com.dkfqs.tools.dns

Class DNSResolver

java.lang.Object

com.dkfqs.tools.dns.DNSResolver

public class DNSResolver
extends java.lang.Object

A DNS resolver with a disabled DNS cache, which supports to set a custom resolve timeout, to set custom DNS servers, and supports to measure the resolve time at application level. Note that this class is *NOT* thread safe. In case if you are using multiple threads, then you should also use an own DNS resolver instance per thread.

See Also:

setDefaultDNSServers(String[])

Field Summary

Fields

Modifier and Type	Field and Description
static int	DEFAULT_RETRIES_PER_DNS_SERVER The default number of resolve-retries per DNS server.
static int	DEFAULT_TIMEOUT_PER_DNS_SERVER_MILLIS The default resolve-timeout which is applied per DNS server.

Constructor Summary

Constructors

Constructor and Description
DNSResolver() Create a new DNS resolver which uses the default DNS server(s).
DNSResolver(java.lang.String[] dnsServers) Create a new DNS resolver which uses custom DNS server(s).

Method Summary

Modifier and Type	Method and Description
static java.lang.String[]	getDefaultDNSServers() Get the default DNS servers which are applied for all new instances of the DNSResolver.
java.lang.String[]	getDNSServers() Get the DNS servers which are set for this DNS resolver.
static java.lang.String[]	getOSDefaultDNSServers() This method works for Java 8 only: Get the default DNS servers which are configured at operating system level.
long	getResolveTimeMillis() Get the local measured resolve time of the last performed resolve.
java.util.ArrayList<org.xbill.DNS.ARecord>	resolveRecordTypeA(java.lang.String hostname) Resolve all IPv4 addresses for a hostname.
java.util.ArrayList<org.xbill.DNS.AAAARecord>	resolveRecordTypeAAAA(java.lang.String hostname) Resolve all IPv6 addresses for a hostname.
org.xbill.DNS.CNAMERecord	resolveRecordTypeCNAME(java.lang.String hostname) Resolve a DNS canonical name for a hostname.
static void	setDefaultDNSServers(java.lang.String[] defaultDNSServers) Set or update the default DNS servers which are applied for all new instances of the DNSResolver.
void	setResolveRetriesPerDNSServer(int resolveRetries) Set the number of resolve-retries per DNS server.
void	setResolveTimeoutPerDNSServerMillis(int resolveTimeoutMillis) Set the DNS resolve timeout applied per DNS server.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEFAULT_TIMEOUT_PER_DNS_SERVER_MILLIS

public static int DEFAULT_TIMEOUT_PER_DNS_SERVER_MILLIS

The default resolve-timeout which is applied per DNS server.

See Also:

setResolveTimeoutPerDNSServerMillis(int)

DEFAULT_RETRIES_PER_DNS_SERVER

public static int DEFAULT_RETRIES_PER_DNS_SERVER

The default number of resolve-retries per DNS server.

See Also:

setResolveRetriesPerDNSServer(int)

Constructor Detail

DNSResolver

public DNSResolver()
            throws java.net.UnknownHostException

Create a new DNS resolver which uses the default DNS server(s).

Throws:

java.lang.RuntimeException - if no default DNS servers have set

java.net.UnknownHostException - if a failure occurred when initializing the resolver.

See Also:

setDefaultDNSServers(String[])

DNSResolver

public DNSResolver(java.lang.String[] dnsServers)
            throws java.net.UnknownHostException

Create a new DNS resolver which uses custom DNS server(s).

Parameters:

dnsServers - an array of custom DNS servers

Throws:

java.net.UnknownHostException - if a failure occurred when initializing the resolver.

Method Detail

setDefaultDNSServers

public static void setDefaultDNSServers(java.lang.String[] defaultDNSServers)

Set or update the default DNS servers which are applied for all new instances of the DNSResolver. Note for Java 8 only: You can pass as argument also return value of getOSDefaultDNSServers().

