Java example source code file (DnsServerAddresses.java)

This example Java source code file (DnsServerAddresses.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

arraylist, default_name_server_array, default_name_server_list, default_name_servers, defaultdnsserveraddresses, dns, dns_port, dnsserveraddresses, dnsserveraddressstream, illegalargumentexception, inetsocketaddress, list, net, network, nullpointerexception, override, reflection, util

The DnsServerAddresses.java Java example source code

/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

package io.netty.resolver.dns;

import io.netty.util.internal.InternalThreadLocalMap;
import io.netty.util.internal.UnstableApi;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;

import java.lang.reflect.Method;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;

/**
 * Provides an infinite sequence of DNS server addresses to {@link DnsNameResolver}.
 */
@UnstableApi
@SuppressWarnings("IteratorNextCanNotThrowNoSuchElementException")
public abstract class DnsServerAddresses {

    private static final InternalLogger logger = InternalLoggerFactory.getInstance(DnsServerAddresses.class);

    private static final List<InetSocketAddress> DEFAULT_NAME_SERVER_LIST;
    private static final InetSocketAddress[] DEFAULT_NAME_SERVER_ARRAY;
    private static final DnsServerAddresses DEFAULT_NAME_SERVERS;

    static {
        final int DNS_PORT = 53;
        final List<InetSocketAddress> defaultNameServers = new ArrayList(2);
        try {
            Class<?> configClass = Class.forName("sun.net.dns.ResolverConfiguration");
            Method open = configClass.getMethod("open");
            Method nameservers = configClass.getMethod("nameservers");
            Object instance = open.invoke(null);

            @SuppressWarnings("unchecked")
            final List<String> list = (List) nameservers.invoke(instance);
            for (String a: list) {
                if (a != null) {
                    defaultNameServers.add(new InetSocketAddress(InetAddress.getByName(a), DNS_PORT));
                }
            }
        } catch (Exception ignore) {
            // Failed to get the system name server list.
            // Will add the default name servers afterwards.
        }

        if (!defaultNameServers.isEmpty()) {
            if (logger.isDebugEnabled()) {
                logger.debug(
                        "Default DNS servers: {} (sun.net.dns.ResolverConfiguration)", defaultNameServers);
            }
        } else {
            Collections.addAll(
                    defaultNameServers,
                    new InetSocketAddress("8.8.8.8", DNS_PORT),
                    new InetSocketAddress("8.8.4.4", DNS_PORT));

            if (logger.isWarnEnabled()) {
                logger.warn(
                        "Default DNS servers: {} (Google Public DNS as a fallback)", defaultNameServers);
            }
        }

        DEFAULT_NAME_SERVER_LIST = Collections.unmodifiableList(defaultNameServers);
        DEFAULT_NAME_SERVER_ARRAY = defaultNameServers.toArray(new InetSocketAddress[defaultNameServers.size()]);
        DEFAULT_NAME_SERVERS = sequential(DEFAULT_NAME_SERVER_ARRAY);
    }

    /**
     * Returns the list of the system DNS server addresses. If it failed to retrieve the list of the system DNS server
     * addresses from the environment, it will return {@code "8.8.8.8"} and {@code "8.8.4.4"}, the addresses of the
     * Google public DNS servers.
     */
    public static List<InetSocketAddress> defaultAddressList() {
        return DEFAULT_NAME_SERVER_LIST;
    }

    /**
     * Returns the {@link DnsServerAddresses} that yields the system DNS server addresses sequentially. If it failed to
     * retrieve the list of the system DNS server addresses from the environment, it will use {@code "8.8.8.8"} and
     * {@code "8.8.4.4"}, the addresses of the Google public DNS servers.
     * <p>
     * This method has the same effect with the following code:
     * <pre>
     * DnsServerAddresses.sequential(DnsServerAddresses.defaultAddressList());
     * </pre>
     * </p>
     */
    public static DnsServerAddresses defaultAddresses() {
        return DEFAULT_NAME_SERVERS;
    }

    /**
     * Returns the {@link DnsServerAddresses} that yields the specified {@code addresses} sequentially. Once the
     * last address is yielded, it will start again from the first address.
     */
    public static DnsServerAddresses sequential(Iterable<? extends InetSocketAddress> addresses) {
        return sequential0(sanitize(addresses));
    }

    /**
     * Returns the {@link DnsServerAddresses} that yields the specified {@code addresses} sequentially. Once the
     * last address is yielded, it will start again from the first address.
     */
    public static DnsServerAddresses sequential(InetSocketAddress... addresses) {
        return sequential0(sanitize(addresses));
    }

    private static DnsServerAddresses sequential0(final InetSocketAddress... addresses) {
        if (addresses.length == 1) {
            return singleton(addresses[0]);
        }

        return new DefaultDnsServerAddresses("sequential", addresses) {
            @Override
            public DnsServerAddressStream stream() {
                return new SequentialDnsServerAddressStream(addresses, 0);
            }
        };
    }

