java::net::InetAddress Class Reference

Inheritance diagram for java::net::InetAddress:

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java::net::Inet4Addressjava::net::Inet6Addressjava::lang::Object
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Collaboration diagram for java::net::InetAddress:

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java::lang::Objectjava::lang::Stringjava::lang::Interfacejava::lang::ObjectRefjava::lang::Comparable
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List of all members.


Detailed Description

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

<blockquote>
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.
</blockquote>

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 vise versa.

InetAddress Caching

The InetAddress class has a cache to store successful as well as unsuccessful host name resolutions. The positive caching is there to guard against DNS spoofing attacks; while the negative caching is used to improve performance.

By default, the result of positive host name resolutions are cached forever, because there is no general rule to decide when it is safe to remove cache entries. The result of unsuccessful host name resolution is cached for a very short period of time (10 seconds) to improve performance.

Under certain circumstances where it can be determined that DNS spoofing attacks are not possible, 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:

<blockquote>

networkaddress.cache.ttl (default: -1)
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.

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".

</blockquote>

Author:
Chris Warth Yuh-Jye Chang
Version:
1.91, 12/03/01
See also:
java.net.InetAddress::getByAddress(byte[])

java.net.InetAddress::getByAddress(java.lang.String, byte[])

java.net.InetAddress::getAllByName(java.lang.String)

java.net.InetAddress::getByName(java.lang.String)

java.net.InetAddress::getLocalHost()

Since:
JDK1.0

Public Types

enum  INET_PROTOCOL { IPv4 = 1, IPv6 }

Public Member Functions

 InetAddress ()
 Constructor for the Socket.accept() method.
virtual jboolean isMulticastAddress () const
 Utility routine to check if the InetAddress is an IP multicast address.
virtual jboolean isAnyLocalAddress () const
 Utility routine to check if the InetAddress in a wildcard address.
virtual jboolean isLoopbackAddress () const
 Utility routine to check if the InetAddress is a loopback address.
virtual jboolean isLinkLocalAddress () const
 Utility routine to check if the InetAddress is an link local address.
virtual jboolean isSiteLocalAddress () const
 Utility routine to check if the InetAddress is a site local address.
virtual jboolean isMCGlobal () const
 Utility routine to check if the multicast address has global scope.
virtual jboolean isMCNodeLocal () const
 Utility routine to check if the multicast address has node scope.
virtual jboolean isMCLinkLocal () const
 Utility routine to check if the multicast address has link scope.
virtual jboolean isMCSiteLocal () const
 Utility routine to check if the multicast address has site scope.
virtual jboolean isMCOrgLocal () const
 Utility routine to check if the multicast address has organization scope.
virtual String getHostName ()
 Gets the host name for this IP address.
virtual String getCanonicalHostName ()
 Gets the fully qualified domain name for this IP address.
virtual Array< jbytegetAddress () const
 Returns the raw IP address of this InetAddress object.
virtual String getHostAddress () const
 Returns the IP address string in textual presentation.
virtual jint getFamily () const
 Returns the address family identifier.
virtual jint hashCode () const
 Returns a hashcode for this IP address.
virtual jboolean equals (const Object &obj) const
 Compares this object against the specified object.
virtual String toString () const
 Converts this IP address to a String.

Static Public Member Functions

static Ref< InetAddressgetByAddress (const String &host, const Array< jbyte > &addr)
 Create an InetAddress based on the provided host name and IP address No name service is checked for the validity of the address.
static Ref< InetAddressgetByName (const String &host)
 Determines the IP address of a host, given the host's name.
static Array< Ref
< InetAddress > > 
getAllByName (const String &host)
 Given the name of a host, returns an array of its IP addresses, based on the configured name service on the system.
static Ref< InetAddressgetByAddress (const Array< jbyte > &addr)
 Returns an InetAddress object given the raw IP address .
static Ref< InetAddressgetLocalHost ()
 Returns the local host.
static Ref< InetAddressanyLocalAddress ()

Static Public Attributes

static jboolean preferIPv6Address
static const jboolean isIPv6Available

Protected Member Functions

 InetAddress (const String &hostName, const Array< jbyte > &addr, jint family)

Protected Attributes

String hostName
Array< jbyteaddress
 Holds a 128-bit (16 bytes) IPv6 or 32-bit (4 bytes) IPv4 address.
jint family
 Specifies the address family type, for instance, '1' for IPv4 addresses, and '2' for IPv6 addresses.

