/*
* 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.commons.configuration.reloading;
import java.io.File;
import java.net.MalformedURLException;
import java.net.URL;
import org.apache.commons.configuration.io.FileHandler;
import org.apache.commons.configuration.io.FileLocatorUtils;
/**
* <p>
* A specialized implementation of {@code ReloadingDetector} which monitors a
* file specified by a {@link FileHandler}.
* </p>
* <p>
* An instance of this class is passed a {@code FileHandler} at construction
* time. Each time the {@code isReloadingRequired()} method is called, it checks
* whether the {@code FileHandler} points to a valid location. If this is the
* case, the file's last modification time is obtained and compared with the
* last stored time. If it has changed, a reload operation should be performed.
* </p>
* <p>
* Because file I/O may be expensive it is possible to configure a refresh delay
* as a time in milliseconds. This is the minimum interval between two checks.
* If the {@code isReloadingRequired()} method is called in shorter intervals,
* it does not perform a check, but directly returns <b>false</b>.
* </p>
* <p>
* To initialize an instance either {@code isReloadingRequired()} or
* {@code reloadingPerformed()} can be called. The first call of
* {@code isReloadingRequired} does not perform a check, but obtains the initial
* modification date of the monitored file. {@code reloadingPerformed()} always
* obtains the file's modification date and stores it internally.
* </p>
*
* @version $Id: FileHandlerReloadingDetector.java 1571735 2014-02-25 16:37:52Z ggregory $
* @since 2.0
*/
public class FileHandlerReloadingDetector implements ReloadingDetector
{
/** Constant for the jar URL protocol. */
private static final String JAR_PROTOCOL = "jar";
/** Constant for the default refresh delay. */
private static final int DEFAULT_REFRESH_DELAY = 5000;
/** The associated file handler. */
private final FileHandler fileHandler;
/** The refresh delay. */
private final long refreshDelay;
/** The last time the configuration file was modified. */
private long lastModified;
/** The last time the file was checked for changes. */
private long lastChecked;
/**
* Creates a new instance of {@code FileHandlerReloadingDetector} and
* initializes it with the {@code FileHandler} to monitor and the refresh
* delay. The handler is directly used, no copy is created. So it is
* possible to change the location monitored by manipulating the
* {@code FileHandler} object.
*
* @param handler the {@code FileHandler} associated with this detector (can
* be <b>null</b>)
* @param refreshDelay the refresh delay; a value of 0 means that a check is
* performed in all cases
*/
public FileHandlerReloadingDetector(FileHandler handler, long refreshDelay)
{
fileHandler = (handler != null) ? handler : new FileHandler();
this.refreshDelay = refreshDelay;
}
/**
* Creates a new instance of {@code FileHandlerReloadingDetector} and
* initializes it with the {@code FileHandler} to monitor and a default
* refresh delay.
*
* @param handler the {@code FileHandler} associated with this detector (can
* be <b>null</b>)
*/
public FileHandlerReloadingDetector(FileHandler handler)
{
this(handler, DEFAULT_REFRESH_DELAY);
}
/**
* Creates a new instance of {@code FileHandlerReloadingDetector} with an
* uninitialized {@code FileHandler} object. The file to be monitored has to
* be set later by manipulating the handler object returned by
* {@code getFileHandler()}.
*/
public FileHandlerReloadingDetector()
{
this(null);
}
/**
* Returns the {@code FileHandler} associated with this object. The
* underlying handler is directly returned, so changing its location also
* changes the file monitored by this detector.
*
* @return the associated {@code FileHandler}
*/
public FileHandler getFileHandler()
{
return fileHandler;
}
/**
* Returns the refresh delay. This is a time in milliseconds. The
* {@code isReloadingRequired()} method first checks whether the time since
* the previous check is more than this value in the past. Otherwise, no
* check is performed. This is a means to limit file I/O caused by this
* class.
*
* @return the refresh delay used by this object
*/
public long getRefreshDelay()
{
return refreshDelay;
}
/**
* {@inheritDoc} This implementation checks whether the associated
* {@link FileHandler} points to a valid file and whether the last
* modification time of this time has changed since the last check. The
* refresh delay is taken into account, too; a check is only performed if at
* least this time has passed since the last check.
*/
@Override
public boolean isReloadingRequired()
{
long now = System.currentTimeMillis();
if (now >= lastChecked + getRefreshDelay())
{
lastChecked = now;
long modified = getLastModificationDate();
if (modified > 0)
{
if (lastModified == 0)
{
// initialization
updateLastModified(modified);
}
else
{
if (modified != lastModified)
{
return true;
}
}
}
}
return false;
}
/**
* {@inheritDoc} This implementation updates the internally stored last
* modification date with the current modification date of the monitored
* file. So the next change is detected when this file is changed again.
*/
@Override
public void reloadingPerformed()
{
updateLastModified(getLastModificationDate());
}
/**
* Returns the date of the last modification of the monitored file. A return
* value of 0 indicates, that the monitored file does not exist.
*
* @return the last modification date
*/
protected long getLastModificationDate()
{
File file = getExistingFile();
return (file != null) ? file.lastModified() : 0;
}
/**
* Updates the last modification date of the monitored file. The need for a
* reload is detected only if the file's modification date is different from
* this value.
*
* @param time the new last modification date
*/
protected void updateLastModified(long time)
{
lastModified = time;
}
/**
* Returns the {@code File} object which is monitored by this object. This
* method is called every time the file's last modification time is needed.
* If it returns <b>null</b>, no check is performed. This base
* implementation obtains the {@code File} from the associated
* {@code FileHandler}. It can also deal with URLs to jar files.
*
* @return the {@code File} to be monitored (can be <b>null</b>)
*/
protected File getFile()
{
URL url = getFileHandler().getURL();
return (url != null) ? fileFromURL(url) : getFileHandler().getFile();
}
/**
* Returns the monitored {@code File} or <b>null</b> if it does not exist.
*
* @return the monitored {@code File} or <b>null</b>
*/
private File getExistingFile()
{
File file = getFile();
if (file != null && !file.exists())
{
file = null;
}
return file;
}
/**
* Helper method for transforming a URL into a file object. This method
* handles file: and jar: URLs.
*
* @param url the URL to be converted
* @return the resulting file or <b>null </b>
*/
private static File fileFromURL(URL url)
{
if (JAR_PROTOCOL.equals(url.getProtocol()))
{
String path = url.getPath();
try
{
return FileLocatorUtils.fileFromURL(new URL(path.substring(0,
path.indexOf('!'))));
}
catch (MalformedURLException mex)
{
return null;
}
}
else
{
return FileLocatorUtils.fileFromURL(url);
}
}
}