/**
    *       Copyright 2010 Newcastle University
    *
    *          http://research.ncl.ac.uk/smart/
    *
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You 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.apache.amber.oauth2.rsfilter;
  
  import javax.servlet.ServletContext;
  import javax.servlet.ServletException;
  
  /**
   *
   *
   *
   */
  public class OAuthUtils {
  
      public static <T> T initiateServletContext(ServletContext context, String key, Class<T> expectedClass)
          throws ServletException {
  
          T provider = (T)context.getAttribute(key);
  
          if (provider != null) {
              return provider;
          }
  
          provider = (T)loadObject(context, key, expectedClass);
  
          // set the provider and validator
          context.setAttribute(key, provider);
  
          return provider;
      }
  
      public static Object loadObject(ServletContext context, String classParamName, Class expectedClass)
          throws ServletException {
  
          Object ob = null;
  
          String providerClassName = context.getInitParameter(classParamName);
          if (isEmpty(providerClassName)) {
              throw new ServletException(classParamName + " context param required");
          }
          try {
              Class<?> clazz = Class.forName(providerClassName);
              if (!expectedClass.isAssignableFrom(clazz)) {
                  throw new ServletException(classParamName + " class: " + providerClassName
                      + " must be an instance of: " + expectedClass.getName());
              }
              ob = createObjectFromClassName(clazz);
          } catch (ClassNotFoundException e) {
              throw new ServletException(classParamName + " class " + providerClassName + " not found");
          } catch (Exception e) {
              throw new ServletException("Cannot instantiate: " + providerClassName);
          }
          return ob;
      }
  
      public static Object createObjectFromClassName(Class clazz)
          throws IllegalAccessException, InstantiationException {
          return clazz.newInstance();
      }
  
      public static boolean isEmpty(String value) {
          return value == null || "".equals(value);
      }
  }