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InetAddress


java.net

Class InetAddress

  • All Implemented Interfaces:
    Serializable
    Direct Known Subclasses:
    Inet4Address, Inet6Address


    public class InetAddress
    extends Object
    implements Serializable
    An Internet Protocol (IP) address. This can be either an IPv4 address or an IPv6 address, and in practice you'll have an instance of either Inet4Address or Inet6Address (this class cannot be instantiated directly). Most code does not need to distinguish between the two families, and should use InetAddress.

    An InetAddress may have a hostname (accessible via getHostName), but may not, depending on how the InetAddress was created.

    IPv4 numeric address formats

    The getAllByName method accepts IPv4 addresses in the "decimal-dotted-quad" form only:

    • "1.2.3.4" - 1.2.3.4

    IPv6 numeric address formats

    The getAllByName method accepts IPv6 addresses in the following forms (this text comes from RFC 2373, which you should consult for full details of IPv6 addressing):

    • The preferred form is x:x:x:x:x:x:x:x, where the 'x's are the hexadecimal values of the eight 16-bit pieces of the address. Note that it is not necessary to write the leading zeros in an individual field, but there must be at least one numeral in every field (except for the case described in the next bullet). Examples:

           FEDC:BA98:7654:3210:FEDC:BA98:7654:3210
           1080:0:0:0:8:800:200C:417A
    • Due to some methods of allocating certain styles of IPv6 addresses, it will be common for addresses to contain long strings of zero bits. In order to make writing addresses containing zero bits easier a special syntax is available to compress the zeros. The use of "::" indicates multiple groups of 16-bits of zeros. The "::" can only appear once in an address. The "::" can also be used to compress the leading and/or trailing zeros in an address. For example the following addresses:
           1080:0:0:0:8:800:200C:417A  a unicast address
           FF01:0:0:0:0:0:0:101        a multicast address
           0:0:0:0:0:0:0:1             the loopback address
           0:0:0:0:0:0:0:0             the unspecified addresses
      may be represented as:
           1080::8:800:200C:417A       a unicast address
           FF01::101                   a multicast address
           ::1                         the loopback address
           ::                          the unspecified addresses
    • An alternative form that is sometimes more convenient when dealing with a mixed environment of IPv4 and IPv6 nodes is x:x:x:x:x:x:d.d.d.d, where the 'x's are the hexadecimal values of the six high-order 16-bit pieces of the address, and the 'd's are the decimal values of the four low-order 8-bit pieces of the address (standard IPv4 representation). Examples:

           0:0:0:0:0:0:13.1.68.3
           0:0:0:0:0:FFFF:129.144.52.38
      or in compressed form:
           ::13.1.68.3
           ::FFFF:129.144.52.38

    Scopes are given using a trailing % followed by the scope id, as in 1080::8:800:200C:417A%2 or 1080::8:800:200C:417A%en0. See RFC 4007 for more on IPv6's scoped address architecture.

    Additionally, for backwards compatibility, IPv6 addresses may be surrounded by square brackets.

    DNS caching

    In Android 4.0 (Ice Cream Sandwich) and earlier, DNS caching was performed both by InetAddress and by the C library, which meant that DNS TTLs could not be honored correctly. In later releases, caching is done solely by the C library and DNS TTLs are honored.

    See Also:
    Inet4Address, Inet6Address, Serialized Form
    • Field Summary

      Fields
      Modifier and Type Field and Description
      static InetAddress UNSPECIFIED
      Used by the DatagramSocket.disconnect implementation.
    • Method Summary

