Ant example source code file (IsReachable.java)

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

Java - Ant tags/keywords

both, buildexception, buildexception, default_timeout, inetaddress, method_name, net, network, no, no, object, reflection, second, string, string, url, url

The IsReachable.java source code

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF 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 org.apache.tools.ant.taskdefs.condition;

import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.Project;
import org.apache.tools.ant.ProjectComponent;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.InetAddress;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.UnknownHostException;

/**
 * Test for a host being reachable using ICMP "ping" packets & echo operations.
 * Ping packets are very reliable for assessing reachability in a LAN or WAN,
 * but they do not get through any well-configured firewall. Echo (port 7) may.
 * <p/>
 * This condition turns unknown host exceptions into false conditions. This is
 * because on a laptop, DNS is one of the first services lost when the network
 * goes; you are implicitly offline.
 * <p/>
 * If a URL is supplied instead of a host, the hostname is extracted and used in
 * the test--all other parts of the URL are discarded.
 * <p/>
 * The test may not work through firewalls; that is, something may be reachable
 * using a protocol such as HTTP, while the lower level ICMP packets get dropped
 * on the floor. Similarly, a host may be detected as reachable with ICMP, but not
 * reachable on other ports (i.e. port 80), because of firewalls.
 * <p/>
 * Requires Java1.5+ to work properly. On Java1.4 and earlier, if a hostname
 * can be resolved, the destination is assumed to be reachable.
 *
 * @since Ant 1.7
 */
public class IsReachable extends ProjectComponent implements Condition {

    private static final int SECOND = 1000; // millis per second
    private String host;
    private String url;

    /**
     * The default timeout.
     */
    public static final int DEFAULT_TIMEOUT = 30;
    private int timeout = DEFAULT_TIMEOUT;
    /**
     * Error when no hostname is defined
     */
    public static final String ERROR_NO_HOSTNAME = "No hostname defined";
    /**
     * Error when invalid timeout value is defined
     */
    public static final String ERROR_BAD_TIMEOUT = "Invalid timeout value";
    /**
     * Unknown host message is seen.
     */
    private static final String WARN_UNKNOWN_HOST = "Unknown host: ";
    /**
     * Network error message is seen.
     */
    public static final String ERROR_ON_NETWORK = "network error to ";
    /** Error message when url and host are specified. */
    public static final String ERROR_BOTH_TARGETS
        = "Both url and host have been specified";
    /** Error message when no reachably test avail. */
    public static final String MSG_NO_REACHABLE_TEST
        = "cannot do a proper reachability test on this Java version";
    /** Error message when an invalid url is used. */
    public static final String ERROR_BAD_URL = "Bad URL ";
    /** Error message when no hostname in url. */
    public static final String ERROR_NO_HOST_IN_URL = "No hostname in URL ";
    /** The method name to look for in InetAddress */
    public static final String METHOD_NAME = "isReachable";

    /**
     * Set the host to ping.
     *
     * @param host the host to ping.
     */
    public void setHost(String host) {
        this.host = host;
    }

    /**
     * Set the URL from which to extract the hostname.
     *
     * @param url a URL object.
     */
    public void setUrl(String url) {
        this.url = url;
    }

    /**
     * Set the timeout for the reachability test in seconds.
     *
     * @param timeout the timeout in seconds.
     */
    public void setTimeout(int timeout) {
        this.timeout = timeout;
    }

    /**
     * emptyness test
     *
     * @param string param to check
     *
     * @return true if it is empty
     */
    private boolean empty(String string) {
        return string == null || string.length() == 0;
    }

    private static Class[] parameterTypes = {Integer.TYPE};

    /**
     * Evaluate the condition.
     *
     * @return true if the condition is true.
     *
     * @throws org.apache.tools.ant.BuildException
     *          if an error occurs
     */
    public boolean eval() throws BuildException {
        if (empty(host) && empty(url)) {
            throw new BuildException(ERROR_NO_HOSTNAME);
        }
        if (timeout < 0) {
            throw new BuildException(ERROR_BAD_TIMEOUT);
        }
        String target = host;
        if (!empty(url)) {
            if (!empty(host)) {
                throw new BuildException(ERROR_BOTH_TARGETS);
            }
            try {
                //get the host of a url
                URL realURL = new URL(url);
                target = realURL.getHost();
                if (empty(target)) {
                    throw new BuildException(ERROR_NO_HOST_IN_URL + url);
                }
            } catch (MalformedURLException e) {
                throw new BuildException(ERROR_BAD_URL + url, e);
            }
        }
        log("Probing host " + target, Project.MSG_VERBOSE);
        InetAddress address;
        try {
            address = InetAddress.getByName(target);
        } catch (UnknownHostException e1) {
            log(WARN_UNKNOWN_HOST + target);
            return false;
        }
        log("Host address = " + address.getHostAddress(),
                Project.MSG_VERBOSE);
        boolean reachable;
        //Java1.5: reachable = address.isReachable(timeout * 1000);
        Method reachableMethod = null;
        try {
            reachableMethod = InetAddress.class.getMethod(METHOD_NAME,
                    parameterTypes);
            Object[] params = new Object[1];
            params[0] = new Integer(timeout * SECOND);
            try {
                reachable = ((Boolean) reachableMethod.invoke(address, params))
                        .booleanValue();
            } catch (IllegalAccessException e) {
                //utterly implausible, but catered for anyway
                throw new BuildException("When calling " + reachableMethod);
            } catch (InvocationTargetException e) {
                //assume this is an IOexception about un readability
                Throwable nested = e.getTargetException();
                log(ERROR_ON_NETWORK + target + ": " + nested.toString());
                //any kind of fault: not reachable.
                reachable = false;
            }
        } catch (NoSuchMethodException e) {
            //java1.4 or earlier
            log("Not found: InetAddress." + METHOD_NAME, Project.MSG_VERBOSE);
            log(MSG_NO_REACHABLE_TEST);
            reachable = true;

        }

        log("host is" + (reachable ? "" : " not") + " reachable", Project.MSG_VERBOSE);
        return reachable;
    }
}