1 package uk.ac.ebi.intenz.webapp.utilities;
2
3 import org.apache.log4j.Logger;
4
5 import java.util.Hashtable;
6 import java.util.Enumeration;
7
8 /**
9 * This class is responsible for locking entries in process.
10 * <p/>
11 * This will be guaranteed by a synchronized Hashtable which stores the enzyme id of the entry
12 * and the users name.
13 * If a user locks an entry but quits the application without finishing its modifications, the
14 * ModificationBindingListener will take care of releasing the lock.
15 *
16 * @author Michael Darsow
17 * @version $Revision: 1.2 $ $Date: 2008/01/28 12:33:09 $
18 */
19 public class EntryLockSingleton {
20
21 private Logger LOGGER = Logger.getLogger(EntryLockSingleton.class.getName());
22
23 /**
24 * Creates a single statically availble instance of this class, which cannot be redefined.
25 */
26 private static final EntryLockSingleton instance = new EntryLockSingleton();
27
28 private static Hashtable entriesInProcess;
29
30 /**
31 * Initialises the Hashtable for storing enzyme ids of currently modified entries.
32 */
33 protected EntryLockSingleton() {
34 entriesInProcess = new Hashtable();
35 }
36
37 /**
38 * Returns the EntryLockSingleton instance.
39 *
40 * @return the one and only EntryLockSingleton instance.
41 */
42 public static EntryLockSingleton getInstance() {
43 return instance;
44 }
45
46 /**
47 * Sets a lock for an entry in process.
48 * <p/>
49 * This method is synchronized to ensure, that only one user at the time can set a lock, hence only one
50 * user is able to modify one and the same entry.
51 *
52 * @param enzymeId The enzyme id of the entry to be modified.
53 * @param user The user who is modifying the entry.
54 * @return <tt>true</tt>, if no-one else is modifying the entry.
55 */
56 public synchronized boolean setLock(String enzymeId, String user) {
57 if (entriesInProcess.containsKey(enzymeId)) {
58 if (entriesInProcess.get(enzymeId).equals(user)) {
59 return true;
60 } else {
61 return false;
62 }
63 } else
64 entriesInProcess.put(enzymeId, user);
65
66 LOGGER.debug("The enzyme (ID: " + enzymeId + ") has been locked by user " + user);
67 return true;
68 }
69
70 /**
71 * Removes a lock from an entry.
72 *
73 * @param enzymeId The enzyme id of the entry to be released.
74 */
75 public synchronized void releaseLock(String enzymeId) {
76 entriesInProcess.remove(enzymeId);
77 LOGGER.debug("The enzyme (ID: " + enzymeId + ") has been released.");
78 }
79
80 /**
81 * Removes all locks of entries modified by one and the same user.
82 * <p/>
83 * This (and the EntryLockListener) ensures that even if the user does not finish a modification
84 * and closes the browser, that all locked entries will be released.
85 *
86 * @param user The user name.
87 */
88 public synchronized void invalidateLocks(String user) {
89 LOGGER.debug("All locks are being invalidated.");
90 Enumeration keys = entriesInProcess.keys();
91 while (keys.hasMoreElements()) {
92 String key = (String) keys.nextElement();
93 String value = (String) entriesInProcess.get(key);
94 if (value.equals(user)) {
95 entriesInProcess.remove(key);
96 }
97 }
98 }
99 }