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From "Aaron Smuts (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JCS-68) Admin.jsp on remote cache server does not broadcast removes - patch
Date Wed, 02 Sep 2009 18:10:32 GMT

    [ https://issues.apache.org/jira/browse/JCS-68?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12750574#action_12750574
] 

Aaron Smuts commented on JCS-68:
--------------------------------

Yes.  We can restrict the constructor (if needed) and not the class.

> Admin.jsp on remote cache server does not broadcast removes - patch
> -------------------------------------------------------------------
>
>                 Key: JCS-68
>                 URL: https://issues.apache.org/jira/browse/JCS-68
>             Project: JCS
>          Issue Type: Bug
>          Components: RMI Remote Cache
>    Affects Versions: jcs-1.3, jcs-1.4-dev
>         Environment: All
>            Reporter: Niall Gallagher
>            Assignee: Aaron Smuts
>            Priority: Minor
>   Original Estimate: 0.5h
>  Remaining Estimate: 0.5h
>
> We'd like to contribute some patches to fix an issue with the JCSAdmin.jsp when it's
used on a JCS remote cache server.
> We use this JSP on our remote cache server. This allows us to browse the objects stored
in our distributed cache (i.e. uploaded by the client servers), and allows us to remove arbitrary
objects from the distributed cache by clicking 'remove' next to the key of the relevant object
displayed on the JSP.
> The issue is: when we use the unmodified version of the code to remove an object, the
object is successfully removed from the JCS remote server, but the 'remove' event for that
object is not broadcast to all client machines. Client machines which start up after we remove
the object get 'null' when they try to retrieve the object (the desired behaviour). However
client machines which were already running and using this object continue to see the object
in their view of the cache.
> This problem occurs because the JCSAdminBean (used by this JSP) calls the wrong API in
JCS to remove objects from the cache when it's running on the remote cache server. It calls
the CompositeCache API, which is intended for use client-side only.
> Our patches update JCSAdminBean to call this same API when its running on a client machine,
BUT if it's running on a machine on which the JCS remote server is enabled, it calls the RemoteCacheServer
API instead.
> The fix involves replacing 3 methods in org.apache.jcs.admin.JCSAdminBean as follows:
>     /**
>      * Clears all regions in the cache.
>      * <p/>
>      * If this class is running within a remote cache server, clears all regions via
the <code>RemoteCacheServer</code>
>      * API, so that removes will be broadcast to client machines. Otherwise clears all
regions in the cache directly via
>      * the usual cache API.
>      */
>     public void clearAllRegions() throws IOException {
>         if (RemoteCacheServerFactory.getRemoteCacheServer() == null) {
>             // Not running in a remote cache server.
>             // Remove objects from the cache directly, as no need to broadcast removes
to client machines...
>             String[] names = cacheHub.getCacheNames();
>             for (int i = 0; i < names.length; i++) {
>                 cacheHub.getCache(names[i]).removeAll();
>             }
>         }
>         else {
>             // Running in a remote cache server.
>             // Remove objects via the RemoteCacheServer API, so that removes will be
broadcast to client machines...
>             try {
>                 String[] cacheNames = CompositeCacheManager.getInstance().getCacheNames();
>                 // Call remoteCacheServer.removeAll(String) for each cacheName...
>                 // Note: We must do this using reflection to bypass its package-private
access...
>                 Object remoteCacheServerObject = RemoteCacheServerFactory.getRemoteCacheServer();
>                 Method removeAllMethod = remoteCacheServerObject.getClass().getMethod("removeAll",
new Class[]{String.class});
>                 boolean previouslyAccessibility = removeAllMethod.isAccessible();
>                 removeAllMethod.setAccessible(true);
>                 for (int i = 0; i < cacheNames.length; i++) {
>                     String cacheName = cacheNames[i];
>                     removeAllMethod.invoke(remoteCacheServerObject, new Object[]{cacheName});
>                 }
>                 removeAllMethod.setAccessible(previouslyAccessibility);
>             }
>             catch (Exception e) {
>                 throw new IllegalStateException("Failed to remove all elements from all
cache regions: " + e, e);
>             }
>         }
>     }
>     /**
>      * Clears a particular cache region.
>      * <p/>
>      * If this class is running within a remote cache server, clears the region via the
<code>RemoteCacheServer</code>
>      * API, so that removes will be broadcast to client machines. Otherwise clears the
region directly via the usual
>      * cache API.
>      */
>     public void clearRegion(String cacheName) throws IOException {
>         if (cacheName == null) {
>             throw new IllegalArgumentException("The cache name specified was null.");
>         }
>         if (RemoteCacheServerFactory.getRemoteCacheServer() == null) {
>             // Not running in a remote cache server.
>             // Remove objects from the cache directly, as no need to broadcast removes
