/*
* Copyright (c) 2000, 2015, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package javax.imageio.spi;
import java.io.File;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.ServiceLoader;
/**
* A registry for service provider instances.
*
* <p> A <i>service</i> is a well-known set of interfaces and (usually
* abstract) classes. A <i>service provider</i> is a specific
* implementation of a service. The classes in a provider typically
* implement the interface or subclass the class defined by the
* service itself.
*
* <p> Service providers are stored in one or more <i>categories</i>,
* each of which is defined by a class of interface (described by a
* {@code Class} object) that all of its members must implement.
*
* <p>The set of categories supported is limited
* to the following standard Image I/O service types:
*
* <ul>
* <li>{@link ImageInputStreamSpi}
* <li>{@link ImageOutputStreamSpi}
* <li>{@link ImageReaderSpi}
* <li>{@link ImageTranscoderSpi}
* <li>{@link ImageWriterSpi}
* </ul>
*
* <p>An attempt to load a provider that is not a subtype of one of the
* above types will result in {@code IllegalArgumentException}. For
* a general mechanism to load service providers, see
* {@link java.util.ServiceLoader ServiceLoader}.
*
* <p> Only a single instance of a given leaf class (that is, the
* actual class returned by {@code getClass()}, as opposed to any
* inherited classes or interfaces) may be registered. That is,
* suppose that the
* {@code com.mycompany.mypkg.GreenImageReaderProvider} class
* is a subclass of {@code javax.imageio.spi.ImageReaderSpi}.
* If a {@code GreenImageReaderProvider} instance is
* registered, it will be stored in the category defined by the
* {@code ImageReaderSpi} class. If a new instance of
* {@code GreenImageReaderProvider} is registered, it will replace
* the previous instance. In practice, service provider objects are
* usually singletons so this behavior is appropriate.
*
* <p> To declare a service provider, a {@code services}
* subdirectory is placed within the {@code META-INF} directory
* that is present in every JAR file. This directory contains a file
* for each service provider interface that has one or more
* implementation classes present in the JAR file. For example, if
* the JAR file contained a class named
* {@code com.mycompany.mypkg.GreenImageReaderProvider} which implements the
* {@code javax.imageio.spi.ImageReaderSpi} interface, the JAR file
* would contain a file named: <pre>
* META-INF/services/javax.imageio.spi.ImageReaderSpi</pre>
*
* containing the line:
*
* <pre>
* com.mycompany.mypkg.GreenImageReaderProvider
* </pre>
*
* <p> The service provider classes should be to be lightweight and
* quick to load. Implementations of these interfaces should avoid
* complex dependencies on other classes and on native code. The usual
* pattern for more complex services is to register a lightweight
* proxy for the heavyweight service.
*
* <p> An application may customize the contents of a registry as it
* sees fit, so long as it has the appropriate runtime permission.
*
* <p> For more details on declaring service providers, and the JAR
* format in general, see the <a
* href="../../../../technotes/guides/jar/jar.html">
* JAR File Specification</a>.
*
* @see RegisterableService
* @see java.util.ServiceLoader
*/
public class ServiceRegistry {
// Class -> Registry
private Map<Class<?>, SubRegistry> categoryMap = new HashMap<>();
/**
* Constructs a {@code ServiceRegistry} instance with a
* set of categories taken from the {@code categories}
* argument. The categories must all be members of the set
* of service types listed in the class specification.
*
* @param categories an {@code Iterator} containing
* {@code Class} objects to be used to define categories.
*
* @exception IllegalArgumentException if
* {@code categories} is {@code null}, or if
* one of the categories is not an allowed service type.
*/
public ServiceRegistry(Iterator<Class<?>> categories) {
if (categories == null) {
throw new IllegalArgumentException("categories == null!");
}
while (categories.hasNext()) {
Class<?> category = categories.next();
checkClassAllowed(category);
SubRegistry reg = new SubRegistry(this, category);
categoryMap.put(category, reg);
}
}
/**
* Searches for implementations of a particular service class
* using the given class loader.
*
* <p>The service class must be one of the service types listed
* in the class specification. If it is not, {@code IllegalArgumentException}
* will be thrown.
