Admin.jsp on remote cache server does not broadcast removes - patch
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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
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 a 3 methods in org.apache.jcs.admin.JCSAdminBean
with 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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