Class DiscoverClass
Discover class that implements a given service interface, with discovery and configuration features similar to that employed by standard Java APIs such as JAXP.
In the context of this package, a service interface is defined by a Service Provider Interface (SPI). The SPI is expressed as a Java interface, abstract class, or (base) class that defines an expected programming interface.
DiscoverClass provides the find
methods for locating a
class that implements a service interface (SPI). Each form of
find
varies slightly, but they all perform the same basic
function.
The DiscoverClass.find
methods proceed as follows:
-
Get the name of an implementation class. The name is the first
non-null value obtained from the following resources:
-
The value of the (scoped) system property whose name is the same as
the SPI's fully qualified class name (as given by SPI.class.getName()).
The
ScopedProperties
class provides a way to bind properties by classloader, in a secure hierarchy similar in concept to the way classloader find class and resource files. SeeScopedProperties
for more details.If the ScopedProperties are not set by users, then behaviour is equivalent to
System.getProperty()
. -
The value of a
Properties properties
property, if provided as a parameter, whose name is the same as the SPI's fully qualifed class name (as given by SPI.class.getName()). -
The value obtained using the JDK1.3+ 'Service Provider' specification
(http://java.sun.com/j2se/1.3/docs/guide/jar/jar.html) to locate a
service named
SPI.class.getName()
. This is implemented internally, so there is not a dependency on JDK 1.3+.
-
The value of the (scoped) system property whose name is the same as
the SPI's fully qualified class name (as given by SPI.class.getName()).
The
-
If the name of the implementation class is non-null, load that class.
The class loaded is the first class loaded by the following sequence
of class loaders:
- Thread Context Class Loader
- DiscoverSingleton's Caller's Class Loader
- SPI's Class Loader
- DiscoverSingleton's (this class or wrapper) Class Loader
- System Class Loader
-
If the name of the implementation class is null, AND the default
implementation class name (
defaultImpl
) is null, then an exception is thrown. -
If the name of the implementation class is null, AND the default
implementation class (
defaultImpl
) is non-null, then load the default implementation class. The class loaded is the first class loaded by the following sequence of class loaders:- SPI's Class Loader
- DiscoverSingleton's (this class or wrapper) Class Loader
- System Class Loader
This limits the scope in which the default class loader can be found to the SPI, DiscoverSingleton, and System class loaders. The assumption here is that the default implementation is closely associated with the SPI or system, and is not defined in the user's application space.
An exception is thrown if the class cannot be loaded.
- Verify that the loaded class implements the SPI: an exception is thrown if the loaded class does not implement the SPI.
IMPLEMENTATION NOTE - This implementation is modelled after the SAXParserFactory and DocumentBuilderFactory implementations (corresponding to the JAXP pluggability APIs) found in Apache Xerces.
- Version:
- $Revision: 1090010 $ $Date: 2011-04-07 23:05:58 +0200 (Thu, 07 Apr 2011) $
-
Field Summary
FieldsModifier and TypeFieldDescriptionstatic final PropertiesHolder
Readable placeholder for a null value. -
Constructor Summary
ConstructorsConstructorDescriptionCreate a class instance with dynamic environment (thread context class loader is determined on each call).DiscoverClass
(ClassLoaders classLoaders) Create a class instance with dynamic environment (thread context class loader is determined on each call). -
Method Summary
Modifier and TypeMethodDescriptionstatic <T> String[]
discoverClassNames
(SPInterface<T> spi, Properties properties) Discover names of SPI implementation Classes from properties.<T,
S extends T>
Class<S> Find class implementing SPI.<T,
S extends T>
Class<S> Find class implementing SPI.<T,
S extends T>
Class<S> Find class implementing SPI.<T,
S extends T>
Class<S> find
(Class<T> spiClass, Properties properties) Find class implementing SPI.<T,
S extends T>
Class<S> find
(Class<T> spiClass, Properties properties, String defaultImpl) Find class implementing SPI.static <T,
S extends T>
Class<S> find
(ClassLoaders loaders, SPInterface<T> spi, PropertiesHolder properties, DefaultClassHolder<T> defaultImpl) Find class implementing SPI.getClassLoaders
(Class<?> spiClass) Return the class loaders holder for the given SPI.static String
getManagedProperty
(String propertyName) Load the class whose name is given by the value of a (Managed) System Property.<T> T
newInstance
(Class<T> spiClass) Create new instance of class implementing SPI.<T> T
newInstance
(Class<T> spiClass, String defaultImpl) Create new instance of class implementing SPI.<T> T
newInstance
(Class<T> spiClass, String propertiesFileName, String defaultImpl) Create new instance of class implementing SPI.<T> T
newInstance
(Class<T> spiClass, Properties properties) Create new instance of class implementing SPI.<T> T
newInstance
(Class<T> spiClass, Properties properties, String defaultImpl) Create new instance of class implementing SPI.static <T> T
newInstance
(ClassLoaders loaders, SPInterface<T> spi, PropertiesHolder properties, DefaultClassHolder<T> defaultImpl) Create new instance of class implementing SPI.
