org.apache.shindig.gadgets.parse.CompactHtmlSerializer.java Source code

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Here is the source code for org.apache.shindig.gadgets.parse.CompactHtmlSerializer.java

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/*
 * 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.shindig.gadgets.parse;

import com.google.common.collect.ImmutableSortedSet;

import org.w3c.dom.Node;
import org.apache.commons.lang.StringUtils;

import java.io.IOException;

/**
 * Performs simple content compaction while writing HTML documents. The compaction includes:
 * <ul>
 * <li>Collapsing consecutive whitespaces while preserving those within style, pre and script tags
 * <li>Removing HTML comments while preserving IE conditional comments
 * </ul>
 *
 * TODO - Consider adding attribute quoting elimination, empty attribute elimination where safe
 * end-tag elmination where safe.
 */
public class CompactHtmlSerializer extends DefaultHtmlSerializer {

    private static final ImmutableSortedSet<String> SPECIAL_TAGS = ImmutableSortedSet
            .orderedBy(String.CASE_INSENSITIVE_ORDER).add("style", "pre", "script", "textarea").build();
    private static final String HTML_WHITESPACE = " \t\r\n";

    @Override
    protected void writeText(Node n, Appendable output) throws IOException {
        if (isSpecialTag(n.getParentNode().getNodeName())) {
            super.writeText(n, output);
        } else {
            collapseWhitespace(n.getTextContent(), output);
        }
    }

    @Override
    protected void writeComment(Node n, Appendable output) throws IOException {
        if (isSpecialTag(n.getParentNode().getNodeName())) {
            super.writeComment(n, output);
        } else if (isIeConditionalComment(n)) {
            super.writeComment(n, output);
        }
    }

    /**
     * See <a href="http://msdn.microsoft.com/en-us/library/ms537512(printer).aspx">MSDN</a>
     * and <a href="http://www.quirksmode.org/css/condcom.html">PPK</a>
     */
    private boolean isIeConditionalComment(Node n) {
        String comment = n.getTextContent();
        return comment.contains("[if ") && comment.contains("[endif]");
    }

    /**
     * Returns true if a tag with a given tagName should preserve any whitespaces
     * in its children nodes.
     */
    static boolean isSpecialTag(String tagName) {
        return SPECIAL_TAGS.contains(tagName);
    }

    /**
     * Collapse any consecutive HTML whitespace characters inside a string into
     * one space character (0x20). This method will not output any characters when
     * the given string is entirely composed of whitespaces.  
     *
     * References:
     * <ul>
     * <li>http://www.w3.org/TR/html401/struct/text.html#h-9.1</li>
     * <li>http://java.sun.com/javase/6/docs/api/java/lang/Character.html#isWhitespace(char)</li>
     * </ul>
     */
    static void collapseWhitespace(String str, Appendable output) throws IOException {
        str = StringUtils.stripStart(str, HTML_WHITESPACE);

        // Whitespaces between a sequence of non-whitespace characters
        boolean seenWhitespace = false;
        for (int i = 0; i < str.length(); i++) {
            char c = str.charAt(i);

            if (HTML_WHITESPACE.indexOf(c) != -1) {
                seenWhitespace = true;
            } else {
                if (seenWhitespace) {
                    output.append(' ');
                }
                output.append(c);

                seenWhitespace = false;
            }
        }
    }
}