Jmeter Beashell 获取日期

import java.text.SimpleDateFormat;
import java.util.Date;
import java.text.*;
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
//SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
//获取当前月第一天：
    Calendar c = Calendar.getInstance();   
    c.add(Calendar.MONTH, 0);
//    c.set(Calendar.HOUR_OF_DAY,0);
//    c.set(Calendar.MINUTE,0);
//    c.set(Calendar.SECOND,0);
    c.set(Calendar.DAY_OF_MONTH,1);//设置为1号,当前日期既为本月第一天 
    String first = format.format(c.getTime());
    vars.put("firstContributionStartDate",first);

//获取下个月第一天：
    Calendar c = Calendar.getInstance();   
    c.add(Calendar.MONTH, 1);
    c.set(Calendar.DAY_OF_MONTH,1);
    String first = format.format(c.getTime());
    vars.put("secondContributionStartDate",first);

//获取上个月10号：
    Calendar c = Calendar.getInstance();   
    c.add(Calendar.MONTH, -1);
    c.set(Calendar.DAY_OF_MONTH,10);
    String first = format.format(c.getTime());
    vars.put("contributionBillGenerationDate",first);