InetAddress JDK 1.6)

Description

public class InetAddress

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

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.

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.

Host Name Resolution

Host name-to-IP address resolution is accomplished through the use of a combination of local machine configuration information and network naming services such as the Domain Name System (DNS) and Network Information Service(NIS). The particular naming services(s) being used is by default the local machine configured one. 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 InetAddress class provides methods to resolve host names to their IP addresses and vice versa.

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.

Two 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 as 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.negative.ttl (default: 10)

Indicates the caching policy for un-successful name lookups from the name service. The value is specified as as 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".

See also: InetAddress.getByAddress(byte[]) InetAddress.getByAddress(java.lang.String, byte[]) InetAddress.getAllByName(java.lang.String) InetAddress.getByName(java.lang.String) InetAddress.getLocalHost()

Methods

Hide/Show inherited methods

pack-privatestatic InetAddress anyLocalAddress ()

public boolean equals (Object obj)

Compares this object against the specified object.

Compares this object against the specified object. The result is true if and only if the argument is not null and it represents the same IP address as this object.

Two instances of InetAddress represent the same IP address if the length of the byte arrays returned by getAddress is the same for both, and each of the array components is the same for the byte arrays.
Returns: true if the objects are the same; false otherwise.
Parameters:
- obj - the object to compare against.
See Also: InetAddress.getAddress(),

public byte getAddress ()

Returns the raw IP address of this InetAddress object.

Returns the raw IP address of this InetAddress
object. The result is in network byte order: the highest order
byte of the address is in getAddress()[0].
Returns: the raw IP address of this object.

publicstatic InetAddress getAllByName (String host) throws UnknownHostException

Given the name of a host, returns an array of its IP addresses, based on the configured name service on the system.

pack-privatestatic InetAddress getAllByName0 (String host, boolean check) throws UnknownHostException

package private so SocketPermission can call it

publicstatic InetAddress getByAddress (byte[] addr) throws UnknownHostException

Returns an InetAddress object given the raw IP address .

Returns an InetAddress object given the raw IP address . The argument is in network byte order: the highest order byte of the address is in getAddress()[0].

This method doesn't block, i.e. no reverse name service lookup is performed.

IPv4 address byte array must be 4 bytes long and IPv6 byte array must be 16 bytes long
Returns: an InetAddress object created from the raw IP address.
Parameters:
- addr - the raw IP address in network byte order
Throws:
- UnknownHostException - if IP address is of illegal length
Since: 1.4

publicstatic InetAddress getByAddress (String host, byte[] addr) throws UnknownHostException

Create an InetAddress based on the provided host name and IP address No name service is checked for the validity of the address.

publicstatic InetAddress getByName (String host) throws UnknownHostException

Determines the IP address of a host, given the host's name.

The host name can either be a machine name, such as "java.sun.com", or a textual representation of its IP address. If a literal IP address is supplied, only the validity of the address format is checked.

For host specified in literal IPv6 address, either the form defined in RFC 2732 or the literal IPv6 address format defined in RFC 2373 is accepted. IPv6 scoped addresses are also supported. See here for a description of IPv6 scoped addresses.

If the host is null then an InetAddress representing an address of the loopback interface is returned. See RFC 3330 section 2 and RFC 2373 section 2.5.3.

Returns: an IP address for the given host name.
Parameters:
- host - the specified host, or null.
Throws:
- UnknownHostException - if no IP address for the host could be found, or if a scope_id was specified for a global IPv6 address.
- SecurityException - if a security manager exists and its checkConnect method doesn't allow the operation

public String getCanonicalHostName ()

Gets the fully qualified domain name for this IP address.

public String getHostAddress ()

Returns the IP address string in textual presentation.

public String getHostName ()

Gets the host name for this IP address.

pack-private String getHostName (boolean check)

Returns the hostname for this address.

publicstatic InetAddress getLocalHost () throws UnknownHostException

Returns the local host.

public int hashCode ()

Returns a hashcode for this IP address.

public boolean isAnyLocalAddress ()

Utility routine to check if the InetAddress in a wildcard address.

Utility routine to check if the InetAddress in a wildcard address.
Returns: a boolean indicating if the Inetaddress is a wildcard address.
Since: 1.4

public boolean isLinkLocalAddress ()

Utility routine to check if the InetAddress is an link local address.

Utility routine to check if the InetAddress is an link local address.
Returns: a boolean indicating if the InetAddress is a link local address; or false if address is not a link local unicast address.
Since: 1.4

public boolean isLoopbackAddress ()

Utility routine to check if the InetAddress is a loopback address.

Utility routine to check if the InetAddress is a loopback address.
Returns: a boolean indicating if the InetAddress is a loopback address; or false otherwise.
Since: 1.4

public boolean isMCGlobal ()

Utility routine to check if the multicast address has global scope.

Utility routine to check if the multicast address has global scope.
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
Since: 1.4

public boolean isMCLinkLocal ()

Utility routine to check if the multicast address has link scope.

Utility routine to check if the multicast address has link scope.
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
Since: 1.4

public boolean isMCNodeLocal ()

Utility routine to check if the multicast address has node scope.

Utility routine to check if the multicast address has node scope.
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
Since: 1.4

public boolean isMCOrgLocal ()

Utility routine to check if the multicast address has organization scope.

Utility routine to check if the multicast address has organization scope.
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
Since: 1.4

public boolean isMCSiteLocal ()

Utility routine to check if the multicast address has site scope.

Utility routine to check if the multicast address has site scope.
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
Since: 1.4

public boolean isMulticastAddress ()

Utility routine to check if the InetAddress is an IP multicast address.

Utility routine to check if the InetAddress is an
IP multicast address.
Returns: a boolean indicating if the InetAddress is an IP multicast address
Since: JDK1.1

public boolean isReachable (int timeout) throws IOException

Test whether that address is reachable.

public boolean isReachable (NetworkInterface netif, int ttl, int timeout) throws IOException

Test whether that address is reachable.

public boolean isSiteLocalAddress ()

Utility routine to check if the InetAddress is a site local address.

Utility routine to check if the InetAddress is a site local address.
Returns: a boolean indicating if the InetAddress is a site local address; or false if address is not a site local unicast address.
Since: 1.4

pack-privatestatic Object loadImpl (String implName)

public String toString ()

Converts this IP address to a String.

Converts this IP address to a String. The
string returned is of the form: hostname / literal IP
address.

If the host name is unresolved, no reverse name service loopup
is performed. The hostname part will be represented by an empty string.
Returns: a string representation of this IP address.