to client machines...
>             cacheHub.getCache(cacheName).removeAll();
>         }
>         else {
>             // Running in a remote cache server.
>             // Remove objects via the RemoteCacheServer API, so that removes will be
broadcast to client machines...
>             try {
>                 // Call remoteCacheServer.removeAll(String)...
>                 // Note: We must do this using reflection to bypass its package-private
access...
>                 Object remoteCacheServerObject = RemoteCacheServerFactory.getRemoteCacheServer();
>                 Method removeAllMethod = remoteCacheServerObject.getClass().getMethod("removeAll",
new Class[]{String.class});
>                 boolean previouslyAccessibility = removeAllMethod.isAccessible();
>                 removeAllMethod.setAccessible(true);
>                 removeAllMethod.invoke(remoteCacheServerObject, new Object[]{cacheName});
>                 removeAllMethod.setAccessible(previouslyAccessibility);
>             }
>             catch (Exception e) {
>                 throw new IllegalStateException("Failed to remove all elements from cache
region [" + cacheName + "]: " + e, e);
>             }
>         }
>     }
>     /**
>      * Removes a particular item from a particular region.
>      * <p/>
>      * If this class is running within a remote cache server, removes the item via the
<code>RemoteCacheServer</code>
>      * API, so that removes will be broadcast to client machines. Otherwise clears the
region directly via the usual
>      * cache API.
>      *
>      * @param cacheName
>      * @param key
>      *
>      * @throws IOException
>      */
>     public void removeItem(String cacheName, String key) throws IOException {
>         if (cacheName == null) {
>             throw new IllegalArgumentException("The cache name specified was null.");
>         }
>         if (key == null) {
>             throw new IllegalArgumentException("The key specified was null.");
>         }
>         if (RemoteCacheServerFactory.getRemoteCacheServer() == null) {
>             // Not running in a remote cache server.
>             // Remove objects from the cache directly, as no need to broadcast removes
to client machines...
>             cacheHub.getCache(cacheName).remove(key);
>         }
>         else {
>             // Running in a remote cache server.
>             // Remove objects via the RemoteCacheServer API, so that removes will be
broadcast to client machines...
>             try {
>                 Object keyToRemove = null;
>                 CompositeCache cache = CompositeCacheManager.getInstance().getCache(cacheName);
>                 // A String key was supplied, but to remove elements via the RemoteCacheServer
API, we need the
>                 // actual key object as stored in the cache (i.e. a Serializable object).
To find the key in this form,
>                 // we iterate through all keys stored in the memory cache until we find
one whose toString matches
>                 // the string supplied...
>                 Object[] allKeysInCache = cache.getMemoryCache().getKeyArray();
>                 for (int i = 0; i < allKeysInCache.length; i++) {
>                     Object keyInCache = allKeysInCache[i];
>                     if (keyInCache.toString().equals(key)) {
>                         if (keyToRemove == null) {
>                             keyToRemove = keyInCache;
>                         }
>                         else {
>                             // A key matching the one specified was already found...
>                             throw new IllegalStateException("Unexpectedly found duplicate
keys in the cache region matching the key specified.");
>                         }
>                     }
>                 }
>                 if (keyToRemove == null) {
>                     throw new IllegalStateException("No match for this key could be found
in the set of keys retrieved from the memory cache.");
>                 }
>                 if (!(keyToRemove instanceof Serializable)) {
>                     throw new IllegalStateException("Found key [" + keyToRemove + ",
" + keyToRemove.getClass() + "] in cache matching key specified, however key found in cache
is unexpectedly not serializable.");
>                 }
>                 // At this point, we have retrieved the matching Serializable key.
>                 // Call remoteCacheServer.remove(String, Serializable)...
>                 // Note: We must fo this using reflection to bypass its package-private
access...
>                 Object remoteCacheServerObject = RemoteCacheServerFactory.getRemoteCacheServer();
>                 Method removeMethod = remoteCacheServerObject.getClass().getMethod("remove",
new Class[]{String.class, Serializable.class});
>                 boolean previouslyAccessibility = removeMethod.isAccessible();
>                 removeMethod.setAccessible(true);
>                 removeMethod.invoke(remoteCacheServerObject, new Object[]{cacheName,
keyToRemove});
>                 removeMethod.setAccessible(previouslyAccessibility);
>             }
>             catch (Exception e) {
>                 throw new IllegalStateException("Failed to remove element with key ["
+ key + ", " + key.getClass() + "] from cache region [" + cacheName + "]: " + e, e);
>             }
>         }
>     }

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