jsr370-api-m4/src/main/java/javax/ws/rs/client/FactoryFinder.java

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package javax.ws.rs.client;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Properties;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Factory finder utility class.
 *
 * @author Paul Sandoz
 * @author Marc Hadley
 * @since 1.0
 */
final class FactoryFinder {

    private static final Logger LOGGER = Logger.getLogger(FactoryFinder.class.getName());

    private FactoryFinder() {
        // prevents instantiation
    }

    static ClassLoader getContextClassLoader() {
        return AccessController.doPrivileged(
                new PrivilegedAction<ClassLoader>() {

                    @Override
                    public ClassLoader run() {
                        ClassLoader cl = null;
                        try {
                            cl = Thread.currentThread().getContextClassLoader();
                        } catch (SecurityException ex) {
                            LOGGER.log(
                                    Level.WARNING,
                                    "Unable to get context classloader instance.",
                                    ex);
                        }
                        return cl;
                    }
                });
    }

    /**
     * Creates an instance of the specified class using the specified
     * <code>ClassLoader</code> object.
     *
     * @param className   name of the class to be instantiated.
     * @param classLoader class loader to be used.
     * @return instance of the specified class.
     * @throws ClassNotFoundException if the given class could not be found
     *                                or could not be instantiated
     */
    private static Object newInstance(final String className, final ClassLoader classLoader) throws ClassNotFoundException {
        try {
            Class spiClass;
            if (classLoader == null) {
                spiClass = Class.forName(className);
            } else {
                try {
                    spiClass = Class.forName(className, false, classLoader);
                } catch (ClassNotFoundException ex) {
                    LOGGER.log(
                            Level.FINE,
                            "Unable to load provider class " + className
                                    + " using custom classloader " + classLoader.getClass().getName()
                                    + " trying again with current classloader.",
                            ex);
                    spiClass = Class.forName(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 ClassNotFoundException if the given class could not be found
     *                                or could not be instantiated
     */
    static Object find(final String factoryId, final String fallbackClassName) throws ClassNotFoundException {
        
        try {
            // If we are deployed into an OSGi environment, leverage it
            Class factoryClass = FactoryFinder.class.getClassLoader().loadClass(factoryId);
            Class spiClass = org.apache.servicemix.specs.locator.OsgiLocator.locate(factoryClass, factoryId);
            if (spiClass != null) {
                return spiClass.newInstance();
            }
        } catch (Throwable e) {
        }

        ClassLoader classLoader = getContextClassLoader();

        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) {
            LOGGER.log(Level.FINER, "Failed to load service " + factoryId + " from " + serviceId, 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) {
            LOGGER.log(Level.FINER, "Failed to load service " + factoryId
                    + " from $java.home/lib/jaxrs.properties", ex);
        }


        // Use the system property
        try {
            String systemProp = System.getProperty(factoryId);
            if (systemProp != null) {
                return newInstance(systemProp, classLoader);
            }
        } catch (SecurityException se) {
            LOGGER.log(Level.FINER, "Failed to load service " + factoryId
                    + " from a system property", se);
        }

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

        return newInstance(fallbackClassName, classLoader);
    }
}