FileDocCategorySizeDatePackage
ServiceRegistry.javaAPI DocJava SE 6 API29993Tue Jun 10 00:26:08 BST 2008javax.imageio.spi

ServiceRegistry

public class ServiceRegistry extends Object
A registry for service provider instances.

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.SomeService 
containing 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.

see
RegisterableService
version
0.5

Fields Summary
private Map
categoryMap
Constructors Summary
public ServiceRegistry(Iterator categories)
Constructs a ServiceRegistry instance with a set of categories taken from the categories argument.

param
categories an Iterator containing Class objects to be used to define categories.
exception
IllegalArgumentException if categories is null.


                                          
       
        if (categories == null) {
            throw new IllegalArgumentException("categories == null!");
        }
        while (categories.hasNext()) {
            Class category = (Class)categories.next();
            SubRegistry reg = new SubRegistry(this, category);
            categoryMap.put(category, reg);
        }
    
Methods Summary
public booleancontains(java.lang.Object provider)
Returns true if provider is currently registered.

param
provider the service provider object to be queried.
return
true if the given provider has been registered.
exception
IllegalArgumentException if provider is null.

        if (provider == null) {
            throw new IllegalArgumentException("provider == null!");
        }
        Iterator regs = getSubRegistries(provider);
        while (regs.hasNext()) {
            SubRegistry reg = (SubRegistry)regs.next();
            if (reg.contains(provider)) {
                return true;
            }
        }

        return false;
    
public voidderegisterAll(java.lang.Class category)
Deregisters all service provider object currently registered under the given category.

param
category the category to be emptied.
exception
IllegalArgumentException if there is no category corresponding to category.

        SubRegistry reg = (SubRegistry)categoryMap.get(category);
        if (reg == null) {
            throw new IllegalArgumentException("category unknown!");
        }
        reg.clear();
    
public voidderegisterAll()
Deregisters all currently registered service providers from all categories.

        Iterator iter = categoryMap.values().iterator();
        while (iter.hasNext()) {
            SubRegistry reg = (SubRegistry)iter.next();
            reg.clear();
        }
    
public voidderegisterServiceProvider(java.lang.Object provider)
Removes a service provider object from all categories that contain it.

param
provider the service provider object to be deregistered.
exception
IllegalArgumentException if provider is null.

        if (provider == null) {
            throw new IllegalArgumentException("provider == null!");
        }
        Iterator regs = getSubRegistries(provider);
        while (regs.hasNext()) {
            SubRegistry reg = (SubRegistry)regs.next();
            reg.deregisterServiceProvider(provider);
        }
    
public booleanderegisterServiceProvider(T provider, java.lang.Class 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.

param
provider the service provider object to be deregistered.
param
category the category from which to deregister the provider.
return
true if the provider was previously registered in the same category category, false otherwise.
exception
IllegalArgumentException if provider is null.
exception
IllegalArgumentException if there is no category corresponding to category.
exception
ClassCastException if provider does not implement the class defined by category.

        if (provider == null) {
            throw new IllegalArgumentException("provider == null!");
        }
        SubRegistry reg = (SubRegistry)categoryMap.get(category);
        if (reg == null) {
            throw new IllegalArgumentException("category unknown!");
        }
        if (!category.isAssignableFrom(provider.getClass())) {
            throw new ClassCastException();
        }
        return reg.deregisterServiceProvider(provider);
    
public voidfinalize()
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.

exception
Throwable if an error occurs during superclass finalization.

        deregisterAll();
        super.finalize();
    
public java.util.IteratorgetCategories()
Returns an Iterator of Class objects indicating the current set of categories. The iterator will be empty if no categories exist.

return
an Iterator containing Classobjects.

        Set keySet = categoryMap.keySet();
        return keySet.iterator();
    
public TgetServiceProviderByClass(java.lang.Class 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.

param
providerClass the Class of the desired service provider object.
return
a currently registered service provider object with the desired Classtype, or null is none is present.
exception
IllegalArgumentException if providerClass is null.

        if (providerClass == null) {
            throw new IllegalArgumentException("providerClass == null!");
        }
        Iterator iter = categoryMap.keySet().iterator();
        while (iter.hasNext()) {
            Class c = (Class)iter.next();
            if (c.isAssignableFrom(providerClass)) {
                SubRegistry reg = (SubRegistry)categoryMap.get(c);
                T provider = reg.getServiceProviderByClass(providerClass);
                if (provider != null) {
                    return provider;
                }
            }
        }
        return null;
    
public java.util.IteratorgetServiceProviders(java.lang.Class 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.

param
category the category to be retrieved from.
param
useOrdering true if pairwise orderings should be taken account in ordering the returned objects.
return
an Iterator containing service provider objects from the given category, possibly in order.
exception
IllegalArgumentException if there is no category corresponding to category.

        SubRegistry reg = (SubRegistry)categoryMap.get(category);
        if (reg == null) {
            throw new IllegalArgumentException("category unknown!");
        }
        return reg.getServiceProviders(useOrdering);
    
public java.util.IteratorgetServiceProviders(java.lang.Class category, javax.imageio.spi.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).

param
category the category to be retrieved from.
param
filter an instance of ServiceRegistry.Filter whose filter method will be invoked.
param
useOrdering true if pairwise orderings should be taken account in ordering the returned objects.
return
an Iterator containing service provider objects from the given category, possibly in order.
exception
IllegalArgumentException if there is no category corresponding to category.