-
Field Details
-
nullProperties
Readable placeholder for a null value.
-
-
Constructor Details
-
DiscoverClass
public DiscoverClass()Create a class instance with dynamic environment (thread context class loader is determined on each call). Dynamically construct class loaders on each call. -
DiscoverClass
Create a class instance with dynamic environment (thread context class loader is determined on each call). Cache static list of class loaders for each call.- Parameters:
classLoaders
- The class loaders holder
-
-
Method Details
-
getClassLoaders
Return the class loaders holder for the given SPI.- Parameters:
spiClass
- The SPI type- Returns:
- The class loaders holder for the given SPI
-
find
Find class implementing SPI.- Type Parameters:
T
- The SPI typeS
- Any class extending T- Parameters:
spiClass
- Service Provider Interface Class.- Returns:
- Class implementing the SPI.
- Throws:
DiscoveryException
- Thrown if the name of a class implementing the SPI cannot be found, if the class cannot be loaded, or if the resulting class does not implement (or extend) the SPI.
-
find
public <T,S extends T> Class<S> find(Class<T> spiClass, Properties properties) throws DiscoveryException Find class implementing SPI.- Type Parameters:
T
- The SPI typeS
- Any class extending T- Parameters:
spiClass
- Service Provider Interface Class.properties
- Used to determine name of SPI implementation.- Returns:
- Class implementing the SPI.
- Throws:
DiscoveryException
- Thrown if the name of a class implementing the SPI cannot be found, if the class cannot be loaded, or if the resulting class does not implement (or extend) the SPI.
-
find
public <T,S extends T> Class<S> find(Class<T> spiClass, String defaultImpl) throws DiscoveryException Find class implementing SPI.- Type Parameters:
T
- The SPI typeS
- Any class extending T- Parameters:
spiClass
- Service Provider Interface Class.defaultImpl
- Default implementation name.- Returns:
- Class implementing the SPI.
- Throws:
DiscoveryException
- Thrown if the name of a class implementing the SPI cannot be found, if the class cannot be loaded, or if the resulting class does not implement (or extend) the SPI.
-
find
public <T,S extends T> Class<S> find(Class<T> spiClass, Properties properties, String defaultImpl) throws DiscoveryException Find class implementing SPI.- Type Parameters:
T
- The SPI typeS
- Any class extending T- Parameters:
spiClass
- Service Provider Interface Class.properties
- Used to determine name of SPI implementation,.defaultImpl
- Default implementation class.- Returns:
- Class implementing the SPI.
- Throws:
DiscoveryException
- Thrown if the name of a class implementing the SPI cannot be found, if the class cannot be loaded, or if the resulting class does not implement (or extend) the SPI.
-
find
public <T,S extends T> Class<S> find(Class<T> spiClass, String propertiesFileName, String defaultImpl) throws DiscoveryException Find class implementing SPI.- Type Parameters:
T
- The SPI typeS
- Any class extending T- Parameters:
spiClass
- Service Provider Interface Class.propertiesFileName
- Used to determine name of SPI implementation,.defaultImpl
- Default implementation class.- Returns:
- Class implementing the SPI.
- Throws:
DiscoveryException
- Thrown if the name of a class implementing the SPI cannot be found, if the class cannot be loaded, or if the resulting class does not implement (or extend) the SPI.
-
find
public static <T,S extends T> Class<S> find(ClassLoaders loaders, SPInterface<T> spi, PropertiesHolder properties, DefaultClassHolder<T> defaultImpl) throws DiscoveryException Find class implementing SPI.- Type Parameters:
T
- The SPI typeS
- Any class extending T- Parameters:
loaders
- The class loaders holderspi
- Service Provider Interface Class.properties
- Used to determine name of SPI implementation,.defaultImpl
- Default implementation class.- Returns:
- Class implementing the SPI.
- Throws:
DiscoveryException
- Thrown if the name of a class implementing the SPI cannot be found, if the class cannot be loaded, or if the resulting class does not implement (or extend) the SPI.
-
newInstance
public <T> T newInstance(Class<T> spiClass) throws DiscoveryException, InstantiationException, IllegalAccessException, NoSuchMethodException, InvocationTargetException Create new instance of class implementing SPI.- Type Parameters:
T
- The SPI type- Parameters:
spiClass
- Service Provider Interface Class.- Returns:
- Instance of a class implementing the SPI.
- Throws:
DiscoveryException
- Thrown if the name of a class implementing the SPI cannot be found, if the class cannot be loaded and instantiated, or if the resulting class does not implement (or extend) the SPI.InstantiationException
- seeClass.newInstance()
IllegalAccessException
- seeClass.newInstance()
NoSuchMethodException
- seeClass.newInstance()
InvocationTargetException
- seeClass.newInstance()
-
newInstance
public <T> T newInstance(Class<T> spiClass, Properties properties) throws DiscoveryException, InstantiationException, IllegalAccessException, NoSuchMethodException, InvocationTargetException Create new instance of class implementing SPI.- Type Parameters:
T
- The SPI type- Parameters:
spiClass
- Service Provider Interface Class.properties
- Used to determine name of SPI implementation, and passed to implementation.init() method if implementation implements Service interface.- Returns:
- Instance of a class implementing the SPI.
