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ServiceLoader.java
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ServiceLoader.java
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/*
* Copyright (c) 2005, 2022, 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
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.util;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.net.URL;
import java.net.URLConnection;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.util.function.Consumer;
import java.util.function.Supplier;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;
import sun.nio.cs.UTF_8;
import jdk.internal.loader.BootLoader;
import jdk.internal.loader.ClassLoaders;
import jdk.internal.access.JavaLangAccess;
import jdk.internal.access.SharedSecrets;
import jdk.internal.misc.VM;
import jdk.internal.module.ServicesCatalog;
import jdk.internal.module.ServicesCatalog.ServiceProvider;
import jdk.internal.reflect.CallerSensitive;
import jdk.internal.reflect.Reflection;
/**
* A facility to load implementations of a service.
*
* <p> A <i>service</i> is a well-known interface or class for which zero, one,
* or many service providers exist. A <i>service provider</i> (or just
* <i>provider</i>) is a class that implements or subclasses the well-known
* interface or class. A {@code ServiceLoader} is an object that locates and
* loads service providers deployed in the run time environment at a time of an
* application's choosing. Application code refers only to the service, not to
* service providers, and is assumed to be capable of choosing between multiple
* service providers (based on the functionality they expose through the service),
* and handling the possibility that no service providers are located.
*
* <h2> Obtaining a service loader </h2>
*
* <p> An application obtains a service loader for a given service by invoking
* one of the static {@code load} methods of {@code ServiceLoader}. If the
* application is a module, then its module declaration must have a <i>uses</i>
* directive that specifies the service; this helps to locate providers and ensure
* they will execute reliably. In addition, if the application module does not
* contain the service, then its module declaration must have a <i>requires</i>
* directive that specifies the module which exports the service. It is strongly
* recommended that the application module does <b>not</b> require modules which
* contain providers of the service.
*
* <p> A service loader can be used to locate and instantiate providers of the
* service by means of the {@link #iterator() iterator} method. {@code ServiceLoader}
* also defines the {@link #stream() stream} method to obtain a stream of providers
* that can be inspected and filtered without instantiating them.
*
* <p> As an example, suppose the service is {@code com.example.CodecFactory}, an
* interface that defines methods for producing encoders and decoders:
*
* <pre>{@code
* package com.example;
* public interface CodecFactory {
* Encoder getEncoder(String encodingName);
* Decoder getDecoder(String encodingName);
* }
* }</pre>
*
* <p> The following code obtains a service loader for the {@code CodecFactory}
* service, then uses its iterator (created automatically by the enhanced-for
* loop) to yield instances of the service providers that are located:
*
* <pre>{@code
* ServiceLoader<CodecFactory> loader = ServiceLoader.load(CodecFactory.class);
* for (CodecFactory factory : loader) {
* Encoder enc = factory.getEncoder("PNG");
* if (enc != null)
* ... use enc to encode a PNG file
* break;
* }
* }</pre>
*
* <p> If this code resides in a module, then in order to refer to the
* {@code com.example.CodecFactory} interface, the module declaration would
* require the module which exports the interface. The module declaration would
* also specify use of {@code com.example.CodecFactory}:
* <pre>{@code
* requires com.example.codec.core;
* uses com.example.CodecFactory;
* }</pre>
*
* <p> Sometimes an application may wish to inspect a service provider before
* instantiating it, in order to determine if an instance of that service
* provider would be useful. For example, a service provider for {@code
* CodecFactory} that is capable of producing a "PNG" encoder may be annotated
* with {@code @PNG}. The following code uses service loader's {@code stream}
* method to yield instances of {@code Provider<CodecFactory>} in contrast to
* how the iterator yields instances of {@code CodecFactory}:
* <pre>{@code
* ServiceLoader<CodecFactory> loader = ServiceLoader.load(CodecFactory.class);
* Set<CodecFactory> pngFactories = loader
* .stream() // Note a below
* .filter(p -> p.type().isAnnotationPresent(PNG.class)) // Note b
* .map(Provider::get) // Note c
* .collect(Collectors.toSet());
* }</pre>
* <ol type="a">
* <li> A stream of {@code Provider<CodecFactory>} objects </li>
* <li> {@code p.type()} yields a {@code Class<CodecFactory>} </li>
* <li> {@code get()} yields an instance of {@code CodecFactory} </li>
* </ol>
*
* <h2> Designing services </h2>
*
* <p> A service is a single type, usually an interface or abstract class. A
* concrete class can be used, but this is not recommended. The type may have
* any accessibility. The methods of a service are highly domain-specific, so
* this API specification cannot give concrete advice about their form or
