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package com.sun.enterprise.pluggable;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.util.Properties;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* An abstract base class for implementing a PluggableFeatureFactory interface i * using dynamic proxies. This class does not directly implement the interface
* PluggableFeatureFactory, but an proxy instance implementing the interface
* can be obtained by a call to the static method getInstance(). In reality,
* this class implements InvocationHnalder interface used to handle method
* invocations on a dynamic proxy object.
*/
public abstract class PluggableFeatureFactoryBaseImpl implements InvocationHandler {
/**
* Reference to a logger used to log exceptions.
*/
private Logger _logger;
/**
* A property object that keeps interface names and the names of
* corresponding implementation classes.
*/
private Properties _featureImplClasses;
/**
* Private constructor. The public instances of this object are not
* available. The instance of this class is however used as invocation
* handler for dynamic proxy returned by static method getInstance().
*/
protected PluggableFeatureFactoryBaseImpl(Logger logger) {
_logger = logger;
}
/**
* Handle a invocation on a proxy object. This implementation looks for
* a property key matching the return type of the method, then takes the
* value of the property, assumes it to be a class name, assumes that the
* class has a default public constructor and then creates an instance of
* that class and returns it.
*/
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
String featureName = findFeatureFromMethod(method);
String className = _featureImplClasses.getProperty(featureName);
Object featureImpl = Class.forName(className).newInstance();
return featureImpl;
}
protected abstract String getDefaultFeatureFactoryPropertyName();
/**
* Get an instance of a pluggable feature factory using the system
* property com.sun.appserv.pluggable.features. The value of the system
* property is expected to be the name of a class that extends
* java.util.Properties and defines one property for every supported
* pluggable feature. This method calls getInstance(String) if the
* value of com.sun.appserv.pluggable.features is not null.
*
* The property com.sun.appserv.pluggable.features is defined as a
* constant in the interface PluggableFeatureFactory and the implementation
* uses that (PluggableFeatureFactory.PLUGGABLE_FEATURES_PROPERTY_NAME)
*
* @return the return value from call to getInstance(String) if the
* system property is defined, null otherwise.
* @see getInstance(String propClassName)
*/
public Object getInstance() {
String propClassName = System.getProperty(
getDefaultFeatureFactoryPropertyName());
return getInstance(propClassName);
}
/**
* Get an instance of a pluggable feature factory using specified property
* class name. The method expects name of a class that extends
* java.util.Properties and has a default (null or no argument) constructor.
* This method will create an instance of specified class and then
* call getInstance(Properties). If an instance of specified class name can
* not be created, the method logs the exception to the logger specified
* by setLogger() method, or to System.err (if no logger was set).
*
* @param propClassName name of a class that extends Properties and contains
* a property for every supported pluggable feature.
*
* @return the return value from getInstance(Properties) if propClassName
* is not null and an instance of the class represented by propClassName
* was successfully created, null otherwise.
* @see getInstance(java.util.Properties props)
*/
public Object getInstance(String propClassName) {
if (propClassName == null) {
return null;
}
Properties props = null;
try {
props = (Properties)Class.forName(propClassName).newInstance();
} catch (Exception ex) {
String msg = "Error loading pluggable features class "
+ propClassName;
if (_logger != null) {
_logger.log(Level.WARNING, msg, ex);
} else {
System.err.println(msg + "\nStack Trace:");
ex.printStackTrace();
}
}
return getInstance(props);
}
/**
* Get an instance of a pluggable feature factory. The method expects
* a property object as parameter that has one property for every supported
* pluggable feature. The property name is the name of the interface
* (without package name) and property value is the fully qualified name of
* the class that implements the interface. The implementing class must
* have a default public constructor.
*
* @param props properties defining name of feature and implementing
* classes. Name of the feature is the class name of the interface
* defining the feature.
* @return a proxy object implementing the interface
* PluggableFeatureFactory. If specified parameter props is null,
* the method returns null.
*/
protected abstract Object createFeatureFactory(InvocationHandler handler);
public Object getInstance(Properties props) {
if (props == null) {
return null;
}
_featureImplClasses = props;
return createFeatureFactory(this);
}
/**
* Find feature name from a method. For the interface
* PluggableFeatureFactory, a feature name is name of the interface
* defining the feature. The return type of any method in the interface
* PluggableFeatureFactory is the interface defining the feature (Note
* that the interface only contains getter methods). For example, if one
* of the pluggable features is defined by the interface
* com.sun.enterprise.server.pluggable.CoolStuff, the corresponding
* feature name is CoolStuff.
*/
private String findFeatureFromMethod(Method method) {
Class returnType = method.getReturnType();
return Utils.getNQClassName(returnType);
}
}
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