mybatis+oracle添加一条数据并返回所添加数据的主键问题

@RequestMapping("/addplan")
    public @ResponseBody OnlineAddplanWithBLOBs insertOnlineAddplan(OnlineAddplanWithBLOBs plan) throws Exception{
         
　　　　 //plan是添加的数据,planid为数据主键，此时对象中主键为null
        int n = service.insertOnlineAddplan(plan);
    
　　　　 //获取对象主键
        System.out.println("返回的主键值是"+plan.getPlanid()); 
        
        return plan;
    }

<insert id="insert" parameterType="com.online.pojo.OnlineAddplanWithBLOBs" >
    
    //获取序列值，并赋值到对象的planid字段
    <selectKey keyProperty="planid" resultType="DECIMAL" order="BEFORE">  
            select online_sequence.nextval from dual  
    </selectKey>
    
    insert into ONLINE_ADDPLAN (PLANID, COMPLETETIME, PERSON, 
      OPERATION, USERNAME, EVENTNODE, 
      WORKPLAN, CHENGGUOMIAOSHU)
　　//获取上面对象中planid字段的值
    values (#{planid,jdbcType=DECIMAL}, #{completetime,jdbcType=TIMESTAMP}, #{person,jdbcType=VARCHAR}, 
      #{operation,jdbcType=VARCHAR}, #{username,jdbcType=VARCHAR}, #{eventnode,jdbcType=CLOB}, 
      #{workplan,jdbcType=CLOB}, #{chengguomiaoshu,jdbcType=CLOB})
  </insert>