* function. However, there are two general guidelines:
* <ol>
* <li><p> A service should declare as many methods as needed to allow service
* providers to communicate their domain-specific properties and other
* quality-of-implementation factors. An application which obtains a service
* loader for the service may then invoke these methods on each instance of
* a service provider, in order to choose the best provider for the
* application. </p></li>
* <li><p> A service should express whether its service providers are intended
* to be direct implementations of the service or to be an indirection
* mechanism such as a "proxy" or a "factory". Service providers tend to be
* indirection mechanisms when domain-specific objects are relatively
* expensive to instantiate; in this case, the service should be designed
* so that service providers are abstractions which create the "real"
* implementation on demand. For example, the {@code CodecFactory} service
* expresses through its name that its service providers are factories
* for codecs, rather than codecs themselves, because it may be expensive
* or complicated to produce certain codecs. </p></li>
* </ol>
*
* <h2> <a id="developing-service-providers">Developing service providers</a> </h2>
*
* <p> A service provider is a single type, usually a concrete class. An
* interface or abstract class is permitted because it may declare a static
* provider method, discussed later. The type must be public and must not be
* an inner class.
*
* <p> A service provider and its supporting code may be developed in a module,
* which is then deployed on the application module path or in a modular
* image. Alternatively, a service provider and its supporting code may be
* packaged as a JAR file and deployed on the application class path. The
* advantage of developing a service provider in a module is that the provider
* can be fully encapsulated to hide all details of its implementation.
*
* <p> An application that obtains a service loader for a given service is
* indifferent to whether providers of the service are deployed in modules or
* packaged as JAR files. The application instantiates service providers via
* the service loader's iterator, or via {@link Provider Provider} objects in
* the service loader's stream, without knowledge of the service providers'
* locations.
*
* <h2> Deploying service providers as modules </h2>
*
* <p> A service provider that is developed in a module must be specified in a
* <i>provides</i> directive in the module declaration. The provides directive
* specifies both the service and the service provider; this helps to locate the
* provider when another module, with a <i>uses</i> directive for the service,
* obtains a service loader for the service. It is strongly recommended that the
* module does not export the package containing the service provider. There is
* no support for a module specifying, in a <i>provides</i> directive, a service
* provider in another module.
*
* <p> A service provider that is developed in a module has no control over when
* it is instantiated, since that occurs at the behest of the application, but it
* does have control over how it is instantiated:
*
* <ul>
*
* <li> If the service provider declares a provider method, then the service
* loader invokes that method to obtain an instance of the service provider. A
* provider method is a public static method named "provider" with no formal
* parameters and a return type that is assignable to the service's interface
* or class.
* <p> In this case, the service provider itself need not be assignable to the
* service's interface or class. </li>
*
* <li> If the service provider does not declare a provider method, then the
* service provider is instantiated directly, via its provider constructor. A
* provider constructor is a public constructor with no formal parameters.
* <p> In this case, the service provider must be assignable to the service's
* interface or class </li>
*
* </ul>
*
* <p> A service provider that is deployed as an
* {@linkplain java.lang.module.ModuleDescriptor#isAutomatic automatic module} on
* the application module path must have a provider constructor. There is no
* support for a provider method in this case.
*
* <p> As an example, suppose a module specifies the following directive:
* <pre>{@code
* provides com.example.CodecFactory with com.example.impl.StandardCodecs,
* com.example.impl.ExtendedCodecsFactory;
* }</pre>
*
* <p> where
*
* <ul>
* <li> {@code com.example.CodecFactory} is the two-method service from
* earlier. </li>
*
* <li> {@code com.example.impl.StandardCodecs} is a public class that implements
* {@code CodecFactory} and has a public no-args constructor. </li>
*
* <li> {@code com.example.impl.ExtendedCodecsFactory} is a public class that
* does not implement CodecFactory, but it declares a public static no-args
* method named "provider" with a return type of {@code CodecFactory}. </li>
* </ul>
*
* <p> A service loader will instantiate {@code StandardCodecs} via its
* constructor, and will instantiate {@code ExtendedCodecsFactory} by invoking
* its {@code provider} method. The requirement that the provider constructor or
* provider method is public helps to document the intent that the class (that is,
* the service provider) will be instantiated by an entity (that is, a service
* loader) which is outside the class's package.