*
* <p> This method transforms the name of the given service class
* into a provider-configuration filename as described in the
* class comment and then uses the {@code getResources}
* method of the given class loader to find all available files
* with that name. These files are then read and parsed to
* produce a list of provider-class names. The iterator that is
* returned uses the given class loader to look up and then
* instantiate each element of the list.
*
* <p> Because it is possible for extensions to be installed into
* a running Java virtual machine, this method may return
* different results each time it is invoked.
*
* @param providerClass a {@code Class} object indicating the
* class or interface of the service providers being detected.
*
* @param loader the class loader to be used to load
* provider-configuration files and instantiate provider classes,
* or {@code null} if the system class loader (or, failing that
* the bootstrap class loader) is to be used.
*
* @param <T> the type of the providerClass.
*
* @return An {@code Iterator} that yields provider objects
* for the given service, in some arbitrary order. The iterator
* will throw an {@code Error} if a provider-configuration
* file violates the specified format or if a provider class
* cannot be found and instantiated.
*
* @exception IllegalArgumentException if
* {@code providerClass} is {@code null}, or if it is
* not one of the allowed service types.
*/
public static <T> Iterator<T> lookupProviders(Class<T> providerClass,
ClassLoader loader)
{
if (providerClass == null) {
throw new IllegalArgumentException("providerClass == null!");
}
checkClassAllowed(providerClass);
return ServiceLoader.load(providerClass, loader).iterator();
}
/**
* Locates and incrementally instantiates the available providers
* of a given service using the context class loader. This
* convenience method is equivalent to:
*
* <pre>
* ClassLoader cl = Thread.currentThread().getContextClassLoader();
* return Service.providers(service, cl);
* </pre>
*
* <p>The service class must be one of the service types listed
* in the class specification. If it is not, {@code IllegalArgumentException}
* will be thrown.
*
* @param providerClass a {@code Class} object indicating the
* class or interface of the service providers being detected.
*
* @param <T> the type of the providerClass.
*
* @return An {@code Iterator} that yields provider objects
* for the given service, in some arbitrary order. The iterator
* will throw an {@code Error} if a provider-configuration
* file violates the specified format or if a provider class
* cannot be found and instantiated.
*
* @exception IllegalArgumentException if
* {@code providerClass} is {@code null}, or if it is
* not one of the allowed service types.
*/
public static <T> Iterator<T> lookupProviders(Class<T> providerClass) {
if (providerClass == null) {
throw new IllegalArgumentException("providerClass == null!");
}
checkClassAllowed(providerClass);
return ServiceLoader.load(providerClass).iterator();
}
/**
* Returns an {@code Iterator} of {@code Class} objects
* indicating the current set of categories. The iterator will be
* empty if no categories exist.
*
* @return an {@code Iterator} containing
* {@code Class} objects.
*/
public Iterator<Class<?>> getCategories() {
Set<Class<?>> keySet = categoryMap.keySet();
return keySet.iterator();
}
/**
* Returns an Iterator containing the subregistries to which the
* provider belongs.
*/
private Iterator<SubRegistry> getSubRegistries(Object provider) {
List<SubRegistry> l = new ArrayList<>();
Iterator<Class<?>> iter = categoryMap.keySet().iterator();
while (iter.hasNext()) {
Class<?> c = iter.next();
if (c.isAssignableFrom(provider.getClass())) {
l.add(categoryMap.get(c));
}
}
return l.iterator();
}
/**
* Adds a service provider object to the registry. The provider
* is associated with the given category.
*
* <p> If {@code provider} implements the
* {@code RegisterableService} interface, its
* {@code onRegistration} method will be called. Its
* {@code onDeregistration} method will be called each time
* it is deregistered from a category, for example if a
* category is removed or the registry is garbage collected.
*
* @param provider the service provide object to be registered.
* @param category the category under which to register the
* provider.
* @param <T> the type of the provider.
*
* @return true if no provider of the same class was previously
* registered in the same category category.
*
* @exception IllegalArgumentException if {@code provider} is
* {@code null}.
* @exception IllegalArgumentException if there is no category
* corresponding to {@code category}.
* @exception ClassCastException if provider does not implement
* the {@code Class} defined by {@code category}.
