com.sun.xml.ws.util.ServiceFinder Maven / Gradle / Ivy
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/*
* Copyright (c) 1997, 2021 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Distribution License v. 1.0, which is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
package com.sun.xml.ws.util;
import com.sun.istack.NotNull;
import com.sun.istack.Nullable;
import com.sun.xml.ws.api.Component;
import com.sun.xml.ws.api.ComponentEx;
import com.sun.xml.ws.api.server.ContainerResolver;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.ServiceLoader;
/**
* A simple service-provider lookup mechanism. A service is a
* well-known set of interfaces and (usually abstract) classes. A service
* provider is a specific implementation of a service. The classes in a
* provider typically implement the interfaces and subclass the classes defined
* in the service itself. Service providers may be installed in an
* implementation of the Java platform in the form of extensions, that is, jar
* files placed into any of the usual extension directories. Providers may
* also be made available by adding them to the applet or application class
* path or by some other platform-specific means.
*
* In this lookup mechanism a service is represented by an interface or an
* abstract class. (A concrete class may be used, but this is not
* recommended.) A provider of a given service contains one or more concrete
* classes that extend this service class with data and code specific to
* the provider. This provider class will typically not be the entire
* provider itself but rather a proxy that contains enough information to
* decide whether the provider is able to satisfy a particular request together
* with code that can create the actual provider on demand. The details of
* provider classes tend to be highly service-specific; no single class or
* interface could possibly unify them, so no such class has been defined. The
* only requirement enforced here is that provider classes must have a
* zero-argument constructor so that they may be instantiated during lookup.
*
*
A service provider identifies itself by placing a provider-configuration
* file in the resource directory {@code META-INF/services}. The file's name
* should consist of the fully-qualified name of the abstract service class.
* The file should contain a list of fully-qualified concrete provider-class
* names, one per line. Space and tab characters surrounding each name, as
* well as blank lines, are ignored. The comment character is {@code '#'}
* ({@code 0x23}); on each line all characters following the first comment
* character are ignored. The file must be encoded in UTF-8.
*
*
If a particular concrete provider class is named in more than one
* configuration file, or is named in the same configuration file more than
* once, then the duplicates will be ignored. The configuration file naming a
* particular provider need not be in the same jar file or other distribution
* unit as the provider itself. The provider must be accessible from the same
* class loader that was initially queried to locate the configuration file;
* note that this is not necessarily the class loader that found the file.
*
*
Example: Suppose we have a service class named
* {@code java.io.spi.CharCodec}. It has two abstract methods:
*
*
* public abstract CharEncoder getEncoder(String encodingName);
* public abstract CharDecoder getDecoder(String encodingName);
*
*
* Each method returns an appropriate object or {@code null} if it cannot
* translate the given encoding. Typical {@code CharCodec} providers will
* support more than one encoding.
*
* If {@code sun.io.StandardCodec} is a provider of the {@code CharCodec}
* service then its jar file would contain the file
* {@code META-INF/services/java.io.spi.CharCodec}. This file would contain
* the single line:
*
*
* sun.io.StandardCodec # Standard codecs for the platform
*
*
* To locate an codec for a given encoding name, the internal I/O code would
* do something like this:
*
*
* CharEncoder getEncoder(String encodingName) {
* for( CharCodec cc : ServiceFinder.find(CharCodec.class) ) {
* CharEncoder ce = cc.getEncoder(encodingName);
* if (ce != null)
* return ce;
* }
* return null;
* }
*
*
* The provider-lookup mechanism always executes in the security context of the
* caller. Trusted system code should typically invoke the methods in this
* class from within a privileged security context.
