Jmeter While Controller 使用${__jexl2(,)}

String [] str ={"1","2","3"};
vars.putObject("strArray",str);
int length=str.length ;
log.info("length==="+length);
//vars.putObject("index",0);
//vars.putObject("strArrayLength",length);
vars.put("index","0");
vars.put("strArrayLength",String.valueOf(length));
vars.putObject("strArray",str);
//Boolean a=${__groovy(vars.get("index")==vars.get("strArrayLength"))};
Boolean a=${__groovy(vars.get("index")==0)};
log.info("a===="+a);
log.info("================="+${__jexl2("${index}"<"${strArrayLength}",)});

log.info("--------${__jm__WC__idx}");
//int indexWC =vars.getObject("index")+1;
int indexWC =Integer.parseInt("${index}")+1;
log.info("indexWC=========="+indexWC);
vars.putObject("index",indexWC);
String [] cc=vars.getObject("strArray");
log.info("cc["+${__jm__WC__idx}+"]====="+cc[${__jm__WC__idx}]);