Implement MD5 cache clear routine

src/main/java/com/sheepit/client/Configuration.java

@@ -265,8 +265,7 @@ import lombok.Data;
 							if (md5_local.equals(name) == false) {
 								file.delete();
 							}
-							
+							Md5.remove(file.getAbsolutePath());
-							// TODO: remove old one
 						}
 						else {
 							file.delete();

src/main/java/com/sheepit/client/Md5.java

@@ -28,23 +28,73 @@ import java.security.DigestInputStream;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.util.HashMap;
+import java.util.Iterator;
 import java.util.Map;
+import java.util.Objects;
 
+/**
+ * Provides facilities to get an MD5 checksum and cache the results thereof
+ */
 public class Md5 {
-	private static Map<String, String> cache = new HashMap<>();
+	/**
+	 * Hashmap of all files uniqueMD5keys (last modification time + file)
+	 * and their checksums that have been calculated so far
+	 */
+	private static final Map<UniqueMD5Key, String> cache = new HashMap<>();
+	private static final int cacheCleanTrigger = 64; //After how many cache hits to check and clean the cache
+	private static int cacheHits = 0;
 	
-	// TODO: to avoid memory increase, check if files are deleted
 
+	
+	/**
+	 * Removes a file from cache
+	 * @param path Path to the file
+	 */
+	public static void remove(String path) {
+		UniqueMD5Key key = new UniqueMD5Key(path);
+		cache.remove(key); //Doesn't handle entries that the files moved or had their lastModified changed
+	}
+	
+	/**
+	 * Gets a MD5 checksum either from the cache or computes it and puts it into the cache
+	 *
+	 * @param path Path of the file to get the MD5 checksum for
+	 * @return the string The MD5 checksum
+	 */
 	public String get(String path) {
-		String key = getUniqueKey(path);
+		UniqueMD5Key key = new UniqueMD5Key(path);
 		if (cache.containsKey(key) == false) {
 			generate(path);
 		}
+		if (cacheHits >= cacheCleanTrigger){
+			cacheCheck();
+			cacheHits = 0;
+		} else {
+			cacheHits++;
+		}
 		return cache.get(key);
 	}
 	
+	/**
+	 * Checks cache for files that don't exist anymore according to cached values and removes them
+	 * Catches entries tha fall through the cracks
+	 */
+	private void cacheCheck(){
+		Iterator<Map.Entry<UniqueMD5Key, String>> it = cache.entrySet().iterator();
+		while (it.hasNext()) {
+			UniqueMD5Key itKey = (UniqueMD5Key)it.next();
+			if (itKey.exists() == false) {
+				it.remove(); //Iterator instead of foreach because we remove items
+			}
+		}
+	}
+	
+	/**
+	 * Calculates the md5 checksum for a given file
+	 * @param path Path to the file to calculate the checksum for
+	 */
 	private void generate(String path) {
-		String key = getUniqueKey(path);
+		UniqueMD5Key key = new UniqueMD5Key(path);
 		try {
 			MessageDigest md = MessageDigest.getInstance("MD5");
 			InputStream is = Files.newInputStream(Paths.get(path));
@@ -52,18 +102,65 @@ public class Md5 {
 			byte[] buffer = new byte[8192];
 			while (dis.read(buffer) > 0)
 				; // process the entire file
-			String data = Utils.convertBinaryToHex(md.digest());
+			String checksum = Utils.convertBinaryToHex(md.digest());
 			dis.close();
 			is.close();
-			cache.put(key, data);
+			cache.put(key, checksum);
 		}
 		catch (NoSuchAlgorithmException | IOException e) {
 			cache.put(key, "");
 		}
 	}
+}
 
-	private String getUniqueKey(String path) {
+/**
-		File file = new File(path);
+ * Used as key for the hashmap that is the cache
-		return Long.toString(file.lastModified()) + '_' + path;
+ * while also making it accessible to check if key is still valid
+ */
+class UniqueMD5Key {
+	private final long lastModified;
+	private final File file;
+	
+	/**
+	 * Returns a UniqueMD5Key for a given filepath
+	 * Automatically fills in lastModified time
+	 * @param filepath The filepath to the file
+	 */
+	public UniqueMD5Key(String filepath) {
+		this.file = new File(filepath);
+		this.lastModified = this.file.lastModified();
+	}
+	/**
+	 * @see File#exists()
+	 * also takes lastModified into account.
+	 */
+	public boolean exists(){
+		return file.exists() && lastModified == this.file.lastModified();
+	}
+	
+	/**
+	 * @see Object#toString()
+	 */
+	@Override public String toString() {
+		return "UniqueMD5Key{" + "lastModified=" + lastModified + ", file=" + file + '}';
+	}
+	
+	/**
+	 * @see Object#equals(Object)
+	 */
+	@Override public boolean equals(Object o) {
+		if (this == o)
+			return true;
+		if (o == null || getClass() != o.getClass())
+			return false;
+		UniqueMD5Key that = (UniqueMD5Key) o;
+		return lastModified == that.lastModified && Objects.equals(file, that.file);
+	}
+	
+	/**
+	 * @see Object#hashCode()
+	 */
+	@Override public int hashCode() {
+		return Objects.hash(lastModified, file);
 	}
 }

src/main/java/com/sheepit/client/Utils.java

@@ -237,6 +237,7 @@ public class Utils {
 			}
 		}
 		file.delete();
+		Md5.remove(file.getAbsolutePath());
 	}
 	
 	/**