import static com.cronutils.model.field.expression.FieldExpressionFactory.always;import static com.cronutils.model.field.expression.FieldExpressionFactory.every;import static com.cronutils.model.field.expression.FieldExpressionFactory.on;import static com.cronutils.model.field.expression.FieldExpressionFactory.questionMark;import com.cronutils.builder.CronBuilder;import com.cronutils.model.Cron;import com.cronutils.model.CronType;import com.cronutils.model.definition.CronDefinitionBuilder;public class Test {		public static void main(String[] args) {		Cron cron = CronBuilder.cron(CronDefinitionBuilder.instanceDefinitionFor(CronType.QUARTZ))			    .withYear(always())			    .withDoW(questionMark())			    .withMonth(always())			    .withDoM(always())			    .withHour(always())			    .withMinute(every(5))			    .withSecond(on(0))			    .instance();			// Obtain the string expression			String cronAsString = cron.asString(); // 0 */5 * * * ? * 每5分钟一次									System.out.println(cronAsString);	}}

https://github.com/jmrozanec/cron-utils

https://www.cnblogs.com/be-come/p/6165293.html

http://cron.qqe2.com/