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package javax.ws.rs.sse;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Iterator;
import java.util.Properties;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Factory finder utility class.
 *
 * @author Paul Sandoz
 * @author Marc Hadley
 * @author Marek Potociar
 * @since 2.1
 */
final class FactoryFinder {

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

    private FactoryFinder() {
        // prevents instantiation
    }

    private static ClassLoader getContextClassLoader() {
        return AccessController.doPrivileged((PrivilegedAction<ClassLoader>) () -> {
            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} 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.getDeclaredConstructor().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} for the given factory name,
     * or if that fails, finds the {@code Class} for the given fallback
     * class name and create its instance. 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} to indicate that
     *                          there is no fallback class name.
     * @param service           service to be found.
     * @param <T>               type of the service to be found.
     * @return the instance of the specified service; may not be {@code null}.
     * @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 {
        ClassLoader classLoader = getContextClassLoader();

        try {
            Iterator<T> iterator = ServiceLoader.load(service, FactoryFinder.getContextClassLoader()).iterator();

            if(iterator.hasNext()) {
                return iterator.next();
            }
        } catch (Exception | ServiceConfigurationError ex) {
            LOGGER.log(Level.FINER, "Failed to load service " + factoryId + ".", ex);
        }

        try {
            Iterator<T> iterator = ServiceLoader.load(service, FactoryFinder.class.getClassLoader()).iterator();

            if(iterator.hasNext()) {
                return iterator.next();
            }
        } catch (Exception | ServiceConfigurationError ex) {
            LOGGER.log(Level.FINER, "Failed to load service " + factoryId + ".", ex);
        }

        // try to read from $java.home/lib/jaxrs.properties
        FileInputStream inputStream = null;
        String configFile = null;
        try {
            String javah = System.getProperty("java.home");
            configFile = javah + File.separator + "lib" + File.separator + "jaxrs.properties";
            File f = new File(configFile);
            if (f.exists()) {
                Properties props = new Properties();
                inputStream = new FileInputStream(f);
                props.load(inputStream);
                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);
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException ex) {
                    LOGGER.log(Level.FINER, String.format("Error closing %s file.", configFile), 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);
    }
}
