筆記:將FileItem存放於快取

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.UUID;

import org.apache.commons.fileupload.FileItem;

/**
 * 
 * @ClassName: FileItemHelper
 * @description: 存放臨時檔案,此類僅支援檔案較小，並且存放時間極短的檔案，除此型別的檔案請存放於硬碟。
 * @author: QUINN
 * @date: 2014年6月4日 上午10:47:53
 * @version: V1.0
 * 
 */
public class FileItemHelper {

	private FileItemHelper() {

	}

	// 臨時檔案存放時間 超時4分鐘
	private final int TIMEOUT = 1000 * 60 * 4;

	private boolean isCheck = false;

	private static FileItemHelper INSTANCE;

	public static FileItemHelper getInstance() {
		if (FileItemHelper.INSTANCE == null) {
			synchronized (sync) {
				if (FileItemHelper.INSTANCE == null)
					FileItemHelper.INSTANCE = new FileItemHelper();
			}
		}
		return FileItemHelper.INSTANCE;
	}

	// 執行緒鎖物件
	private static Object sync = 1;

	public String putItem(FileItem item) {
		synchronized (sync) {
			String uuid = UUID.randomUUID().toString().replace("-", "");
			datas.put(uuid, item);
			timeouts.put(uuid, System.currentTimeMillis());
			isCheck = true;
			this.checkThread.start();
			return uuid;
		}
	}

	private Thread checkThread = new Thread() {
		public void run() {
			while (true) {
				if (isCheck)
					synchronized (sync) {
						if (timeouts.isEmpty()) {
							isCheck = false;
							break;
						}
						long now = System.currentTimeMillis();
						Iterator<String> ite = timeouts.keySet().iterator();
						while (ite.hasNext()) {
							String key = ite.next();
							long time = timeouts.get(key);
							if (now - time > TIMEOUT) {
								datas.remove(key);
								ite.remove();
							}
						}
					}

				try {
					Thread.sleep(5 * 1000);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		};
	};

	/**
	 * 
	 * 
	 * @Title: getFileItem
	 * @Description: 獲取了FileItem後會自動刪除
	 * @param: <p>
	 * @param key
	 * @param: <p>
	 * @return <p>
	 * @date: 2014年6月4日
	 * @return: FileItem
	 * @throws
	 * 
	 */
	public FileItem getFileItem(String key) {
		synchronized (sync) {
			FileItem item = this.datas.get(key);
			this.datas.remove(key);
			this.timeouts.remove(key);
			if (timeouts.isEmpty())
				this.isCheck = false;

			return item;
		}
	}

	// 存檔案
	private Map<String, FileItem> datas = new HashMap<String, FileItem>();
	// 超時時間
	private Map<String, Long> timeouts = new HashMap<String, Long>();


}