AbstractTagHandler.java

/*
 * 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.templates.tags;

import org.apache.shindig.gadgets.parse.HtmlSerialization;
import org.apache.shindig.gadgets.templates.TemplateProcessor;
import org.w3c.dom.DocumentFragment;
import org.w3c.dom.Element;
import org.w3c.dom.Node;

import java.io.IOException;

/**
 * Abstract implementation of TagHandler, provides convenience methods
 * for resolving values in context.
 */
public abstract class AbstractTagHandler implements TagHandler {

  private final String tagName;
  private final String namespaceUri;

  /**
   * Create the tag handler instance.
   * @param namespaceUri the namespace of element this tag parses.
   * @param tagName the local name of the element this tag parses.
   */
  public AbstractTagHandler(String namespaceUri, String tagName) {
    this.tagName = tagName;
    this.namespaceUri = namespaceUri;
  }

  public String getTagName() {
    return tagName;
  }

  public String getNamespaceUri() {
    return namespaceUri;
  }

  /**
   * Returns the value of a tag attribute, evaluating any contained EL
   * expressions if necessary.
   * 
   * @param <T> the type of the value
   * @param tag the element
   * @param name the attribute name
   * @param processor the template processor
   * @param type the type of the value
   * @return the value of the attribute, or null if the attribute is not
   *     present.
   */
  protected final <T> T getValueFromTag(Element tag, String name,
      TemplateProcessor processor, Class<T> type) {
    if (tag.hasAttribute(name)) {
      return processor.evaluate(tag.getAttribute(name), type, null);
    } else {
      return null;
    }
  }

  protected final DocumentFragment processChildren(Element tag,
      TemplateProcessor processor) {
    DocumentFragment fragment = tag.getOwnerDocument().createDocumentFragment();
    processor.processChildNodes(fragment, tag);
    return fragment;
  }

  /**
   * Create a text node with proper escaping.
   */
  protected final void appendTextNode(Node parent, String text) {
    if (text == null || "".equals(text)) {
      return;
    }

    try {
      StringBuilder sb = new StringBuilder(text.length());
      HtmlSerialization.printEscapedText(text, sb);
      parent.appendChild(parent.getOwnerDocument().createTextNode(sb.toString()));
    } catch (IOException ioe) {
      throw new RuntimeException(ioe);
    }
  }
}