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Java has no built-in domain-registration lookup in InetAddress: that API resolves host names to IP addresses and can perform reverse name lookups. For registration information, use RDAP, the HTTP-based successor that became ICANN’s definitive source for generic top-level domain (gTLD) data on 28 January 2025. WHOIS is not gone everywhere, and the change did not remove a Java feature; it changed the standard route for much gTLD registration data.
Why WHOIS is not a Java DNS feature
There are two different questions a developer might ask about a domain:
- DNS: What IP address does
example.comresolve to? - Registration data: What registration record is available for the domain object?
Java’s InetAddress API addresses the first question. getByName() resolves a host name to an address; getCanonicalHostName() attempts a reverse name lookup through the system’s resolver. Neither method queries a registrar or returns domain registration records.
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WHOIS is a separate registration-data protocol, specified in RFC 3912. RDAP—the Registration Data Access Protocol—is its standardized successor for many registration-data services. So “WHOIS is dead in modern Java” is a useful shorthand for the change in how developers should approach gTLD registration lookups, not a description of a Java API that was removed.
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What changed: RDAP became the standard route for gTLD data
ICANN announced that, as of 28 January 2025, RDAP would be the definitive source for generic top-level domain name (gTLD) registration information in place of sunsetted WHOIS services. Most contractual WHOIS obligations for gTLD registries and registrars ended at that milestone, but ICANN’s user guidance identifies exceptions for .com, .name, and .post. The milestone is gTLD-specific; it should not be generalized to every country-code or other top-level domain.
RDAP has a different interface from WHOIS. It uses HTTP requests and defined query paths, and clients discover the appropriate service base URL through the IANA RDAP bootstrap registry. ICANN describes RDAP as offering standardized access and response formats, internationalization, secure access, authoritative service discovery, and differentiated access. These are protocol and service design benefits, not a guarantee that every server exposes the same data or that all returned information is public.
How to check a domain with RDAP
Choose the lookup route that matches the job. For a one-off check, ICANN provides a browser-based lookup. For repeatable queries, use ICANN’s open-source command-line client or build an RDAP client into your application.
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| Route | Best for | What to expect |
|---|---|---|
| ICANN Lookup | Manually checking an individual domain | Interactive results; ICANN says the service may fall back to a gTLD registry’s WHOIS service if requested information is unavailable through RDAP. |
| ICANN’s RDAP command-line client | Repeatable lookups from a shell or script | ICANN identifies it as an open-source client; the cited guidance does not establish performance or rate-limit guarantees. |
| Your Java application | Integrating registration-data lookups into an application workflow | Requires service discovery, an HTTP request, and parsing the RDAP response; the appropriate service depends on the queried namespace. |
ICANN-reported figures give a sense of adoption, not a service guarantee: its user information page reports more than 10 billion RDAP queries per month across all types of RDAP servers, an estimate published in December 2024, and counts of more than 40 known client implementations and more than 15 known server implementations. These are ICANN’s reported estimates and counts, not independently verified measurements.
Build the lookup flow in Java
For an application, follow RDAP’s discovery model rather than hardcoding one registry URL for every domain. The precise service and the data it returns depend on the domain’s namespace and provider.
- Decide whether registration data is actually needed. If the application only needs an IP address, use DNS resolution. Do not substitute an RDAP request for a hostname lookup.
- Discover the RDAP service. Consult the IANA bootstrap registry to determine the service base URL appropriate to the queried domain namespace.
- Construct the query. Append the domain query path defined by RFC 9082 to that service’s base URL. RFC 9082 specifies RDAP query formats over HTTP; it is not a single universal endpoint.
- Send an HTTP request. Treat the selected RDAP service as an external provider: handle HTTP failures and responses that do not contain the data your application expects.
- Parse the RDAP JSON response. Use the response structure rather than assuming the output resembles a WHOIS text record. The data available can differ by namespace and provider.
The sources cited here establish this architecture, but not a particular Java HTTP or JSON library, current dependency versions, service-wide rate limits, or complete coverage of country-code domains. Choose implementation libraries and operational limits for your application separately; do not assume one gTLD service’s behavior applies to every RDAP server.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When RDAP does not show the information you need
A public lookup may omit nonpublic registration information. Start with ICANN Lookup to see what is available. If the data you need is not public, ICANN describes two possible next steps: submit a request through its Registration Data Request Service (RDRS) when the sponsoring registrar participates, or contact the sponsoring registrar directly. Access depends on the request and applicable process; RDAP does not make restricted data public.
ICANN Lookup also says that when queried information is unavailable through RDAP, its domain query may be redirected to the corresponding gTLD registry’s WHOIS service. That fallback is a behavior of the lookup service, not a reason for Java applications to treat WHOIS as a universal replacement for RDAP.
Practical takeaway for Java developers
Keep the two jobs separate: use Java’s networking and DNS APIs when you need name resolution, and use RDAP when you need domain registration data. For gTLDs, RDAP is the current ICANN-designated source as of 28 January 2025, subject to the stated exceptions; for application code, discover the relevant service and form a standards-based HTTP query rather than assuming a fixed endpoint or universal data coverage.
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