Class ServiceRegistry
- java.lang.Object
-
- javax.imageio.spi.ServiceRegistry
- Direct Known Subclasses:
IIORegistry
public class ServiceRegistry extends Object
A registry for service provider instances for Image I/O service types.
Service providers are stored in one or more categories, each of which is defined by a class or interface (described by a Class
object) that all of its members must implement.
The set of categories supported by this class is limited to the following standard Image I/O service types:
An attempt to load a provider that is not a subtype of one of the above types will result in IllegalArgumentException
.
For the general mechanism to load service providers, see ServiceLoader
, which is the underlying standard mechanism used by this class.
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.GreenImageReaderProvider
class is a subclass of javax.imageio.spi.ImageReaderSpi
. If a GreenImageReaderProvider
instance is registered, it will be stored in the category defined by the ImageReaderSpi
class. If a new instance of GreenImageReaderProvider
is registered, it will replace the previous instance. In practice, service provider objects are usually singletons so this behavior is appropriate.
The service provider classes should 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 information on how to create and deploy service providers, refer to the documentation on ServiceLoader
- See Also:
-
RegisterableService
,ServiceLoader
Nested Class Summary
Modifier and Type | Class | Description |
---|---|---|
static interface | ServiceRegistry.Filter | A simple filter interface used by |
Constructor Summary
Constructor | Description |
---|---|
ServiceRegistry(Iterator<Class<?>> categories) | Constructs a |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
boolean | contains(Object provider) | Returns |
void | deregisterAll() | Deregisters all currently registered service providers from all categories. |
void | deregisterAll(Class<?> category) | Deregisters all service provider object currently registered under the given category. |
void | deregisterServiceProvider(Object provider) | Removes a service provider object from all categories that contain it. |
<T> boolean | deregisterServiceProvider(T provider,
Class<T> category) | Removes a service provider object from the given category. |
void | finalize() | Deprecated. The finalize method has been deprecated. |
Iterator<Class<?>> | getCategories() | Returns an |
<T> T | getServiceProviderByClass(Class<T> providerClass) | Returns the currently registered service provider object that is of the given class type. |
<T> Iterator<T> | getServiceProviders(Class<T> category,
boolean useOrdering) | Returns an |
<T> Iterator<T> | getServiceProviders(Class<T> category,
ServiceRegistry.Filter filter,
boolean useOrdering) | Returns an |
static <T> Iterator<T> | lookupProviders(Class<T> providerClass) | Locates and incrementally instantiates the available providers of a given service using the context class loader. |
static <T> Iterator<T> | lookupProviders(Class<T> providerClass,
ClassLoader loader) | Searches for implementations of a particular service class using the given class loader. |
void | registerServiceProvider(Object provider) | Adds a service provider object to the registry. |
<T> boolean | registerServiceProvider(T provider,
Class<T> category) | Adds a service provider object to the registry. |
void | registerServiceProviders(Iterator<?> providers) | Adds a set of service provider objects, taken from an |
<T> boolean | setOrdering(Class<T> category,
T firstProvider,
T secondProvider) | Sets a pairwise ordering between two service provider objects within a given category. |
<T> boolean | unsetOrdering(Class<T> category,
T firstProvider,
T secondProvider) | Sets a pairwise ordering between two service provider objects within a given category. |
Methods declared in class java.lang.Object
clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Constructor Detail
ServiceRegistry
public ServiceRegistry(Iterator<Class<?>> categories)
Constructs a ServiceRegistry
instance with a set of categories taken from the categories
argument. The categories must all be members of the set of service types listed in the class specification.
- Parameters:
-
categories
- anIterator
containingClass
objects to be used to define categories. - Throws:
-
IllegalArgumentException
- ifcategories
isnull
, or if one of the categories is not an allowed service type.
Method Detail
lookupProviders
public static <T> Iterator<T> lookupProviders(Class<T> providerClass, ClassLoader loader)
Searches for implementations of a particular service class using the given class loader.
