T - the type of the service instance.public final class ServiceFinder<T> extends Object implements Iterable<T>
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.
The default service provider registration/lookup mechanism based on META-INF/services files is described below. For environments, where the basic mechanism is not suitable, clients can enforce a different approach by setting their custom ServiceIteratorProvider by calling setIteratorProvider. The call must be made prior to any lookup attempts.
A service provider identifies itself by placing a provider-configuration file in the resource directory 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 '#' (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 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 null if it cannot translate the given encoding. Typical CharCodec providers will support more than one encoding.
If sun.io.StandardCodec is a provider of the CharCodec service then its jar file would contain the file META-INF/services/java.io.spi.CharCodec. This file would contain the single line:
sun.io.StandardCodec # Standard codecs for the platformTo 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.| Modifier and Type | Class and Description |
|---|---|
static class |
ServiceFinder.DefaultServiceIteratorProvider
The default service iterator provider that looks up provider classes in
META-INF/services files.
|
static class |
ServiceFinder.ServiceIteratorProvider
Supports iteration of provider instances or classes.
|
| Modifier and Type | Method and Description |
|---|---|
static <T> ServiceFinder<T> |
find(Class<T> service)
Locates and incrementally instantiates the available providers of a
given service using the context class loader.
|
static <T> ServiceFinder<T> |
find(Class<T> service,
boolean ignoreOnClassNotFound)
Locates and incrementally instantiates the available providers of a
given service using the context class loader.
|
static <T> ServiceFinder<T> |
find(Class<T> service,
ClassLoader loader)
Locates and incrementally instantiates the available providers of a
given service using the given class loader.
|
static <T> ServiceFinder<T> |
find(Class<T> service,
ClassLoader loader,
boolean ignoreOnClassNotFound)
Locates and incrementally instantiates the available providers of a
given service using the given class loader.
|
static ServiceFinder<?> |
find(String serviceName)
Locates and incrementally instantiates the available classes of a given
service file using the context class loader.
|
Iterator<T> |
iterator()
Returns discovered objects incrementally.
|
static void |
setIteratorProvider(ServiceFinder.ServiceIteratorProvider sip)
Register the service iterator provider to iterate on provider instances
or classes.
|
T[] |
toArray()
Returns discovered objects all at once.
|
Class<T>[] |
toClassArray()
Returns discovered classes all at once.
|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, waitforEach, spliteratorpublic static <T> ServiceFinder<T> find(Class<T> service, ClassLoader loader) throws ServiceConfigurationError
This method transforms the name of the given service class into a provider-configuration filename as described above and then uses the 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.
T - the type of the service instance.service - The service's abstract service classloader - The class loader to be used to load provider-configuration files
and instantiate provider classes, or null if the system
class loader (or, failing that the bootstrap class loader) is to
be usedServiceConfigurationError - If a provider-configuration file violates the specified format
or names a provider class that cannot be found and instantiatedfind(Class)public static <T> ServiceFinder<T> find(Class<T> service, ClassLoader loader, boolean ignoreOnClassNotFound) throws ServiceConfigurationError
This method transforms the name of the given service class into a provider-configuration filename as described above and then uses the 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.
T - the type of the service instance.service - The service's abstract service classloader - The class loader to be used to load provider-configuration files
and instantiate provider classes, or null if the system
class loader (or, failing that the bootstrap class loader) is to
be usedignoreOnClassNotFound - If a provider cannot be loaded by the class loader
then move on to the next available provider.ServiceConfigurationError - If a provider-configuration file violates the specified format
or names a provider class that cannot be found and instantiatedfind(Class)public static <T> ServiceFinder<T> find(Class<T> service) throws ServiceConfigurationError
ClassLoader cl = Thread.currentThread().getContextClassLoader(); return Service.providers(service, cl, false);
T - the type of the service instance.service - The service's abstract service classServiceConfigurationError - If a provider-configuration file violates the specified format
or names a provider class that cannot be found and instantiatedfind(Class, ClassLoader)public static <T> ServiceFinder<T> find(Class<T> service, boolean ignoreOnClassNotFound) throws ServiceConfigurationError
ClassLoader cl = Thread.currentThread().getContextClassLoader(); boolean ingore = ... return Service.providers(service, cl, ignore);
T - the type of the service instance.service - The service's abstract service classignoreOnClassNotFound - If a provider cannot be loaded by the class loader
then move on to the next available provider.ServiceConfigurationError - If a provider-configuration file violates the specified format
or names a provider class that cannot be found and instantiatedfind(Class, ClassLoader)public static ServiceFinder<?> find(String serviceName) throws ServiceConfigurationError
serviceName - the service name correspond to a file in
META-INF/services that contains a list of fully qualified class
namesServiceConfigurationError - If a service file violates the specified format
or names a provider class that cannot be found and instantiatedpublic static void setIteratorProvider(ServiceFinder.ServiceIteratorProvider sip) throws SecurityException
The default implementation registered, ServiceFinder.DefaultServiceIteratorProvider,
looks up provider classes in META-INF/service files.
This method must be called prior to any attempts to obtain provider instances or classes.
sip - the service iterator provider.SecurityException - if the provider cannot be registered.public Iterator<T> iterator()
iterator in interface Iterable<T>public T[] toArray() throws ServiceConfigurationError
ServiceConfigurationError - If a provider-configuration file violates the specified format
or names a provider class that cannot be found and instantiatedpublic Class<T>[] toClassArray() throws ServiceConfigurationError
ServiceConfigurationError - If a provider-configuration file violates the specified format
or names a provider class that cannot be foundCopyright © 2007-2021, Oracle and/or its affiliates. All Rights Reserved. Use is subject to license terms.