An example of how to use Guava to validate hostnames, and IP addresses.

HostIPValidation.java

/*
 * Copyright 2015-2016 Blue Lotus Software, LLC.
 *
 * Licensed 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 com.bluelotussoftware.example;

import com.google.common.net.InetAddresses;
import com.google.common.net.InternetDomainName;
import java.text.MessageFormat;

/**
 *
 * @author John Yeary <[email protected]>
 * @version 1.0
 */
public class HostIPValidation {

    public static void main(String[] args) {

        String hostname = "www.bluelotussoftware.com";

        boolean result = InternetDomainName.isValid(hostname);
        System.out.println(MessageFormat.format("Is Internet Domain Name: {0} valid? {1}", hostname, result));

        hostname = "bluelotussoftware.com";
        result = InternetDomainName.isValid(hostname);
        System.out.println(MessageFormat.format("Is Internet Domain Name: {0} valid? {1}", hostname, result));

        hostname = "bluelotussoftware";
        result = InternetDomainName.isValid(hostname);
        System.out.println(MessageFormat.format("Is Internet Domain Name: {0} valid? {1}", hostname, result));

        hostname = "256.0.0.0";
        result = InternetDomainName.isValid(hostname);
        System.out.println(MessageFormat.format("Is Internet Domain Name: {0} valid? {1}", hostname, result));

        result = InetAddresses.isInetAddress(hostname);
        System.out.println(MessageFormat.format("Is Internet Address: {0} valid? {1}", hostname, result));

        hostname = "255.255.255.0";
        result = InternetDomainName.isValid(hostname);
        System.out.println(MessageFormat.format("Is Internet Domain Name: {0} valid? {1}", hostname, result));

        result = InetAddresses.isInetAddress(hostname);
        System.out.println(MessageFormat.format("Is Internet Address: {0} valid? {1}", hostname, result));

        hostname = "_xyz.bluelotussoftware.com";
        result = InternetDomainName.isValid(hostname);
        System.out.println(MessageFormat.format("Is Internet Domain Name: {0} valid? {1}", hostname, result));
    }
}

If you're lazy, here is the output (Guava 18.0):

Is Internet Domain Name: www.bluelotussoftware.com valid? true
Is Internet Domain Name: bluelotussoftware.com valid? true
Is Internet Domain Name: bluelotussoftware valid? true
Is Internet Domain Name: 256.0.0.0 valid? false
Is Internet Address: 256.0.0.0 valid? false
Is Internet Domain Name: 255.255.255.0 valid? false
Is Internet Address: 255.255.255.0 valid? true
Is Internet Domain Name: _xyz.bluelotussoftware.com valid? false