rangeenumerator.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
 */

/**
 * Enumerates integers using one-based selection.
 * Examples:
 * "1-" all positive integers
 * "1,3-5,7" = "1,3,4,5,7"
 * next() or nextRange() must be called before calling get() for the first time
 */

public class RangeEnumerator {

  public static final int NONE = 0;
  public static final int INFINITY = -1;

  /** current value */
  int value = 0;

  /** limit of "5-7" would be 7 */
  int limit = NONE;

  /** position in the selection string */
  int pos = 0;

  /** selection range */
  String range;

  public RangeEnumerator(String selection) {
    range = selection;
  }

  /**
   * moves the pointer to the next position
   * false if no more
   */
  public synchronized boolean next() {

    if(value < 0)
      return false;
    else if(limit == INFINITY || value < limit) {
      value++;
      return true;
    }
    limit = NONE;

    try {
      // integer expected
      int n = readNextInt();
      if(n > 0) {
	value = n;
	if(pos >= range.length())
	  return true; // last number in range
	else {
	  char c = range.charAt(pos++);
	  if(c == '-') {
	    // determine the limit
	    if(pos >= range.length()) {
	      limit = INFINITY;
	      return true;
	    } else {
	      limit = readNextInt();
	      // skip the comma if any; if none - end of string reached
	      pos++;
	      if(limit >= n)
		return true;
	      else
		value = -1;
	    }
	  } else if(c == ',') {
	    // reset limit
	    limit = NONE;
	    return true;
	  } // else error
	}
      }

    } catch (Exception any) {
    }
    // error
    value = -1;
    return false;
  }

  /**
   * moves the pointer to the next range
   * e.g., if range is 1-3,7-9,15- and get() returns 8, after nextRange(),
   * get() will return 15.  For all other cases, it behaves the same as next()
   * false if no more
   */
  public synchronized boolean nextRange() {

    if (limit != NONE && limit != INFINITY) {
      value = limit;
    }
    return this.next();
  }


  int readNextInt() {

    int p = pos;
    char c = (char)0;

    //    System.err.println("HERE: " + pos);

    while(pos < range.length()) {
      c = range.charAt(pos);
      if((int)c < (int)'0' || (int)c > (int)'9')
	break;
      else
	pos++;
    }

    //    System.err.println("p: " + p + ", pos: " + pos + ", "); // + range.substring(pos, p);
    if(pos > p)
      return Integer.parseInt(range.substring(p, pos));
    //    else if (pos == range.length() - 1)
    //      return Integer.parseInt(range.substring(p));
    else
      throw new RuntimeException();
  }

  /**
   * Gets the current position
   * -1: invalid position
   */
  public synchronized int get() {
    return value;
  }


  /**
   * Gets the current position
   * -1: invalid position
   */
  public synchronized int limit() {
    return limit;
  }

  /**
   * Sets the current position
   */
  public synchronized void set(int nv) {

    value = 0;
    pos = 0;

    while(true) {
      next();
      if(value < 0)
	return; // error
      if(nv < value) {
	value = -1; // out of range on the left
	return;
      } else if( nv == value || (limit == INFINITY || nv <= limit) ) {
	// within range
	value = nv - 1;
	return;
      } // nv > value && (limit == NONE || limit < nv) => continue
    }

  }

  public String toString() {

    return range;
  }

  public static void main(String[] args) throws Exception {

    RangeEnumerator re = new RangeEnumerator(args[0]);
    if(args.length > 1)
      re.set(Integer.parseInt(args[1]));
    while(re.next())
      System.out.println("Next: " + re.get());
  }
}