        SubRegistry reg = (SubRegistry)categoryMap.get(category);
        if (reg == null) {
            throw new IllegalArgumentException("category unknown!");
        }
        Iterator iter = getServiceProviders(category, useOrdering);
        return new FilterIterator(iter, filter);
    
private java.util.IteratorgetSubRegistries(java.lang.Object provider)
Returns an Iterator containing the subregistries to which the provider belongs.

        List l = new ArrayList();
        Iterator iter = categoryMap.keySet().iterator();
        while (iter.hasNext()) {
            Class c = (Class)iter.next();
            if (c.isAssignableFrom(provider.getClass())) {
                l.add((SubRegistry)categoryMap.get(c));
            }
        }
        return l.iterator();
    
public static java.util.IteratorlookupProviders(java.lang.Class providerClass, java.lang.ClassLoader loader)
Searches for implementations of a particular service class using the given class 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.

param
providerClass a Classobject indicating the class or interface of the service providers being detected.
param
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.
return
An 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.
exception
IllegalArgumentException if providerClass is null.

        if (providerClass == null) {
            throw new IllegalArgumentException("providerClass == null!");
        }
	return Service.providers(providerClass, loader);
    
public static java.util.IteratorlookupProviders(java.lang.Class 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);

param
providerClass a Classobject indicating the class or interface of the service providers being detected.
return
An 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.
exception
IllegalArgumentException if providerClass is null.

        if (providerClass == null) {
            throw new IllegalArgumentException("providerClass == null!");
        }
	return Service.providers(providerClass);
    
public booleanregisterServiceProvider(T provider, java.lang.Class 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.

param
provider the service provide object to be registered.
param
category the category under which to register the provider.
return
true if no provider of the same class was previously registered in the same category category.
exception
IllegalArgumentException if provider is null.
exception
IllegalArgumentException if there is no category corresponding to category.
exception
ClassCastException if provider does not implement the Class defined by category.

        if (provider == null) {
            throw new IllegalArgumentException("provider == null!");
        }
        SubRegistry reg = (SubRegistry)categoryMap.get(category);
        if (reg == null) {
            throw new IllegalArgumentException("category unknown!");
        }
        if (!category.isAssignableFrom(provider.getClass())) {
            throw new ClassCastException();
        }
        
        return reg.registerServiceProvider(provider);
    
public voidregisterServiceProvider(java.lang.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.

param
provider the service provider object to be registered.
exception
IllegalArgumentException if provider is null.

        if (provider == null) {
            throw new IllegalArgumentException("provider == null!");
        }
        Iterator regs = getSubRegistries(provider);
        while (regs.hasNext()) {
            SubRegistry reg = (SubRegistry)regs.next();
            reg.registerServiceProvider(provider);
        }
    
public voidregisterServiceProviders(java.util.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.

param
providers an Iterator containing service provider objects to be registered.
exception
IllegalArgumentException if providers is null or contains a null entry.

        if (providers == null) {
            throw new IllegalArgumentException("provider == null!");
        }
        while (providers.hasNext()) {
            registerServiceProvider(providers.next());
        }
    
public booleansetOrdering(java.lang.Class 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.

param
category a Class object indicating the category under which the preference is to be established.
param
firstProvider the preferred provider.
param
secondProvider the provider to which firstProvider is preferred.
return
true if a previously unset ordering was established.
exception
IllegalArgumentException if either provider is null or they are the same object.
exception
IllegalArgumentException if there is no category corresponding to category.

        if (firstProvider == null || secondProvider == null) {
            throw new IllegalArgumentException("provider is null!");
        }
        if (firstProvider == secondProvider) {
            throw new IllegalArgumentException("providers are the same!");
        }
        SubRegistry reg = (SubRegistry)categoryMap.get(category);
        if (reg == null) {
            throw new IllegalArgumentException("category unknown!");
        }
        if (reg.contains(firstProvider) &&
            reg.contains(secondProvider)) {
            return reg.setOrdering(firstProvider, secondProvider);
        }
        return false;
    
public booleanunsetOrdering(java.lang.Class 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.

param
category a Class object indicating the category under which the preference is to be disestablished.
param
firstProvider the formerly preferred provider.
param
secondProvider the provider to which firstProvider was formerly preferred.
return
true if a previously set ordering was disestablished.
exception
IllegalArgumentException if either provider is null or they are the same object.
exception
IllegalArgumentException if there is no category corresponding to category.

        if (firstProvider == null || secondProvider == null) {
            throw new IllegalArgumentException("provider is null!");
        }
        if (firstProvider == secondProvider) {
            throw new IllegalArgumentException("providers are the same!");
        }
        SubRegistry reg = (SubRegistry)categoryMap.get(category);
        if (reg == null) {
            throw new IllegalArgumentException("category unknown!");
        }
        if (reg.contains(firstProvider) &&
            reg.contains(secondProvider)) {
            return reg.unsetOrdering(firstProvider, secondProvider);
        }
        return false;