OpenJDK 1.23 · java.net.InetAddress · APIdia, the JavaDoc alternative

This class represents an Internet Protocol (IP) address.

An IP address is either a 32-bit or 128-bit unsigned number used by IP, a lower-level protocol on which protocols like UDP and TCP are built. The IP address architecture is defined by RFC 790: Assigned Numbers, RFC 1918: Address Allocation for Private Internets, RFC 2365: Administratively Scoped IP Multicast, and RFC 2373: IP Version 6 Addressing Architecture. An instance of an InetAddress consists of an IP address and possibly its corresponding host name (depending on whether it is constructed with a host name or whether it has already done reverse host name resolution).

Address types

Description of unicast and multicast address types
Address Type	Description
unicast	An identifier for a single interface. A packet sent to a unicast address is delivered to the interface identified by that address. The Unspecified Address -- Also called anylocal or wildcard address. It must never be assigned to any node. It indicates the absence of an address. One example of its use is as the target of bind, which allows a server to accept a client connection on any interface, in case the server host has multiple interfaces. The unspecified address must not be used as the destination address of an IP packet. The Loopback Addresses -- This is the address assigned to the loopback interface. Anything sent to this IP address loops around and becomes IP input on the local host. This address is often used when testing a client.
multicast	An identifier for a set of interfaces (typically belonging to different nodes). A packet sent to a multicast address is delivered to all interfaces identified by that address.

IP address scope

Link-local addresses are designed to be used for addressing on a single link for purposes such as auto-address configuration, neighbor discovery, or when no routers are present.

Site-local addresses are designed to be used for addressing inside of a site without the need for a global prefix.

Global addresses are unique across the internet.

Textual representation of IP addresses

The textual representation of an IP address is address family specific.

For IPv4 address format, please refer to Inet4Address#format; For IPv6 address format, please refer to Inet6Address#format.

There is a couple of System Properties affecting how IPv4 and IPv6 addresses are used.

Host Name Resolution

The InetAddress class provides methods to resolve host names to their IP addresses and vice versa. The actual resolution is delegated to an InetAddress resolver.

Host name-to-IP address resolution maps a host name to an IP address. For any host name, its corresponding IP address is returned.

Reverse name resolution means that for any IP address, the host associated with the IP address is returned.

The built-in InetAddress resolver implementation does host name-to-IP address resolution and vice versa through the use of a combination of local machine configuration information and network naming services such as the Domain Name System (DNS) and the Lightweight Directory Access Protocol (LDAP). The particular naming services that the built-in resolver uses by default depends on the configuration of the local machine.

InetAddress has a service provider mechanism for InetAddress resolvers that allows a custom InetAddress resolver to be used instead of the built-in implementation. InetAddressResolverProvider is the service provider class. Its API docs provide all the details on this mechanism.

InetAddress Caching

The InetAddress class has a cache to store successful as well as unsuccessful host name resolutions.

By default, when a security manager is installed, in order to protect against DNS spoofing attacks, the result of positive host name resolutions are cached forever. When a security manager is not installed, the default behavior is to cache entries for a finite (implementation dependent) period of time. The result of unsuccessful host name resolution is cached for a very short period of time (10 seconds) to improve performance.

If the default behavior is not desired, then a Java security property can be set to a different Time-to-live (TTL) value for positive caching. Likewise, a system admin can configure a different negative caching TTL value when needed or extend the usage of the stale data.

Three Java security properties control the TTL values used for positive and negative host name resolution caching:

networkaddress.cache.ttl

Indicates the caching policy for successful name lookups from the name service. The value is specified as an integer to indicate the number of seconds to cache the successful lookup. The default setting is to cache for an implementation specific period of time.

A value of -1 indicates "cache forever".

networkaddress.cache.stale.ttl

Indicates the caching policy for stale names. The value is specified as an integer to indicate the number of seconds that stale names will be kept in the cache. A name is considered stale if the TTL has expired and an attempt to lookup the host name again was not successful. This property is useful if it is preferable to use a stale name rather than fail due to an unsuccessful lookup. The default setting is to cache for an implementation specific period of time.

If the value of this property is larger than "networkaddress.cache.ttl" then "networkaddress.cache.ttl" will be used as a refresh interval of the name in the cache. For example, if this property is set to 1 day and "networkaddress.cache.ttl" is set to 30 seconds, then the positive response will be cached for 1 day but an attempt to refresh it will be done every 30 seconds.

A value of 0 (zero) or if the property is not set means do not use stale names. Negative values are ignored.

networkaddress.cache.negative.ttl (default: 10)

Indicates the caching policy for un-successful name lookups from the name service. The value is specified as an integer to indicate the number of seconds to cache the failure for un-successful lookups.

A value of 0 indicates "never cache". A value of -1 indicates "cache forever".