*/
public <T> boolean registerServiceProvider(T provider,
Class<T> category) {
if (provider == null) {
throw new IllegalArgumentException("provider == null!");
}
SubRegistry reg = categoryMap.get(category);
if (reg == null) {
throw new IllegalArgumentException("category unknown!");
}
if (!category.isAssignableFrom(provider.getClass())) {
throw new ClassCastException();
}
return reg.registerServiceProvider(provider);
}
/**
* Adds a service provider object to the registry. The provider
* is associated within each category present in the registry
* whose {@code Class} it implements.
*
* <p> If {@code provider} implements the
* {@code RegisterableService} interface, its
* {@code onRegistration} method will be called once for each
* category it is registered under. Its
* {@code onDeregistration} method will be called each time
* it is deregistered from a category or when the registry is
* finalized.
*
* @param provider the service provider object to be registered.
*
* @exception IllegalArgumentException if
* {@code provider} is {@code null}.
*/
public void registerServiceProvider(Object provider) {
if (provider == null) {
throw new IllegalArgumentException("provider == null!");
}
Iterator<SubRegistry> regs = getSubRegistries(provider);
while (regs.hasNext()) {
SubRegistry reg = regs.next();
reg.registerServiceProvider(provider);
}
}
/**
* Adds a set of service provider objects, taken from an
* {@code Iterator} to the registry. Each provider is
* associated within each category present in the registry whose
* {@code Class} it implements.
*
* <p> For each entry of {@code providers} that implements
* the {@code RegisterableService} interface, its
* {@code onRegistration} method will be called once for each
* category it is registered under. Its
* {@code onDeregistration} method will be called each time
* it is deregistered from a category or when the registry is
* finalized.
*
* @param providers an Iterator containing service provider
* objects to be registered.
*
* @exception IllegalArgumentException if {@code providers}
* is {@code null} or contains a {@code null} entry.
*/
public void registerServiceProviders(Iterator<?> providers) {
if (providers == null) {
throw new IllegalArgumentException("provider == null!");
}
while (providers.hasNext()) {
registerServiceProvider(providers.next());
}
}
/**
* Removes a service provider object from the given category. If
* the provider was not previously registered, nothing happens and
* {@code false} is returned. Otherwise, {@code true}
* is returned. If an object of the same class as
* {@code provider} but not equal (using {@code ==}) to
* {@code provider} is registered, it will not be
* deregistered.
*
* <p> If {@code provider} implements the
* {@code RegisterableService} interface, its
* {@code onDeregistration} method will be called.
*
* @param provider the service provider object to be deregistered.
* @param category the category from which to deregister the
* provider.
* @param <T> the type of the provider.
*
* @return {@code true} if the provider was previously
* registered in the same category category,
* {@code false} otherwise.
*
* @exception IllegalArgumentException if {@code provider} is
* {@code null}.
* @exception IllegalArgumentException if there is no category
* corresponding to {@code category}.
* @exception ClassCastException if provider does not implement
* the class defined by {@code category}.
*/
public <T> boolean deregisterServiceProvider(T provider,
Class<T> category) {
if (provider == null) {
throw new IllegalArgumentException("provider == null!");
}
SubRegistry reg = categoryMap.get(category);
if (reg == null) {
throw new IllegalArgumentException("category unknown!");
}
if (!category.isAssignableFrom(provider.getClass())) {
throw new ClassCastException();
}
return reg.deregisterServiceProvider(provider);
}
/**
* Removes a service provider object from all categories that
* contain it.
*
* @param provider the service provider object to be deregistered.
*
* @exception IllegalArgumentException if {@code provider} is
* {@code null}.
*/
public void deregisterServiceProvider(Object provider) {
if (provider == null) {
throw new IllegalArgumentException("provider == null!");
}
Iterator<SubRegistry> regs = getSubRegistries(provider);
while (regs.hasNext()) {
SubRegistry reg = regs.next();
reg.deregisterServiceProvider(provider);
}
}
/**
* Returns {@code true} if {@code provider} is currently
* registered.
*
* @param provider the service provider object to be queried.
*
* @return {@code true} if the given provider has been
* registered.
