UDF函数：判断日期是否为月末日期?

需求：判断一个日期是否为当月月末日期？

import org.apache.commons.lang.StringUtils;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.io.BooleanWritable;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

/**
 * 判断日期是否是月的最后一天 返回ture false
 */
public class UDFIsMonthLastDay extends UDF
{
    SimpleDateFormat simDateFormat = new SimpleDateFormat("yyyy-MM-dd");
    Date date;
    Calendar calendar = Calendar.getInstance();
    int dayMax = 0;

    BooleanWritable result = new BooleanWritable();

    public BooleanWritable evaluate(String dateStr) throws ParseException
    {
        if (StringUtils.isBlank(dateStr))
            return null;

        date = simDateFormat.parse(dateStr);
        calendar.setTime(date);
        dayMax = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);

        result.set(false);
        if (dayMax == calendar.get(Calendar.DAY_OF_MONTH))
            result.set(true);
        else
            result.set(false);

        return result;
    }

    public static void main(String[] args) throws Exception
    {
        UDFIsMonthLastDay o = new UDFIsMonthLastDay();
        System.out.println(o.evaluate("2012-02-29"));    
        System.out.println(o.evaluate("2000-02-28"));//false
        System.out.println(o.evaluate("2017-02-28"));
        System.out.println(o.evaluate("2017-02-30"));   //虚假日期，不会报错，但是为false
    }
}

输出结果显示：
true
false
true
false