      Methods
      Modifier and Type Method and Description
      static void clearDnsCache()
      Removes all entries from the VM's DNS cache.
      boolean equals(Object obj)
      Compares this InetAddress instance against the specified address in obj.
      byte[] getAddress()
      Returns the IP address represented by this InetAddress instance as a byte array.
      static InetAddress[] getAllByName(String host)
      Gets all IP addresses associated with the given host identified by name or literal IP address.
      static InetAddress getByAddress(byte[] ipAddress)
      Equivalent to getByAddress(null, ipAddress).
      static InetAddress getByAddress(String hostName, byte[] ipAddress)
      Returns an InetAddress corresponding to the given network-order bytes ipAddress and scopeId.
      static InetAddress getByName(String host)
      Returns the address of a host according to the given host string name host.
      String getCanonicalHostName()
      Returns the fully qualified hostname corresponding to this IP address.
      String getHostAddress()
      Returns the numeric representation of this IP address (such as "127.0.0.1").
      String getHostName()
      Returns the host name corresponding to this IP address.
      static InetAddress getLocalHost()
      Returns an InetAddress for the local host if possible, or the loopback address otherwise.
      static InetAddress getLoopbackAddress()
      Returns the IPv6 loopback address ::1 or the IPv4 loopback address 127.0.0.1.
      int hashCode()
      Gets the hashcode of the represented IP address.
      boolean isAnyLocalAddress()
      Returns whether this is the IPv6 unspecified wildcard address :: or the IPv4 "any" address, 0.0.0.0.
      boolean isLinkLocalAddress()
      Returns whether this address is a link-local address or not.
      boolean isLoopbackAddress()
      Returns whether this address is a loopback address or not.
      boolean isMCGlobal()
      Returns whether this address is a global multicast address or not.
      boolean isMCLinkLocal()
      Returns whether this address is a link-local multicast address or not.
      boolean isMCNodeLocal()
      Returns whether this address is a node-local multicast address or not.
      boolean isMCOrgLocal()
      Returns whether this address is a organization-local multicast address or not.
      boolean isMCSiteLocal()
      Returns whether this address is a site-local multicast address or not.
      boolean isMulticastAddress()
      Returns whether this address is a multicast address or not.
      static boolean isNumeric(String address)
      Returns true if the string is a valid numeric IPv4 or IPv6 address (such as "192.168.0.1").
      boolean isReachable(int timeout)
      Tries to reach this InetAddress.
      boolean isReachable(NetworkInterface networkInterface, int ttl, int timeout)
      Tries to reach this InetAddress.
      boolean isSiteLocalAddress()
      Returns whether this address is a site-local address or not.
      static InetAddress parseNumericAddress(String numericAddress)
      Returns an InetAddress corresponding to the given numeric address (such as "192.168.0.1" or "2001:4860:800d::68").
      String toString()
      Returns a string containing the host name (if available) and host address.
    • Field Detail

      • UNSPECIFIED

        public static final InetAddress UNSPECIFIED
        Used by the DatagramSocket.disconnect implementation.
    • Method Detail

      • equals

        public boolean equals(Object obj)
        Compares this InetAddress instance against the specified address in obj. Two addresses are equal if their address byte arrays have the same length and if the bytes in the arrays are equal.
        Overrides:
        equals in class Object
        Parameters:
        obj - the object to be tested for equality.
        Returns:
        true if both objects are equal, false otherwise.
        See Also:
        Object.hashCode()
      • getAddress

        public byte[] getAddress()
        Returns the IP address represented by this InetAddress instance as a byte array. The elements are in network order (the highest order address byte is in the zeroth element).
        Returns:
        the address in form of a byte array.
      • getAllByName

        public static InetAddress[] getAllByName(String host)
                                          throws UnknownHostException
        Gets all IP addresses associated with the given host identified by name or literal IP address. The IP address is resolved by the configured name service. If the host name is empty or null an UnknownHostException is thrown. If the host name is a literal IP address string an array with the corresponding single InetAddress is returned.
        Parameters:
        host - the hostname or literal IP string to be resolved.
        Returns:
        the array of addresses associated with the specified host.
        Throws:
        UnknownHostException - if the address lookup fails.
      • getByName

        public static InetAddress getByName(String host)
                                     throws UnknownHostException
        Returns the address of a host according to the given host string name host. The host string may be either a machine name or a dotted string IP address. If the latter, the hostName field is determined upon demand. host can be null which means that an address of the loopback interface is returned.
        Parameters:
        host - the hostName to be resolved to an address or null.
        Returns:
        the InetAddress instance representing the host.
        Throws:
        UnknownHostException - if the address lookup fails.
      • getHostAddress

        public String getHostAddress()
        Returns the numeric representation of this IP address (such as "127.0.0.1").
      • getHostName

        public String getHostName()
        Returns the host name corresponding to this IP address. This may or may not be a fully-qualified name. If the IP address could not be resolved, the numeric representation is returned instead (see getHostAddress()).
      • getCanonicalHostName

        public String getCanonicalHostName()
        Returns the fully qualified hostname corresponding to this IP address.
      • getLocalHost

        public static InetAddress getLocalHost()
                                        throws UnknownHostException
        Returns an InetAddress for the local host if possible, or the loopback address otherwise. This method works by getting the hostname, performing a DNS lookup, and then taking the first returned address. For devices with multiple network interfaces and/or multiple addresses per interface, this does not necessarily return the InetAddress you want.