*
* <h2> Deploying service providers on the class path </h2>
*
* A service provider that is packaged as a JAR file for the class path is
* identified by placing a <i>provider-configuration file</i> in the resource
* directory {@code META-INF/services}. The name of the provider-configuration
* file is the fully qualified binary name of the service. The provider-configuration
* file contains a list of fully qualified binary names of service providers, one
* per line.
*
* <p> For example, suppose the service provider
* {@code com.example.impl.StandardCodecs} is packaged in a JAR file for the
* class path. The JAR file will contain a provider-configuration file named:
*
* <blockquote>{@code
* META-INF/services/com.example.CodecFactory
* }</blockquote>
*
* that contains the line:
*
* <blockquote>{@code
* com.example.impl.StandardCodecs # Standard codecs
* }</blockquote>
*
* <p><a id="format">The provider-configuration file must be encoded in UTF-8. </a>
* Space and tab characters surrounding each service provider's name, as well as
* blank lines, are ignored. The comment character is {@code '#'}
* ({@code U+0023} <span style="font-size:smaller;">NUMBER SIGN</span>);
* on each line all characters following the first comment character are ignored.
* If a service provider class name is listed more than once in a
* provider-configuration file then the duplicate is ignored. If a service
* provider class is named in more than one configuration file then the duplicate
* is ignored.
*
* <p> A service provider that is mentioned in a provider-configuration file may
* be located in the same JAR file as the provider-configuration file or in a
* different JAR file. The service provider must be visible from the class loader
* that is initially queried to locate the provider-configuration file; this is
* not necessarily the class loader which ultimately locates the
* provider-configuration file.
*
* <h2> Timing of provider discovery </h2>
*
* <p> Service providers are loaded and instantiated lazily, that is, on demand.
* A service loader maintains a cache of the providers that have been loaded so
* far. Each invocation of the {@code iterator} method returns an {@code Iterator}
* that first yields all of the elements cached from previous iteration, in
* instantiation order, and then lazily locates and instantiates any remaining
* providers, adding each one to the cache in turn. Similarly, each invocation
* of the stream method returns a {@code Stream} that first processes all
* providers loaded by previous stream operations, in load order, and then lazily
* locates any remaining providers. Caches are cleared via the {@link #reload
* reload} method.
*
* <h2> <a id="errors">Errors</a> </h2>
*
* <p> When using the service loader's {@code iterator}, the {@link
* Iterator#hasNext() hasNext} and {@link Iterator#next() next} methods will
* fail with {@link ServiceConfigurationError} if an error occurs locating,
* loading or instantiating a service provider. When processing the service
* loader's stream then {@code ServiceConfigurationError} may be thrown by any
* method that causes a service provider to be located or loaded.
*
* <p> When loading or instantiating a service provider in a module, {@code
* ServiceConfigurationError} can be thrown for the following reasons:
*
* <ul>
*
* <li> The service provider cannot be loaded. </li>
*
* <li> The service provider does not declare a provider method, and either
* it is not assignable to the service's interface/class or does not have a
* provider constructor. </li>
*
* <li> The service provider declares a public static no-args method named
* "provider" with a return type that is not assignable to the service's
* interface or class. </li>
*
* <li> The service provider class file has more than one public static
* no-args method named "{@code provider}". </li>
*
* <li> The service provider declares a provider method and it fails by
* returning {@code null} or throwing an exception. </li>
*
* <li> The service provider does not declare a provider method, and its
* provider constructor fails by throwing an exception. </li>
*
* </ul>
*
* <p> When reading a provider-configuration file, or loading or instantiating
* a provider class named in a provider-configuration file, then {@code
* ServiceConfigurationError} can be thrown for the following reasons:
*
* <ul>
*
* <li> The format of the provider-configuration file violates the <a
* href="ServiceLoader.html#format">format</a> specified above; </li>
*
* <li> An {@link IOException IOException} occurs while reading the
* provider-configuration file; </li>
*
* <li> A service provider cannot be loaded; </li>
*
* <li> A service provider is not assignable to the service's interface or
* class, or does not define a provider constructor, or cannot be
* instantiated. </li>
*
* </ul>
*
* <h2> Security </h2>
*
* <p> Service loaders always execute in the security context of the caller
* of the iterator or stream methods and may also be restricted by the security
* context of the caller that created the service loader.