Parameters:

defaultDNSServers - the default DNS servers which are applied for all new instances of the DNSResolver

See Also:

getOSDefaultDNSServers()

getDefaultDNSServers

public static java.lang.String[] getDefaultDNSServers()

Get the default DNS servers which are applied for all new instances of the DNSResolver.

Returns:

the default DNS servers which are applied for all new instances of the DNSResolver, or null if no default DNS servers have set.

See Also:

setDefaultDNSServers(String[])

setResolveTimeoutPerDNSServerMillis

public void setResolveTimeoutPerDNSServerMillis(int resolveTimeoutMillis)

Set the DNS resolve timeout applied per DNS server. Example: If 3 DNS servers are set, and none of the server responds, the timeout is exceed after 3 x resolveTimeoutMillis

Parameters:

resolveTimeoutMillis - the resolve timeout in milliseconds applied per DNS server

See Also:

DNSResolveTimeoutException, DEFAULT_TIMEOUT_PER_DNS_SERVER_MILLIS

setResolveRetriesPerDNSServer

public void setResolveRetriesPerDNSServer(int resolveRetries)

Set the number of resolve-retries per DNS server.

Parameters:

resolveRetries - the number of resolve-retries per DNS

See Also:

DEFAULT_RETRIES_PER_DNS_SERVER

resolveRecordTypeA

public java.util.ArrayList<org.xbill.DNS.ARecord> resolveRecordTypeA(java.lang.String hostname)
                                                              throws org.xbill.DNS.TextParseException,
                                                                     DNSResolveTimeoutException,
                                                                     java.net.UnknownHostException

Resolve all IPv4 addresses for a hostname.

Parameters:

hostname - the hostname to resolve

Returns:

An array list of received DNS A records

Throws:

org.xbill.DNS.TextParseException - if the hostname is invalid

DNSResolveTimeoutException - if the DNS resolver timeout is exceeded

java.net.UnknownHostException - if no DNS A records are received from the DNS server(s)

java.lang.RuntimeException - if an invalid DNS record type is received from the server(s)

resolveRecordTypeAAAA

public java.util.ArrayList<org.xbill.DNS.AAAARecord> resolveRecordTypeAAAA(java.lang.String hostname)
                                                                    throws org.xbill.DNS.TextParseException,
                                                                           DNSResolveTimeoutException,
                                                                           java.net.UnknownHostException

Resolve all IPv6 addresses for a hostname.

Parameters:

hostname - the hostname to resolve

Returns:

An array list of received DNS AAAA records

Throws:

org.xbill.DNS.TextParseException - if the hostname is invalid

DNSResolveTimeoutException - if the DNS resolver timeout is exceeded

java.net.UnknownHostException - if no DNS AAAA records are received from the DNS server(s)

java.lang.RuntimeException - if an invalid DNS record type is received from the server(s)

resolveRecordTypeCNAME

public org.xbill.DNS.CNAMERecord resolveRecordTypeCNAME(java.lang.String hostname)
                                                 throws org.xbill.DNS.TextParseException,
                                                        DNSResolveTimeoutException

Resolve a DNS canonical name for a hostname.

Parameters:

hostname - the hostname to resolve

Returns:

the received DNS CNAME record, or null if no canonical name is defined for the hostname

Throws:

org.xbill.DNS.TextParseException - if the hostname is invalid

DNSResolveTimeoutException - if the DNS resolver timeout is exceeded

java.lang.RuntimeException - if an invalid DNS record type is received from the server(s)

getResolveTimeMillis

public long getResolveTimeMillis()

Get the local measured resolve time of the last performed resolve.

Returns:

the local measured resolve time in milliseconds, or -1 if no such data is available

getDNSServers

public java.lang.String[] getDNSServers()

Get the DNS servers which are set for this DNS resolver.

Returns:

the DNS servers which are set for this DNS resolver

getOSDefaultDNSServers

public static java.lang.String[] getOSDefaultDNSServers()

This method works for Java 8 only: Get the default DNS servers which are configured at operating system level.

Returns:

the default DNS servers which are configured at operating system level, or null for Java 9 or later Java versions