        Multiple interface/address configurations were relatively rare when this API was designed, but multiple interfaces are the default for modern mobile devices (with separate wifi and radio interfaces), and the need to support both IPv4 and IPv6 has made multiple addresses commonplace. New code should thus avoid this method except where it's basically being used to get a loopback address or equivalent.

        There are two main ways to get a more specific answer:

        • If you have a connected socket, you should probably use Socket.getLocalAddress() instead: that will give you the address that's actually in use for that connection. (It's not possible to ask the question "what local address would a connection to a given remote address use?"; you have to actually make the connection and see.)
        • For other use cases, see NetworkInterface, which lets you enumerate all available network interfaces and their addresses.

        Note that if the host doesn't have a hostname set – as Android devices typically don't – this method will effectively return the loopback address, albeit by getting the name localhost and then doing a lookup to translate that to 127.0.0.1.

        Returns:
        an InetAddress representing the local host, or the loopback address.
        Throws:
        UnknownHostException - if the address lookup fails.
      • clearDnsCache

        public static void clearDnsCache()
        Removes all entries from the VM's DNS cache. This does not affect the C library's DNS cache, nor any caching DNS servers between you and the canonical server.
      • toString

        public String toString()
        Returns a string containing the host name (if available) and host address. For example: "www.google.com/74.125.224.115" or "/127.0.0.1".

        IPv6 addresses may additionally include an interface name or scope id. For example: "www.google.com/2001:4860:4001:803::1013%eth0" or "/2001:4860:4001:803::1013%2".

        Overrides:
        toString in class Object
        Returns:
        a printable representation of this object.
      • isNumeric

        public static boolean isNumeric(String address)
        Returns true if the string is a valid numeric IPv4 or IPv6 address (such as "192.168.0.1"). This copes with all forms of address that Java supports, detailed in the InetAddress class documentation.
      • parseNumericAddress

        public static InetAddress parseNumericAddress(String numericAddress)
        Returns an InetAddress corresponding to the given numeric address (such as "192.168.0.1" or "2001:4860:800d::68"). This method will never do a DNS lookup. Non-numeric addresses are errors.
        Throws:
        IllegalArgumentException - if numericAddress is not a numeric address
      • getLoopbackAddress

        public static InetAddress getLoopbackAddress()
        Returns the IPv6 loopback address ::1 or the IPv4 loopback address 127.0.0.1.
        Since:
        1.7
      • isAnyLocalAddress

        public boolean isAnyLocalAddress()
        Returns whether this is the IPv6 unspecified wildcard address :: or the IPv4 "any" address, 0.0.0.0.
      • isLinkLocalAddress

        public boolean isLinkLocalAddress()
        Returns whether this address is a link-local address or not.

        Valid IPv6 link-local addresses have the prefix fe80::/10.

        RFC 3484 "Default Address Selection for Internet Protocol Version 6 (IPv6)" states that both IPv4 auto-configuration addresses (prefix 169.254/16) and IPv4 loopback addresses (prefix 127/8) have link-local scope, but Inet4Address only considers the auto-configuration addresses to have link-local scope. That is: the IPv4 loopback address returns false.

      • isLoopbackAddress

        public boolean isLoopbackAddress()
        Returns whether this address is a loopback address or not.

        Valid IPv4 loopback addresses have the prefix 127/8.

        The only valid IPv6 loopback address is ::1.

      • isMCGlobal

        public boolean isMCGlobal()
        Returns whether this address is a global multicast address or not.

        Valid IPv6 global multicast addresses have the prefix ffxe::/16, where x is a set of flags and the additional 112 bits make up the global multicast address space.

