/*
    * $Id: ResponseUtils.java 471754 2006-11-06 14:55:09Z husted $
    *
    * 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.struts.util;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  
  import java.net.URLEncoder;
  
  /**
   * General purpose utility methods related to generating a servlet response in
   * the Struts controller framework.
   *
   * @version $Rev: 471754 $ $Date: 2005-08-21 14:46:28 -0400 (Sun, 21 Aug 2005)
   *          $
   */
  public class ResponseUtils {
      // ------------------------------------------------------- Static Variables
  
      /**
       * The message resources for this package.
       */
      protected static MessageResources messages =
          MessageResources.getMessageResources(
              "org.apache.struts.util.LocalStrings");
  
      /**
       * Java 1.4 encode method to use instead of deprecated 1.3 version.
       */
      private static Method encode = null;
  
      /**
       * Commons logging instance.
       */
      private static final Log log = LogFactory.getLog(ResponseUtils.class);
  
      /**
       * Initialize the encode variable with the
       * Java 1.4 method if available.
       */
      static {
          try {
              // get version of encode method with two String args
              Class[] args = new Class[] { String.class, String.class };
  
              encode = URLEncoder.class.getMethod("encode", args);
          } catch (NoSuchMethodException e) {
              log.debug("Could not find Java 1.4 encode method.  Using deprecated version.",
                  e);
          }
      }
  
      // --------------------------------------------------------- Public Methods
  
      /**
       * Filter the specified string for characters that are senstive to HTML
       * interpreters, returning the string with these characters replaced by
       * the corresponding character entities.
       *
       * @param value The string to be filtered and returned
       */
      public static String filter(String value) {
          if ((value == null) || (value.length() == 0)) {
              return value;
          }
  
          StringBuffer result = null;
          String filtered = null;
  
          for (int i = 0; i < value.length(); i++) {
              filtered = null;
  
              switch (value.charAt(i)) {
              case '<':
                  filtered = "&lt;";
  
                  break;
  
             case '>':
                 filtered = "&gt;";
 
                 break;
 
             case '&':
                 filtered = "&amp;";
 
                 break;
 
             case '"':
                 filtered = "&quot;";
 
                 break;
 
             case '\'':
                 filtered = "&#39;";
 
                 break;
             }
 
             if (result == null) {
                 if (filtered != null) {
                     result = new StringBuffer(value.length() + 50);
 
                     if (i > 0) {
                         result.append(value.substring(0, i));
                     }
 
                     result.append(filtered);
                 }
             } else {
                 if (filtered == null) {
                     result.append(value.charAt(i));
                 } else {
                     result.append(filtered);
                 }
             }
         }
 
         return (result == null) ? value : result.toString();
     }
 
     /**
      * URLencodes a string assuming the character encoding is UTF-8.
      *
      * @param url
      * @return String The encoded url in UTF-8
      */
     public static String encodeURL(String url) {
         return encodeURL(url, "UTF-8");
     }
 
     /**
      * Use the new URLEncoder.encode() method from Java 1.4 if available, else
      * use the old deprecated version.  This method uses reflection to find
      * the appropriate method; if the reflection operations throw exceptions,
      * this will return the url encoded with the old URLEncoder.encode()
      * method.
      *
      * @param enc The character encoding the urlencode is performed on.
      * @return String The encoded url.
      */
     public static String encodeURL(String url, String enc) {
         try {
             if ((enc == null) || (enc.length() == 0)) {
                 enc = "UTF-8";
             }
 
             // encode url with new 1.4 method and UTF-8 encoding
             if (encode != null) {
                 return (String) encode.invoke(null, new Object[] { url, enc });
             }
         } catch (IllegalAccessException e) {
             log.debug("Could not find Java 1.4 encode method.  Using deprecated version.",
                 e);
         } catch (InvocationTargetException e) {
             log.debug("Could not find Java 1.4 encode method. Using deprecated version.",
                 e);
         }
 
         return URLEncoder.encode(url);
     }
 }