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/*
 * $Id$
 *
 * 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 $Rev$ $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;
        }

        StringBuilder result = null;
        String filtered = null;

        for (int i = 0; i < value.length(); i++) {
            filtered = null;

            switch (value.charAt(i)) {
            case '<':
                filtered = "<";

                break;

            case '>':
                filtered = ">";

                break;

            case '&':
                filtered = "&";

                break;

            case '"':
                filtered = """;

                break;

            case '\'':
                filtered = "'";

                break;
            }

            if (result == null) {
                if (filtered != null) {
                    result = new StringBuilder(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);
    }
}