*
* @author Mark Reinhold
* @version 1.11, 03/12/19
* @param The type of the service to be loaded by this finder
* @since 1.3
*/
public final class ServiceFinder implements Iterable {
private final @NotNull Class serviceClass;
private final @NotNull ServiceLoader serviceLoader;
private final @Nullable ComponentEx component;
public static ServiceFinder find(@NotNull Class service, @Nullable ClassLoader loader, Component component) {
ClassLoader cl = loader == null ? Thread.currentThread().getContextClassLoader() : loader;
return find(service, component, ServiceLoader.load(service, cl));
}
public static ServiceFinder find(@NotNull Class service, Component component, @NotNull ServiceLoader serviceLoader) {
Class svc = Objects.requireNonNull(service);
ServiceLoader sl = Objects.requireNonNull(serviceLoader);
return new ServiceFinder<>(svc, component, sl);
}
public static ServiceFinder find(@NotNull Class service, Component component) {
return find(service, component, ServiceLoader.load(service, Thread.currentThread().getContextClassLoader()));
}
/**
* Locates and incrementally instantiates the available providers of a
* given service using the given class loader.
*
* This method transforms the name of the given service class into a
* provider-configuration filename as described above 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 lookup and then instantiate each element
* of the list.
*
*
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 The type of the service to be loaded by this finder
* @param service The service's abstract service class
* @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
* @return A new service finder
* @throws ServiceConfigurationError If a provider-configuration file violates the specified format
* or names a provider class that cannot be found and instantiated
* @see #find(Class)
*/
public static ServiceFinder find(@NotNull Class service, @Nullable ClassLoader loader) {
return find(service, loader, ContainerResolver.getInstance().getContainer());
}
/**
* Locates and incrementally instantiates the available providers of a
* given service using the context class loader. This convenience method
* is equivalent to
*
*
* ClassLoader cl = Thread.currentThread().getContextClassLoader();
* return Service.providers(service, cl);
*
*
* @param The type of the service to be loaded by this finder
* @param service The service's abstract service class
* @return A new service finder
*
* @throws ServiceConfigurationError If a provider-configuration file violates the specified format
* or names a provider class that cannot be found and instantiated
* @see #find(Class, ClassLoader)
*/
public static ServiceFinder find(@NotNull Class service) {
return find(service, ServiceLoader.load(service, Thread.currentThread().getContextClassLoader()));
}
public static ServiceFinder find(@NotNull Class service, @NotNull ServiceLoader serviceLoader) {
return find(service, ContainerResolver.getInstance().getContainer(), serviceLoader);
}
private ServiceFinder(Class service, Component component, ServiceLoader serviceLoader) {
this.serviceClass = service;
this.component = getComponentEx(component);
this.serviceLoader = serviceLoader;
}
/**
* Returns discovered objects incrementally.
*
* @return An {@code Iterator} that yields provider objects for the given
* service, in some arbitrary order. The iterator will throw a
* {@code ServiceConfigurationError} if a provider-configuration
* file violates the specified format or if a provider class cannot
* be found and instantiated.
*/
@Override
@SuppressWarnings("unchecked")
public Iterator iterator() {
Iterator it = serviceLoader.iterator();
return component != null
? new CompositeIterator<>(component.getIterableSPI(serviceClass).iterator(), it)
: it;
}
/**
* Returns discovered objects all at once.
*
* @return
* can be empty but never null.
*
* @throws ServiceConfigurationError
*/
public T[] toArray() {
List result = new ArrayList<>();
for (T t : this) {
result.add(t);
}
return result.toArray((T[]) Array.newInstance(serviceClass, result.size()));
}
private static ComponentEx getComponentEx(Component component) {
if (component instanceof ComponentEx) {
return (ComponentEx) component;
}
return component != null ? new ComponentExWrapper(component) : null;
}
private static class ComponentExWrapper implements ComponentEx {
private final Component component;
public ComponentExWrapper(Component component) {
this.component = component;
}
@Override
public S getSPI(Class spiType) {
return component.getSPI(spiType);
}
@Override
public Iterable getIterableSPI(Class spiType) {
S item = getSPI(spiType);
if (item != null) {
Collection c = Collections.singletonList(item);
return c;
}
return Collections.emptySet();
}
}
private static class CompositeIterator implements Iterator {
private final Iterator> it;
private Iterator current = null;
public CompositeIterator(Iterator... iterators) {
it = Arrays.asList(iterators).iterator();
}
@Override
public boolean hasNext() {
if (current != null && current.hasNext()) {
return true;
}
while (it.hasNext()) {
current = it.next();
if (current.hasNext()) {
return true;
}
}
return false;
}
@Override
public T next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
return current.next();
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}
}