[JAVA API] java.net.InetAddress

java.net

Class InetAddress

• java.lang.Object
• • java.net.InetAddress

• All Implemented Interfaces:

  Serializable

  Direct Known Subclasses:

  Inet4Address, Inet6Address

  ---

  
  

  public class InetAddress
  extends Object
  implements Serializable

  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.

  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

  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".

  Since:

  JDK1.0

  See Also:

  getByAddress(byte[]), getByAddress(java.lang.String, byte[]), getAllByName(java.lang.String), getByName(java.lang.String),getLocalHost(), Serialized Form

• • Method Summary

    Methods 

    Modifier and Type	Method and Description
    boolean	equals(Object obj) Compares this object against the specified object.
    byte[]	getAddress() Returns the raw IP address of this InetAddress object.
    static InetAddress[]	getAllByName(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 InetAddress	getByAddress(byte[] addr) Returns an InetAddress object given the raw IP address .
    static InetAddress	getByAddress(String host, byte[] addr) Creates an InetAddress based on the provided host name and IP address.
    static InetAddress	getByName(String host) Determines the IP address of a host, given the host's name.
    String	getCanonicalHostName() Gets the fully qualified domain name for this IP address.
    String	getHostAddress() Returns the IP address string in textual presentation.
    String	getHostName() Gets the host name for this IP address.
    static InetAddress	getLocalHost() Returns the address of the local host.
    static InetAddress	getLoopbackAddress() Returns the loopback address.
    int	hashCode() Returns a hashcode for this IP address.
    boolean	isAnyLocalAddress() Utility routine to check if the InetAddress in a wildcard address.
    boolean	isLinkLocalAddress() Utility routine to check if the InetAddress is an link local address.
    boolean	isLoopbackAddress() Utility routine to check if the InetAddress is a loopback address.
    boolean	isMCGlobal() Utility routine to check if the multicast address has global scope.
    boolean	isMCLinkLocal() Utility routine to check if the multicast address has link scope.
    boolean	isMCNodeLocal() Utility routine to check if the multicast address has node scope.
    boolean	isMCOrgLocal() Utility routine to check if the multicast address has organization scope.
    boolean	isMCSiteLocal() Utility routine to check if the multicast address has site scope.
    boolean	isMulticastAddress() Utility routine to check if the InetAddress is an IP multicast address.
    boolean	isReachable(int timeout) Test whether that address is reachable.
    boolean	isReachable(NetworkInterface netif, int ttl, int timeout) Test whether that address is reachable.
    boolean	isSiteLocalAddress() Utility routine to check if the InetAddress is a site local address.
    String	toString() Converts this IP address to a String.

    • Methods inherited from class java.lang.Object

      clone, finalize, getClass, notify, notifyAll, wait, wait, wait