*
* @exception IllegalArgumentException if {@code provider} is
* {@code null}.
*/
public boolean contains(Object provider) {
if (provider == null) {
throw new IllegalArgumentException("provider == null!");
}
Iterator<SubRegistry> regs = getSubRegistries(provider);
while (regs.hasNext()) {
SubRegistry reg = regs.next();
if (reg.contains(provider)) {
return true;
}
}
return false;
}
/**
* Returns an {@code Iterator} containing all registered
* service providers in the given category. If
* {@code useOrdering} is {@code false}, the iterator
* will return all of the server provider objects in an arbitrary
* order. Otherwise, the ordering will respect any pairwise
* orderings that have been set. If the graph of pairwise
* orderings contains cycles, any providers that belong to a cycle
* will not be returned.
*
* @param category the category to be retrieved from.
* @param useOrdering {@code true} if pairwise orderings
* should be taken account in ordering the returned objects.
* @param <T> the type of the category.
*
* @return an {@code Iterator} containing service provider
* objects from the given category, possibly in order.
*
* @exception IllegalArgumentException if there is no category
* corresponding to {@code category}.
*/
public <T> Iterator<T> getServiceProviders(Class<T> category,
boolean useOrdering) {
SubRegistry reg = categoryMap.get(category);
if (reg == null) {
throw new IllegalArgumentException("category unknown!");
}
@SuppressWarnings("unchecked")
Iterator<T> it = (Iterator<T>)reg.getServiceProviders(useOrdering);
return it;
}
/**
* A simple filter interface used by
* {@code ServiceRegistry.getServiceProviders} to select
* providers matching an arbitrary criterion. Classes that
* implement this interface should be defined in order to make use
* of the {@code getServiceProviders} method of
* {@code ServiceRegistry} that takes a {@code Filter}.
*
* @see ServiceRegistry#getServiceProviders(Class, ServiceRegistry.Filter, boolean)
*/
public interface Filter {
/**
* Returns {@code true} if the given
* {@code provider} object matches the criterion defined
* by this {@code Filter}.
*
* @param provider a service provider {@code Object}.
*
* @return true if the provider matches the criterion.
*/
boolean filter(Object provider);
}
/**
* Returns an {@code Iterator} containing service provider
* objects within a given category that satisfy a criterion
* imposed by the supplied {@code ServiceRegistry.Filter}
* object's {@code filter} method.
*
* <p> The {@code useOrdering} argument controls the
* ordering of the results using the same rules as
* {@code getServiceProviders(Class, boolean)}.
*
* @param category the category to be retrieved from.
* @param filter an instance of {@code ServiceRegistry.Filter}
* whose {@code filter} method will be invoked.
* @param useOrdering {@code true} if pairwise orderings
* should be taken account in ordering the returned objects.
* @param <T> the type of the category.
*
* @return an {@code Iterator} containing service provider
* objects from the given category, possibly in order.
*
* @exception IllegalArgumentException if there is no category
* corresponding to {@code category}.
*/
public <T> Iterator<T> getServiceProviders(Class<T> category,
Filter filter,
boolean useOrdering) {
SubRegistry reg = categoryMap.get(category);
if (reg == null) {
throw new IllegalArgumentException("category unknown!");
}
Iterator<T> iter = getServiceProviders(category, useOrdering);
return new FilterIterator<>(iter, filter);
}
/**
* Returns the currently registered service provider object that
* is of the given class type. At most one object of a given
* class is allowed to be registered at any given time. If no
* registered object has the desired class type, {@code null}
* is returned.
*
* @param providerClass the {@code Class} of the desired
* service provider object.
* @param <T> the type of the provider.
*
* @return a currently registered service provider object with the
* desired {@code Class} type, or {@code null} is none is
* present.
*
* @exception IllegalArgumentException if {@code providerClass} is
* {@code null}.
