activiti边界定时任务 act_ru_job 时间到了为什么不执行?

边界定时事件，act_ru_job 有数据， 就是没有执行......

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans   http://www.springframework.org/schema/beans/spring-beans.xsd">
 
  <bean id="processEngineConfiguration" class="org.activiti.engine.impl.cfg.StandaloneProcessEngineConfiguration">
 
    <property name="jdbcUrl" value="jdbc:mysql://localhost:3306/db_activiti?useUnicode=true&amp;characterEncoding=utf-8"   />
    <property name="jdbcDriver" value="com.mysql.jdbc.Driver" />
    <property name="jdbcUsername" value="root" />
    <property name="jdbcPassword" value="123456" />
 
    <property name="databaseSchemaUpdate" value="true" />
    <!-- 定时任务 -->
    <property name="jobExecutorActivate" value="true" />     
 
  </bean>
 
</beans>