    /**
     * Returns the {@link DnsServerAddresses} that yields the specified {@code address} in a shuffled order. Once all
     * addresses are yielded, the addresses are shuffled again.
     */
    public static DnsServerAddresses shuffled(Iterable<? extends InetSocketAddress> addresses) {
        return shuffled0(sanitize(addresses));
    }

    /**
     * Returns the {@link DnsServerAddresses} that yields the specified {@code addresses} in a shuffled order. Once all
     * addresses are yielded, the addresses are shuffled again.
     */
    public static DnsServerAddresses shuffled(InetSocketAddress... addresses) {
        return shuffled0(sanitize(addresses));
    }

    private static DnsServerAddresses shuffled0(final InetSocketAddress[] addresses) {
        if (addresses.length == 1) {
            return singleton(addresses[0]);
        }

        return new DefaultDnsServerAddresses("shuffled", addresses) {
            @Override
            public DnsServerAddressStream stream() {
                return new ShuffledDnsServerAddressStream(addresses);
            }
        };
    }

    /**
     * Returns the {@link DnsServerAddresses} that yields the specified {@code addresses} in a rotational sequential
     * order. It is similar to {@link #sequential(Iterable)}, but each {@link DnsServerAddressStream} starts from
     * a different starting point.  For example, the first {@link #stream()} will start from the first address, the
     * second one will start from the second address, and so on.
     */
    public static DnsServerAddresses rotational(Iterable<? extends InetSocketAddress> addresses) {
        return rotational0(sanitize(addresses));
    }

    /**
     * Returns the {@link DnsServerAddresses} that yields the specified {@code addresses} in a rotational sequential
     * order. It is similar to {@link #sequential(Iterable)}, but each {@link DnsServerAddressStream} starts from
     * a different starting point.  For example, the first {@link #stream()} will start from the first address, the
     * second one will start from the second address, and so on.
     */
    public static DnsServerAddresses rotational(InetSocketAddress... addresses) {
        return rotational0(sanitize(addresses));
    }

    private static DnsServerAddresses rotational0(final InetSocketAddress[] addresses) {
        if (addresses.length == 1) {
            return singleton(addresses[0]);
        }

        return new RotationalDnsServerAddresses(addresses);
    }

    /**
     * Returns the {@link DnsServerAddresses} that yields only a single {@code address}.
     */
    public static DnsServerAddresses singleton(final InetSocketAddress address) {
        if (address == null) {
            throw new NullPointerException("address");
        }
        if (address.isUnresolved()) {
            throw new IllegalArgumentException("cannot use an unresolved DNS server address: " + address);
        }

        return new SingletonDnsServerAddresses(address);
    }

    private static InetSocketAddress[] sanitize(Iterable<? extends InetSocketAddress> addresses) {
        if (addresses == null) {
            throw new NullPointerException("addresses");
        }

        final List<InetSocketAddress> list;
        if (addresses instanceof Collection) {
            list = new ArrayList<InetSocketAddress>(((Collection) addresses).size());
        } else {
            list = new ArrayList<InetSocketAddress>(4);
        }

        for (InetSocketAddress a : addresses) {
            if (a == null) {
                break;
            }
            if (a.isUnresolved()) {
                throw new IllegalArgumentException("cannot use an unresolved DNS server address: " + a);
            }
            list.add(a);
        }

        if (list.isEmpty()) {
            throw new IllegalArgumentException("empty addresses");
        }

        return list.toArray(new InetSocketAddress[list.size()]);
    }

    private static InetSocketAddress[] sanitize(InetSocketAddress[] addresses) {
        if (addresses == null) {
            throw new NullPointerException("addresses");
        }

        List<InetSocketAddress> list = InternalThreadLocalMap.get().arrayList(addresses.length);
        for (InetSocketAddress a: addresses) {
            if (a == null) {
                break;
            }
            if (a.isUnresolved()) {
                throw new IllegalArgumentException("cannot use an unresolved DNS server address: " + a);
            }
            list.add(a);
        }

        if (list.isEmpty()) {
            return DEFAULT_NAME_SERVER_ARRAY;
        }

        return list.toArray(new InetSocketAddress[list.size()]);
    }

    /**
     * Starts a new infinite stream of DNS server addresses. This method is invoked by {@link DnsNameResolver} on every
     * uncached {@link DnsNameResolver#resolve(String)}or {@link DnsNameResolver#resolveAll(String)}.
     */
    public abstract DnsServerAddressStream stream();
}