link.java

google gdata API 很好用的API

/* Copyright (c) 2006 Google Inc.
 *
 * 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.gdata.data;

import com.google.gdata.util.common.xml.XmlWriter;
import com.google.gdata.util.Namespaces;
import com.google.gdata.util.ParseException;

import java.io.IOException;
import java.util.ArrayList;


/**
 * External link type.
 *
 * 
 */
public class Link extends ExtensionPoint {


  public static final class Rel {

    /**
     * Link provides the URI of the feed or entry. If this
     * relation appears on a feed that is the result of performing a
     * query, then this URI includes the same query parameters (or at
     * least querying this URI produces the same result as querying with
     * those parameters).
     */
    public static final String SELF = "self";


    /** Link provides the URI of previous page in a paged feed. */
    public static final String PREVIOUS = "previous";


    /** Link provides the URI of next page in a paged feed. */
    public static final String NEXT = "next";


    /**
     * Link provides the URI of an alternate format of the
     * entry's or feed's contents. The {@code type} property of the link
     * specifies a media type.
     */
    public static final String ALTERNATE = "alternate";

    /**
     * Link provides the URI of a related link to the entry
     */
    public static final String RELATED = "related";

    /**
     * Link provides the URI of the full feed (without any
     * query parameters).
     */
    public static final String FEED = Namespaces.gPrefix + "feed";


    /**
     * Link provides the URI that can be used to post new
     * entries to the feed. This relation does not exist if the feed is
     * read-only.
     */
    public static final String ENTRY_POST = Namespaces.gPrefix + "post";


    /**
     * Link provides the URI that can be used to edit the entry.
     * This relation does not exist if the entry is read-only.
     */
    public static final String ENTRY_EDIT = "edit";

    /**
     * Link provides the URI that can be used to edit the media
     * associated with an entry.  This relation does not exist if 
     * there is no associated media or the media is read-only.
     */
    public static final String MEDIA_EDIT = "media-edit";

    /**
     * Link provides the URI that can be used to insert, update
     * and delete entries on this feed. This relation does not exist
     * if the feed is read-only or if batching not enabled on this
     * feed.
     */
    public static final String FEED_BATCH = Namespaces.gPrefix + "batch";

    /**
     * Link provides the URI that of link that provides the data
     * for the content in the feed.
     */
    public static final String VIA = "via";
  }


  public static final class Type {


    /** Defines the link type used for Atom content. */
    public static final String ATOM = "application/atom+xml";


    /** Defines the link type used for HTML content. */
    public static final String HTML = "text/html";
  }


  public Link() {};


  public Link(String rel, String type, String href) {
    this.rel = rel;
    this.type = type;
    setHref(href);
  }

  /**
   * Link relation type.  Possible values include {@code self}, {@code
   * prev}, {@code next}, {@code enclosure}, etc.
   */
  protected String rel;
  public String getRel() {
    return rel != null ? rel : Rel.ALTERNATE;
  }
  public void setRel(String v) { rel = v; }


  /** MIME type of the link target. */
  protected String type;
  public String getType() { return type; }
  public void setType(String v) { type = v; }


  /** Link URI. */
  protected String href;
  public String getHref() { return href; }
  public void setHref(String v) { href = v; }


  /** Language of resource pointed to by href. */
  protected String hrefLang;
  public String getHrefLang() { return hrefLang; }
  public void setHrefLang(String v) { hrefLang = v; }


  /** Link title. */
  protected String title;
  public String getTitle() { return title; }
  public void setTitle(String v) { title = v; }


  /** Language of link title. */
  protected String titleLang;
  public String getTitleLang() { return titleLang; }
  public void setTitleLang(String v) { titleLang = v; }


  /** Length of the resource pointed to by href, in bytes. */
  protected long length = -1;
  public long getLength() { return length; }
  public void setLength(long v) { length = v; }


  /**
   * Generates XML in the Atom format.
   *
   * @param   w
   *            Output writer.
   *
   * @param   extProfile
   *            Extension profile.
   *
   * @throws  IOException
   */
  public void generateAtom(XmlWriter w,
                           ExtensionProfile extProfile) throws IOException {

    ArrayList<XmlWriter.Attribute> attrs =
      new ArrayList<XmlWriter.Attribute>(3);

    if (rel != null) {
      attrs.add(new XmlWriter.Attribute("rel", rel));
    }

    if (type != null) {
      attrs.add(new XmlWriter.Attribute("type", type));
    }

    if (href != null) {
      attrs.add(new XmlWriter.Attribute("href", href));
    }

    if (hrefLang != null) {
      attrs.add(new XmlWriter.Attribute("hreflang", hrefLang));
    }

    if (title != null) {
      attrs.add(new XmlWriter.Attribute("title", title));
    }

    if (titleLang != null) {
      attrs.add(new XmlWriter.Attribute("xml:lang", titleLang));
    }

    if (length != -1) {
      attrs.add(new XmlWriter.Attribute("length", String.valueOf(length)));
    }

    generateStartElement(w, Namespaces.atomNs, "link", attrs, null);

    // Invoke ExtensionPoint.
    generateExtensions(w, extProfile);

    w.endElement(Namespaces.atomNs, "link");
  }


  /**
   * Generates XML in the RSS format.
   *
   * @param   w
   *            Output writer.
   *
   * @throws  IOException
   */
  public void generateRss(XmlWriter w) throws IOException {

    ArrayList<XmlWriter.Attribute> attrs =
      new ArrayList<XmlWriter.Attribute>(3);

    if (rel != null && rel.equals("enclosure")) {

      if (type != null) {
        attrs.add(new XmlWriter.Attribute("type", type));
      }

      if (href != null) {
        attrs.add(new XmlWriter.Attribute("url", href));
      }

      if (length != -1) {
        attrs.add(new XmlWriter.Attribute("length", String.valueOf(length)));
      }

      w.simpleElement(Namespaces.rssNs, "enclosure", attrs, null);

    } else if ("comments".equals(rel)) {
      w.simpleElement(Namespaces.rssNs, "comments", null, href);
    } else if (Rel.ALTERNATE.equals(rel)) {
      w.simpleElement(Namespaces.rssNs, "link", null, href);
    } else if (Rel.VIA.equals(rel))  {

      if (href != null) {
        attrs.add(new XmlWriter.Attribute("url", href));
        w.simpleElement(Namespaces.rssNs, "source", attrs, null);
      }
    }
  }


  /** &lt;atom:link&gt; parser. */
  public class AtomHandler extends ExtensionPoint.ExtensionHandler {


    public AtomHandler(ExtensionProfile extProfile) throws IOException {
      super(extProfile, Link.class);
    }


    public void processAttribute(String namespace,
                                 String localName,
                                 String value)
        throws ParseException {

      if (namespace.equals("") && localName.equals("rel")) {
        rel = value;
      } else if (namespace.equals("") && localName.equals("type")) {
        type = value;
      } else if (namespace.equals("") && localName.equals("href")) {
        href = getAbsoluteUri(value);
      } else if (namespace.equals("") && localName.equals("hreflang")) {
        hrefLang = value;
      } else if (namespace.equals("") && localName.equals("title")) {
        title = value;
      } else if (namespace.equals("") && localName.equals("length")) {
        try {
          length = Integer.valueOf(value).longValue();
        } catch (NumberFormatException e) {
          throw new ParseException("Length must be an integer");
        }
      }
    }


    public void processEndElement() throws ParseException {

      if (href == null) {
        throw new ParseException(
          "Link must have an 'href' attribute.");
      }

      titleLang = xmlLang;

      // Allow undefined content.
    }
  }
}