java生成cron表达式构造器

package org.oreframework.util.scheduling;

import java.util.Calendar;



public class CronBuilder {

	protected static final String ALL_SPEC = "*";
    protected static final String NO_SPEC = "?";
    protected static final String HYPHEN_SPEC = "-";
    protected static final String SLASH_SPEC = "/";
    protected static final String COMMA_SPEC = ",";
    protected static final String SPACE_SPEC = " ";
    
	private String second = ALL_SPEC;
	private String minute = ALL_SPEC;
	private String hour = ALL_SPEC;
	private String dayOfMonth = ALL_SPEC;
	private String month = ALL_SPEC;
	private String dayOfWeek = NO_SPEC;
	private String year = ALL_SPEC;
    
    private stat