/* $Id$ */
/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.manifoldcf.authorities.mapping;
import org.apache.manifoldcf.core.interfaces.*;
import org.apache.manifoldcf.authorities.interfaces.*;
import java.util.*;
import org.apache.manifoldcf.authorities.interfaces.CacheKeyFactory;
import org.apache.manifoldcf.authorities.system.ManifoldCF;
/** Implementation of the authority connection manager functionality.
*
* <br><br>
* <b>mapconnections</b>
* <table border="1" cellpadding="3" cellspacing="0">
* <tr class="TableHeadingColor">
* <th>Field</th><th>Type</th><th>Description </th>
* <tr><td>mappingname</td><td>VARCHAR(32)</td><td>Primary Key</td></tr>
* <tr><td>description</td><td>VARCHAR(255)</td><td></td></tr>
* <tr><td>classname</td><td>VARCHAR(255)</td><td></td></tr>
* <tr><td>maxcount</td><td>BIGINT</td><td></td></tr>
* <tr><td>configxml</td><td>LONGTEXT</td><td></td></tr>
* </table>
* <br><br>
*
*/
public class MappingConnectionManager extends org.apache.manifoldcf.core.database.BaseTable implements IMappingConnectionManager
{
public static final String _rcsid = "@(#)$Id$";
// Special field suffix
private final static String passwordSuffix = "password";
protected final static String nameField = "connname"; // Changed this to work around a bug in postgresql
protected final static String descriptionField = "description";
protected final static String classNameField = "classname";
protected final static String maxCountField = "maxcount";
protected final static String configField = "configxml";
protected final static String mappingField = "mappingname";
// Cache manager
protected final ICacheManager cacheManager;
// Thread context
protected final IThreadContext threadContext;
// Lock manager
protected final ILockManager lockManager;
protected final static String mappingsLock = "MAPPINGS_LOCK";
/** Constructor.
*@param threadContext is the thread context.
*/
public MappingConnectionManager(IThreadContext threadContext, IDBInterface database)
throws ManifoldCFException
{
super(database,"mapconnections");
cacheManager = CacheManagerFactory.make(threadContext);
lockManager = LockManagerFactory.make(threadContext);
this.threadContext = threadContext;
}
/** Install the manager.
*/
@Override
public void install()
throws ManifoldCFException
{
// Always do a loop, in case upgrade needs it.
while (true)
{
Map existing = getTableSchema(null,null);
if (existing == null)
{
// Install the "objects" table.
HashMap map = new HashMap();
map.put(nameField,new ColumnDescription("VARCHAR(32)",true,false,null,null,false));
map.put(descriptionField,new ColumnDescription("VARCHAR(255)",false,true,null,null,false));
map.put(classNameField,new ColumnDescription("VARCHAR(255)",false,false,null,null,false));
map.put(maxCountField,new ColumnDescription("BIGINT",false,false,null,null,false));
map.put(configField,new ColumnDescription("LONGTEXT",false,true,null,null,false));
map.put(mappingField,new ColumnDescription("VARCHAR(32)",false,true,null,null,false));
performCreate(map,null);
}
else
{
// Upgrade code goes here
}
// Index management goes here
break;
}
}
/** Uninstall the manager.
*/
@Override
public void deinstall()
throws ManifoldCFException
{
performDrop(null);
}
/** Export configuration */
@Override
public void exportConfiguration(java.io.OutputStream os)
throws java.io.IOException, ManifoldCFException
{
// Write a version indicator
ManifoldCF.writeDword(os,1);
// Get the authority list
IMappingConnection[] list = getAllConnections();
// Write the number of authorities
ManifoldCF.writeDword(os,list.length);
// Loop through the list and write the individual mapping info
for (IMappingConnection conn : list)
{
ManifoldCF.writeString(os,conn.getName());
ManifoldCF.writeString(os,conn.getDescription());
ManifoldCF.writeString(os,conn.getClassName());
ManifoldCF.writeString(os,conn.getConfigParams().toXML());
ManifoldCF.writeDword(os,conn.getMaxConnections());
ManifoldCF.writeString(os,conn.getPrerequisiteMapping());
}
}
/** Import configuration */
@Override
public void importConfiguration(java.io.InputStream is)
throws java.io.IOException, ManifoldCFException
{
int version = ManifoldCF.readDword(is);
if (version != 1)
throw new java.io.IOException("Unknown mapping configuration version: "+Integer.toString(version));
int count = ManifoldCF.readDword(is);
for (int i = 0; i < count; i++)
{
IMappingConnection conn = create();
conn.setName(ManifoldCF.readString(is));
conn.setDescription(ManifoldCF.readString(is));
conn.setClassName(ManifoldCF.readString(is));
conn.getConfigParams().fromXML(ManifoldCF.readString(is));
conn.setMaxConnections(ManifoldCF.readDword(is));
conn.setPrerequisiteMapping(ManifoldCF.readString(is));
// Attempt to save this connection
save(conn);
}
}
/** Obtain a list of the mapping connections, ordered by name,
* excluding those that would form a prerequisite loop if chosen.