* Trusted system code should typically invoke the methods in this class, and
* the methods of the iterators which they return, from within a privileged
* security context.
*
* <h2> Concurrency </h2>
*
* <p> Instances of this class are not safe for use by multiple concurrent
* threads.
*
* <h3> Null handling </h3>
*
* <p> Unless otherwise specified, passing a {@code null} argument to any
* method in this class will cause a {@link NullPointerException} to be thrown.
*
* @param <S>
* The type of the service to be loaded by this loader
*
* @author Mark Reinhold
* @since 1.6
* @revised 9
*/
public final class ServiceLoader<S>
implements Iterable<S>
{
// The class or interface representing the service being loaded
private final Class<S> service;
// The class of the service type
private final String serviceName;
// The module layer used to locate providers; null when locating
// providers using a class loader
private final ModuleLayer layer;
// The class loader used to locate, load, and instantiate providers;
// null when locating provider using a module layer
private final ClassLoader loader;
// The access control context taken when the ServiceLoader is created
@SuppressWarnings("removal")
private final AccessControlContext acc;
// The lazy-lookup iterator for iterator operations
private Iterator<Provider<S>> lookupIterator1;
private final List<S> instantiatedProviders = new ArrayList<>();
// The lazy-lookup iterator for stream operations
private Iterator<Provider<S>> lookupIterator2;
private final List<Provider<S>> loadedProviders = new ArrayList<>();
private boolean loadedAllProviders; // true when all providers loaded
// Incremented when reload is called
private int reloadCount;
private static JavaLangAccess LANG_ACCESS;
static {
LANG_ACCESS = SharedSecrets.getJavaLangAccess();
}
/**
* Represents a service provider located by {@code ServiceLoader}.
*
* <p> When using a loader's {@link ServiceLoader#stream() stream()} method
* then the elements are of type {@code Provider}. This allows processing
* to select or filter on the provider class without instantiating the
* provider. </p>
*
* @param <S> The service type
* @since 9
*/
public static interface Provider<S> extends Supplier<S> {
/**
* Returns the provider type. There is no guarantee that this type is
* accessible or that it has a public no-args constructor. The {@link
* #get() get()} method should be used to obtain the provider instance.
*
* <p> When a module declares that the provider class is created by a
* provider factory then this method returns the return type of its
* public static "{@code provider()}" method.
*
* @return The provider type
*/
Class<? extends S> type();
/**
* Returns an instance of the provider.
*
* @return An instance of the provider.
*
* @throws ServiceConfigurationError
* If the service provider cannot be instantiated, or in the
* case of a provider factory, the public static
* "{@code provider()}" method returns {@code null} or throws
* an error or exception. The {@code ServiceConfigurationError}
* will carry an appropriate cause where possible.
*/
@Override S get();
}
/**
* Initializes a new instance of this class for locating service providers
* in a module layer.
*
* @throws ServiceConfigurationError
* If {@code svc} is not accessible to {@code caller} or the caller
* module does not use the service type.
*/
@SuppressWarnings("removal")
private ServiceLoader(Class<?> caller, ModuleLayer layer, Class<S> svc) {
Objects.requireNonNull(caller);
Objects.requireNonNull(layer);
Objects.requireNonNull(svc);
checkCaller(caller, svc);
this.service = svc;
this.serviceName = svc.getName();
this.layer = layer;
this.loader = null;
this.acc = (System.getSecurityManager() != null)
? AccessController.getContext()
: null;
}
/**
* Initializes a new instance of this class for locating service providers
* via a class loader.
*
* @throws ServiceConfigurationError
* If {@code svc} is not accessible to {@code caller} or the caller
* module does not use the service type.
*/
@SuppressWarnings("removal")
private ServiceLoader(Class<?> caller, Class<S> svc, ClassLoader cl) {
Objects.requireNonNull(svc);
if (VM.isBooted()) {
checkCaller(caller, svc);
if (cl == null) {
cl = ClassLoader.getSystemClassLoader();
}
} else {
// if we get here then it means that ServiceLoader is being used
// before the VM initialization has completed. At this point then
// only code in the java.base should be executing.
