Factory.java

// Copyright 2000-2004, FreeHEP.
package org.freehep.util;

import java.io.*;
import java.util.*;

/**
 * Methods to use factories (a la JAXP).
 *
 * @author Mark Donszelmann
 * @version $Id: Factory.java 8584 2006-08-10 23:06:37Z duns $
 */
public class Factory {

    // static class
    private Factory() {
    }

    /**
     * Find the correct factory name, based on the following procedure:
     * <ol>
     * <li>Use the specified system property: factoryName.
     * <li>Use the specified property file in JAVA_HOME/lib/<factoryFile> and the
     *     specified property: factoryName.
     * <li>Use the Services API (as detailed in the JAR specification) to look
     *     for the classname in META-INF/services/<factoryName>.
     * <li>Use the specfied default factory: defaultFactory.
     * </ol>
     *
     * @param factoryName name to be used for lookup
     * @param factoryFile filename to look for in JAVA_HOME/lib
     * @param defaultFactory name of the default factory
     * @return the name of the factory according to the procedure above
     */
    public static String findFactory(String factoryName, String factoryFile, String defaultFactory) {
        // try System Property
        String factory = null;
        try {
            factory = System.getProperty(factoryName);
            if (factory != null) {
                return factory;
            }
        } catch(SecurityException securityexception) {
        }

        // try JAVA_HOME/lib
        try {
            String javaHome = System.getProperty("java.home");
            String configFile = javaHome + File.separator + "lib" + File.separator + factoryFile;
            File file = new File(configFile);
            if (file.exists()) {
                Properties props = new Properties();
                props.load(new FileInputStream(file));
                factory = props.getProperty(factoryName);
                if (factory != null) {
                    return factory;
                }
            }
        } catch(Exception e) {
            e.printStackTrace();
        }

        // try Services API
        String service1 = "meta-inf/services/" + factoryName;
        String service2 = "META-INF/services/" + factoryName;
        try {
            ClassLoader loader = null;
            try {
                loader = Class.forName("org.freehep.util.Factory").getClassLoader();
            } catch(ClassNotFoundException cnfe) {
                cnfe.printStackTrace();
            }

            InputStream stream = null;
            if (loader == null) {
                stream = ClassLoader.getSystemResourceAsStream(service1);
            } else {
                stream = loader.getResourceAsStream(service1);
            }

            if (stream == null) {
                if (loader == null) {
                    stream = ClassLoader.getSystemResourceAsStream(service2);
                } else {
                    stream = loader.getResourceAsStream(service2);
                }
            }

            if(stream != null) {
                BufferedReader reader = new BufferedReader(new InputStreamReader(stream));
                factory = reader.readLine();
                reader.close();
                if (factory != null && !factory.equals("")) {
                    return factory;
                }
            }
        } catch(Exception e) {
            e.printStackTrace();
        }
        return defaultFactory;
    }

    public static Object loadFactory(String name, String file, String defaultImplementation) {
        String factoryName = findFactory(name, file, defaultImplementation);
        try {
            System.out.println("Loading factory: "+factoryName);
            Class factoryClass = Class.forName(factoryName);
            return factoryClass.newInstance();
        } catch (Exception e) {
            System.err.println("Unable to load factory: "+factoryName);
            e.printStackTrace();
        }
        return null;
    }
}