*@param startingConnectionName is the name of the connection we would be starting with.
* Pass null for all connections.
*@return an array of connection objects.
*/
public IMappingConnection[] getAllNonLoopingConnections(String startingConnectionName)
throws ManifoldCFException
{
// The point of this method is to prune connections from the list that, if a new prereq was established
// between the specified starting connection name and the listed mapping connection, a loop would develop.
IMappingConnection[] connections = getAllConnections();
// Degenerate case: no (existing) starting point.
if (startingConnectionName == null)
return connections;
List<IMappingConnection> finalConnections = new ArrayList<IMappingConnection>();
Map<String,IMappingConnection> connectionMap = new HashMap<String,IMappingConnection>();
for (IMappingConnection thisConnection : connections)
{
connectionMap.put(thisConnection.getName(), thisConnection);
}
for (IMappingConnection connectionToEvaluate : connections)
{
// The algorithm we want is as follows (from Wikipedia):
//
// L <- Empty list where we put the sorted elements
// Q <- Set of all nodes with no incoming edges
// while Q is non-empty do
// remove a node n from Q
// insert n into L
// for each node m with an edge e from n to m do
// remove edge e from the graph
// if m has no other incoming edges then
// insert m into Q
// if graph has edges then
// output error message (graph has a cycle)
// else
// output message (proposed topologically sorted order: L)
//
// In order to "remove" a link, we have to either keep a list of links we've already processed, or copy the
// structure to another one where we *can* remove links. I opt for the former.
// The second issue is that we need to generate Q up front. This is easy enough; just keep a hash of connections
// that have not been referenced (yet), and remove connections from the hash as refs are found.
// Also interesting: we don't actually need to keep L.
// The set of nodes with NO incoming edges
Set<String> Q = new HashSet<String>();
// The set of links in the graph
Set<String> links = new HashSet<String>();
// The count of the number of incoming links to a node
Map<String,Integer> incomingCount = new HashMap<String,Integer>();
for (int i = 0; i < connections.length; i++)
{
Q.add(connections[i].getName());
}
for (int i = 0; i < connections.length; i++)
{
String connectionName = connections[i].getName();
String prerequisite;
if (connectionName.equals(startingConnectionName))
{
// We ignore what's saved and instead substitute a hypothetical
// There is a "proposed" edge from the current connection, ending at connectionToEvaluate,
// so for the purpose of determining cycles, add that one too into the graph
prerequisite = connectionToEvaluate.getName();
}
else
{
// Use what's actually saved
prerequisite = connections[i].getPrerequisiteMapping();
}
if (prerequisite != null)
{
Integer x = incomingCount.get(prerequisite);
if (x == null)
incomingCount.put(prerequisite,new Integer(1));
else
incomingCount.put(prerequisite,new Integer(x.intValue()+1));
Q.remove(prerequisite);
links.add(connectionName + ":" + prerequisite);
}
}
// Now, repeat until Q is empty
while (!Q.isEmpty())
{
Iterator<String> iter = Q.iterator();
String checkConnectionName = iter.next();
Q.remove(checkConnectionName);
// Get prereqs for the connection, those that are still in the graph
String s;
if (checkConnectionName.equals(startingConnectionName))
{
// We have a hypothetical link to evaluate and remove
s = connectionToEvaluate.getName();
}
else
{
IMappingConnection sourceConnection = connectionMap.get(checkConnectionName);
s = sourceConnection.getPrerequisiteMapping();
}
if (s != null)
{
String edgeName = checkConnectionName + ":" + s;
if (links.contains(edgeName))
{
// Remove edgeName from graph
links.remove(edgeName);
// If s has no other incoming edges then insert it into Q
Integer x = incomingCount.get(s);
if (x.intValue() == 1)
{
incomingCount.remove(s);
Q.add(s);
}
else
incomingCount.put(s,new Integer(x.intValue() - 1));
}
}
}
// If there are links, we've failed to remove them and thus they must be part of cycles
if (links.isEmpty())
{
// No cycles. Add this connection to the final list.
