Java - Write code to Replace characters that may be confused by a HTML parser with their equivalent character entity references.

Requirements

Write code to Replace characters that may be confused by a HTML parser with their equivalent character entity references.

Demo

/*
 * Static String formatting and query routines.
 * Copyright (C) 2001-2005 Stephen Ostermiller
 * http://ostermiller.org/contact.pl?regarding=Java+Utilities
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.//from w ww  . j av a 2  s  . c o  m
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * See COPYING.TXT for details.
 */
//package com.book2s;

public class Main {
    public static void main(String[] argv) {
        String s = "book2s.com";
        System.out.println(escapeHTML(s));
    }

    /**
     * Replaces characters that may be confused by a HTML
     * parser with their equivalent character entity references.
     * <p>
     * Any data that will appear as text on a web page should
     * be be escaped.  This is especially important for data
     * that comes from untrusted sources such as Internet users.
     * A common mistake in CGI programming is to ask a user for
     * data and then put that data on a web page.  For example:<pre>
     * Server: What is your name?
     * User: &lt;b&gt;Joe&lt;b&gt;
     * Server: Hello <b>Joe</b>, Welcome</pre>
     * If the name is put on the page without checking that it doesn't
     * contain HTML code or without sanitizing that HTML code, the user
     * could reformat the page, insert scripts, and control the the
     * content on your web server.
     * <p>
     * This method will replace HTML characters such as &gt; with their
     * HTML entity reference (&amp;gt;) so that the html parser will
     * be sure to interpret them as plain text rather than HTML or script.
     * <p>
     * This method should be used for both data to be displayed in text
     * in the html document, and data put in form elements. For example:<br>
     * <code>&lt;html&gt;&lt;body&gt;<i>This in not a &amp;lt;tag&amp;gt;
     * in HTML</i>&lt;/body&gt;&lt;/html&gt;</code><br>
     * and<br>
     * <code>&lt;form&gt;&lt;input type="hidden" name="date" value="<i>This data could
     * be &amp;quot;malicious&amp;quot;</i>"&gt;&lt;/form&gt;</code><br>
     * In the second example, the form data would be properly be resubmitted
     * to your cgi script in the URLEncoded format:<br>
     * <code><i>This data could be %22malicious%22</i></code>
     *
     * @param s String to be escaped
     * @return escaped String
     * @throws NullPointerException if s is null.
     *
     * @since ostermillerutils 1.00.00
     */
    public static String escapeHTML(String s) {
        int length = s.length();
        int newLength = length;
        boolean someCharacterEscaped = false;
        // first check for characters that might
        // be dangerous and calculate a length
        // of the string that has escapes.
        for (int i = 0; i < length; i++) {
            char c = s.charAt(i);
            int cint = 0xffff & c;
            if (cint < 32) {
                switch (c) {
                case '\r':
                case '\n':
                case '\t':
                case '\f': {
                }
                    break;
                default: {
                    newLength -= 1;
                    someCharacterEscaped = true;
                }
                }
            } else {
                switch (c) {
                case '\"': {
                    newLength += 5;
                    someCharacterEscaped = true;
                }
                    break;
                case '&':
                case '\'': {
                    newLength += 4;
                    someCharacterEscaped = true;
                }
                    break;
                case '<':
                case '>': {
                    newLength += 3;
                    someCharacterEscaped = true;
                }
                    break;
                }
            }
        }
        if (!someCharacterEscaped) {
            // nothing to escape in the string
            return s;
        }
        StringBuffer sb = new StringBuffer(newLength);
        for (int i = 0; i < length; i++) {
            char c = s.charAt(i);
            int cint = 0xffff & c;
            if (cint < 32) {
                switch (c) {
                case '\r':
                case '\n':
                case '\t':
                case '\f': {
                    sb.append(c);
                }
                    break;
                default: {
                    // Remove this character
                }
                }
            } else {
                switch (c) {
                case '\"': {
                    sb.append("&quot;");
                }
                    break;
                case '\'': {
                    sb.append("&#39;");
                }
                    break;
                case '&': {
                    sb.append("&amp;");
                }
                    break;
                case '<': {
                    sb.append("&lt;");
                }
                    break;
                case '>': {
                    sb.append("&gt;");
                }
                    break;
                default: {
                    sb.append(c);
                }
                }
            }
        }
        return sb.toString();
    }
}

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