nestedattribute.java

数字图书馆的互操作接口

package dli2fe.helpers;

/**
 * Title:        Digial Library Interoperable Interface Fudan Edition
 * Description:  This project contains all the classes required for DLI2FE interface. Developers use these classes to implement the wrapper and client side codes. The basic functions of DLI2FE is as follows:
 * Search: Search a digital library source site.
 * Metadata: Fetch metadata for a site.
 * ResultAccess: Get results for a given query.
 * DLI2FE uses Dublin Core as the basic attribute model, DAV/DASL as the general XML-based query language and CORBA as distributed object transportation mechanism.
 * Copyright:    Copyright (c) 2001
 * Company:      Fudan University
 * @author Carl Tao
 * @version 1.0
 */
import java.util.*;

import dli2fe.DLI2FEException;
/* holder for integer values */
import org.omg.CORBA.IntHolder;
/* transport module libraries */
import dli2fe.helpers.*;
/* following packages are imported only if DOM-aware XMLObjects are used */
import dli2fe.xml.*;
import org.w3c.dom.*;
/* DLI2FE XML element names */
import dli2fe.DLI2FE;

/**
 * NestedAttribute represents a flat list of XML elements.
 * For example, nested attribute
 * <pre>
 *   &lt;coordinate&gt;
 *     &lt;x/&gt;
 *   &lt;/coordinate&gt;
 * </pre>
 * is represented by an element vector
 * <pre>
 *   coordinate, x
 * </pre>
 * NestedAttributes can be collected from the list of document properties requested by the client, or from the metadata returned by the client using the method <tt>collectAttributes</tt>. This class can also be used to filter out the attributes requested by the client from a complete document/resource description using <tt>matchDoc</tt>.
 */

public class NestedAttribute {

  Vector list;
  String propName;
  String propDesc;

  public NestedAttribute(Vector v) {
    list = (Vector)v.clone();
    init();
  }

  public NestedAttribute(Enumeration en) {

    list = new Vector();
    while(en.hasMoreElements()) {
      list.addElement(en.nextElement());
    }
    init();
  }

  /**
   * returns the last element in the list
   */
  public Element getLast() {

    return (Element)list.elementAt(list.size()-1);
  }

  public Element elementAt(int i) {
    return (Element)list.elementAt(i);
  }

  public int size() {
    return list.size();
  }

  /**
   * returns a nested representation of the element list
   */
  public Element getNestedElements() {

    Element top = null, current = null;
    for(Enumeration en = list.elements(); en.hasMoreElements();) {
      Element e = (Element)en.nextElement();
      Element tmp = (Element)e.cloneNode(false);
      if(current == null)
	current = tmp;
      else {
	current.appendChild(tmp);
	current = tmp;
      }
      if(top == null)
	top = tmp;
    }
    return top;
  }

  void init() {

    if(list.size() == 0)
      throw new IllegalArgumentException("[NestedAttribute] cannot be empty");

    propName = DOMUtil.getChildText(getLast(), DLI2FE.propName);
    propDesc = DOMUtil.getChildText(getLast(), DLI2FE.propDesc);

    if(propName == null) {
      // compute a canonical name
      propName = "";
      for(Enumeration en = list.elements(); en.hasMoreElements();) {
	Element e = (Element)en.nextElement();
	if(!"".equals(propName))
	  propName += ".";
	propName += getName(e.getTagName());
      }
    }
  }

  static int getNSEnd(String name) {
    // first try to detemine namespace directly
    int l = name.length()-1;
    do {
      char c = name.charAt(l);
      if(c == '#' || c == ':' || c == '/')
	break;
      l--;
    } while (l >= 0);
    l++;
    return l;
  }

  public static String getNS(String name) {
    int l = getNSEnd(name);
    if(l > 0) {
      return name.substring(0, l);
    } else
      return "";
  }

  public static String getName(String name) {
    int l = getNSEnd(name);
    if(l > 0) {
      return name.substring(l);
    } else
      return name;
  }


  public String getPropName() {

    return propName;
  }

  public String getPropDesc() {

    return propDesc == null ? "" : propDesc;
  }

  /**
   * Collects a vector of NestedAttributes from metadata inside <tt>DLI2FE:propList</tt> tag.
   */
  public static Vector collectAttributes(Element e) {

    if(e == null)
      return null;
    Stack stack = new Stack();
    Vector attrs = new Vector();
    collectAttributes(attrs, stack, e);
    return attrs;
  }

