src/main/java/org/apache/commons/configuration2/reloading/FileHandlerReloadingDetector.java - commons-configuration - Git at Google

 /*
  * 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.configuration2.reloading;

 import java.io.File;
 import java.net.MalformedURLException;
 import java.net.URL;

 import org.apache.commons.configuration2.io.FileHandler;
 import org.apache.commons.configuration2.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>
  *
  * @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_MILLIS = 5000;

     /**
      * 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(final URL url) {
         if (JAR_PROTOCOL.equals(url.getProtocol())) {
             final String path = url.getPath();
             try {
                 return FileLocatorUtils.fileFromURL(new URL(path.substring(0, path.indexOf('!'))));
             } catch (final MalformedURLException mex) {
                 return null;
             }
         }
         return FileLocatorUtils.fileFromURL(url);
     }

     /** The associated file handler. */
     private final FileHandler fileHandler;

     /** The refresh delay. */
     private final long refreshDelayMillis;

     /** The last time the configuration file was modified. */
     private long lastModifiedMillis;

     /** The last time the file was checked for changes. */
     private long lastCheckedMillis;

     /**
      * 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);
     }

     /**
      * 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(final FileHandler handler) {
         this(handler, DEFAULT_REFRESH_DELAY_MILLIS);
     }

     /**
      * 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 refreshDelayMillis the refresh delay; a value of 0 means that a check is performed in all cases
      */
     public FileHandlerReloadingDetector(final FileHandler handler, final long refreshDelayMillis) {
         fileHandler = handler != null ? handler : new FileHandler();
         this.refreshDelayMillis = refreshDelayMillis;
     }

     /**
      * Gets 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;
     }

     /**
      * Gets 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() {
         final URL url = getFileHandler().getURL();
         return url != null ? fileFromURL(url) : getFileHandler().getFile();
     }

     /**
      * Gets 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;
     }

     /**
      * Gets 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 in milliseconds.
      */
     protected long getLastModificationDate() {
         final File file = getExistingFile();
         return file != null ? file.lastModified() : 0;
     }

     /**
      * Gets 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 refreshDelayMillis;
     }

     /**
      * {@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() {
         final long nowMillis = System.currentTimeMillis();
         if (nowMillis >= lastCheckedMillis + getRefreshDelay()) {
             lastCheckedMillis = nowMillis;

             final long modifiedMillis = getLastModificationDate();
             if (modifiedMillis > 0) {
                 if (lastModifiedMillis != 0) {
                     return modifiedMillis != lastModifiedMillis;
                 }
                 // initialization
                 updateLastModified(modifiedMillis);
             }
         }

         return false;
     }

     /**
      * Tells this implementation that the internally stored state should be refreshed. This method is intended to be called
      * after the creation of an instance.
      */
     public void refresh() {
         updateLastModified(getLastModificationDate());
     }

     /**
      * {@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());
     }

     /**
      * 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 timeMillis the new last modification date
      */
     protected void updateLastModified(final long timeMillis) {
         lastModifiedMillis = timeMillis;
     }
 }
	/*
	* 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.configuration2.reloading;

	import java.io.File;
	import java.net.MalformedURLException;
	import java.net.URL;

	import org.apache.commons.configuration2.io.FileHandler;
	import org.apache.commons.configuration2.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>
	*
	* @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_MILLIS = 5000;

	/**
	* 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(final URL url) {
	if (JAR_PROTOCOL.equals(url.getProtocol())) {
	final String path = url.getPath();
	try {
	return FileLocatorUtils.fileFromURL(new URL(path.substring(0, path.indexOf('!'))));
	} catch (final MalformedURLException mex) {
	return null;
	}
	}
	return FileLocatorUtils.fileFromURL(url);
	}

	/** The associated file handler. */
	private final FileHandler fileHandler;

	/** The refresh delay. */
	private final long refreshDelayMillis;

	/** The last time the configuration file was modified. */
	private long lastModifiedMillis;

	/** The last time the file was checked for changes. */
	private long lastCheckedMillis;

	/**
	* 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);
	}

	/**
	* 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(final FileHandler handler) {
	this(handler, DEFAULT_REFRESH_DELAY_MILLIS);
	}

	/**
	* 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 refreshDelayMillis the refresh delay; a value of 0 means that a check is performed in all cases
	*/
	public FileHandlerReloadingDetector(final FileHandler handler, final long refreshDelayMillis) {
	fileHandler = handler != null ? handler : new FileHandler();
	this.refreshDelayMillis = refreshDelayMillis;
	}

	/**
	* Gets 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;
	}

	/**
	* Gets 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() {
	final URL url = getFileHandler().getURL();
	return url != null ? fileFromURL(url) : getFileHandler().getFile();
	}

	/**
	* Gets 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;
	}

	/**
	* Gets 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 in milliseconds.
	*/
	protected long getLastModificationDate() {
	final File file = getExistingFile();
	return file != null ? file.lastModified() : 0;
	}

	/**
	* Gets 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 refreshDelayMillis;
	}

	/**
	* {@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() {
	final long nowMillis = System.currentTimeMillis();
	if (nowMillis >= lastCheckedMillis + getRefreshDelay()) {
	lastCheckedMillis = nowMillis;

	final long modifiedMillis = getLastModificationDate();
	if (modifiedMillis > 0) {
	if (lastModifiedMillis != 0) {
	return modifiedMillis != lastModifiedMillis;
	}
	// initialization
	updateLastModified(modifiedMillis);
	}
	}

	return false;
	}

	/**
	* Tells this implementation that the internally stored state should be refreshed. This method is intended to be called
	* after the creation of an instance.
	*/
	public void refresh() {
	updateLastModified(getLastModificationDate());
	}

	/**
	* {@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());
	}

	/**
	* 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 timeMillis the new last modification date
	*/
	protected void updateLastModified(final long timeMillis) {
	lastModifiedMillis = timeMillis;
	}
	}