任务Cron更新逻辑优化，改为rescheduleJob，同时防止cron重复设置；

README.md

 - 5、执行参数编辑时丢失问题修复；
 - 6、新增任务测试Demo，方便在开发时进行任务逻辑测试；
 
+#### 6.16 版本 V1.8.0 特性[Coding]
+- 1、任务Cron更新逻辑优化，改为rescheduleJob，同时防止cron重复设置；
+
 #### TODO LIST
 - 1、任务权限管理：执行器为粒度分配权限，核心操作校验权限；
 - 2、任务分片：一个任务被拆分成N个独立的任务单元，然后由分布式部署的执行器分别执行某一个或几个分片单元；

xxl-job-admin/src/main/java/com/xxl/job/admin/core/schedule/XxlJobDynamicScheduler.java

         
         // TriggerKey : name + group
         TriggerKey triggerKey = TriggerKey.triggerKey(jobName, jobGroup);
-        JobKey jobKey = new JobKey(jobName, jobGroup);
-        
-        // CronTrigger : TriggerKey + cronExpression
-        CronScheduleBuilder cronScheduleBuilder = CronScheduleBuilder.cronSchedule(cronExpression).withMisfireHandlingInstructionDoNothing();
-        CronTrigger cronTrigger = TriggerBuilder.newTrigger().withIdentity(triggerKey).withSchedule(cronScheduleBuilder).build();
-        
-        //scheduler.rescheduleJob(triggerKey, cronTrigger);
-        
-        // JobDetail-JobDataMap fresh
-        JobDetail jobDetail = scheduler.getJobDetail(jobKey);
-    	/*JobDataMap jobDataMap = jobDetail.getJobDataMap();
-    	jobDataMap.clear();
-    	jobDataMap.putAll(JacksonUtil.readValue(jobInfo.getJobData(), Map.class));*/
-    	
-    	// Trigger fresh
-    	HashSet<Trigger> triggerSet = new HashSet<Trigger>();
-    	triggerSet.add(cronTrigger);
-        
-        scheduler.scheduleJob(jobDetail, triggerSet, true);
+        CronTrigger oldTrigger = (CronTrigger) scheduler.getTrigger(triggerKey);
+
+        if (oldTrigger != null) {
+            // avoid repeat
+            String oldCron = oldTrigger.getCronExpression();
+            if (oldCron.equals(cronExpression)){
+                return true;
+            }
+
+            // CronTrigger : TriggerKey + cronExpression
+            CronScheduleBuilder cronScheduleBuilder = CronScheduleBuilder.cronSchedule(cronExpression).withMisfireHandlingInstructionDoNothing();
+            oldTrigger = oldTrigger.getTriggerBuilder().withIdentity(triggerKey).withSchedule(cronScheduleBuilder).build();
+
+            // rescheduleJob
+            scheduler.rescheduleJob(triggerKey, oldTrigger);
+        } else {
+            // CronTrigger : TriggerKey + cronExpression
+            CronScheduleBuilder cronScheduleBuilder = CronScheduleBuilder.cronSchedule(cronExpression).withMisfireHandlingInstructionDoNothing();
+            CronTrigger cronTrigger = TriggerBuilder.newTrigger().withIdentity(triggerKey).withSchedule(cronScheduleBuilder).build();
+
+            // JobDetail-JobDataMap fresh
+            JobKey jobKey = new JobKey(jobName, jobGroup);
+            JobDetail jobDetail = scheduler.getJobDetail(jobKey);
+            /*JobDataMap jobDataMap = jobDetail.getJobDataMap();
+            jobDataMap.clear();
+            jobDataMap.putAll(JacksonUtil.readValue(jobInfo.getJobData(), Map.class));*/
+
+            // Trigger fresh
+            HashSet<Trigger> triggerSet = new HashSet<Trigger>();
+            triggerSet.add(cronTrigger);
+
+            scheduler.scheduleJob(jobDetail, triggerSet, true);
+        }
+
         logger.info(">>>>>>>>>>> resumeJob success, JobGroup:{}, JobName:{}", jobGroup, jobName);
         return true;
     }