com

API

RDAPClient

Method	Returns	Description
RDAPClient()		Creates client with default HttpClient
RDAPClient(HttpClient)		Creates client with custom HttpClient
checkDomain(String domain)	RDAPResult	Queries RDAP for the domain
registerServer(String tld, String serverUrl)	void	Registers a custom RDAP server for a TLD

RDAPResult

Method	Returns	Description
getDomain()	String	The queried domain
isRegistered()	boolean	true if HTTP 200, false if 404
getServerUrl()	String	RDAP server used
getNameservers()	List<String>	Nameservers from the RDAP response

Exceptions

• RDAPException – network errors or no RDAP server found for TLD
• IllegalArgumentException – null/blank/invalid domain

How it works

1. TLD extraction – Extracts the top-level domain from the input (e.g. example.com → com)
2. Server lookup – Checks custom servers → IANA bootstrap → built-in fallback
3. RDAP query – Sends GET {serverUrl}/domain/{domain} with Accept: application/rdap+json
4. Result – HTTP 200 → registered, HTTP 404 → not registered

Supported TLDs

Source	Count	Examples
IANA bootstrap	~1200	.com, .org, .net, .uk, .fr
Built-in fallback	5	.de, .ch, .us, .no, .nl

Missing a TLD? Open an issue or use registerServer() to add it yourself.