java.lang.Objectjava.net.InetAddress
All Implemented Interfaces:
java$io$Serializable
Direct Known Subclasses:
Inet6Address, Inet4Address
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).
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.
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.
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.
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.
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".
Chris
- WarthJDK1.0
- Nested Class Summary: | ||
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static final class | InetAddress.CacheEntry | Represents a cache entry |
static final class | InetAddress.Cache | A cache that manages entries based on a policy specified at creation time. |
Field Summary | ||
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static final int | IPv4 | Specify the address family: Internet Protocol, Version 4
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static final int | IPv6 | Specify the address family: Internet Protocol, Version 6
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static transient boolean | preferIPv6Address | |
String | hostName |
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int | address | Holds a 32-bit IPv4 address.
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int | family | Specifies the address family type, for instance, '1' for IPv4
addresses, and '2' for IPv6 addresses.
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static InetAddress[] | unknown_array | |
static InetAddressImpl | impl |
Constructor: |
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Method from java.net.InetAddress Summary: |
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anyLocalAddress, equals, getAddress, getAllByName, getAllByName0, getByAddress, getByAddress, getByName, getCanonicalHostName, getHostAddress, getHostName, getHostName, getLocalHost, getLoopbackAddress, hashCode, isAnyLocalAddress, isLinkLocalAddress, isLoopbackAddress, isMCGlobal, isMCLinkLocal, isMCNodeLocal, isMCOrgLocal, isMCSiteLocal, isMulticastAddress, isReachable, isReachable, isSiteLocalAddress, loadImpl, toString |
Methods from java.lang.Object: |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Method from java.net.InetAddress Detail: |
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true if and only if the argument is
not null and it represents the same IP address as
this object.
Two instances of |
InetAddress
object. The result is in network byte order: the highest order
byte of the address is in getAddress()[0] . |
The host name can either be a machine name, such as
" For 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. If there is a security manager and |
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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 |
The host name can either be a machine name, such as
" No validity checking is done on the host name either. 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 |
The host name can either be a machine name, such as
" For 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. |
If there is a security manager, this method first
calls its |
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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
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If there is a security manager, this method first
calls its |
InetAddress .
Note: The resolved address may be cached for a short period of time. If there is a security manager, its
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The InetAddress returned will represent the IPv4 loopback address, 127.0.0.1, or the IPv6 loopback address, ::1. The IPv4 loopback address returned is only one of many in the form 127.*.*.* |
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The timeout value, in milliseconds, indicates the maximum amount of time the try should take. If the operation times out before getting an answer, the host is deemed unreachable. A negative value will result in an IllegalArgumentException being thrown. |
The The timeout value, in milliseconds, indicates the maximum amount of time the try should take. If the operation times out before getting an answer, the host is deemed unreachable. A negative value will result in an IllegalArgumentException being thrown. |
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String . The
string returned is of the form: hostname / literal IP
address.
If the host name is unresolved, no reverse name service lookup
is performed. The hostname part will be represented by an empty string. |