*/
public <T> T getServiceProviderByClass(Class<T> providerClass) {
if (providerClass == null) {
throw new IllegalArgumentException("providerClass == null!");
}
Iterator<Class<?>> iter = categoryMap.keySet().iterator();
while (iter.hasNext()) {
Class<?> c = iter.next();
if (c.isAssignableFrom(providerClass)) {
SubRegistry reg = categoryMap.get(c);
T provider = reg.getServiceProviderByClass(providerClass);
if (provider != null) {
return provider;
}
}
}
return null;
}
/**
* Sets a pairwise ordering between two service provider objects
* within a given category. If one or both objects are not
* currently registered within the given category, or if the
* desired ordering is already set, nothing happens and
* {@code false} is returned. If the providers previously
* were ordered in the reverse direction, that ordering is
* removed.
*
* <p> The ordering will be used by the
* {@code getServiceProviders} methods when their
* {@code useOrdering} argument is {@code true}.
*
* @param category a {@code Class} object indicating the
* category under which the preference is to be established.
* @param firstProvider the preferred provider.
* @param secondProvider the provider to which
* {@code firstProvider} is preferred.
* @param <T> the type of the category.
*
* @return {@code true} if a previously unset ordering
* was established.
*
* @exception IllegalArgumentException if either provider is
* {@code null} or they are the same object.
* @exception IllegalArgumentException if there is no category
* corresponding to {@code category}.
*/
public <T> boolean setOrdering(Class<T> category,
T firstProvider,
T secondProvider) {
if (firstProvider == null || secondProvider == null) {
throw new IllegalArgumentException("provider is null!");
}
if (firstProvider == secondProvider) {
throw new IllegalArgumentException("providers are the same!");
}
SubRegistry reg = categoryMap.get(category);
if (reg == null) {
throw new IllegalArgumentException("category unknown!");
}
if (reg.contains(firstProvider) &&
reg.contains(secondProvider)) {
return reg.setOrdering(firstProvider, secondProvider);
}
return false;
}
/**
* Sets a pairwise ordering between two service provider objects
* within a given category. If one or both objects are not
* currently registered within the given category, or if no
* ordering is currently set between them, nothing happens
* and {@code false} is returned.
*
* <p> The ordering will be used by the
* {@code getServiceProviders} methods when their
* {@code useOrdering} argument is {@code true}.
*
* @param category a {@code Class} object indicating the
* category under which the preference is to be disestablished.
* @param firstProvider the formerly preferred provider.
* @param secondProvider the provider to which
* {@code firstProvider} was formerly preferred.
* @param <T> the type of the category.
*
* @return {@code true} if a previously set ordering was
* disestablished.
*
* @exception IllegalArgumentException if either provider is
* {@code null} or they are the same object.
* @exception IllegalArgumentException if there is no category
* corresponding to {@code category}.
*/
public <T> boolean unsetOrdering(Class<T> category,
T firstProvider,
T secondProvider) {
if (firstProvider == null || secondProvider == null) {
throw new IllegalArgumentException("provider is null!");
}
if (firstProvider == secondProvider) {
throw new IllegalArgumentException("providers are the same!");
}
SubRegistry reg = categoryMap.get(category);
if (reg == null) {
throw new IllegalArgumentException("category unknown!");
}
if (reg.contains(firstProvider) &&
reg.contains(secondProvider)) {
return reg.unsetOrdering(firstProvider, secondProvider);
}
return false;
}
/**
* Deregisters all service provider object currently registered
* under the given category.
*
* @param category the category to be emptied.
*
* @exception IllegalArgumentException if there is no category
* corresponding to {@code category}.
*/
public void deregisterAll(Class<?> category) {
SubRegistry reg = categoryMap.get(category);
if (reg == null) {
throw new IllegalArgumentException("category unknown!");
}
reg.clear();
}
/**
* Deregisters all currently registered service providers from all
* categories.
*/
public void deregisterAll() {
Iterator<SubRegistry> iter = categoryMap.values().iterator();
while (iter.hasNext()) {
SubRegistry reg = iter.next();
reg.clear();
}
}
/**
* Finalizes this object prior to garbage collection. The
* {@code deregisterAll} method is called to deregister all
* currently registered service providers. This method should not
* be called from application code.
*
* @exception Throwable if an error occurs during superclass
* finalization.
*/
public void finalize() throws Throwable {
deregisterAll();
super.finalize();
}
/**
* Checks whether the provided class is one of the allowed
* ImageIO service provider classes. If it is, returns normally.