Member Enumeration Documentation

enum java::net::InetAddress::INET_PROTOCOL

Enumerator:
IPv4  Specify the address family: Internet Protocol, Version 4.

Since:
1.4
IPv6  Specify the address family: Internet Protocol, Version 6.

Since:
1.4


Constructor & Destructor Documentation

java::net::InetAddress::InetAddress (  ) 

Constructor for the Socket.accept() method.

This creates an empty InetAddress, which is filled in by the accept() method. This InetAddress, however, is not put in the address cache, since it is not created by name.

java::net::InetAddress::InetAddress ( const String hostName,
const Array< jbyte > &  addr,
jint  family 
) [protected]


Member Function Documentation

virtual jboolean java::net::InetAddress::isMulticastAddress (  )  const [virtual]

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

Reimplemented in java::net::Inet4Address, and java::net::Inet6Address.

virtual jboolean java::net::InetAddress::isAnyLocalAddress (  )  const [virtual]

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

Reimplemented in java::net::Inet4Address, and java::net::Inet6Address.

virtual jboolean java::net::InetAddress::isLoopbackAddress (  )  const [virtual]

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

Reimplemented in java::net::Inet4Address, and java::net::Inet6Address.

virtual jboolean java::net::InetAddress::isLinkLocalAddress (  )  const [virtual]

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

Reimplemented in java::net::Inet4Address, and java::net::Inet6Address.

virtual jboolean java::net::InetAddress::isSiteLocalAddress (  )  const [virtual]

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

Reimplemented in java::net::Inet4Address, and java::net::Inet6Address.

virtual jboolean java::net::InetAddress::isMCGlobal (  )  const [virtual]

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

Reimplemented in java::net::Inet4Address, and java::net::Inet6Address.

virtual jboolean java::net::InetAddress::isMCNodeLocal (  )  const [virtual]

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

Reimplemented in java::net::Inet4Address, and java::net::Inet6Address.

virtual jboolean java::net::InetAddress::isMCLinkLocal (  )  const [virtual]

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

Reimplemented in java::net::Inet4Address, and java::net::Inet6Address.

virtual jboolean java::net::InetAddress::isMCSiteLocal (  )  const [virtual]

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

Reimplemented in java::net::Inet4Address, and java::net::Inet6Address.

virtual jboolean java::net::InetAddress::isMCOrgLocal (  )  const [virtual]

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

Reimplemented in java::net::Inet4Address, and java::net::Inet6Address.

virtual String java::net::InetAddress::getHostName (  )  [virtual]

Gets the host name for this IP address.

If this InetAddress was created with a host name, this host name will be remembered and returned; otherwise, a reverse name lookup will be performed and the result will be returned based on the system configured name lookup service. If a lookup of the name service is required, call getCanonicalHostName.

If there is a security manager, its checkConnect method is first called with the hostname and -1 as its arguments to see if the operation is allowed. If the operation is not allowed, it will return the textual representation of the IP address.

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.
See also:
InetAddress::getCanonicalHostName

SecurityManager::checkConnect

virtual String java::net::InetAddress::getCanonicalHostName (  )  [virtual]

Gets the fully qualified domain name for this IP address.

Best effort method, meaning we may not be able to return the FQDN depending on the underlying system configuration.

If there is a security manager, this method first calls its checkConnect method with the hostname and -1 as its arguments to see if the calling code is allowed to know the hostname for this IP address, i.e., to connect to the host. If the operation is not allowed, it will return the textual representation of the IP address.

