Like.java

/*****************************************************************************
      SQLJEP - Java SQL Expression Parser 0.2
      November 1 2006
         (c) Copyright 2006, Alexey Gaidukov
      SQLJEP Author: Alexey Gaidukov

      SQLJEP is based on JEP 2.24 (http://www.singularsys.com/jep/)
           (c) Copyright 2002, Nathan Funk
 
      See LICENSE.txt for license information.
*****************************************************************************/

package com.meidusa.amoeba.sqljep.function;

import java.util.Hashtable;
import java.util.ArrayList;
import java.util.regex.*;

import com.meidusa.amoeba.sqljep.function.PostfixCommand;
import com.meidusa.amoeba.sqljep.ASTFunNode;
import com.meidusa.amoeba.sqljep.JepRuntime;
import com.meidusa.amoeba.sqljep.ParseException;

/**
 * SQL�е�like�����
 * �ж������ַ����Ƿ�����
 * Like algorithm. It supports two variants of syntax. The first is SQL syntax. 
 * The second is JRE regexp syntax. By default SQL syntax is used. To use regexp
 * syntax put pattern into slashes. For example "/^10*.?/"
 */
public final class Like extends PostfixCommand {
	protected static final Integer ZERO_OR_MORE_CHARS = 0; 
	protected static final Integer ONE_CHAR = 1; 

	protected static Hashtable<String,Pattern> patterns = new Hashtable<String,Pattern>();

	final public int getNumberOfParameters() {
		return 2;
	}
	
	public Comparable<?>[] evaluate(ASTFunNode node, JepRuntime runtime) throws ParseException {
		node.childrenAccept(runtime.ev, null);
		Comparable<?>  param2 = runtime.stack.pop();
		Comparable<?>  param1 = runtime.stack.pop();
		return new Comparable<?>[]{param1,param2};
	}

	public static boolean like(Comparable<?>  param1, Comparable<?>  param2){
		if (param1 == null || param2 == null) {
			return false;
		}
		String source = param1.toString();
		String match = param2.toString();
		Pattern pattern = patterns.get(match);
		if (pattern == null) {
			ArrayList<Object> p = compile(match);
			String regexp = toRegExp(p);
			pattern = Pattern.compile(regexp);
			patterns.put(match, pattern);
		}
		Matcher m = pattern.matcher(source);
		return m.find();
	}
	
	protected static ArrayList<Object> compile(String pattern) {
		ArrayList<Object> format = new ArrayList<Object>();
		StringBuilder fill = new StringBuilder();
		final int plen = pattern.length();
		Character lastSymbol = null;
		if (pattern.length() > 2 && pattern.charAt(0) == '/' && pattern.charAt(pattern.length()-1) == '/') {
			format.add(pattern.substring(1, pattern.length()-2));
		} else {
			for (int i = 0; i < plen; i++) {
				char c = pattern.charAt(i);
				if (lastSymbol != null && lastSymbol.charValue() == '\\') {
					lastSymbol = null;
					fill.append(c);
				} else {
					if (c == '%') {
						if (fill.length() > 0) {
							format.add(fill.toString());
							fill.setLength(0);
						}
						format.add(ZERO_OR_MORE_CHARS); 
					}
					else if (c == '_') {
						if (fill.length() > 0) {
							format.add(fill.toString());
							fill.setLength(0);
						}
						format.add(ONE_CHAR); 
					} else {
						fill.append(c);
					}
					lastSymbol = c;
				}
			}
			if (fill.length() > 0) {
				format.add(fill.toString());
			}
		}
		return format;
	}
	
	public static String toRegExp(ArrayList<Object> pattern) {
		if (pattern != null) {
			StringBuilder str = new StringBuilder("^");
			for (Object o : pattern) {
				if (o == ZERO_OR_MORE_CHARS) {
					str.append(".*?");
				}
				else if (o == ONE_CHAR) {
					str.append(".?");
				} else {
					str.append((String)o);
				}
			}
			return str.toString();
		} else {
			return null;
		}
	}
	
	public static String toString(ArrayList<Object> pattern) {
		if (pattern != null) {
			StringBuilder str = new StringBuilder();
			for (Object o : pattern) {
				if (o == ZERO_OR_MORE_CHARS) {
					str.append('%');
				}
				else if (o == ONE_CHAR) {
					str.append('_');
				} else {
					str.append((String)o);
				}
			}
			return str.toString();
		} else {
			return null;
		}
	}
	
	public static void main(String[] args){
		System.out.println(like("%asdf","%asdf%"));
		Comparative one = new Comparative(Comparative.Like,"%abc");
		Comparative two = new Comparative(Comparative.Like,"%bc");
		System.out.println(like(one,two));
	}

	public Comparable<?> getResult(Comparable<?>... comparables)
			throws ParseException {
		return like(comparables[0], comparables[1]);
	}
}