The service class must be one of the service types listed in the class specification. If it is not, IllegalArgumentException
will be thrown.
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.
- Type Parameters:
-
T
- the type of the providerClass. - Parameters:
-
providerClass
- aClass
object 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, ornull
if the system class loader (or, failing that the bootstrap class loader) is to be used. - Returns:
- An
Iterator
that yields provider objects for the given service, in some arbitrary order. The iterator will throw anError
if a provider-configuration file violates the specified format or if a provider class cannot be found and instantiated. - Throws:
-
IllegalArgumentException
- ifproviderClass
isnull
, or if it is not one of the allowed service types.
lookupProviders
public static <T> Iterator<T> lookupProviders(Class<T> providerClass)
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);
The service class must be one of the service types listed in the class specification. If it is not, IllegalArgumentException
will be thrown.
- Type Parameters:
-
T
- the type of the providerClass. - Parameters:
-
providerClass
- aClass
object indicating the class or interface of the service providers being detected. - Returns:
- An
Iterator
that yields provider objects for the given service, in some arbitrary order. The iterator will throw anError
if a provider-configuration file violates the specified format or if a provider class cannot be found and instantiated. - Throws:
-
IllegalArgumentException
- ifproviderClass
isnull
, or if it is not one of the allowed service types.
getCategories
public Iterator<Class<?>> getCategories()
Returns an Iterator
of Class
objects indicating the current set of categories. The iterator will be empty if no categories exist.
- Returns:
- an
Iterator
containingClass
objects.
registerServiceProvider
public <T> boolean registerServiceProvider(T provider, Class<T> category)
Adds a service provider object to the registry. The provider is associated with the given 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.
- Type Parameters:
-
T
- the type of the provider. - Parameters:
-
provider
- the service provide object to be registered. -
category
- the category under which to register the provider. - Returns:
- true if no provider of the same class was previously registered in the same category category.
- Throws:
-
IllegalArgumentException
- ifprovider
isnull
. -
IllegalArgumentException
- if there is no category corresponding tocategory
. -
ClassCastException
- if provider does not implement theClass
defined bycategory
.
registerServiceProvider
public void registerServiceProvider(Object provider)
Adds a service provider object to the registry. The provider is associated within each category present in the registry whose 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.
- Parameters:
-
provider
- the service provider object to be registered. - Throws:
-
IllegalArgumentException
- ifprovider
isnull
.
registerServiceProviders
public void registerServiceProviders(Iterator<?> providers)
Adds a set of service provider objects, taken from an 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.
- Parameters:
-
providers
- an Iterator containing service provider objects to be registered. - Throws:
-
IllegalArgumentException
- ifproviders
isnull
or contains anull
entry.
deregisterServiceProvider
public <T> boolean deregisterServiceProvider(T provider, Class<T> category)
Removes a service provider object from the given category. If the provider was not previously registered, nothing happens and 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.
- Type Parameters:
-
T
- the type of the provider. - Parameters:
-
provider
- the service provider object to be deregistered. -
category
- the category from which to deregister the provider. - Returns:
-
true
if the provider was previously registered in the same category category,false
otherwise. - Throws:
-
IllegalArgumentException
- ifprovider
isnull
. -
IllegalArgumentException
- if there is no category corresponding tocategory
. -
ClassCastException
- if provider does not implement the class defined bycategory
.
deregisterServiceProvider
public void deregisterServiceProvider(Object provider)
Removes a service provider object from all categories that contain it.
- Parameters:
-
provider
- the service provider object to be deregistered. - Throws:
-
IllegalArgumentException
- ifprovider
isnull
.
contains
public boolean contains(Object provider)
Returns true
if provider
is currently registered.
- Parameters:
-
provider
- the service provider object to be queried. - Returns:
-
true
if the given provider has been registered. - Throws:
-
IllegalArgumentException
- ifprovider
isnull
.
getServiceProviders
public <T> Iterator<T> getServiceProviders(Class<T> category, boolean useOrdering)
Returns an 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.
