org.apache.commons.discovery.tools
public class DiscoverClass extends Object
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:
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.
See ScopedProperties
for more details.
If the ScopedProperties are not set by users, then behaviour
is equivalent to System.getProperty()
.
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()).
SPI.class.getName()
. This is implemented
internally, so there is not a dependency on JDK 1.3+.
defaultImpl
) is null,
then an exception is thrown.
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:
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.
IMPLEMENTATION NOTE - This implementation is modelled after the SAXParserFactory and DocumentBuilderFactory implementations (corresponding to the JAXP pluggability APIs) found in Apache Xerces.
Version: $Revision: 165666 $ $Date: 2005-05-02 20:37:26 +0100 (Mon, 02 May 2005) $
Field Summary | |
---|---|
static DefaultClassHolder | nullDefaultImpl
Readable placeholder for a null value. |
static PropertiesHolder | nullProperties
Readable placeholder for a null value. |
Constructor Summary | |
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DiscoverClass()
Create 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 | |
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static String[] | discoverClassNames(SPInterface spi, Properties properties) Discover names of SPI implementation Classes from properties. |
Class | find(Class spiClass)
Find class implementing SPI.
|
Class | find(Class spiClass, Properties properties)
Find class implementing SPI.
|
Class | find(Class spiClass, String defaultImpl)
Find class implementing SPI.
|
Class | find(Class spiClass, Properties properties, String defaultImpl)
Find class implementing SPI.
|
Class | find(Class spiClass, String propertiesFileName, String defaultImpl)
Find class implementing SPI.
|
static Class | find(ClassLoaders loaders, SPInterface spi, PropertiesHolder properties, DefaultClassHolder defaultImpl)
Find class implementing SPI.
|
ClassLoaders | getClassLoaders(Class spiClass) |
static String | getManagedProperty(String propertyName)
Load the class whose name is given by the value of a (Managed)
System Property.
|
Object | newInstance(Class spiClass)
Create new instance of class implementing SPI.
|
Object | newInstance(Class spiClass, Properties properties)
Create new instance of class implementing SPI.
|
Object | newInstance(Class spiClass, String defaultImpl)
Create new instance of class implementing SPI.
|
Object | newInstance(Class spiClass, Properties properties, String defaultImpl)
Create new instance of class implementing SPI.
|
Object | newInstance(Class spiClass, String propertiesFileName, String defaultImpl)
Create new instance of class implementing SPI.
|
static Object | newInstance(ClassLoaders loaders, SPInterface spi, PropertiesHolder properties, DefaultClassHolder defaultImpl)
Create new instance of class implementing SPI.
|
Discover names of SPI implementation Classes from properties. The names are the non-null values, in order, obtained from the following resources:
Parameters: properties 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.
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.
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.
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.
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.
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.
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.
Parameters: attribute the name of the system property whose value is the name of the class to load.
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.
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.
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.
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.
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.
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.