        Valid IPv4 global multicast addresses are the range of addresses from 224.0.1.0 to 238.255.255.255.

      • isMCLinkLocal

        public boolean isMCLinkLocal()
        Returns whether this address is a link-local multicast address or not.

        Valid IPv6 link-local multicast addresses have the prefix ffx2::/16, where x is a set of flags and the additional 112 bits make up the link-local multicast address space.

        Valid IPv4 link-local multicast addresses have the prefix 224.0.0/24.

      • isMCNodeLocal

        public boolean isMCNodeLocal()
        Returns whether this address is a node-local multicast address or not.

        Valid IPv6 node-local multicast addresses have the prefix ffx1::/16, where x is a set of flags and the additional 112 bits make up the link-local multicast address space.

        There are no valid IPv4 node-local multicast addresses.

      • isMCOrgLocal

        public boolean isMCOrgLocal()
        Returns whether this address is a organization-local multicast address or not.

        Valid IPv6 organization-local multicast addresses have the prefix ffx8::/16, where x is a set of flags and the additional 112 bits make up the link-local multicast address space.

        Valid IPv4 organization-local multicast addresses have the prefix 239.192/14.

      • isMCSiteLocal

        public boolean isMCSiteLocal()
        Returns whether this address is a site-local multicast address or not.

        Valid IPv6 site-local multicast addresses have the prefix ffx5::/16, where x is a set of flags and the additional 112 bits make up the link-local multicast address space.

        Valid IPv4 site-local multicast addresses have the prefix 239.255/16.

      • isMulticastAddress

        public boolean isMulticastAddress()
        Returns whether this address is a multicast address or not.

        Valid IPv6 multicast addresses have the prefix ff::/8.

        Valid IPv4 multicast addresses have the prefix 224/4.

      • isSiteLocalAddress

        public boolean isSiteLocalAddress()
        Returns whether this address is a site-local address or not.

        For the purposes of this method, valid IPv6 site-local addresses have the deprecated prefix fec0::/10 from RFC 1884, not the modern prefix fc00::/7 from RFC 4193.

        RFC 3484 "Default Address Selection for Internet Protocol Version 6 (IPv6)" states that IPv4 private addresses have the prefix 10/8, 172.16/12, or 192.168/16.

        Returns:
        true if this instance represents a site-local address, false otherwise.
      • isReachable

        public boolean isReachable(int timeout)
                            throws IOException
        Tries to reach this InetAddress. This method first tries to use ICMP (ICMP ECHO REQUEST), falling back to a TCP connection on port 7 (Echo) of the remote host.
        Parameters:
        timeout - timeout in milliseconds before the test fails if no connection could be established.
        Returns:
        true if this address is reachable, false otherwise.
        Throws:
        IOException - if an error occurs during an I/O operation.
        IllegalArgumentException - if timeout is less than zero.
      • isReachable

        public boolean isReachable(NetworkInterface networkInterface,
                          int ttl,
                          int timeout)
                            throws IOException
        Tries to reach this InetAddress. This method first tries to use ICMP (ICMP ECHO REQUEST), falling back to a TCP connection on port 7 (Echo) of the remote host.
        Parameters:
        networkInterface - the network interface on which to connection should be established.
        ttl - the maximum count of hops (time-to-live).
        timeout - timeout in milliseconds before the test fails if no connection could be established.
        Returns:
        true if this address is reachable, false otherwise.
        Throws:
        IOException - if an error occurs during an I/O operation.
        IllegalArgumentException - if ttl or timeout is less than zero.
      • getByAddress

        public static InetAddress getByAddress(String hostName,
                               byte[] ipAddress)
                                        throws UnknownHostException
        Returns an InetAddress corresponding to the given network-order bytes ipAddress and scopeId.

        For an IPv4 address, the byte array must be of length 4. For IPv6, the byte array must be of length 16. Any other length will cause an UnknownHostException.

        No reverse lookup is performed. The given hostName (which may be null) is associated with the new InetAddress with no validation done.

        (Note that numeric addresses such as "127.0.0.1" are names for the purposes of this API. Most callers probably want getAllByName(java.lang.String) instead.)

        Throws:
        UnknownHostException - if ipAddress is null or the wrong length.


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