public class ServiceRegistry extends Object
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 interface or subclass the class defined by the service itself.
Service providers are stored in one or more categories, each of which is defined by a class of interface (described by a Class object) that all of its members must implement. The set of categories may be changed dynamically.
Only a single instance of a given leaf class (that is, the actual class returned by getClass(), as opposed to any inherited classes or interfaces) may be registered. That is, suppose that the com.mycompany.mypkg.GreenServiceProvider class implements the com.mycompany.mypkg.MyService interface. If a GreenServiceProvider instance is registered, it will be stored in the category defined by the MyService class. If a new instance of GreenServiceProvider is registered, it will replace the previous instance. In practice, service provider objects are usually singletons so this behavior is appropriate.
To declare a service provider, a services subdirectory is placed within the 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 com.mycompany.mypkg.MyServiceImpl which implements the javax.someapi.SomeService interface, the JAR file would contain a file named:
META-INF/services/javax.someapi.SomeServicecontaining the line:
com.mycompany.mypkg.MyService
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.
An application may customize the contents of a registry as it sees fit, so long as it has the appropriate runtime permission.
For more details on declaring service providers, and the JAR format in general, see the JAR File Specification.
RegisterableService
| Modifier and Type | Class and Description |
|---|---|
static interface |
ServiceRegistry
A simple filter interface used by
ServiceRegistry.getServiceProviders to select providers matching an arbitrary criterion.
|
| Constructor and Description |
|---|
ServiceRegistry(Iterator
Constructs a
ServiceRegistry instance with a set of categories taken from the
categories argument.
|
| Modifier and Type | Method and Description |
|---|---|
boolean |
contains(Object
Returns
true if
provider is currently registered.
|
void |
deregisterAll()
Deregisters all currently registered service providers from all categories.
|
void |
deregisterAll(Class
Deregisters all service provider object currently registered under the given category.
|
void |
deregisterServiceProvider(Object
Removes a service provider object from all categories that contain it.
|
<T> boolean |
deregisterServiceProvider(T provider, Class
Removes a service provider object from the given category.
|
void |
finalize()
Finalizes this object prior to garbage collection.
|
Iterator |
getCategories()
Returns an
Iterator of
Class objects indicating the current set of categories.
|
<T> T |
getServiceProviderByClass(Class
Returns the currently registered service provider object that is of the given class type.
|
<T> Iterator |
getServiceProviders(Class
Returns an
Iterator containing all registered service providers in the given category.
|
<T> Iterator |
getServiceProviders(Class
Returns an
Iterator containing service provider objects within a given category that satisfy a criterion imposed by the supplied
ServiceRegistry.Filter object's
filter method.
|
static <T> Iterator |
lookupProviders(Class
Locates and incrementally instantiates the available providers of a given service using the context class loader.
|
static <T> Iterator |
lookupProviders(Class
Searches for implementations of a particular service class using the given class loader.
|
void |
registerServiceProvider(Object
Adds a service provider object to the registry.
|
<T> boolean |
registerServiceProvider(T provider, Class
Adds a service provider object to the registry.
|
void |
registerServiceProviders(Iterator
Adds a set of service provider objects, taken from an
Iterator to the registry.
|
<T> boolean |
setOrdering(Class
Sets a pairwise ordering between two service provider objects within a given category.
|
<T> boolean |
unsetOrdering(Class
Sets a pairwise ordering between two service provider objects within a given category.
|
public ServiceRegistry(Iterator<Class <?>> categories)
ServiceRegistry instance with a set of categories taken from the
categories argument.
categories - an
Iterator containing
Class objects to be used to define categories.
IllegalArgumentException - if
categories is
null.
public static <T> Iterator<T> lookupProviders(Class <T> providerClass, ClassLoader loader)
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 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.
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 providerClass.
providerClass - a
Classobject indicating the class or interface of the service providers being detected.
loader - 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 used.
Iterator that yields provider objects for the given service, in some arbitrary order. The iterator will throw an
Error if a provider-configuration file violates the specified format or if a provider class cannot be found and instantiated.
IllegalArgumentException - if
providerClass is
null.
public static <T> Iterator<T> lookupProviders(Class <T> providerClass)
ClassLoader cl = Thread.currentThread().getContextClassLoader(); return Service.providers(service, cl);
T - the type of the providerClass.
providerClass - a
Classobject indicating the class or interface of the service providers being detected.
Iterator that yields provider objects for the given service, in some arbitrary order. The iterator will throw an
Error if a provider-configuration file violates the specified format or if a provider class cannot be found and instantiated.
IllegalArgumentException - if
providerClass is
null.
public Iterator<Class <?>> getCategories()
Iterator of
Class objects indicating the current set of categories. The iterator will be empty if no categories exist.
Iterator containing
Classobjects.
public <T> boolean registerServiceProvider(T provider,
Class<T> category)
If provider implements the RegisterableService interface, its onRegistration method will be called. Its 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.