Nested and Inner Type Summary

Modifier and Type	Class and Description
private static interface	InetAddress.Addresses
private static class	InetAddress.CachedLocalHost
private static class	InetAddress.CachedLookup A cached result of a name service lookup.
private static class	InetAddress.HostsFileResolver The HostsFileResolver provides host address mapping by reading the entries in a hosts file, which is specified by `jdk.net.hosts.file` system property The file format is that which corresponds with the /etc/hosts file IP Address host alias list.
pack-priv static class	InetAddress.InetAddressHolder
private static class	InetAddress.NameServiceAddresses
private static class	InetAddress.PlatformResolver The default InetAddressResolver implementation, which delegates to the underlying OS network libraries to resolve host address mappings.
private static class	InetAddress.ValidCachedLookup A cached valid lookup containing addresses whose validity may be temporarily extended by an additional stale period pending the mapping being refreshed or updated.

Field Summary

Modifier and Type	Field and Description
private static volatile InetAddressResolver	bootstrapResolver
private static final InetAddressResolver	BUILTIN_RESOLVER
private static final ConcurrentMap<String, InetAddress.Addresses>	cache
private static volatile InetAddress.CachedLocalHost	cachedLocalHost
private transient String	canonicalHostName Used to store the best available hostname.
private static final NavigableSet<InetAddress.CachedLookup>	expirySet
private static final long	FIELDS_OFFSET
pack-priv final transient InetAddress.InetAddressHolder	holder
private static final String	HOSTS_FILE_NAME
pack-priv static final InetAddressImpl	impl
private static final RuntimePermission	INET_ADDRESS_RESOLVER_PERMISSION The `RuntimePermission("inetAddressResolverProvider")` is necessary to subclass and instantiate the `InetAddressResolverProvider` class, as well as to obtain resolver from an instance of that class, and it is also required to obtain the operating system name resolution configurations.
pack-priv static final int	IPv4 Specify the address family: Internet Protocol, Version 4
pack-priv static final int	IPv6 Specify the address family: Internet Protocol, Version 6
pack-priv static final InetAddressResolver.LookupPolicy	PLATFORM_LOOKUP_POLICY Platform-wide `LookupPolicy` initialized from `"java.net.preferIPv4Stack"`, `"java.net.preferIPv6Addresses"` system properties.
private static final String	PREFER_IPV4_STACK_VALUE
private static final String	PREFER_IPV6_ADDRESSES_VALUE
private static volatile InetAddressResolver	resolver
private static final ReentrantLock	RESOLVER_LOCK
private static final ObjectStreamField[]	serialPersistentFields
private static final long	serialVersionUID use serialVersionUID from JDK 1.0.2 for interoperability
private static final Unsafe	UNSAFE

Constructor Summary

Access	Constructor and Description
pack-priv	InetAddress() Constructor for the Socket.accept() method.