  /**
   * Whether attribute is searchable
   */
  public boolean isSearchable() {

    return DOMUtil.getChild(getLast(), DLI2FE.searchable) != null;
  }

  /**
   * Whether attribute is retrievable
   */
  public boolean isRetrievable() {

    return DOMUtil.getChild(getLast(), DLI2FE.retrievable) != null;
  }

  private static void collectAttributes(Vector attrs, Stack stack, Element e) {

    Element eRetrievable = DOMUtil.getChild(e, DLI2FE.retrievable);
    Element eSearchable = DOMUtil.getChild(e, DLI2FE.searchable);
    NodeList propList = DOMUtil.getChildElements(e, "*");

    if(eRetrievable != null || eSearchable != null || propList.getLength() == 0) {

      attrs.addElement(new NestedAttribute(stack));

    } else {

      for(int j=0; j < propList.getLength(); j++) {
	Element eProp = (Element)propList.item(j);
	stack.push(eProp);
	collectAttributes(attrs, stack, eProp);
	stack.pop();
      }
    }
  }

  /**
   * Returns a subset of attributes from <tt>eDoc</tt> that match NestedAttributes in <tt>attrs</tt>
   */
  public static Element matchDoc(Vector attrs, Element eDoc) {

    if(attrs == null) // no filter
      return (Element)eDoc.cloneNode(true);

    Element eDoc2 = (Element)eDoc.cloneNode(false);
    eDoc2.appendChild( DOMUtil.getChild(eDoc, DLI2FE.DID).cloneNode(true) );
    Element ePropList = DOMUtil.getChild(eDoc, DLI2FE.propList);
    Element ePropList2 = NestedAttribute.match(attrs, ePropList);
    if(ePropList2 == null) // nothing found
      ePropList2 = (Element)ePropList.cloneNode(false);
    eDoc2.appendChild(ePropList2);
    return eDoc2;
  }

  /**
   * Copies from ePropList a subset of values that match attributes listed in <tt>attrs</tt>.
   * Use this function for selective delivery of results to the client.
   * Pass <tt>propList</tt> element as parameter.
   */
  public static Element match(Vector attrs, Element e) {

    NodeList clist = DOMUtil.getChildElements(e, "*");

    if(clist.getLength() == 0) { // terminal
      // check whether this attribute value is requested
      for(int j = 0; j < attrs.size(); j++) {
	NestedAttribute a = (NestedAttribute)attrs.elementAt(j);
	// check whether the attribute matches the path that leads to e
	Element p = e;
	boolean matched = true;
	for(int h = a.size() - 1; h >=0; h--, p = (Element)e.getParentNode() ) {
	  if(!p.getTagName().equals(a.elementAt(h).getTagName())) {
	    matched = false;
	    break;
	  }
	}
	if(matched) { // clone the content including text and return it
	  return (Element)e.cloneNode(true);
	}
      }
      return null; // terminal not matched anything
    }

    // match children

    Element ePropagator = null;
    for(int i = 0; i < clist.getLength(); i++) {
      Element c = (Element)clist.item(i);
      Element eMatched = match(attrs, c);
      if(eMatched != null) { // make sure to propagate this match
	if(ePropagator == null)
	  ePropagator = (Element)e.cloneNode(false);
	ePropagator.appendChild(eMatched);
      }
    }
    return ePropagator;
  }

  /**
   * Returns an enumeration of values for the NestedAttribute found inside the given XML element
   */
  public Enumeration matchValues(Element e) {

    Vector v = new Vector();
    matchValues(v, e, -1); // propList => -1
    return v.elements();
  }

  private void matchValues(Vector v, Element e, int i) {

    if(i == list.size() - 1) { // found match
      v.addElement(DOMUtil.getText(e));

    } else {

      i++;
      NodeList propList = DOMUtil.getChildElements(e, ((Element)list.elementAt(i)).getTagName());
      for(int j=0; j < propList.getLength(); j++) {
	Element eProp = (Element)propList.item(j);
	matchValues(v, eProp, i);
      }
    }
  }

  public String toString() {
    dli2fe.xml.XMLObject obj = new XMLObject(getNestedElements());
    return obj.getString();
  }

}