extensionpoint.java

google gdata API 很好用的API

                                 Class extendedClass) throws IOException {

      this.extProfile = extProfile;
      this.extendedClass = extendedClass;
      initializeArbitraryXml(extProfile, extendedClass, this);
    }


    private final ExtensionProfile extProfile;
    private final Class extendedClass;


    public ElementHandler getChildHandler(String namespace,
                                          String localName,
                                          Attributes attrs)
        throws ParseException, IOException {
      // Try ExtensionPoint. It returns {@code null} if there's no handler.
      ElementHandler extensionHandler =
        getExtensionHandler(extProfile, extendedClass,
                            namespace, localName, attrs);
      if (extensionHandler != null) {
        return extensionHandler;
      }

      return super.getChildHandler(namespace, localName, attrs);
    }
  }



  /** Retrieves the manifest for the specified class. */
  protected Manifest getManifest(
      ExtensionProfile extProfile,
      Class<? extends ExtensionPoint> extendedClass) {

    if (manifest == null) {
      manifest = extProfile.getManifest(extendedClass);
    }

    return manifest;
  }


 /**
   * Generates XML corresponding to the type implementing {@link
   * ExtensionPoint}. The reason this routine is necessary is that the
   * embedded XML blob may contain namespace declarations.
   */
  protected void generateStartElement(XmlWriter w,
                                      XmlWriter.Namespace namespace,
                                      String elementName,
                                      Collection<XmlWriter.Attribute>
                                       additionalAttrs,
                                      Collection<XmlWriter.Namespace>
                                       additionalNs)
      throws IOException {

    XmlBlob.startElement(w, namespace, elementName, xmlBlob,
                         additionalAttrs, additionalNs);
  }


  /**
   * Generates XML corresponding to extended properties. Implementations in
   * extended classes should always call the base class to allow for nested
   * extensions.
   *
   * @param   w
   *            Output writer.
   *
   * @param   extProfile
   *            Extension profile for use by nested extensions.
   *
   * @throws  IOException
   */
  protected void generateExtensions(XmlWriter w,
                                    ExtensionProfile extProfile)
      throws IOException {

    for (Extension ext: nonRepeatingExtensionMap.values()) {
      ext.generate(w, extProfile);
    }

    for (List<Extension> extList: repeatingExtensionMap.values()) {
      w.startRepeatingElement();
      for (Extension ext: extList) {
        ext.generate(w, extProfile);
      }
      w.endRepeatingElement();
    }

    if (xmlBlob != null) {
      w.innerXml(xmlBlob.getBlob());
    }
  }


  /**
   * Initializes parser handler's XML blob state.
   * Should be called by the handler's constructor in order to honor
   * {@link ExtensionProfile#declareArbitraryXmlExtension(Class)}.
   */
  protected void initializeArbitraryXml(ExtensionProfile profile,
                                        Class extPoint,
                                        ElementHandler handler)
      throws IOException {

    Manifest manifest = getManifest(profile, extPoint);
    if (manifest != null && manifest.arbitraryXml) {
      handler.initializeXmlBlob(xmlBlob,
                                /* mixedContent */ false,
                                /* fullTextIndex */ false);
    }
  }


  /**
   * XML parser callback for extended properties. Implementations in
   * extended classes should always call the base class to allow for
   * nested extensions.
   *
   * @param   extProfile
   *            Extension profile for use by nested element handlers.
   *
   * @param   extPoint
   *            Current active ExtensionPoint class within which you're
   *            looking for a handler for a nested extension element.
   *
   * @param   namespaceUri
   *            Namespace URI of the XML element.
   *
   * @param   localName
   *            Name of the XML element.
   *
   * @param   attrs
   *            Child element attributes. These attributes will be
   *            communicated to the returned {@link ElementHandler}
   *            through its {@link
   *            ElementHandler#processAttribute(String, String,
   *            String)} method. They are passed here because sometimes
   *            the value of some attribute determines the element's
   *            content type, so different element handlers may be
   *            needed.
   *
   * @return  Element handler for the custom tag or {@code null} if the tag
   *          is not recognized. Unrecognized tags are stored in the XML blob.
   *
   * @throws  ParseException
   *            XML schema error. Could be a result of having a
   *            duplicate entry, illegal contents (such as unrecognized
   *            attributes or nested elements), etc.
   */
  protected ElementHandler getExtensionHandler(ExtensionProfile extProfile,
                                               Class extPoint,
                                               String namespaceUri,
                                               String localName,
                                               Attributes attrs)
      throws ParseException, IOException {

    Manifest manifest = getManifest(extProfile, extPoint);
    if (manifest == null) {
      return null;
    }