Module callerModule = caller.getModule();
Module base = Object.class.getModule();
Module svcModule = svc.getModule();
if (callerModule != base || svcModule != base) {
fail(svc, "not accessible to " + callerModule + " during VM init");
}
// restricted to boot loader during startup
cl = null;
}
this.service = svc;
this.serviceName = svc.getName();
this.layer = null;
this.loader = cl;
this.acc = (System.getSecurityManager() != null)
? AccessController.getContext()
: null;
}
/**
* Initializes a new instance of this class for locating service providers
* via a class loader.
*
* @apiNote For use by ResourceBundle
*
* @throws ServiceConfigurationError
* If the caller module does not use the service type.
*/
@SuppressWarnings("removal")
private ServiceLoader(Module callerModule, Class<S> svc, ClassLoader cl) {
if (!callerModule.canUse(svc)) {
fail(svc, callerModule + " does not declare `uses`");
}
this.service = Objects.requireNonNull(svc);
this.serviceName = svc.getName();
this.layer = null;
this.loader = cl;
this.acc = (System.getSecurityManager() != null)
? AccessController.getContext()
: null;
}
/**
* Checks that the given service type is accessible to types in the given
* module, and check that the module declares that it uses the service type.
*/
private static void checkCaller(Class<?> caller, Class<?> svc) {
if (caller == null) {
fail(svc, "no caller to check if it declares `uses`");
}
// Check access to the service type
Module callerModule = caller.getModule();
int mods = svc.getModifiers();
if (!Reflection.verifyMemberAccess(caller, svc, null, mods)) {
fail(svc, "service type not accessible to " + callerModule);
}
// If the caller is in a named module then it should "uses" the
// service type
if (!callerModule.canUse(svc)) {
fail(svc, callerModule + " does not declare `uses`");
}
}
private static void fail(Class<?> service, String msg, Throwable cause)
throws ServiceConfigurationError
{
throw new ServiceConfigurationError(service.getName() + ": " + msg,
cause);
}
private static void fail(Class<?> service, String msg)
throws ServiceConfigurationError
{
throw new ServiceConfigurationError(service.getName() + ": " + msg);
}
private static void fail(Class<?> service, URL u, int line, String msg)
throws ServiceConfigurationError
{
fail(service, u + ":" + line + ": " + msg);
}
/**
* Returns {@code true} if the provider is in an explicit module
*/
private boolean inExplicitModule(Class<?> clazz) {
Module module = clazz.getModule();
return module.isNamed() && !module.getDescriptor().isAutomatic();
}
/**
* Returns the public static "provider" method if found.
*
* @throws ServiceConfigurationError if there is an error finding the
* provider method or there is more than one public static
* provider method
*/
@SuppressWarnings("removal")
private Method findStaticProviderMethod(Class<?> clazz) {
List<Method> methods = null;
try {
methods = LANG_ACCESS.getDeclaredPublicMethods(clazz, "provider");
} catch (Throwable x) {
fail(service, "Unable to get public provider() method", x);
}
if (methods.isEmpty()) {
// does not declare a public provider method
return null;
}
// locate the static methods, can be at most one
Method result = null;
for (Method method : methods) {
int mods = method.getModifiers();
assert Modifier.isPublic(mods);
if (Modifier.isStatic(mods)) {
if (result != null) {
fail(service, clazz + " declares more than one"
+ " public static provider() method");
}
result = method;
}
}
if (result != null) {
Method m = result;
PrivilegedAction<Void> pa = () -> {
m.setAccessible(true);
return null;
};
AccessController.doPrivileged(pa);
}
return result;
}
/**
* Returns the public no-arg constructor of a class.
*
* @throws ServiceConfigurationError if the class does not have
* public no-arg constructor
*/
@SuppressWarnings("removal")
private Constructor<?> getConstructor(Class<?> clazz) {
PrivilegedExceptionAction<Constructor<?>> pa
= new PrivilegedExceptionAction<>() {
@Override
public Constructor<?> run() throws Exception {
Constructor<?> ctor = clazz.getConstructor();
if (inExplicitModule(clazz))
ctor.setAccessible(true);
return ctor;
}
};
Constructor<?> ctor = null;
try {
ctor = AccessController.doPrivileged(pa);
} catch (Throwable x) {
if (x instanceof PrivilegedActionException)
x = x.getCause();
String cn = clazz.getName();
fail(service, cn + " Unable to get public no-arg constructor", x);
}
return ctor;
}
/**
* A Provider implementation that supports invoking, with reduced
* permissions, the static factory to obtain the provider or the
* provider's no-arg constructor.
