org.dspace.utils.servicemanager.ProviderStack Maven / Gradle / Ivy
/**
* The contents of this file are subject to the license and copyright
* detailed in the LICENSE and NOTICE files at the root of the source
* tree and available online at
*
* http://www.dspace.org/license/
*/
package org.dspace.utils.servicemanager;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.NoSuchElementException;
import org.dspace.kernel.ServiceManager;
import org.dspace.kernel.mixins.OrderedService;
/**
* This class stores a list of providers in a specific order
* (determined by insertion order and the {@link OrderedService}
* settings).
*
* Should be thread safe.
*
* @author Aaron Zeckoski (azeckoski @ gmail.com)
*/
public final class ProviderStack {
protected final List> providers;
/**
* Default empty constructor.
*
* This is mostly only useful if you are planning to add new
* providers later. You should probably use the other contructors.
*/
public ProviderStack() {
providers = Collections.synchronizedList(new ArrayList>());
}
/**
* Construct a provider holder with all currently known providers of
* the given type.
*
* @param serviceManager the system service manager
* @param providerType the interface type of the providers we care about
*/
public ProviderStack(ServiceManager serviceManager, Class providerType) {
providers = Collections.synchronizedList(new ArrayList>());
List foundProviders = serviceManager.getServicesByType(providerType);
// filter out the NotProviders first
for (Iterator iterator = foundProviders.iterator(); iterator.hasNext();) {
T t = iterator.next();
if (t instanceof NotProvider) {
iterator.remove();
}
}
Collections.sort(foundProviders, new OrderedServiceComparator());
for (T t : foundProviders) {
providers.add( new ProviderHolder(t) );
}
}
/**
* Construct a provider holder with a given set of providers.
* This will maintain the current order as long as it does not
* violate the rules for {@link OrderedService}s.
*
* @param currentProviders the current set of providers to register in this stack
*/
public ProviderStack(T[] currentProviders) {
providers = Collections.synchronizedList(new ArrayList>());
ArrayList tList = new ArrayList();
// first add in the ordered ones
for (int i = 0; i < currentProviders.length; i++) {
T t = currentProviders[i];
if (t instanceof NotProvider) {
continue; // skip all the NotProviders
}
if (t instanceof OrderedService) {
tList.add( t );
}
}
// sort the ordered ones
Collections.sort(tList, new OrderedServiceComparator());
// now add in the rest in the order given
for (int i = 0; i < currentProviders.length; i++) {
T t = currentProviders[i];
if (! (t instanceof OrderedService)) {
if (t instanceof NotProvider) {
continue; // skip all the NotProviders
}
tList.add( t );
}
}
// now put these into holders
for (T t : tList) {
providers.add( new ProviderHolder(t) );
}
tList.clear();
}
/**
* Add a provider to the stack of providers.
* This will be placed at the bottom if the order is less than or
* equal to 0 or this provider is not ordered.
*
* @param provider the provider to add to the stack
* @return the position in the stack that this provider was added
*/
public int addProvider(T provider) {
if (provider == null) {
throw new IllegalArgumentException("provider to add cannot be null");
}
int position = 0;
refresh();
int providerOrder = 0;
if (provider instanceof NotProvider) {
throw new IllegalArgumentException("Cannot place anything that implements NotProvider into the provider stack, failure for: " + provider);
}
if (provider instanceof OrderedService) {
providerOrder = ((OrderedService)provider).getOrder();
}
// place at the bottom of the stack
providers.add( new ProviderHolder(provider) );
if (providerOrder > 0) {
// re-sort the providers
Collections.sort(this.providers, new ProviderStackComparator());
}
return position;
}
/**
* Remove a provider based on the position in the stack (starting at
* 0 and ending at size-1).
* @param position the position to remove the provider from
* @return true if the provider position was found and removed OR false if not found
*/
public boolean removeProvider(final int position) {
boolean removed = false;
try {
this.providers.remove(position);
removed = true;
} catch (IndexOutOfBoundsException e) {
removed = false;
}
refresh();
return removed;
}
/**
* Remove a provider by the object equality.