Method Summary

Modifier and Type	Method and Description
pack-priv static InetAddress	anyLocalAddress()
private static InetAddressResolverProvider.Configuration	builtinConfiguration()
private static InetAddressResolver	Returns: an InetAddressResolver createBuiltinInetAddressResolver() Create an instance of the InetAddressResolver interface based on the setting of the `jdk.net.hosts.file` system property.
public boolean	Returns: `true` if the objects are the same; `false` otherwise. equals(Object the object to compare against. obj) Overrides java.lang.Object.equals. Compares this object against the specified object.
public byte[]	Returns: the raw IP address of this object. getAddress() Returns the raw IP address of this `InetAddress` object.
pack-priv static InetAddress[]	getAddressesFromNameService(String host)
public static InetAddress[]	Returns: an array of all the IP addresses for a given host name. getAllByName(String the name of the host, or `null`. host) Given the name of a host, returns an array of its IP addresses, based on the system-wide resolver.
pack-priv static InetAddress[]	getAllByName0(String host, boolean check) package private so SocketPermission can call it
private static InetAddress[]	Returns: array of InetAddress(es) getAllByName0(String host name to look up host, boolean perform security check check, boolean use cached value if not expired else always perform name service lookup (and cache the result) useCache) Designated lookup method.
public static InetAddress	Returns: an InetAddress object created from the raw IP address. getByAddress(String the specified host host, byte[] the raw IP address in network byte order addr) Creates an InetAddress based on the provided host name and IP address.
public static InetAddress	Returns: an InetAddress object created from the raw IP address. getByAddress(byte[] the raw IP address in network byte order addr) Returns an `InetAddress` object given the raw IP address .
public static InetAddress	Returns: an IP address for the given host name. getByName(String the specified host, or `null`. host) Determines the IP address of a host, given the host's name.
public String	Returns: the fully qualified domain name for this IP address. If either the operation is not allowed by the security check or the system-wide resolver wasn't able to determine the fully qualified domain name for the IP address, the textual representation of the IP address is returned instead. getCanonicalHostName() Gets the fully qualified domain name for this IP address using the system-wide resolver.
public String	Returns: the raw IP address in a string format. getHostAddress() Returns the IP address string in textual presentation.
private static String	Returns: the fully qualified domain name for the given IP address. If either the operation is not allowed by the security check or the system-wide resolver wasn't able to determine the fully qualified domain name for the IP address, the textual representation of the IP address is returned instead. getHostFromNameService(InetAddress addr, boolean make security check if true check) Returns the fully qualified domain name for the given address.
public String	Returns: the host name for this IP address, or if the operation is not allowed by the security check, the textual representation of the IP address. getHostName() Gets the host name for this IP address.
pack-priv String	Returns: the host name for this IP address, or if the operation is not allowed by the security check, the textual representation of the IP address. getHostName(boolean make security check if true check) Returns the hostname for this address.
public static InetAddress	Returns: the address of the local host. getLocalHost() Returns the address of the local host.
public static InetAddress	Returns: the InetAddress loopback instance. getLoopbackAddress() Returns the loopback address.
public int	Returns: a hash code value for this IP address. hashCode() Overrides java.lang.Object.hashCode. Returns a hashcode for this IP address.
pack-priv InetAddress.InetAddressHolder	holder()
private static native void	init() Perform class load-time initializations.
private static final InetAddressResolver.LookupPolicy	initializePlatformLookupPolicy() Creates an address lookup policy from `"java.net.preferIPv4Stack"`, `"java.net.preferIPv6Addresses"` system property values, and O/S configuration.
private static UnknownHostException	invalidIPv6LiteralException(String host, boolean wrapInBrackets)
pack-priv static boolean	ipv4AddressesFirst(int lookupCharacteristics)
pack-priv static boolean	ipv6AddressesFirst(int lookupCharacteristics)
public boolean	Returns: a `boolean` indicating if the InetAddress is a wildcard address. isAnyLocalAddress() Utility routine to check if the InetAddress is a wildcard address.
private static native boolean	isIPv4Available()
private static native boolean	isIPv6Supported()
public boolean	Returns: a `boolean` indicating if the InetAddress is a link local address; or false if address is not a link local unicast address. isLinkLocalAddress() Utility routine to check if the InetAddress is a link local address.
public boolean	Returns: a `boolean` indicating if the InetAddress is a loopback address; or false otherwise. isLoopbackAddress() Utility routine to check if the InetAddress is a loopback address.
public boolean	Returns: a `boolean` indicating if the address has is a multicast address of global scope, false if it is not of global scope or it is not a multicast address isMCGlobal() Utility routine to check if the multicast address has global scope.
public boolean	Returns: a `boolean` indicating if the address has is a multicast address of link-local scope, false if it is not of link-local scope or it is not a multicast address isMCLinkLocal() Utility routine to check if the multicast address has link scope.
public boolean	Returns: a `boolean` indicating if the address has is a multicast address of node-local scope, false if it is not of node-local scope or it is not a multicast address isMCNodeLocal() Utility routine to check if the multicast address has node scope.
public boolean	Returns: a `boolean` indicating if the address has is a multicast address of organization-local scope, false if it is not of organization-local scope or it is not a multicast address isMCOrgLocal() Utility routine to check if the multicast address has organization scope.
public boolean	Returns: a `boolean` indicating if the address has is a multicast address of site-local scope, false if it is not of site-local scope or it is not a multicast address isMCSiteLocal() Utility routine to check if the multicast address has site scope.
public boolean	Returns: a `boolean` indicating if the InetAddress is an IP multicast address isMulticastAddress() Utility routine to check if the InetAddress is an IP multicast address.
public boolean	Returns: a `boolean` indicating if the address is reachable. isReachable(int the time, in milliseconds, before the call aborts timeout) Test whether that address is reachable.
public boolean	Returns: a `boolean` indicating if the address is reachable. isReachable(NetworkInterface the NetworkInterface through which the test will be done, or null for any interface netif, int the maximum numbers of hops to try or 0 for the default ttl, int the time, in milliseconds, before the call aborts timeout) Test whether that address is reachable.
public boolean	Returns: a `boolean` indicating if the InetAddress is a site local address; or false if address is not a site local unicast address. isSiteLocalAddress() Utility routine to check if the InetAddress is a site local address.
private static InetAddressResolver	loadResolver()
public static InetAddress	Returns: an `InetAddress` object with no hostname set, and constructed from the provided IP address literal. ofLiteral(String the textual representation of an IP address. ipAddressLiteral) Creates an `InetAddress` based on the provided textual representation of an IP address.
private void	readObject(ObjectInputStream the `ObjectInputStream` from which data is read s) Restores the state of this object from the stream.
private Object	Returns: the alternate object to the de-serialized object. readResolve() Replaces the de-serialized object with an Inet4Address object.
private static InetAddressResolver	resolver()
pack-priv static boolean	systemAddressesOrder(int lookupCharacteristics)
public String	Returns: a string representation of this IP address. toString() Overrides java.lang.Object.toString. Converts this IP address to a `String`.
private static void	validate(String host)
private void	writeObject(ObjectOutputStream the `ObjectOutputStream` to which data is written s) Writes the state of this object to the stream.

Inherited from java.lang.Object:: clone finalize getClass notify notifyAll wait wait wait

public sealed Class InetAddress