com.google.common.html.HtmlEscapers.java Source code

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Here is the source code for com.google.common.html.HtmlEscapers.java

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/*
 * Copyright (C) 2009 The Guava 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.
 */

package com.google.common.html;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.escape.Escaper;
import com.google.common.escape.Escapers;

/**
 * {@code Escaper} instances suitable for strings to be included in HTML
 * attribute values and <em>most</em> elements' text contents. When possible,
 * avoid manual escaping by using templating systems and high-level APIs that
 * provide autoescaping.
 * One Google-authored templating system available for external use is <a
 * href="https://developers.google.com/closure/templates/">Closure
 * Templates</a>.
 *
 * <p>HTML escaping is particularly tricky: For example, <a
 * href="http://goo.gl/5TgZb">some elements' text contents must not be HTML
 * escaped</a>. As a result, it is impossible to escape an HTML document
 * correctly without domain-specific knowledge beyond what {@code HtmlEscapers}
 * provides. We strongly encourage the use of HTML templating systems.
 *
 * @author Sven Mawson
 * @author David Beaumont
 * @since 15.0
 */
@Beta
@GwtCompatible
public final class HtmlEscapers {
    /**
     * Returns an {@link Escaper} instance that escapes HTML metacharacters as
     * specified by <a href="http://www.w3.org/TR/html4/">HTML 4.01</a>. The
     * resulting strings can be used both in attribute values and in <em>most</em>
     * elements' text contents, provided that the HTML document's character
     * encoding can encode any non-ASCII code points in the input (as UTF-8 and
     * other Unicode encodings can).
     *
     *
     * <p><b>Note:</b> This escaper only performs minimal escaping to make content
     * structurally compatible with HTML. Specifically, it does not perform entity
     * replacement (symbolic or numeric), so it does not replace non-ASCII code
     * points with character references. This escaper escapes only the following
     * five ASCII characters: {@code '"&<>}.
     */
    public static Escaper htmlEscaper() {
        return HTML_ESCAPER;
    }

    // For each xxxEscaper() method, please add links to external reference pages
    // that are considered authoritative for the behavior of that escaper.

    private static final Escaper HTML_ESCAPER = Escapers.builder().addEscape('"', "&quot;")
            // Note: "&apos;" is not defined in HTML 4.01.
            .addEscape('\'', "&#39;").addEscape('&', "&amp;").addEscape('<', "&lt;").addEscape('>', "&gt;").build();

    private HtmlEscapers() {
    }
}