*/
private static class ProviderImpl<S> implements Provider<S> {
final Class<S> service;
final Class<? extends S> type;
final Method factoryMethod; // factory method or null
final Constructor<? extends S> ctor; // public no-args constructor or null
@SuppressWarnings("removal")
final AccessControlContext acc;
ProviderImpl(Class<S> service,
Class<? extends S> type,
Method factoryMethod,
@SuppressWarnings("removal") AccessControlContext acc) {
this.service = service;
this.type = type;
this.factoryMethod = factoryMethod;
this.ctor = null;
this.acc = acc;
}
ProviderImpl(Class<S> service,
Class<? extends S> type,
Constructor<? extends S> ctor,
@SuppressWarnings("removal") AccessControlContext acc) {
this.service = service;
this.type = type;
this.factoryMethod = null;
this.ctor = ctor;
this.acc = acc;
}
@Override
public Class<? extends S> type() {
return type;
}
@Override
public S get() {
if (factoryMethod != null) {
return invokeFactoryMethod();
} else {
return newInstance();
}
}
/**
* Invokes the provider's "provider" method to instantiate a provider.
* When running with a security manager then the method runs with
* permissions that are restricted by the security context of whatever
* created this loader.
*/
@SuppressWarnings("removal")
private S invokeFactoryMethod() {
Object result = null;
Throwable exc = null;
if (acc == null) {
try {
result = factoryMethod.invoke(null);
} catch (Throwable x) {
exc = x;
}
} else {
PrivilegedExceptionAction<?> pa = new PrivilegedExceptionAction<>() {
@Override
public Object run() throws Exception {
return factoryMethod.invoke(null);
}
};
// invoke factory method with permissions restricted by acc
try {
result = AccessController.doPrivileged(pa, acc);
} catch (Throwable x) {
if (x instanceof PrivilegedActionException)
x = x.getCause();
exc = x;
}
}
if (exc != null) {
if (exc instanceof InvocationTargetException)
exc = exc.getCause();
fail(service, factoryMethod + " failed", exc);
}
if (result == null) {
fail(service, factoryMethod + " returned null");
}
@SuppressWarnings("unchecked")
S p = (S) result;
return p;
}
/**
* Invokes Constructor::newInstance to instantiate a provider. When running
* with a security manager then the constructor runs with permissions that
* are restricted by the security context of whatever created this loader.
*/
@SuppressWarnings("removal")
private S newInstance() {
S p = null;
Throwable exc = null;
if (acc == null) {
try {
p = ctor.newInstance();
} catch (Throwable x) {
exc = x;
}
} else {
PrivilegedExceptionAction<S> pa = new PrivilegedExceptionAction<>() {
@Override
public S run() throws Exception {
return ctor.newInstance();
}
};
// invoke constructor with permissions restricted by acc
try {
p = AccessController.doPrivileged(pa, acc);
} catch (Throwable x) {
if (x instanceof PrivilegedActionException)
x = x.getCause();
exc = x;
}
}
if (exc != null) {
if (exc instanceof InvocationTargetException)
exc = exc.getCause();
String cn = ctor.getDeclaringClass().getName();
fail(service,
"Provider " + cn + " could not be instantiated", exc);
}
return p;
}
// For now, equals/hashCode uses the access control context to ensure
// that two Providers created with different contexts are not equal
// when running with a security manager.
@Override
public int hashCode() {
return Objects.hash(service, type, acc);
}
@Override
public boolean equals(Object ob) {
return ob instanceof @SuppressWarnings("unchecked")ProviderImpl<?> that
&& this.service == that.service
&& this.type == that.type
&& Objects.equals(this.acc, that.acc);
}
}
/**
* Loads a service provider in a module.
*
* Returns {@code null} if the service provider's module doesn't read
* the module with the service type.
