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A DNS library for Java and Android systems

There is a newer version: 1.1.1

/*
 * Copyright 2015-2020 the original author or authors
 *
 * This software is licensed under the Apache License, Version 2.0,
 * the GNU Lesser General Public License version 2 or later ("LGPL")
 * and the WTFPL.
 * You may choose either license to govern your use of this software only
 * upon the condition that you accept all of the terms of either
 * the Apache License 2.0, the LGPL 2.1+ or the WTFPL.
 */
package org.minidns.dnsserverlookup;

import org.minidns.util.PlatformDetection;

import java.lang.reflect.Method;
import java.net.InetAddress;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Level;

/**
 * Try to retrieve the list of DNS server by calling SystemProperties.
 */
public class AndroidUsingReflection extends AbstractDnsServerLookupMechanism {

    public static final DnsServerLookupMechanism INSTANCE = new AndroidUsingReflection();
    public static final int PRIORITY = 1000;

    protected AndroidUsingReflection() {
        super(AndroidUsingReflection.class.getSimpleName(), PRIORITY);
    }

    @Override
    public List getDnsServerAddresses() {
        try {
            Class SystemProperties =
                    Class.forName("android.os.SystemProperties");
            Method method = SystemProperties.getMethod("get",
                    new Class[] { String.class });

            ArrayList servers = new ArrayList(5);

            for (String propKey : new String[] {
                    "net.dns1", "net.dns2", "net.dns3", "net.dns4"}) {

                String value = (String) method.invoke(null, propKey);

                if (value == null) continue;
                if (value.length() == 0) continue;
                if (servers.contains(value)) continue;

                InetAddress ip = InetAddress.getByName(value);

                if (ip == null) continue;

                value = ip.getHostAddress();

                if (value == null) continue;
                if (value.length() == 0) continue;
                if (servers.contains(value)) continue;

                servers.add(value);
            }

            if (servers.size() > 0) {
                return servers;
            }
        } catch (Exception e) {
            // we might trigger some problems this way
            LOGGER.log(Level.WARNING, "Exception in findDNSByReflection", e);
        }
        return null;
    }

    @Override
    public boolean isAvailable() {
        return PlatformDetection.isAndroid();
    }

}