- Type Parameters:
-
T
- the type of the category. - Parameters:
-
category
- the category to be retrieved from. -
useOrdering
-true
if pairwise orderings should be taken account in ordering the returned objects. - Returns:
- an
Iterator
containing service provider objects from the given category, possibly in order. - Throws:
-
IllegalArgumentException
- if there is no category corresponding tocategory
.
getServiceProviders
public <T> Iterator<T> getServiceProviders(Class<T> category, ServiceRegistry.Filter filter, boolean useOrdering)
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.
The useOrdering
argument controls the ordering of the results using the same rules as getServiceProviders(Class, boolean)
.
- Type Parameters:
-
T
- the type of the category. - Parameters:
-
category
- the category to be retrieved from. -
filter
- an instance ofServiceRegistry.Filter
whosefilter
method will be invoked. -
useOrdering
-true
if pairwise orderings should be taken account in ordering the returned objects. - Returns:
- an
Iterator
containing service provider objects from the given category, possibly in order. - Throws:
-
IllegalArgumentException
- if there is no category corresponding tocategory
.
getServiceProviderByClass
public <T> T getServiceProviderByClass(Class<T> providerClass)
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, null
is returned.
- Type Parameters:
-
T
- the type of the provider. - Parameters:
-
providerClass
- theClass
of the desired service provider object. - Returns:
- a currently registered service provider object with the desired
Class
type, ornull
is none is present. - Throws:
-
IllegalArgumentException
- ifproviderClass
isnull
.
setOrdering
public <T> boolean setOrdering(Class<T> category, T firstProvider, T secondProvider)
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 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
.
- Type Parameters:
-
T
- the type of the category. - Parameters:
-
category
- aClass
object indicating the category under which the preference is to be established. -
firstProvider
- the preferred provider. -
secondProvider
- the provider to whichfirstProvider
is preferred. - Returns:
-
true
if a previously unset ordering was established. - Throws:
-
IllegalArgumentException
- if either provider isnull
or they are the same object. -
IllegalArgumentException
- if there is no category corresponding tocategory
.
unsetOrdering
public <T> boolean unsetOrdering(Class<T> category, T firstProvider, T secondProvider)
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 false
is returned.
The ordering will be used by the getServiceProviders
methods when their useOrdering
argument is true
.
- Type Parameters:
-
T
- the type of the category. - Parameters:
-
category
- aClass
object indicating the category under which the preference is to be disestablished. -
firstProvider
- the formerly preferred provider. -
secondProvider
- the provider to whichfirstProvider
was formerly preferred. - Returns:
-
true
if a previously set ordering was disestablished. - Throws:
-
IllegalArgumentException
- if either provider isnull
or they are the same object. -
IllegalArgumentException
- if there is no category corresponding tocategory
.
deregisterAll
public void deregisterAll(Class<?> category)
Deregisters all service provider object currently registered under the given category.
- Parameters:
-
category
- the category to be emptied. - Throws:
-
IllegalArgumentException
- if there is no category corresponding tocategory
.
deregisterAll
public void deregisterAll()
Deregisters all currently registered service providers from all categories.
finalize
@Deprecated(since="9") public void finalize() throws Throwable
finalize
method has been deprecated. Subclasses that override finalize
in order to perform cleanup should be modified to use alternative cleanup mechanisms and to remove the overriding finalize
method. When overriding the finalize
method, its implementation must explicitly ensure that super.finalize()
is invoked as described in Object.finalize()
. See the specification for Object.finalize()
for further information about migration options.Finalizes this object prior to garbage collection. The deregisterAll
method is called to deregister all currently registered service providers. This method should not be called from application code.
- Overrides:
-
finalize
in classObject
- Throws:
-
Throwable
- if an error occurs during superclass finalization. - See Also:
-
WeakReference
,PhantomReference