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With inspiration from other libraries

There is a newer version: 2.12.15

/**
 * MVEL 2.0
 * Copyright (C) 2007 The Codehaus
 * Mike Brock, Dhanji Prasanna, John Graham, Mark Proctor
 *
 * 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://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License 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.
 */
package org.mvel2.integration;

/**
 * A set of tools for dealing with factorys, specifically to make chaining issues easy to deal with.
 *
 * @author Christopher Brock
 */
public class ResolverTools {
  /**
   * Based on a root factory, append the new factory to the end of the chain.
   *
   * @param root       The root factory
   * @param newFactory The new factory
   * @return An instance of the new factory
   */
  public static  T appendFactory(VariableResolverFactory root, T newFactory) {
    if (root.getNextFactory() == null) {
      root.setNextFactory(newFactory);
    }
    else {
      VariableResolverFactory vrf = root;

      while (vrf.getNextFactory() != null) {
        vrf = vrf.getNextFactory();
      }
      vrf.setNextFactory(newFactory);
    }

    return newFactory;
  }

  /**
   * Based on the root factory, insert the new factory right after the root, and before any other in the chain.
   *
   * @param root       The root factory
   * @param newFactory The new factory
   * @return An instance of the new factory.
   */
  public static  T insertFactory(VariableResolverFactory root, T newFactory) {
    if (root.getNextFactory() == null) {
      root.setNextFactory(newFactory);
    }
    else {
      newFactory.setNextFactory(root.getNextFactory());
      root.setNextFactory(newFactory);
    }

    return newFactory;
  }
}