T - the type of the provider.
provider - the service provide object to be registered.
category - the category under which to register the provider.
IllegalArgumentException - if
provider is
null.
IllegalArgumentException - if there is no category corresponding to
category.
ClassCastException - if provider does not implement the
Class defined by
category.
public void registerServiceProvider(Objectprovider)
Class it implements.
If provider implements the RegisterableService interface, its onRegistration method will be called once for each category it is registered under. Its onDeregistration method will be called each time it is deregistered from a category or when the registry is finalized.
provider - the service provider object to be registered.
IllegalArgumentException - if
provider is
null.
public void registerServiceProviders(Iterator<?> providers)
Iterator to the registry. Each provider is associated within each category present in the registry whose
Class it implements.
For each entry of providers that implements the RegisterableService interface, its onRegistration method will be called once for each category it is registered under. Its onDeregistration method will be called each time it is deregistered from a category or when the registry is finalized.
providers - an Iterator containing service provider objects to be registered.
IllegalArgumentException - if
providers is
null or contains a
null entry.
public <T> boolean deregisterServiceProvider(T provider,
Class<T> category)
false is returned. Otherwise,
true is returned. If an object of the same class as
provider but not equal (using
==) to
provider is registered, it will not be deregistered.
If provider implements the RegisterableService interface, its onDeregistration method will be called.
T - the type of the provider.
provider - the service provider object to be deregistered.
category - the category from which to deregister the provider.
true if the provider was previously registered in the same category category,
false otherwise.
IllegalArgumentException - if
provider is
null.
IllegalArgumentException - if there is no category corresponding to
category.
ClassCastException - if provider does not implement the class defined by
category.
public void deregisterServiceProvider(Objectprovider)
provider - the service provider object to be deregistered.
IllegalArgumentException - if
provider is
null.
public boolean contains(Objectprovider)
true if
provider is currently registered.
provider - the service provider object to be queried.
true if the given provider has been registered.
IllegalArgumentException - if
provider is
null.
public <T> Iterator<T> getServiceProviders(Class <T> category, boolean useOrdering)
Iterator containing all registered service providers in the given category. If
useOrdering is
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.
T - the type of the category.
category - the category to be retrieved from.
useOrdering -
true if pairwise orderings should be taken account in ordering the returned objects.
Iterator containing service provider objects from the given category, possibly in order.
IllegalArgumentException - if there is no category corresponding to
category.
public <T> Iterator<T> getServiceProviders(Class <T> category, ServiceRegistry .Filter filter, boolean useOrdering)
Iterator containing service provider objects within a given category that satisfy a criterion imposed by the supplied
ServiceRegistry.Filter object's
filter method.
The useOrdering argument controls the ordering of the results using the same rules as getServiceProviders(Class, boolean).
T - the type of the category.
category - the category to be retrieved from.
filter - an instance of
ServiceRegistry.Filter whose
filter method will be invoked.
useOrdering -
true if pairwise orderings should be taken account in ordering the returned objects.
Iterator containing service provider objects from the given category, possibly in order.
IllegalArgumentException - if there is no category corresponding to
category.
public <T> T getServiceProviderByClass(Class<T> providerClass)
null is returned.
T - the type of the provider.
providerClass - the
Class of the desired service provider object.
Classtype, or
null is none is present.
IllegalArgumentException - if
providerClass is
null.
public <T> boolean setOrdering(Class<T> category, T firstProvider, T secondProvider)
false is returned. If the providers previously were ordered in the reverse direction, that ordering is removed.
The ordering will be used by the getServiceProviders methods when their useOrdering argument is true.
T - the type of the category.
category - a
Class object indicating the category under which the preference is to be established.
firstProvider - the preferred provider.
secondProvider - the provider to which
firstProvider is preferred.
true if a previously unset ordering was established.
IllegalArgumentException - if either provider is
null or they are the same object.
IllegalArgumentException - if there is no category corresponding to
category.
public <T> boolean unsetOrdering(Class<T> category, T firstProvider, T secondProvider)
false is returned.
The ordering will be used by the getServiceProviders methods when their useOrdering argument is true.
T - the type of the category.
category - a
Class object indicating the category under which the preference is to be disestablished.
firstProvider - the formerly preferred provider.
secondProvider - the provider to which
firstProvider was formerly preferred.
true if a previously set ordering was disestablished.
IllegalArgumentException - if either provider is
null or they are the same object.
IllegalArgumentException - if there is no category corresponding to
category.
public void deregisterAll(Class<?> category)
category - the category to be emptied.
IllegalArgumentException - if there is no category corresponding to
category.
public void deregisterAll()
public void finalize()
throws Throwable
deregisterAll method is called to deregister all currently registered service providers. This method should not be called from application code.
finalize in class
Object
Throwable - if an error occurs during superclass finalization.
WeakReference,
PhantomReference