examcloud-components/src/main/java/cn/com/qmth/examcloud/commons/helpers/FileChangeWatchdog.java

package cn.com.qmth.examcloud.commons.helpers;

import java.io.File;

import cn.com.qmth.examcloud.commons.logging.ExamCloudLog;
import cn.com.qmth.examcloud.commons.logging.ExamCloudLogFactory;

/**
 * 文件变更监视器
 *
 * @author WANGWEI
 */
public abstract class FileChangeWatchdog extends Thread {
	/**
	 * 属性注释
	 */
	private static final ExamCloudLog LOG = ExamCloudLogFactory.getLog(FileChangeWatchdog.class);

	/**
	 * 属性注释
	 */
	static final public long DEFAULT_DELAY = 60000;

	/**
	 * 属性注释
	 */
	protected String path;

	/**
	 * 属性注释
	 */
	protected long delay = DEFAULT_DELAY;

	/**
	 * 属性注释
	 */
	protected File file;

	/**
	 * 属性注释
	 */
	protected long lastModif = 0;

	/**
	 * 属性注释
	 */
	protected boolean warnedAlready = false;

	/**
	 * 属性注释
	 */
	protected boolean interrupted = false;

	/**
	 * 构造函数
	 *
	 * @param path
	 */
	protected FileChangeWatchdog(String path) {
		super("FileChangeWatchdog");
		LOG.info("new a FileChangeWatchdog. path=" + path);
		this.path = path;
		file = new File(path);
		setDaemon(true);
		checkAndConfigure();
	}

	/**
	 * 方法注释
	 *
	 * @author WANGWEI
	 * @param delay
	 */
	public void setDelay(long delay) {
		this.delay = delay;
	}

	/**
	 * 方法注释
	 *
	 * @author WANGWEI
	 */
	abstract protected void doOnChange();

	/**
	 * 方法注释
	 *
	 * @author WANGWEI
	 */
	protected void checkAndConfigure() {
		boolean fileExists;
		try {
			fileExists = file.exists();
		} catch (SecurityException e) {
			LOG.warn("Was not allowed to read check file existance, file:[" + path + "].");
			interrupted = true;
			return;
		}

		if (fileExists) {
			long l = file.lastModified();

			if (l > lastModif) {
				lastModif = l;
				doOnChange();
				warnedAlready = false;
			}
		} else {
			if (!warnedAlready) {
				LOG.debug("[" + path + "] does not exist.");
				warnedAlready = true;
			}
		}
	}

	/*
	 * 实现
	 *
	 * @author WANGWEI
	 * 
	 * @see java.lang.Thread#run()
	 */
	@Override
	public void run() {
		while (!interrupted) {
			try {
				Thread.sleep(delay);
			} catch (InterruptedException e) {
				LOG.error("unexpected interruption.", e);
			}
			checkAndConfigure();
		}
	}
}