Java Class Load loadClassViaContext(String fqcn)

Description

load Class Via Context

License

Apache License

Declaration

private static Class<?> loadClassViaContext(String fqcn) 

Method Source Code

//package com.java2s;
/*//  w ww .  jav  a2  s .c o  m
 * Copyright 2011-2016 Amazon Technologies, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 *
 *    http://aws.amazon.com/apache2.0
 *
 * This file is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES
 * OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and
 * limitations under the License.
 */

public class Main {
    private static Class<?> loadClassViaContext(String fqcn) {
        ClassLoader loader = Thread.currentThread().getContextClassLoader();
        try {
            return loader == null ? null : loader.loadClass(fqcn);
        } catch (ClassNotFoundException e) {
        }
        return null;
    }

    /**
     * Loads the class via the optionally specified classes in the order of
     * their specification, and if not found, via the context class loader of
     * the current thread, and if not found, from the caller class loader as the
     * last resort.
     *
     * @param fqcn fully qualified class name of the target class to be loaded
     * @param classes class loader providers
     * @return the class loaded; never null
     * @throws ClassNotFoundException if failed to load the class
     */
    public static Class<?> loadClass(String fqcn, Class<?>... classes) throws ClassNotFoundException {
        return loadClass(fqcn, true, classes);
    }

    /**
     * If classesFirst is false, loads the class via the context class loader of
     * the current thread, and if not found, via the class loaders of the
     * optionally specified classes in the order of their specification, and if
     * not found, from the caller class loader as the last resort.
     * <p>
     * If classesFirst is true, loads the class via the optionally specified
     * classes in the order of their specification, and if not found, via the
     * context class loader of the current thread, and if not found, from the
     * caller class loader as the last resort.
     *
     * @param fqcn fully qualified class name of the target class to be loaded
     * @param classesFirst true if the class loaders of the optionally specified
     *            classes take precedence over the context class loader of the
     *            current thread; false if the opposite is true.
     * @param classes class loader providers
     * @return the class loaded; never null
     * @throws ClassNotFoundException if failed to load the class
     */
    public static Class<?> loadClass(String fqcn, boolean classesFirst, Class<?>... classes)
            throws ClassNotFoundException {
        Class<?> target = null;
        if (classesFirst) {
            target = loadClassViaClasses(fqcn, classes);
            if (target == null) {
                target = loadClassViaContext(fqcn);
            }
        } else {
            target = loadClassViaContext(fqcn);
            if (target == null) {
                target = loadClassViaClasses(fqcn, classes);
            }
        }
        return target == null ? Class.forName(fqcn) : target;
    }

    private static Class<?> loadClassViaClasses(String fqcn, Class<?>[] classes) {
        if (classes != null) {
            for (Class<?> c : classes) {
                ClassLoader loader = c.getClassLoader();
                if (loader != null) {
                    try {
                        return loader.loadClass(fqcn);
                    } catch (ClassNotFoundException e) {
                        // move on to try the next class loader
                    }
                }
            }
        }
        return null;
    }
}

Related

1. loadClassOrReturnNull(ClassLoader loader, String className)
2. loadClassReflectively(ClassLoader classLoader, String fullyQualifiedClassName)
3. loadClassSafe(final String klassName)
4. loadClassSilently(ClassLoader cl, String name)
5. loadClassUsingClass(Class clazz, String name)
6. loadClassWithTCCL(String name)