* If it is not, throws IllegalArgumentException.
*
* @param clazz
* @throws IllegalArgumentException if clazz is null or is not one of the allowed set
*/
private static void checkClassAllowed(Class<?> clazz) {
if (clazz == null) {
throw new IllegalArgumentException("class must not be null");
}
if ( clazz != ImageInputStreamSpi.class
&& clazz != ImageOutputStreamSpi.class
&& clazz != ImageReaderSpi.class
&& clazz != ImageTranscoderSpi.class
&& clazz != ImageWriterSpi.class) {
throw new IllegalArgumentException(clazz.getName() + " is not an ImageIO SPI class");
}
}
}
/**
* A portion of a registry dealing with a single superclass or
* interface.
*/
class SubRegistry {
ServiceRegistry registry;
Class<?> category;
// Provider Objects organized by partial oridering
PartiallyOrderedSet<Object> poset = new PartiallyOrderedSet<>();
// Class -> Provider Object of that class
// No way to express heterogeneous map, we want
// Map<Class<T>, T>, where T is ?
Map<Class<?>, Object> map = new HashMap<>();
public SubRegistry(ServiceRegistry registry, Class<?> category) {
this.registry = registry;
this.category = category;
}
public synchronized boolean registerServiceProvider(Object provider) {
Object oprovider = map.get(provider.getClass());
boolean present = oprovider != null;
if (present) {
deregisterServiceProvider(oprovider);
}
map.put(provider.getClass(), provider);
poset.add(provider);
if (provider instanceof RegisterableService) {
RegisterableService rs = (RegisterableService)provider;
try {
rs.onRegistration(registry, category);
} catch (Throwable t) {
System.err.println("Caught and handled this exception :");
t.printStackTrace();
}
}
return !present;
}
/**
* If the provider was not previously registered, do nothing.
*
* @return true if the provider was previously registered.
*/
public synchronized boolean deregisterServiceProvider(Object provider) {
Object oprovider = map.get(provider.getClass());
if (provider == oprovider) {
map.remove(provider.getClass());
poset.remove(provider);
if (provider instanceof RegisterableService) {
RegisterableService rs = (RegisterableService)provider;
rs.onDeregistration(registry, category);
}
return true;
}
return false;
}
public synchronized boolean contains(Object provider) {
Object oprovider = map.get(provider.getClass());
return oprovider == provider;
}
public synchronized boolean setOrdering(Object firstProvider,
Object secondProvider) {
return poset.setOrdering(firstProvider, secondProvider);
}
public synchronized boolean unsetOrdering(Object firstProvider,
Object secondProvider) {
return poset.unsetOrdering(firstProvider, secondProvider);
}
public synchronized Iterator<Object> getServiceProviders
(boolean useOrdering) {
if (useOrdering) {
return poset.iterator();
} else {
return map.values().iterator();
}
}
@SuppressWarnings("unchecked")
public synchronized <T> T getServiceProviderByClass
(Class<T> providerClass) {
return (T)map.get(providerClass);
}
public synchronized void clear() {
Iterator<Object> iter = map.values().iterator();
while (iter.hasNext()) {
Object provider = iter.next();
iter.remove();
if (provider instanceof RegisterableService) {
RegisterableService rs = (RegisterableService)provider;
rs.onDeregistration(registry, category);
}
}
poset.clear();
}
public synchronized void finalize() {
clear();
}
}
/**
* A class for wrapping {@code Iterators} with a filter function.
* This provides an iterator for a subset without duplication.
*/
class FilterIterator<T> implements Iterator<T> {
private Iterator<? extends T> iter;
private ServiceRegistry.Filter filter;
private T next = null;
public FilterIterator(Iterator<? extends T> iter,
ServiceRegistry.Filter filter) {
this.iter = iter;
this.filter = filter;
advance();
}
private void advance() {
while (iter.hasNext()) {
T elt = iter.next();
if (filter.filter(elt)) {
next = elt;
return;
}
}
next = null;
}
public boolean hasNext() {
return next != null;
}
public T next() {
if (next == null) {
throw new NoSuchElementException();
}
T o = next;
advance();
return o;
}
public void remove() {
throw new UnsupportedOperationException();
}
}