finalConnections.add(connectionToEvaluate);
}
}
return finalConnections.toArray(new IMappingConnection[0]);
}
/** Obtain a list of the repository connections, ordered by name.
*@return an array of connection objects.
*/
@Override
public IMappingConnection[] getAllConnections()
throws ManifoldCFException
{
lockManager.enterReadLock(mappingsLock);
try
{
// Read all the tools
StringSetBuffer ssb = new StringSetBuffer();
ssb.add(getMappingConnectionsKey());
StringSet localCacheKeys = new StringSet(ssb);
IResultSet set = performQuery("SELECT "+nameField+",lower("+nameField+") AS sortfield FROM "+getTableName()+" ORDER BY sortfield ASC",null,
localCacheKeys,null);
String[] names = new String[set.getRowCount()];
for (int i = 0; i < names.length; i++)
{
IResultRow row = set.getRow(i);
names[i] = row.getValue(nameField).toString();
}
return loadMultiple(names);
}
finally
{
lockManager.leaveReadLock(mappingsLock);
}
}
/** Load a mapping connection by name.
*@param name is the name of the mapping connection.
*@return the loaded connection object, or null if not found.
*/
@Override
public IMappingConnection load(String name)
throws ManifoldCFException
{
return loadMultiple(new String[]{name})[0];
}
protected final static int FETCH_MAX = 200;
/** Load multiple mapping connections by name.
*@param names are the names to load.
*@return the loaded connection objects.
*/
@Override
public IMappingConnection[] loadMultiple(String[] names)
throws ManifoldCFException
{
IMappingConnection[] rval = new IMappingConnection[names.length];
if (names.length == 0)
return rval;
int inputIndex = 0;
int outputIndex = 0;
while (names.length - inputIndex > FETCH_MAX)
{
outputIndex = loadMultipleInternal(rval,outputIndex,names,inputIndex,FETCH_MAX);
inputIndex += FETCH_MAX;
}
loadMultipleInternal(rval,outputIndex,names,inputIndex,names.length-inputIndex);
return rval;
}
protected int loadMultipleInternal(IMappingConnection[] rval, int outputIndex, String[] fetchNames, int inputIndex, int length)
throws ManifoldCFException
{
// Build description objects
MappingConnectionDescription[] objectDescriptions = new MappingConnectionDescription[length];
StringSetBuffer ssb = new StringSetBuffer();
for (int i = 0; i < length; i++)
{
ssb.clear();
String name = fetchNames[inputIndex + i];
ssb.add(getMappingConnectionKey(name));
objectDescriptions[i] = new MappingConnectionDescription(name,new StringSet(ssb));
}
MappingConnectionExecutor exec = new MappingConnectionExecutor(this,objectDescriptions);
cacheManager.findObjectsAndExecute(objectDescriptions,null,exec,getTransactionID());
IMappingConnection[] results = exec.getResults();
for (IMappingConnection result : results)
{
rval[outputIndex++] = result;
}
return outputIndex;
}
/** Create a new repository connection object.
*@return the new object.
*/
@Override
public IMappingConnection create()
throws ManifoldCFException
{
MappingConnection rval = new MappingConnection();
return rval;
}
/** Save a mapping connection object.
*@param object is the object to save.
*@return true if the object is created, false otherwise.
