DiscCache implementation for com.nostra13.universalimageloader

ImageDiscCache.java

import java.io.File;
import java.util.Arrays;
import java.util.HashMap;
import com.nostra13.universalimageloader.cache.disc.DiscCache;

/**
 * DiscCache implementation that takes care that
 * the cache is not growing like cancer 
 * 
 * As argument for deleting we use the lastModified TimeStamp
 * old files get deleted
 * for every use of the file we update the lastModified
 * to the actual time so that files that are used are not killed
 * 
 * @author ligi
 *
 */
public class ImageDiscCache extends DiscCache {
	
	private final static int MAX_FILES=200;	
	private final static int CALL_EVERY=400;
	
	private int call_to_getFile_count=0;	
	
	public ImageDiscCache(File cacheDir) {
		super(cacheDir);
		checkAndDeleteFilesRun();
	}
	
	/**
	 * checks if we have to many files and if we do:
	 * remove the ones with the oldest lastMod timestamp
	 */
	private void checkAndDeleteFilesRun() {

		call_to_getFile_count=0;
		
		File[] files_in_cache=getCacheDir().listFiles();
		
		if (files_in_cache==null)
			return;
		
		if (files_in_cache.length<MAX_FILES)
			return; // not to many files nothing to do yet 
		
		HashMap <Long,File> lastMod2file=new HashMap<Long,File>();
		
		for (File act_file : files_in_cache) {
			Long key=act_file.lastModified();
			while (lastMod2file.containsKey(key))
				key++;
			lastMod2file.put(key, act_file);
		}
		
			
		
		Long[] timestamp_arr=lastMod2file.keySet().toArray(new Long[] {});
		
		Arrays.sort(timestamp_arr);
		
		for (int i=0;i<(files_in_cache.length-MAX_FILES);i++) { 
			lastMod2file.get(timestamp_arr[i]).delete();
		}
	}
	
	@Override
	public File getFile(String url) {
		String fileName = String.valueOf(url.hashCode());
		
		if ((call_to_getFile_count++)>CALL_EVERY) 
			checkAndDeleteFilesRun();

		File res=new File(getCacheDir(), fileName);
		res.setLastModified(System.currentTimeMillis()); // if the file gets used we want to keep it - no matter when it came in
                return res;
	}
}