*
* @throws ServiceConfigurationError if the class cannot be loaded or
* isn't the expected sub-type (or doesn't define a provider
* factory method that returns the expected type)
*/
@SuppressWarnings("removal")
private Provider<S> loadProvider(ServiceProvider provider) {
Module module = provider.module();
if (!module.canRead(service.getModule())) {
// module does not read the module with the service type
return null;
}
String cn = provider.providerName();
Class<?> clazz = null;
if (acc == null) {
try {
clazz = Class.forName(module, cn);
} catch (LinkageError e) {
fail(service, "Unable to load " + cn, e);
}
} else {
PrivilegedExceptionAction<Class<?>> pa = () -> Class.forName(module, cn);
try {
clazz = AccessController.doPrivileged(pa);
} catch (Throwable x) {
if (x instanceof PrivilegedActionException)
x = x.getCause();
fail(service, "Unable to load " + cn, x);
return null;
}
}
if (clazz == null) {
fail(service, "Provider " + cn + " not found");
}
int mods = clazz.getModifiers();
if (!Modifier.isPublic(mods)) {
fail(service, clazz + " is not public");
}
// if provider in explicit module then check for static factory method
if (inExplicitModule(clazz)) {
Method factoryMethod = findStaticProviderMethod(clazz);
if (factoryMethod != null) {
Class<?> returnType = factoryMethod.getReturnType();
if (!service.isAssignableFrom(returnType)) {
fail(service, factoryMethod + " return type not a subtype");
}
@SuppressWarnings("unchecked")
Class<? extends S> type = (Class<? extends S>) returnType;
return new ProviderImpl<S>(service, type, factoryMethod, acc);
}
}
// no factory method so must be a subtype
if (!service.isAssignableFrom(clazz)) {
fail(service, clazz.getName() + " not a subtype");
}
@SuppressWarnings("unchecked")
Class<? extends S> type = (Class<? extends S>) clazz;
@SuppressWarnings("unchecked")
Constructor<? extends S> ctor = (Constructor<? extends S> ) getConstructor(clazz);
return new ProviderImpl<S>(service, type, ctor, acc);
}
/**
* Implements lazy service provider lookup of service providers that
* are provided by modules in a module layer (or parent layers)
*/
private final class LayerLookupIterator<T>
implements Iterator<Provider<T>>
{
Deque<ModuleLayer> stack = new ArrayDeque<>();
Set<ModuleLayer> visited = new HashSet<>();
Iterator<ServiceProvider> iterator;
Provider<T> nextProvider;
ServiceConfigurationError nextError;
LayerLookupIterator() {
visited.add(layer);
stack.push(layer);
}
private Iterator<ServiceProvider> providers(ModuleLayer layer) {
ServicesCatalog catalog = LANG_ACCESS.getServicesCatalog(layer);
return catalog.findServices(serviceName).iterator();
}
@Override
public boolean hasNext() {
while (nextProvider == null && nextError == null) {
// get next provider to load
while (iterator == null || !iterator.hasNext()) {
// next layer (DFS order)
if (stack.isEmpty())
return false;
ModuleLayer layer = stack.pop();
List<ModuleLayer> parents = layer.parents();
for (int i = parents.size() - 1; i >= 0; i--) {
ModuleLayer parent = parents.get(i);
if (visited.add(parent)) {
stack.push(parent);
}
}
iterator = providers(layer);
}
// attempt to load provider
ServiceProvider provider = iterator.next();
try {
@SuppressWarnings("unchecked")
Provider<T> next = (Provider<T>) loadProvider(provider);
nextProvider = next;
} catch (ServiceConfigurationError e) {
nextError = e;
}
}
return true;
}
@Override
public Provider<T> next() {
if (!hasNext())
throw new NoSuchElementException();
Provider<T> provider = nextProvider;
if (provider != null) {
nextProvider = null;
return provider;
} else {
ServiceConfigurationError e = nextError;
assert e != null;
nextError = null;
throw e;
}
}
}
/**
* Implements lazy service provider lookup of service providers that
* are provided by modules defined to a class loader or to modules in
* layers with a module defined to the class loader.
*/
private final class ModuleServicesLookupIterator<T>
implements Iterator<Provider<T>>
{
ClassLoader currentLoader;
Iterator<ServiceProvider> iterator;
Provider<T> nextProvider;
ServiceConfigurationError nextError;
ModuleServicesLookupIterator() {
this.currentLoader = loader;