*/
@Override
public boolean save(IMappingConnection object)
throws ManifoldCFException
{
StringSetBuffer ssb = new StringSetBuffer();
ssb.add(getMappingConnectionsKey());
ssb.add(getMappingConnectionKey(object.getName()));
StringSet cacheKeys = new StringSet(ssb);
while (true)
{
long sleepAmt = 0L;
try
{
lockManager.enterNonExWriteLock(mappingsLock);
try
{
ICacheHandle ch = cacheManager.enterCache(null,cacheKeys,getTransactionID());
try
{
beginTransaction();
try
{
//performLock();
ManifoldCF.noteConfigurationChange();
boolean isNew = object.getIsNew();
// See whether the instance exists
ArrayList params = new ArrayList();
String query = buildConjunctionClause(params,new ClauseDescription[]{
new UnitaryClause(nameField,object.getName())});
IResultSet set = performQuery("SELECT * FROM "+getTableName()+" WHERE "+
query+" FOR UPDATE",params,null,null);
HashMap values = new HashMap();
values.put(descriptionField,object.getDescription());
values.put(classNameField,object.getClassName());
values.put(maxCountField,new Long((long)object.getMaxConnections()));
values.put(configField,object.getConfigParams().toXML());
values.put(mappingField,object.getPrerequisiteMapping());
boolean isCreated;
if (set.getRowCount() > 0)
{
// If the object is supposedly new, it is bad that we found one that already exists.
if (isNew)
throw new ManifoldCFException("Authority connection '"+object.getName()+"' already exists");
isCreated = false;
// Update
params.clear();
query = buildConjunctionClause(params,new ClauseDescription[]{
new UnitaryClause(nameField,object.getName())});
performUpdate(values," WHERE "+query,params,null);
}
else
{
// If the object is not supposed to be new, it is bad that we did not find one.
if (!isNew)
throw new ManifoldCFException("Mapping connection '"+object.getName()+"' no longer exists");
isCreated = true;
// Insert
values.put(nameField,object.getName());
// We only need the general key because this is new.
performInsert(values,null);
}
cacheManager.invalidateKeys(ch);
return isCreated;
}
catch (ManifoldCFException e)
{
signalRollback();
throw e;
}
catch (Error e)
{
signalRollback();
throw e;
}
finally
{
endTransaction();
}
}
finally
{
cacheManager.leaveCache(ch);
}
}
finally
{
lockManager.leaveNonExWriteLock(mappingsLock);
}
}
catch (ManifoldCFException e)
{
// Is this a deadlock exception? If so, we want to try again.
if (e.getErrorCode() != ManifoldCFException.DATABASE_TRANSACTION_ABORT)
throw e;
sleepAmt = getSleepAmt();
}
finally
{
sleepFor(sleepAmt);
}
}
}
/** Delete an authority connection.
*@param name is the name of the connection to delete. If the
* name does not exist, no error is returned.
*/
@Override
public void delete(String name)
throws ManifoldCFException
{
// Grab authority connection manager handle, to check on legality of deletion.
IAuthorityConnectionManager authManager = AuthorityConnectionManagerFactory.make(threadContext);
StringSetBuffer ssb = new StringSetBuffer();
ssb.add(getMappingConnectionsKey());
ssb.add(getMappingConnectionKey(name));
StringSet cacheKeys = new StringSet(ssb);
lockManager.enterNonExWriteLock(mappingsLock);
try
{
ICacheHandle ch = cacheManager.enterCache(null,cacheKeys,getTransactionID());
try
{
beginTransaction();
try
{
// Check if any other mapping refers to this connection name
if (isReferenced(name))
throw new ManifoldCFException("Can't delete mapping connection '"+name+"': existing mapping connections refer to it");
if (authManager.isMappingReferenced(name))
throw new ManifoldCFException("Can't delete mapping connection '"+name+"': existing authority connections refer to it");
ManifoldCF.noteConfigurationChange();
ArrayList params = new ArrayList();
String query = buildConjunctionClause(params,new ClauseDescription[]{
new UnitaryClause(nameField,name)});
performDelete("WHERE "+query,params,null);
cacheManager.invalidateKeys(ch);
}
catch (ManifoldCFException e)
{
signalRollback();
throw e;
}
catch (Error e)
{
signalRollback();
throw e;
}
finally
{
endTransaction();
}
}
finally
{
cacheManager.leaveCache(ch);
}
}
finally
{
lockManager.leaveNonExWriteLock(mappingsLock);
}
}
/** Get the mapping connection name column.
