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/*
* Copyright(C) OASIS(R) 2005,2009. All Rights Reserved.
* OASIS trademark, IPR and other policies apply.
*/
package org.oasisopen.sca.client.impl;
import java.io.BufferedReader;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.Properties;
import org.oasisopen.sca.SCARuntimeException;
import org.oasisopen.sca.client.SCAClientFactory;
/**
* This is a default class that returns an SCAClientFactory implementation -
* this class can be replaced by a vendor implementation.
*
* @see SCAClientFactory
* @author OASIS Open
*/
public class SCAClientFactoryFinder {
/**
* The name of the System Property used to determine the SPI implementation
* to use for the SCAClientFactory.
*/
private static final String SCA_CLIENT_FACTORY_PROVIDER_KEY = SCAClientFactory.class.getName();
/**
* The name of the file loaded from the ClassPath to determine 2488 the SPI
* implementation to use for the SCAClientFactory. 2489
*/
private static final String SCA_CLIENT_FACTORY_PROVIDER_META_INF_SERVICE = "META-INF/services/" + SCA_CLIENT_FACTORY_PROVIDER_KEY;
/**
* Private Constructor.
*/
private SCAClientFactoryFinder() {
}
/**
* Creates an instance of the SCAClientFactory implementation. This
* discovers the SCAClientFactory implementation and instantiates the
* provider's implementation.
*
* @param properties Properties that may be used when creating a new
* instance of the SCAClient
* @param classLoader ClassLoader that may be used when creating a new
* instance of the SCAClient
* @return new instance of the SCAClientFactory
* @throws SCARuntimeException Failed to create SCAClientFactory
* implementation.
*/
public static SCAClientFactory find(Properties properties, ClassLoader classLoader) {
if (classLoader == null) {
classLoader = getThreadContextClassLoader();
if (classLoader == null) {
classLoader = SCAClientFactoryFinder.class.getClassLoader();
}
}
final String factoryImplClassName = discoverProviderFactoryImplClass(properties, classLoader);
final Class<? extends SCAClientFactory> factoryImplClass = loadProviderFactoryClass(factoryImplClassName, classLoader);
final SCAClientFactory factory = instantiateSCAClientFactoryClass(factoryImplClass);
return factory;
}
/**
* Gets the Context ClassLoader for the current Thread.
*
* @return The Context ClassLoader for the current Thread.
*/
private static ClassLoader getThreadContextClassLoader() {
final ClassLoader threadClassLoader = Thread.currentThread().getContextClassLoader();
return threadClassLoader;
}
/**
* Attempts to discover the class name for the SCAClientFactory
* implementation from the specified Properties, the System Properties or
* the specified ClassLoader.
*
* @return The class name of the SCAClientFactory implementation
* @throw SCARuntimeException Failed to find implementation for
* SCAClientFactory.
*/
private static String discoverProviderFactoryImplClass(Properties properties, ClassLoader classLoader) throws SCARuntimeException {
String providerClassName = checkPropertiesForSPIClassName(properties);
if (providerClassName != null) {
return providerClassName;
}
providerClassName = checkPropertiesForSPIClassName(System.getProperties());
if (providerClassName != null) {
return providerClassName;
}
return checkMETAINFServicesForClassName(classLoader);
}
/**
* Attempts to find the class name for the SCAClientFactory implementation
* from the specified Properties.
*
* @return The class name for the SCAClientFactory implementation or
* <code>null</code> if not found.
*/
private static String checkPropertiesForSPIClassName(Properties properties) {
if (properties == null) {
return null;
}
final String providerClassName = properties.getProperty(SCA_CLIENT_FACTORY_PROVIDER_KEY);
if (providerClassName != null && providerClassName.length() > 0) {
return providerClassName;
}
return null;
}
/**
* Attempts to find the class name for the SCAClientFactory implementation
* from the META-INF/services directory
*
* @return The class name for the SCAClientFactory implementation or
* <code>null</code> if not found.
*/
private static String checkMETAINFServicesForClassName(ClassLoader cl) {
final URL url = cl.getResource(SCA_CLIENT_FACTORY_PROVIDER_META_INF_SERVICE);
if (url == null) {
return null;
}
InputStream in = null;
try {
in = url.openStream();
BufferedReader reader = null;
try {
reader = new BufferedReader(new InputStreamReader(in, "UTF-8"));
String line;
while ((line = readNextLine(reader)) != null) {
if (!line.startsWith("#") && line.length() > 0) {
return line;
}
}
return null;
} finally {
closeStream(reader);
}
} catch (IOException ex) {
throw new SCARuntimeException("Failed to discover SCAClientFactory provider", ex);
} finally {
closeStream(in);
}
}
/**
* Reads the next line from the reader and returns the trimmed version of
* that line
*
* @param reader The reader from which to read the next line
* @return The trimmed next line or <code>null</code> if the end of the
* stream has been reached
* @throws IOException I/O error occurred while reading from Reader
*/
private static String readNextLine(BufferedReader reader) throws IOException {
String line = reader.readLine();
if (line != null) {
line = line.trim();
}
return line;
}
/**
* Loads the specified SCAClientFactory implementation class.
*
* @param factoryImplClassName The name of the SCAClientFactory
* Implementation class to load
* @return The specified SCAClientFactory Implementation class
* @throws SCARuntimeException Failed to load the SCAClientFactory
* implementation class
*/
private static Class<? extends SCAClientFactory> loadProviderFactoryClass(String factoryImplClassName, ClassLoader classLoader)
throws SCARuntimeException {
try {
final Class<?> providerClass = classLoader.loadClass(factoryImplClassName);
final Class<? extends SCAClientFactory> providerFactoryClass = providerClass.asSubclass(SCAClientFactory.class);
return providerFactoryClass;
} catch (ClassNotFoundException ex) {
throw new SCARuntimeException("Failed to load SCAClientFactory implementation class " + factoryImplClassName, ex);
} catch (ClassCastException ex) {
throw new SCARuntimeException("Loaded SCAClientFactory implementation class " + factoryImplClassName
+ " is not a subclass of "
+ SCAClientFactory.class.getName(), ex);
}
}
/**
* Instantiate an instance of the specified SCAClientFactory implementation
* class.
*
* @param factoryImplClass The SCAClientFactory implementation class to
* instantiate.
* @return An instance of the SCAClientFactory implementation class
* @throws SCARuntimeException Failed to instantiate the specified specified
* SCAClientFactory implementation class
*/
private static SCAClientFactory instantiateSCAClientFactoryClass(Class<? extends SCAClientFactory> factoryImplClass) throws SCARuntimeException {
try {
final SCAClientFactory provider = factoryImplClass.newInstance();
return provider;
} catch (Throwable ex) {
throw new SCARuntimeException("Failed to instantiate SCAClientFactory implementation class " + factoryImplClass, ex);
}
}
/**
* Utility method for closing Closeable Object.
*
* @param closeable The Object to close.
*/
private static void closeStream(Closeable closeable) {
if (closeable != null) {
try {
closeable.close();
} catch (IOException ex) {
throw new SCARuntimeException("Failed to close stream", ex);
}
}
}
}
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