javax.xml.parsers.ClassStuff Maven / Gradle / Ivy

/* 
Copyright (C) 2004  Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */

package javax.xml.parsers;

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

import java.lang.reflect.Method;

import java.util.Properties;


/**
 * Package-private utility methods for sharing magic related to class loading.
 * NOTE: This is cloned in javax.xml.transform, where a different exception is
 * thrown (bleech). Keep changes to the two copies in sync.
 *
 * @author David Brownell
 * @version 1.2
 */
final class ClassStuff {
    /**
     * Creates a new ClassStuff object.
     */
    private ClassStuff() {
    }

    /**
     * Get the default factory using the four-stage defaulting mechanism
     * defined by JAXP.
     *
     * @param label DOCUMENT ME!
     * @param defaultClass DOCUMENT ME!
     *
     * @return DOCUMENT ME!
     *
     * @throws FactoryConfigurationError DOCUMENT ME!
     * @throws UnknownError DOCUMENT ME!
     */
    static Object createFactory(
        String label,
        String defaultClass
    )
        throws FactoryConfigurationError {
        String name = null;
        ClassLoader loader = null;

        // figure out which class loader to use.
        // source compiles on jdk 1.1, but works with jdk 1.2+ security
        try {
            Method m = null;

            // Can we use JDK 1.2 APIs? Preferred: security policies apply.
            m = Thread.class.getMethod(
                    "getContextClassLoader",
                    null
                );
            loader = (ClassLoader) m.invoke(
                    Thread.currentThread(),
                    null
                );
        } catch (NoSuchMethodException e) {
            // Assume that we are running JDK 1.1; use current ClassLoader
            loader = ClassStuff.class.getClassLoader();
        } catch (NoSuchMethodError e) {
            // evidently IE does this (one of its bugs)
            loader = ClassStuff.class.getClassLoader();
        } catch (Throwable e) {
            // "should not happen"
            throw new UnknownError(e.getMessage());
        }

        // 1. Check System Property
        // ... normally fails in applet environments
        try {
            name = System.getProperty(label);
        } catch (SecurityException e) { /* IGNORE */
        }

        // 2. Check in $JAVA_HOME/lib/jaxp.properties
        try {
            if (name == null) {
                String javaHome;
                File file;

                javaHome = System.getProperty("java.home");
                file = new File(
                        new File(
                            javaHome,
                            "lib"
                        ),
                        "jaxp.properties"
                    );

                if (file.exists() == true) {
                    FileInputStream in = new FileInputStream(file);
                    Properties props = new Properties();

                    props.load(in);
                    name = props.getProperty(label);
                    in.close();
                }
            }
        } catch (Exception e) { /* IGNORE */
        }

        // 3. Check Services API
        if (name == null) {
            try {
                String service = "META-INF/services/" + label;
                InputStream in;
                BufferedReader reader;

                if (loader == null)
                    in = ClassLoader.getSystemResourceAsStream(service);
                else
                    in = loader.getResourceAsStream(service);

                if (in != null) {
                    reader =
                        new BufferedReader(new InputStreamReader(
                                in,
                                "UTF8"
                            )
                        );
                    name = reader.readLine();
                    in.close();
                }
            } catch (Exception e2) { /* IGNORE */
            }
        }

        // 4. Distro-specific fallback
        if (name == null)
            name = defaultClass;

        // Instantiate!
        try {
            Class klass;

            if (loader == null)
                klass = Class.forName(name);
            else
                klass = loader.loadClass(name);

            return klass.newInstance();
        } catch (ClassNotFoundException e) {
            throw new FactoryConfigurationError(e,
                "Factory class " + name + " not found"
            );
        } catch (IllegalAccessException e) {
            throw new FactoryConfigurationError(e,
                "Factory class " + name + " found but cannot be loaded"
            );
        } catch (InstantiationException e) {
            throw new FactoryConfigurationError(e,
                "Factory class " + name + " loaded but cannot be instantiated"
                + " ((no default constructor?)"
            );
        }
    }
}