*@return the name column.
*/
@Override
public String getMappingNameColumn()
{
return nameField;
}
/** Return true if the specified mapping name is referenced.
*@param mappingName is the mapping name.
*@return true if referenced, false otherwise.
*/
protected boolean isReferenced(String mappingName)
throws ManifoldCFException
{
StringSetBuffer ssb = new StringSetBuffer();
ssb.add(getMappingConnectionsKey());
StringSet localCacheKeys = new StringSet(ssb);
ArrayList params = new ArrayList();
String query = buildConjunctionClause(params,new ClauseDescription[]{
new UnitaryClause(mappingField,mappingName)});
IResultSet set = performQuery("SELECT "+nameField+" FROM "+getTableName()+" WHERE "+query,params,
localCacheKeys,null);
return set.getRowCount() > 0;
}
// Caching strategy: Individual connection descriptions are cached, and there is a global cache key for the list of
// repository connections.
/** Construct a key which represents the general list of mapping connectors.
*@return the cache key.
*/
protected static String getMappingConnectionsKey()
{
return CacheKeyFactory.makeMappingConnectionsKey();
}
/** Construct a key which represents an individual mapping connection.
*@param connectionName is the name of the connector.
*@return the cache key.
*/
protected static String getMappingConnectionKey(String connectionName)
{
return CacheKeyFactory.makeMappingConnectionKey(connectionName);
}
// Other utility methods.
/** Fetch multiple mapping connections at a single time.
*@param connectionNames are a list of connection names.
*@return the corresponding mapping connection objects.
*/
protected MappingConnection[] getMappingConnectionsMultiple(String[] connectionNames)
throws ManifoldCFException
{
MappingConnection[] rval = new MappingConnection[connectionNames.length];
HashMap returnIndex = new HashMap();
int i = 0;
while (i < connectionNames.length)
{
rval[i] = null;
returnIndex.put(connectionNames[i],new Integer(i));
i++;
}
beginTransaction();
try
{
i = 0;
ArrayList params = new ArrayList();
int j = 0;
int maxIn = maxClauseGetMappingConnectionsChunk();
while (i < connectionNames.length)
{
if (j == maxIn)
{
getMappingConnectionsChunk(rval,returnIndex,params);
params.clear();
j = 0;
}
params.add(connectionNames[i]);
i++;
j++;
}
if (j > 0)
getMappingConnectionsChunk(rval,returnIndex,params);
return rval;
}
catch (Error e)
{
signalRollback();
throw e;
}
catch (ManifoldCFException e)
{
signalRollback();
throw e;
}
finally
{
endTransaction();
}
}
/** Find the maximum number of clauses for getMappingConnectionsChunk.
*/
protected int maxClauseGetMappingConnectionsChunk()
{
return findConjunctionClauseMax(new ClauseDescription[]{});
}
/** Read a chunk of mapping connections.
*@param rval is the place to put the read policies.
*@param returnIndex is a map from the object id (resource id) and the rval index.
*@param params is the set of parameters.
*/
protected void getMappingConnectionsChunk(MappingConnection[] rval, Map returnIndex, ArrayList params)
throws ManifoldCFException
{
ArrayList list = new ArrayList();
String query = buildConjunctionClause(list,new ClauseDescription[]{
new MultiClause(nameField,params)});
IResultSet set = performQuery("SELECT * FROM "+getTableName()+" WHERE "+
query,list,null,null);
int i = 0;
while (i < set.getRowCount())
{
IResultRow row = set.getRow(i++);
String name = row.getValue(nameField).toString();
int index = ((Integer)returnIndex.get(name)).intValue();
MappingConnection rc = new MappingConnection();
rc.setIsNew(false);
rc.setName(name);
rc.setDescription((String)row.getValue(descriptionField));
rc.setClassName((String)row.getValue(classNameField));
rc.setMaxConnections((int)((Long)row.getValue(maxCountField)).longValue());
rc.setPrerequisiteMapping((String)row.getValue(mappingField));
String xml = (String)row.getValue(configField);
if (xml != null && xml.length() > 0)
rc.getConfigParams().fromXML(xml);
rval[index] = rc;
}
}
// The cached instance will be a MappingConnection. The cached version will be duplicated when it is returned
// from the cache.