* @param provider the provider to remove from the stack
* @return true if the provider was found and removed OR false if not found
*/
public boolean removeProvider(T provider) {
if (provider == null) {
throw new IllegalArgumentException("provider to remove cannot be null");
}
boolean removed = false;
refresh();
for (Iterator> iterator = providers.iterator(); iterator.hasNext();) {
ProviderHolder holder = iterator.next();
T p = holder.getProvider();
if (p == null) {
iterator.remove();
} else {
if (p.equals(provider)) {
iterator.remove();
removed = true;
}
}
}
return removed;
}
/**
* Get the list of all providers currently in the stack.
*
* WARNING: this should not be held onto; it should be only used for
* iteration and then discarded.
* @return a read-only list of all providers in the stack in the correct order, highest priority first
*/
public List getProviders() {
List l = refresh();
return Collections.unmodifiableList(l);
}
/**
* This allows access to the provider holders.
* @return a read only list of the provider holders in the correct order
*/
public List> getProviderHolders() {
return Collections.unmodifiableList(providers);
}
/**
* Get the iterator of all providers currently in the stack.
* This will load up lazy so it can be held onto safely but should not be
* used more than once (i.e. only iterate over this completely once:
* stopping and continuing later is likely to produce failures).
*
* NOTE: This will attempt to iterate over all the valid providers
* in the stack, but if the provider has been garbage collected
* during the iteration then a {@link NoSuchElementException} will
* be thrown if the provider was the last one in the stack and
* next() is called. You should probably handle the exception by
* assuming this indicates all items were iterated over.
* @return an iterator over all the providers in the stack in order of priority
*/
public Iterator getIterator() {
return new Iterator() {
protected ListIterator> it = null;
public synchronized boolean hasNext() {
if (it == null) {
it = providers.listIterator();
}
return it.hasNext();
}
public synchronized T next() {
if (it == null) {
it = providers.listIterator();
}
/* get the next provider if it is not null, otherwise keep going until we find a non-null one
* or just return null if there are none left
*/
T t = null;
while (it.hasNext()) {
ProviderHolder holder = it.next();
t = holder.getProvider();
if (t != null) {
break;
}
}
if (t == null) {
throw new NoSuchElementException("No more providers remain with valid weak references");
}
return t;
}
public void remove() {
it.remove();
}
};
}
/**
* Get a provider based on the position in the stack (starting at 0
* and ending at size-1).
*
* @param position the position to check for the provider
* @return the provider from the position OR null if there is no provider at that position
*/
public T getProvider(final int position) {
T provider = null;
ProviderHolder holder = getProviderHolder(position);
if (holder != null) {
provider = holder.getProvider();
}
return provider;
}
/**
* Get the provider holder from the position in the stack if there
* is one.
*
* @param position the position to check for the provider
* @return the holder from the position OR null if there is no provider at that position
*/
public ProviderHolder getProviderHolder(final int position) {
refresh();
ProviderHolder holder;
try {
holder = providers.get(position);
} catch (IndexOutOfBoundsException e) {
// no provider at that position
holder = null;
}
return holder;
}
/**
* Check the number of current providers which are available in this
* stack.
*
* @return the total number of viable providers
*/
public int size() {
refresh();
return providers.size();
}
/**
* Delete all providers from the current provider stack.
*/
public void clear() {
providers.clear();
}
/**
* Check to make sure all providers are refreshed and any that are
* no longer valid are flushed out of the list.
* @return list of valid providers
*/
protected List refresh() {
ArrayList l = new ArrayList();
for (Iterator> iterator = providers.iterator(); iterator.hasNext();) {
ProviderHolder holder = iterator.next();
T provider = holder.getProvider();
if (provider == null) {
iterator.remove();
} else {
l.add(provider);
}
}
return l;
}
}