src/jsr311-api/src/javax/ws/rs/ext/FactoryFinder.java

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/*
 * FactoryFinder.java
 *
 * Created on November 16, 2007, 3:14 PM
 *
 */
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.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Properties;

class FactoryFinder {
    
    static ClassLoader getContextClassLoader() { 
        return AccessController.doPrivileged( 
            new PrivilegedAction<ClassLoader>() { 
                public ClassLoader run() { 
                    ClassLoader cl = null;
                    try { 
                        cl = Thread.currentThread().getContextClassLoader(); 
                    } catch (SecurityException ex) { } 
                    return cl; 
                } 
        }); 
    }

    /**
     * Creates an instance of the specified class using the specified 
     * <code>ClassLoader</code> object.
     *
     * @exception 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 {
                try { 
                    spiClass = Class.forName(className, false, classLoader); 
                } catch (ClassNotFoundException 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.
     *
     * @return the <code>Class</code> object of the specified message factory;
     *         may not be <code>null</code>
     *
     * @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
     * @exception WebServiceException if there is an error
     */
    static Object find(String factoryId, String fallbackClassName) throws ClassNotFoundException {
        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) {
        }


        // 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);
    }
}