//
// The description object is based completely on the name.
/** This is the object description for a mapping connection object.
*/
protected static class MappingConnectionDescription extends org.apache.manifoldcf.core.cachemanager.BaseDescription
{
protected String connectionName;
protected String criticalSectionName;
protected StringSet cacheKeys;
public MappingConnectionDescription(String connectionName, StringSet invKeys)
{
super("mappingconnectioncache");
this.connectionName = connectionName;
criticalSectionName = getClass().getName()+"-"+connectionName;
cacheKeys = invKeys;
}
public String getConnectionName()
{
return connectionName;
}
public int hashCode()
{
return connectionName.hashCode();
}
public boolean equals(Object o)
{
if (!(o instanceof MappingConnectionDescription))
return false;
MappingConnectionDescription d = (MappingConnectionDescription)o;
return d.connectionName.equals(connectionName);
}
public String getCriticalSectionName()
{
return criticalSectionName;
}
/** Get the cache keys for an object (which may or may not exist yet in
* the cache). This method is called in order for cache manager to throw the correct locks.
* @return the object's cache keys, or null if the object should not
* be cached.
*/
public StringSet getObjectKeys()
{
return cacheKeys;
}
}
/** This is the executor object for locating mapping connection objects.
*/
protected static class MappingConnectionExecutor extends org.apache.manifoldcf.core.cachemanager.ExecutorBase
{
// Member variables
protected MappingConnectionManager thisManager;
protected MappingConnection[] returnValues;
protected HashMap returnMap = new HashMap();
/** Constructor.
*@param manager is the ToolManager.
*@param objectDescriptions are the object descriptions.
*/
public MappingConnectionExecutor(MappingConnectionManager manager, MappingConnectionDescription[] objectDescriptions)
{
super();
thisManager = manager;
returnValues = new MappingConnection[objectDescriptions.length];
int i = 0;
while (i < objectDescriptions.length)
{
returnMap.put(objectDescriptions[i].getConnectionName(),new Integer(i));
i++;
}
}
/** Get the result.
*@return the looked-up or read cached instances.
*/
public MappingConnection[] getResults()
{
return returnValues;
}
/** Create a set of new objects to operate on and cache. This method is called only
* if the specified object(s) are NOT available in the cache. The specified objects
* should be created and returned; if they are not created, it means that the
* execution cannot proceed, and the execute() method will not be called.
* @param objectDescriptions is the set of unique identifier of the object.
* @return the newly created objects to cache, or null, if any object cannot be created.
* The order of the returned objects must correspond to the order of the object descriptinos.
*/
public Object[] create(ICacheDescription[] objectDescriptions) throws ManifoldCFException
{
// Turn the object descriptions into the parameters for the ToolInstance requests
String[] connectionNames = new String[objectDescriptions.length];
int i = 0;
while (i < connectionNames.length)
{
MappingConnectionDescription desc = (MappingConnectionDescription)objectDescriptions[i];
connectionNames[i] = desc.getConnectionName();
i++;
}
return thisManager.getMappingConnectionsMultiple(connectionNames);
}
/** Notify the implementing class of the existence of a cached version of the
* object. The object is passed to this method so that the execute() method below
* will have it available to operate on. This method is also called for all objects
* that are freshly created as well.
* @param objectDescription is the unique identifier of the object.
* @param cachedObject is the cached object.
*/
public void exists(ICacheDescription objectDescription, Object cachedObject) throws ManifoldCFException
{
// Cast what came in as what it really is
MappingConnectionDescription objectDesc = (MappingConnectionDescription)objectDescription;
MappingConnection ci = (MappingConnection)cachedObject;
// Duplicate it!
if (ci != null)
ci = ci.duplicate();
// In order to make the indexes line up, we need to use the hashtable built by
// the constructor.
returnValues[((Integer)returnMap.get(objectDesc.getConnectionName())).intValue()] = ci;
}
/** Perform the desired operation. This method is called after either createGetObject()
* or exists() is called for every requested object.
*/
public void execute() throws ManifoldCFException
{
// Does nothing; we only want to fetch objects in this cacher.
}
}
}