jaxrs-api-2.1/src/main/java/javax/ws/rs/ext/FactoryFinder.java

/*
 * The contents of this file are subject to the terms
 * of the Common Development and Distribution License
 * (the "License").  You may not use this file except
 * in compliance with the License.
 *
 * You can obtain a copy of the license at
 * http://www.opensource.org/licenses/cddl1.php
 * See the License for the specific language governing
 * permissions and limitations under the License.
 */
package javax.ws.rs.ext;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Properties;

public class FactoryFinder {

    /**
     * Creates an instance of the specified class using the specified
     * <code>ClassLoader</code> object.
     *
     * @throws ClassNotFoundException if the given class could not be found
     *                                or could not be instantiated
     */
    private static Object newInstance(String className,
                                      ClassLoader classLoader) throws ClassNotFoundException {
        try {
            Class spiClass;
            if (classLoader == null) {
                spiClass = Class.forName(className);
            } else {
                spiClass = classLoader.loadClass(className);
            }
            return spiClass.newInstance();
        } catch (ClassNotFoundException x) {
            throw x;
        } catch (Exception x) {
            throw new ClassNotFoundException(
                    "Provider " + className + " could not be instantiated: " + x,
                    x);
        }
    }

    /**
     * Finds the implementation <code>Class</code> object for the given
     * factory name, or if that fails, finds the <code>Class</code> object
     * for the given fallback class name. The arguments supplied MUST be
     * used in order. If using the first argument is successful, the second
     * one will not be used.
     * <p/>
     * This method is package private so that this code can be shared.
     *
     * @param factoryId         the name of the factory to find, which is
     *                          a system property
     * @param fallbackClassName the implementation class name, which is
     *                          to be used only if nothing else
     *                          is found; <code>null</code> to indicate that
     *                          there is no fallback class name
     * @return the <code>Class</code> object of the specified message factory;
     *         may not be <code>null</code>
     * @throws WebServiceException if there is an error
     */
    static Object find(final String factoryId, final String fallbackClassName) throws ClassNotFoundException {
        return find(factoryId, fallbackClassName, null);
    }
    
    /**
     * Finds the implementation <code>Class</code> object for the given
     * factory name, or if that fails, finds the <code>Class</code> object
     * for the given fallback class name. The arguments supplied MUST be
     * used in order. If using the first argument is successful, the second
     * one will not be used.
     * <P>
     * This method is package private so that this code can be shared.
     *
     * @param factoryId         the name of the factory to find, which is
     *                          a system property
     * @param fallbackClassName the implementation class name, which is
     *                          to be used only if nothing else
     *                          is found; <code>null</code> to indicate that
     *                          there is no fallback class name
     * @param service           The interface class of the service
     * @return the <code>Class</code> object of the specified message factory;
     *         may not be <code>null</code>
     * @throws ClassNotFoundException if the given class could not be found
     *                                or could not be instantiated
     */
    static <T> Object find(final String factoryId, final String fallbackClassName, Class<T> service) throws ClassNotFoundException {
        
        try {
            // If we are deployed into an OSGi environment, leverage it
            Class factoryClass = null;
            try {
                factoryClass = FactoryFinder.class.getClassLoader().loadClass(factoryId);
            } catch (Throwable t) {
                if (service != null) {
                    factoryClass = service;
                } else {
                    throw t;
                }
            }
            Class spiClass = org.apache.servicemix.specs.locator.OsgiLocator.locate(factoryClass, factoryId);
            if (spiClass != null) {
                return spiClass.newInstance();
            }
        } catch (Throwable e) {
        }
        
        ClassLoader classLoader;
        try {
            classLoader = Thread.currentThread().getContextClassLoader();
        } catch (Exception x) {
            throw new ClassNotFoundException(x.toString(), x);
        }

        String serviceId = "META-INF/services/" + factoryId;
        // try to find services in CLASSPATH
        try {
            InputStream is;
            if (classLoader == null) {
                is = ClassLoader.getSystemResourceAsStream(serviceId);
            } else {
                is = classLoader.getResourceAsStream(serviceId);
            }

            if (is != null) {
                BufferedReader rd =
                        new BufferedReader(new InputStreamReader(is, "UTF-8"));

                String factoryClassName = rd.readLine();
                rd.close();

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


        // try to read from $java.home/lib/jaxrs.properties
        try {
            String javah = System.getProperty("java.home");
            String configFile = javah + File.separator +
                    "lib" + File.separator + "jaxrs.properties";
            File f = new File(configFile);
            if (f.exists()) {
                Properties props = new Properties();
                props.load(new FileInputStream(f));
                String factoryClassName = props.getProperty(factoryId);
                return newInstance(factoryClassName, classLoader);
            }
        } catch (Exception ex) {
        }


        // Use the system property
        try {
            String systemProp =
                    System.getProperty(factoryId);
            if (systemProp != null) {
                return newInstance(systemProp, classLoader);
            }
        } catch (SecurityException se) {
        }

        if (fallbackClassName == null) {
            throw new ClassNotFoundException(
                    "Provider for " + factoryId + " cannot be found", null);
        }

        return newInstance(fallbackClassName, classLoader);
    }

}