- Throws:
DiscoveryException
- Thrown if the name of a class implementing the SPI cannot be found, if the class cannot be loaded and instantiated, or if the resulting class does not implement (or extend) the SPI.InstantiationException
- seeClass.newInstance()
IllegalAccessException
- seeClass.newInstance()
NoSuchMethodException
- seeClass.newInstance()
InvocationTargetException
- seeClass.newInstance()
-
newInstance
public <T> T newInstance(Class<T> spiClass, String defaultImpl) throws DiscoveryException, InstantiationException, IllegalAccessException, NoSuchMethodException, InvocationTargetException Create new instance of class implementing SPI.- Type Parameters:
T
- The SPI type- Parameters:
spiClass
- Service Provider Interface Class.defaultImpl
- Default implementation.- Returns:
- Instance of a class implementing the SPI.
- Throws:
DiscoveryException
- Thrown if the name of a class implementing the SPI cannot be found, if the class cannot be loaded and instantiated, or if the resulting class does not implement (or extend) the SPI.InstantiationException
- seeClass.newInstance()
IllegalAccessException
- seeClass.newInstance()
NoSuchMethodException
- seeClass.newInstance()
InvocationTargetException
- seeClass.newInstance()
-
newInstance
public <T> T newInstance(Class<T> spiClass, Properties properties, String defaultImpl) throws DiscoveryException, InstantiationException, IllegalAccessException, NoSuchMethodException, InvocationTargetException Create new instance of class implementing SPI.- Type Parameters:
T
- The SPI type- Parameters:
spiClass
- Service Provider Interface Class.properties
- Used to determine name of SPI implementation, and passed to implementation.init() method if implementation implements Service interface.defaultImpl
- Default implementation.- Returns:
- Instance of a class implementing the SPI.
- Throws:
DiscoveryException
- Thrown if the name of a class implementing the SPI cannot be found, if the class cannot be loaded and instantiated, or if the resulting class does not implement (or extend) the SPI.InstantiationException
- seeClass.newInstance()
IllegalAccessException
- seeClass.newInstance()
NoSuchMethodException
- seeClass.newInstance()
InvocationTargetException
- seeClass.newInstance()
-
newInstance
public <T> T newInstance(Class<T> spiClass, String propertiesFileName, String defaultImpl) throws DiscoveryException, InstantiationException, IllegalAccessException, NoSuchMethodException, InvocationTargetException Create new instance of class implementing SPI.- Type Parameters:
T
- The SPI type- Parameters:
spiClass
- Service Provider Interface Class.propertiesFileName
- Used to determine name of SPI implementation, and passed to implementation.init() method if implementation implements Service interface.defaultImpl
- Default implementation.- Returns:
- Instance of a class implementing the SPI.
- Throws:
DiscoveryException
- Thrown if the name of a class implementing the SPI cannot be found, if the class cannot be loaded and instantiated, or if the resulting class does not implement (or extend) the SPI.InstantiationException
- seeClass.newInstance()
IllegalAccessException
- seeClass.newInstance()
NoSuchMethodException
- seeClass.newInstance()
InvocationTargetException
- seeClass.newInstance()
-
newInstance
public static <T> T newInstance(ClassLoaders loaders, SPInterface<T> spi, PropertiesHolder properties, DefaultClassHolder<T> defaultImpl) throws DiscoveryException, InstantiationException, IllegalAccessException, NoSuchMethodException, InvocationTargetException Create new instance of class implementing SPI.- Type Parameters:
T
- The SPI type- Parameters:
loaders
- The class loaders holderspi
- Service Provider Interface Class.properties
- Used to determine name of SPI implementation, and passed to implementation.init() method if implementation implements Service interface.defaultImpl
- Default implementation.- Returns:
- Instance of a class implementing the SPI.
- Throws:
DiscoveryException
- Thrown if the name of a class implementing the SPI cannot be found, if the class cannot be loaded and instantiated, or if the resulting class does not implement (or extend) the SPI.InstantiationException
- seeClass.newInstance()
IllegalAccessException
- seeClass.newInstance()
NoSuchMethodException
- seeClass.newInstance()
InvocationTargetException
- seeClass.newInstance()
-
discoverClassNames
Discover names of SPI implementation Classes from properties. The names are the non-null values, in order, obtained from the following resources:
- ManagedProperty.getProperty(SPI.class.getName());
- properties.getProperty(SPI.class.getName());
- Type Parameters:
T
- The SPI type- Parameters:
spi
- The SPI representationproperties
- Properties that may define the implementation class name(s).- Returns:
- String[] Name of classes implementing the SPI.
- Throws:
DiscoveryException
- Thrown if the name of a class implementing the SPI cannot be found.
-
getManagedProperty
Load the class whose name is given by the value of a (Managed) System Property.- Parameters:
propertyName
- the name of the system property whose value is the name of the class to load.- Returns:
- The managed property value
- See Also:
-