FactoryLocator.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package javax.xml.stream;

import java.io.InputStream;
import java.io.File;
import java.io.FileInputStream;

import java.util.Arrays;
import java.util.Properties;
import java.io.BufferedReader;
import java.io.InputStreamReader;

/*
 * Here is the beef on the finding the Factory Class
 * 
 * 1. Use the javax.xml.stream.XMLInputFactory system property. 2. Use the
 * properties file "lib/stax.properties" in the JRE directory. This
 * configuration file is in standard java.util.Properties format and contains
 * the fully qualified name of the implementation class with the key being the
 * system property defined above. 3. Use the Services API (as detailed in the
 * JAR specification), if available, to determine the classname. The Services
 * API will look for a classname in the file
 * META-INF/services/javax.xml.stream.XMLInputFactory in jars available to the
 * runtime. Platform default XMLInputFactory instance.
 * 
 * If the user provided a classloader we'll use that...if not, we'll assume the 
 * classloader of this class.
 */

class FactoryLocator {
	static Object locate(String factoryId) throws FactoryConfigurationError {
		return locate(factoryId, null);
	}

	static Object locate(String factoryId, String[] altClassName)
			throws FactoryConfigurationError {
		return locate(factoryId, altClassName,
                              Thread.currentThread().getContextClassLoader());
	}

	static Object locate(String factoryId, String[] altClassName,
                         ClassLoader classLoader) throws FactoryConfigurationError {
        try {
            // If we are deployed into an OSGi environment, leverage it
            ClassLoader cl = FactoryLocator.class.getClassLoader();
            if (cl == null) {
                cl = ClassLoader.getSystemClassLoader();
            }
            Class factoryClass = cl.loadClass(factoryId);
            Class spiClass = org.apache.servicemix.specs.locator.OsgiLocator.locate(factoryClass, factoryId);
            if (spiClass != null) {
                return spiClass.newInstance();
            }
        } catch (Throwable e) {
        }

        try {
			String prop = System.getProperty(factoryId);
			if (prop != null) {
				return loadFactory(prop, classLoader);
			}
		} catch (Exception e) {
		}

		try {
			String configFile = System.getProperty("java.home")
					+ File.separator + "lib" + File.separator
					+ "stax.properties";
			File f = new File(configFile);
			if (f.exists()) {
				Properties props = new Properties();
				props.load(new FileInputStream(f));
				String factoryClassName = props.getProperty(factoryId);
				return loadFactory(factoryClassName, classLoader);
			}
		} catch (Exception e) {
		}

		String serviceId = "META-INF/services/" + factoryId;
		try {
			InputStream is = null;

			if (classLoader == null) {
				is = ClassLoader.getSystemResourceAsStream(serviceId);
			} else {
				is = classLoader.getResourceAsStream(serviceId);
			}

			if (is != null) {
				BufferedReader br = new BufferedReader(new InputStreamReader(
						is, "UTF-8"));
				String factoryClassName = br.readLine();
				br.close();

				if (factoryClassName != null && !"".equals(factoryClassName)) {
					return loadFactory(factoryClassName, classLoader);
				}
			}
		} catch (Exception ex) {
		}

		if (altClassName == null) {
			throw new FactoryConfigurationError("Unable to locate factory for "
					+ factoryId + ".", null);
		}
		return loadFactory(altClassName, classLoader);
	}

    private static Object loadFactory(String[] classNames, ClassLoader classLoader)
            throws FactoryConfigurationError {
        for (String className : classNames) {
            try {
                Class factoryClass = classLoader == null ? Class.forName(className)
                        : classLoader.loadClass(className);

                return factoryClass.newInstance();
            } catch (Exception x) {
            }
        }
        throw new FactoryConfigurationError("Requested factory "
                + Arrays.asList(classNames).toString()
                + " could not be instantiated");
    }

	private static Object loadFactory(String className, ClassLoader classLoader)
			throws FactoryConfigurationError {
		try {
			Class factoryClass = classLoader == null ? Class.forName(className)
					: classLoader.loadClass(className);

			return factoryClass.newInstance();
		} catch (ClassNotFoundException x) {
			throw new FactoryConfigurationError("Requested factory "
					+ className + " cannot be located.  Classloader ="
					+ classLoader.toString(), x);
		} catch (Exception x) {
			throw new FactoryConfigurationError("Requested factory "
					+ className + " could not be instantiated: " + x, x);
		}
	}
}