/**
* Scans for factory plug-ins of the given category, with guard against recursivities. The
* recursivity check make debugging easier than inspecting a {@link StackOverflowError}.
*
* @param loader The class loader to use.
* @param category The category to scan for plug-ins.
*/
private <T> void scanForPlugins(final Collection<ClassLoader> loaders, final Class<T> category) {
if (!scanningCategories.addAndCheck(category)) {
throw new RecursiveSearchException(category);
}
try {
final StringBuilder message = getLogHeader(category);
boolean newServices = false;
/*
* First, scan META-INF/services directories (the default mechanism).
*/
for (final ClassLoader loader : loaders) {
newServices |= register(lookupProviders(category, loader), category, message);
newServices |= registerFromSystemProperty(loader, category, message);
}
/*
* Next, query the user-provider iterators, if any.
*/
final FactoryIteratorProvider[] fip = FactoryIteratorProviders.getIteratorProviders();
for (int i = 0; i < fip.length; i++) {
final Iterator<T> it = fip[i].iterator(category);
if (it != null) {
newServices |= register(it, category, message);
}
}
/*
* Finally, log the list of registered factories.
*/
if (newServices) {
log("scanForPlugins", message);
}
} finally {
scanningCategories.removeAndCheck(category);
}
}
/** Returns {@code true} if the specified factory is available. */
private boolean isAvailable(final Object provider) {
if (!(provider instanceof OptionalFactory)) {
return true;
}
final OptionalFactory factory = (OptionalFactory) provider;
final Class<? extends OptionalFactory> type = factory.getClass();
if (!testingAvailability.addAndCheck(type)) {
throw new RecursiveSearchException(type);
}
try {
return factory.isAvailable();
} finally {
testingAvailability.removeAndCheck(type);
}
}
/**
* Returns {@code true} is the specified {@code factory} meets the requirements specified by a map
* of {@code hints}. This method checks only the hints; it doesn't check the {@link Filter}, the
* {@linkplain OptionalFactory#isAvailable availability} or the user-overrideable {@link
* #isAcceptable(Object, Class, Hints)} method. This method invokes itself recursively.
*
* @param factory The factory to checks.
* @param category The factory category. Usually an interface.
* @param hints The user requirements ({@code null} not allowed).
* @param alreadyDone Should be {@code null} except on recursive calls (for internal use only).
* @return {@code true} if the {@code factory} meets the hints requirements.
*/
private boolean usesAcceptableHints(
final Factory factory, final Class<?> category, final Hints hints, Set<Factory> alreadyDone) {
/*
* Ask for implementation hints with special care against infinite recursivity.
* Some implementations use deferred algorithms fetching dependencies only when
* first needed. The call to getImplementationHints() is sometime a trigger for
* fetching dependencies (in order to return accurate hints). For example the
* BufferedCoordinateOperationFactory implementation asks for an other instance
* of CoordinateOperationFactory, the instance to cache behind a buffer, which
* should not be itself. Of course BufferedCoordinateOperation will checks that
* it is not caching itself, but its test happen too late for preventing a never-
* ending loop if we don't put a 'testingHints' guard here. It is also a safety
* against broken factory implementations.
*/
if (!testingHints.addAndCheck(factory)) {
return false;
}
final Map<RenderingHints.Key, ?> implementationHints;
try {
implementationHints = Hints.stripNonKeys(factory.getImplementationHints());
} finally {
testingHints.removeAndCheck(factory);
}
if (implementationHints == null) {
// factory was bad and did not meet contract - assume it used no Hints
return true;
}
/*
* We got the implementation hints. Now tests their compatibility.
*/
Hints remaining = null;
for (final Map.Entry<?, ?> entry : implementationHints.entrySet()) {
final Object key = entry.getKey();
final Object value = entry.getValue();
final Object expected = hints.get(key);
if (expected != null) {
/*
* We have found a hint that matter. Check if the
* available factory meets the user's criterions.
*/
if (expected instanceof Class<?>) {
if (!((Class<?>) expected).isInstance(value)) {
return false;
}
} else if (expected instanceof Class<?>[]) {
final Class<?>[] types = (Class<?>[]) expected;
int i = 0;
do if (i >= types.length) return false;
while (!types[i++].isInstance(value));
} else if (!expected.equals(value)) {
return false;
}
}
/*
* Checks recursively in factory dependencies, if any. Note that the dependencies
* will be checked against a subset of user's hints. More specifically, all hints
* processed by the current pass will NOT be passed to the factories dependencies.
* This is because the same hint may appears in the "parent" factory and a "child"
* dependency with different value. For example the FORCE_LONGITUDE_FIRST_AXIS_ORDER
* hint has the value TRUE in OrderedAxisAuthorityFactory, but the later is basically
* a wrapper around the ThreadedEpsgFactory (typically), which has the value FALSE
* for the same hint.
*
* Additional note: The 'alreadyDone' set is a safety against cyclic dependencies,
* in order to protect ourself against never-ending loops. This is not the same
* kind of dependencies than 'testingHints'. It is a "factory A depends on factory
* B which depends on factory A" loop, which is legal.
*/
if (value instanceof Factory) {
final Factory dependency = (Factory) value;
if (alreadyDone == null) {
alreadyDone = new HashSet<Factory>();
}
if (!alreadyDone.contains(dependency)) {
alreadyDone.add(factory);
if (remaining == null) {
remaining = new Hints(hints);
remaining.keySet().removeAll(implementationHints.keySet());
}
final Class<?> type;
if (key instanceof Hints.Key) {
type = ((Hints.Key) key).getValueClass();
} else {
type = Factory.class; // Kind of unknown factory type...
}
// Recursive call to this method for scanning dependencies.
if (!usesAcceptableHints(dependency, type, remaining, alreadyDone)) {
return false;
}
}
}
}
return true;
}
