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https://issues.apache.org/jira/browse/JCS-68?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12749878#action_12749878
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Niall Gallagher commented on JCS-68:
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We had to use reflection because the RemoteCacheServer class is
package-private, the reflection bypasses the access restriction. Re: Tim's
question on the mailing list- I'm not sure but this might also be why
RemoteCacheServer is missing from the JavaDocs.
Can we make the RemoteCacheServer API public? This would allow us to call it
without reflection. In fact without reflection these patches would be fairly
simple indeed.
Here's the relevant class in trunk..
http://svn.apache.org/viewvc/jakarta/jcs/trunk/src/java/org/apache/jcs/auxiliary/remote/server/RemoteCacheServer.java?revision=727172
It looks like the required 'removeXXX' methods are already public. It's just
the class that's not public. So we just need to add the keyword 'public' to the
class declaration. Can we do this?
> 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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