newinstance.java

来自「java jdk 1.4的源码」· Java 代码 · 共 62 行

package org.xml.sax.helpers;

/**
 * This code is designed to run on JDK version 1.1 and later including JVMs
 * that perform early linking like the Microsoft JVM in IE 5.  Note however
 * that it must be compiled on a JDK version 1.2 or later system since it
 * calls Thread#getContextClassLoader().  The code also runs both as part
 * of an unbundled jar file and when bundled as part of the JDK.
 */
class NewInstance {
    /**
     * Creates a new instance of the specified class name
     *
     * Package private so this code is not exposed at the API level.
     */
    static Object newInstance(String className)
        throws ClassNotFoundException, IllegalAccessException,
            InstantiationException
    {
        ClassLoader classLoader;
        try {
            // Construct the name of the concrete class to instantiate
            Class clazz = Class.forName(NewInstance.class.getName()
                                        + "$ClassLoaderFinderConcrete");
            ClassLoaderFinder clf = (ClassLoaderFinder) clazz.newInstance();
            classLoader = clf.getContextClassLoader();
        } catch (LinkageError le) {
            // Assume that we are running JDK 1.1, use the current ClassLoader
            classLoader = NewInstance.class.getClassLoader();
        } catch (ClassNotFoundException x) {
            // This case should not normally happen.  MS IE can throw this
            // instead of a LinkageError the second time Class.forName() is
            // called so assume that we are running JDK 1.1 and use the
            // current ClassLoader
            classLoader = NewInstance.class.getClassLoader();
        }

        Class driverClass;
        if (classLoader == null) {
            driverClass = Class.forName(className);
        } else {
            driverClass = classLoader.loadClass(className);
        }
        return driverClass.newInstance();
    }

    /*
     * The following nested classes allow getContextClassLoader() to be
     * called only on JDK 1.2 and yet run in older JDK 1.1 JVMs
     */

    private static abstract class ClassLoaderFinder {
        abstract ClassLoader getContextClassLoader();
    }

    static class ClassLoaderFinderConcrete extends ClassLoaderFinder {
        ClassLoader getContextClassLoader() {
            return Thread.currentThread().getContextClassLoader();
        }
    }
}