Returns:
the fully qualified domain name for this IP address, or if the operation is not allowed by the security check, the textual representation of the IP address.
See also:
SecurityManager::checkConnect
Since:
1.4

virtual Array<jbyte> java::net::InetAddress::getAddress (  )  const [virtual]

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.

virtual String java::net::InetAddress::getHostAddress (  )  const [virtual]

Returns the IP address string in textual presentation.

Returns:
the raw IP address in a string format.
Since:
JDK1.0.2

Reimplemented in java::net::Inet4Address, and java::net::Inet6Address.

virtual jint java::net::InetAddress::getFamily (  )  const [virtual]

Returns the address family identifier.

Returns:
the address family.

virtual jint java::net::InetAddress::hashCode (  )  const [virtual]

Returns a hashcode for this IP address.

Returns:
a hash code value for this IP address.

Reimplemented from java::lang::Object.

virtual jboolean java::net::InetAddress::equals ( const Object obj  )  const [virtual]

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.

Parameters:
obj the object to compare against.
Returns:
true if the objects are the same; false otherwise.
See also:
java.net.InetAddress::getAddress()

Reimplemented from java::lang::Object.

virtual String java::net::InetAddress::toString (  )  const [virtual]

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.

Reimplemented from java::lang::Object.

static Ref<InetAddress> java::net::InetAddress::getByAddress ( const String host,
const Array< jbyte > &  addr 
) [static]

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

The host name can either be a machine name, such as "<code>java.sun.com</code>", or a textual representation of its IP address.

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.

If addr specifies an IPv4 address an instance of Inet4Address will be returned; otherwise, an instance of Inet6Address will be returned.

IPv4 address byte array must be 4 bytes long and IPv6 byte array must be 16 bytes long

Parameters:
host the specified host
addr the raw IP address in network byte order
Returns:
an InetAddress object created from the raw IP address.
Exceptions:
UnknownHostException if IP address is of illegal length
Since:
1.4

static Ref<InetAddress> java::net::InetAddress::getByName ( const String host  )  [static]

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

The host name can either be a machine name, such as "<code>java.sun.com</code>", 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.

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

static Array<Ref<InetAddress> > java::net::InetAddress::getAllByName ( const String host  )  [static]

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

The host name can either be a machine name, such as "<code>java.sun.com</code>", 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.

If there is a security manager and host is not null and host.length() is not equal to zero, the security manager's checkConnect method is called with the hostname and -1 as its arguments to see if the operation is allowed.

Parameters:
host the name of the host.
Returns:
an array of all the IP addresses for a given host name.
Exceptions:
UnknownHostException if no IP address for the host could be found.
SecurityException if a security manager exists and its checkConnect method doesn't allow the operation.
See also:
SecurityManager::checkConnect

static Ref<InetAddress> java::net::InetAddress::getByAddress ( const Array< jbyte > &  addr  )  [static]

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

Parameters:
addr the raw IP address in network byte order
Returns:
an InetAddress object created from the raw IP address.
Exceptions:
UnknownHostException if IP address is of illegal length
Since:
1.4

static Ref<InetAddress> java::net::InetAddress::getLocalHost (  )  [static]

Returns the local host.

If there is a security manager, its checkConnect method is called with the local host name and -1 as its arguments to see if the operation is allowed. If the operation is not allowed, an InetAddress representing the loopback address is returned.

Returns:
the IP address of the local host.
Exceptions:
UnknownHostException if no IP address for the host could be found.
See also:
SecurityManager::checkConnect

static Ref<InetAddress> java::net::InetAddress::anyLocalAddress (  )  [static]


Member Data Documentation

jboolean java::net::InetAddress::preferIPv6Address [static]

const jboolean java::net::InetAddress::isIPv6Available [static]

String java::net::InetAddress::hostName [protected]

Array<jbyte> java::net::InetAddress::address [protected]

Holds a 128-bit (16 bytes) IPv6 or 32-bit (4 bytes) IPv4 address.

jint java::net::InetAddress::family [protected]

Specifies the address family type, for instance, '1' for IPv4 addresses, and '2' for IPv6 addresses.


The documentation for this class was generated from the following file:
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