    // Look for an explicit match, followed by a wildcarded namespace match.
    ExtensionDescription extDescription =
      manifest.supportedExtensions.get(new Pair(namespaceUri, localName));

    if (extDescription == null) {

      extDescription =
        manifest.supportedExtensions.get(new Pair(namespaceUri, "*"));

      if (extDescription == null) {

        // extension point) could just live here.
        return null;
      }
    }

    Class<? extends Extension> extClass = extDescription.getExtensionClass();
    if (extClass == null) {
      return null;
    }

    Extension extension = null;

    // If an aggregate extension type, retrieve existing instance (if any)
    if (extDescription.isAggregate()) {
      extension = getExtension(extClass);
    }

    boolean needsAdd = true;
    if (extension == null) {
      // Create an extension instance.
      try {
        extension = extClass.newInstance();
      } catch (InstantiationException e) {
        throw new ParseException("Unable to create extension", e);
      } catch (IllegalAccessException e) {
        throw new ParseException("Unable to create extension", e);
      }
    } else {
      needsAdd = false;
    }

    // Retrieve the handler.
    ElementHandler handler = extension.getHandler(extProfile, namespaceUri,
                                                  localName, attrs);

    // Store the new extension instance.
    if (needsAdd) {

      if (extDescription.isRepeatable()) {
        addRepeatingExtension(extension, extClass);
      } else {
        boolean added = addExtension(extension, extClass);
        if (!added) {
          throw new ParseException(
            "Duplicate extension element " + namespaceUri + ":" + localName);
        }
      }
    }
    return handler;
  }


  /** Checks whether all required extensions are present. */
  protected void checkRequiredExtensions(Manifest manifest)
      throws ParseException {

    for (ExtensionDescription extDescription:
         manifest.supportedExtensions.values()) {

      Class extClass = extDescription.getExtensionClass();
      if (extDescription.isRequired()) {
        boolean found = (extDescription.isRepeatable()
                         ? repeatingExtensionMap.containsKey(extClass)
                         : nonRepeatingExtensionMap.containsKey(extClass));
        if (!found) {
          throw new ParseException(
            "Required extension element " +
            extDescription.getNamespace().getAlias() + ":" +
            extDescription.getNamespace().getUri() + " not found.");
        }
      }
    }
  }

  /**
   * ElementHandler implementation for handlers associated with an
   * ExtensionPoint class. Provides common initialization and
   * code for looking up handlers defined within the ExtensionProfile
   * associated with the ExtensionPoint.
   */
  public class ExtensionHandler extends XmlParser.ElementHandler {

    protected ExtensionProfile extProfile;
    protected Class extendedClass;
    protected boolean hasExtensions;


    /**
     * Constructs a new Handler instance that process extensions on
     * a class associated with the ExtensionPoint
     *
     * @param   profile
     *            The extension profile associatd with the Handler.
     *
     * @param   extendedClass
     *            The extended class within the profile for this handler
     */
    public ExtensionHandler(ExtensionProfile profile, Class extendedClass)
        throws java.io.IOException {

      this.extProfile = profile;
      this.extendedClass = extendedClass;

      // If the extended class is defined within the profile, then enable
      // extension handling and arbitrary XML handling.
      Manifest manifest = profile.getManifest(extendedClass);
      if (manifest != null) {

        hasExtensions = true;

        if (manifest.arbitraryXml) {
          initializeArbitraryXml(extProfile, extendedClass, this);
        }
      }
    }


    public XmlParser.ElementHandler getChildHandler(String namespace,
                                                    String localName,
                                                    Attributes attrs)
        throws ParseException, IOException {

      // If extensions have been defined for the extended class, then
      // look for a handler.
      if (hasExtensions) {

        XmlParser.ElementHandler extensionHandler =
          getExtensionHandler(extProfile, extendedClass,
                              namespace, localName, attrs);
        if (extensionHandler != null) {
          return extensionHandler;
        }
      }

      return super.getChildHandler(namespace, localName, attrs);
    }


    public void processEndElement() throws ParseException {

      super.processEndElement();

      //
      // Iterate through all contained Extension instances and enable them
      // to validate against the full ExtensionPoint state (including
      // sibling Extension instances).
      //
      for (Extension extension :  nonRepeatingExtensionMap.values()) {
        if (extension instanceof ValidatingExtension) {
          ((ValidatingExtension) extension).validate(ExtensionPoint.this);
        }
      }

      for (List<Extension> extList : repeatingExtensionMap.values()) {
        for (Extension extension : extList) {
          if (extension instanceof ValidatingExtension) {
            ((ValidatingExtension) extension).validate(ExtensionPoint.this);
          }
        }
      }
    }
  }
}