java.lang.Object java.net.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).
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 .
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.
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:
- 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".
Method Summary | |
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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) Create an InetAddress based on the provided host name and IP address No name service is checked for the validity of the 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 local host. |
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
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 |
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clone , finalize , getClass , notify , notifyAll , wait , wait , wait |
Method Detail |
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public boolean isMulticastAddress()
public boolean isAnyLocalAddress()
public boolean isLoopbackAddress()
public boolean isLinkLocalAddress()
public boolean isSiteLocalAddress()
public boolean isMCGlobal()
public boolean isMCNodeLocal()
public boolean isMCLinkLocal()
public boolean isMCSiteLocal()
public boolean isMCOrgLocal()
public boolean isReachable (int timeout) throws IOException
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.
public boolean isReachable ( NetworkInterface netif, int ttl, int timeout) throws IOException
The network interface and ttl parameters let the caller specify which network interface the test will go through and the maximum number of hops the packets should go through. A negative value for the ttl will result in an IllegalArgumentException being thrown.
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.
public String getHostName()
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.
public String getCanonicalHostName()
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.
public byte[] getAddress()
public String getHostAddress()
public int hashCode()
public boolean equals(Object obj)
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.
public String toString()
public static InetAddress getByAddress(String host, byte[] addr) throws UnknownHostException
The host name can either be a machine name, such as "java.sun.com", or a textual representation of its IP address.
No validity checking is done on the host name either.
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
public static InetAddress getByName(String host) throws UnknownHostException
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.
public static InetAddress[] getAllByName(String host) throws UnknownHostException
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
,
address,
either the form defined in RFC 2732 or the literal IPv6 address format defined in RFC 2373 is accepted.
A literal IPv6 address may also be qualified by appending a scoped zone identifier or scope_id. The syntax and usage of scope_ids is described
here
.
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 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.
public static InetAddress getByAddress(byte[] addr) throws UnknownHostException
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
public static InetAddress getLocalHost() throws UnknownHostException
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.