Java HTML Unescape htmlUnescape(String s)

Description

Turn HTML character references into their plain text UNICODE equivalent.

License

Apache License

Declaration

public static String htmlUnescape(String s) 

Method Source Code

//package com.java2s;
/*/*from ww  w . j a va2 s .co  m*/
 * Copyright 2002-2004 the original author or authors.
 * 
 * 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.
 */

import java.util.HashMap;
import java.util.Map;

public class Main {
    private static final String EMPTY_REFERENCE = "&;";
    private static final String MALFORMED_REFERENCE = "&#;";
    private static final Map ENTITIES = new HashMap();

    /**
     * Turn HTML character references into their plain text UNICODE equivalent.
     * <p>Handles complete character set defined in HTML 4.01 recommendation
     * and all reference types (decimal, hex, and entity).
     * <p>Correctly converts the following formats:
     * <blockquote>
     * &#<i>Decimal</i>; - <i>(Example: &#68;)</i><br>
     * &#x<i>Hex</i>;<br> - <i>(Example: &#xE5;) case insensitive</i>
     * &#<i>Entity</i>; - <i>(Example: &amp;) case sensitive</i>
     * </blockquote>
     * Gracefully handles malformed character references by copying original
     * characters as is when encountered.<p>
     * <p>Reference:
     * <a href="http://www.w3.org/TR/html4/sgml/entities.html">
     * http://www.w3.org/TR/html4/sgml/entities.html
     * </a>
     */
    public static String htmlUnescape(String s) {
        if (s == null) {
            return null;
        }

        StringBuffer unescaped = new StringBuffer(s.length());
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (c == '&') {
                // don't look more than 12 chars ahead as reference like strings
                // should not be longer than 12 chars in length (including ';')
                // prevents the entire string from being searched when an '&'
                // with no following ';' is an encountered
                int start = Math.min(i + 1, s.length() - 1);
                int end = Math.min(s.length(), start + 12);

                String reference = s.substring(start, end);
                int semi = reference.indexOf(';');

                if (semi == -1) {
                    unescaped.append(c);
                    continue;
                }

                reference = reference.substring(0, semi);
                i = start + semi;

                // try entity reference first
                Integer iso = (Integer) ENTITIES.get(reference);
                if (iso != null) {
                    unescaped.append((char) iso.intValue());
                    continue;
                }

                if (reference.length() == 0) {
                    unescaped.append(EMPTY_REFERENCE);
                    continue;
                }

                if (reference.charAt(0) == '#') {
                    if (reference.length() > 2) {
                        int index = 1;
                        if (reference.charAt(1) == 'x' || reference.charAt(1) == 'X') {
                            index = 2;
                        }
                        try {
                            unescaped.append(
                                    (char) Integer.parseInt(reference.substring(index), (index == 1) ? 10 : 16));
                            continue;
                        } catch (NumberFormatException e) {
                            // wasn't hex or decimal, copy original chars
                            unescaped.append('&' + reference + ';');
                            continue;
                        }
                    }
                    unescaped.append(MALFORMED_REFERENCE);
                    continue;
                }

                // may not be valid reference, forget it
                i = start - 1;
            }
            unescaped.append(c);
        }
        return unescaped.toString();
    }
}

Related

1. htmlUnescape(String source)
2. unEscapeHTML(final String escapedHTML)
3. unescapeHtml(final String input)
4. unescapeHTML(String comment)