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场景

今天本来准备写一个增加和修改，当存在这条数据，就修改，不存在这条数据就新建一条
代码如下， 不细细的写了，稍微粗略的来一点，有那个意思就行

 /*** 保存课程播放记录更新学习记录** @param courseLearnFlow 课程学习记录明细*/@Transactional(rollbackFor = Exception.class)public void saveFlowAndUpdateRecord(CourseLearnFlow courseLearnFlow) {CoursePlayRecord userCatalogPlayRecord = coursePlayRecordBiz.findUserCatalogPlayRecord(courseLearnFlow.getUserId(), courseLearnFlow.getBuyCourseId(), courseLearnFlow.getCourseId(), courseLearnFlow.getCatalogId());CoursePlayRecord catalogPlayRecord = new CoursePlayRecord();if (ObjectUtils.isNotEmpty(userCatalogPlayRecord)) {catalogPlayRecord.setUserId(courseLearnFlow.getUserId());catalogPlayRecord.setId(userCatalogPlayRecord.getId());// 拼接字符串，更新（CoursePlayRecord）StringBuilder sql = new StringBuilder("id =");sql.append(catalogPlayRecord.getId());sql.append(" and userId = ");sql.append(courseLearnFlow.getUserId());// 更新播放记录coursePlayRecordBiz.updateByWhereSql(catalogPlayRecord, sql.toString());} else {catalogPlayRecord.setUserId(courseLearnFlow.getUserId());// 保存播放记录coursePlayRecordBiz.save(catalogPlayRecord);}}

但是我发现我如果我在非常短的时间内调用两次这个方法，就会产生两条记录，因为两个线程几乎同时执行，系统无法判断是否生成形容新的数据，这时候就得使用锁了，我选择了比较简单的synchronized，主要是因为简单，然后我就把这整个方法都锁上，但是后来我又觉得这么锁的话，锁的颗粒好像有点大，然后我就决定根据userId也就是用户id来加锁

 /*** 保存课程播放记录更新学习记录** @param courseLearnFlow 课程学习记录明细*/@Transactional(rollbackFor = Exception.class)public void saveFlowAndUpdateRecord(CourseLearnFlow courseLearnFlow) {CoursePlayRecord userCatalogPlayRecord = coursePlayRecordBiz.findUserCatalogPlayRecord(courseLearnFlow.getUserId(), courseLearnFlow.getBuyCourseId(), courseLearnFlow.getCourseId(), courseLearnFlow.getCatalogId());CoursePlayRecord catalogPlayRecord = new CoursePlayRecord();synchronized(courseLearnFlow.getUserId()){if (ObjectUtils.isNotEmpty(userCatalogPlayRecord)) {catalogPlayRecord.setUserId(courseLearnFlow.getUserId());catalogPlayRecord.setId(userCatalogPlayRecord.getId());// 拼接字符串，更新（CoursePlayRecord）StringBuilder sql = new StringBuilder("id =");sql.append(catalogPlayRecord.getId());sql.append(" and userId = ");sql.append(courseLearnFlow.getUserId());// 更新播放记录coursePlayRecordBiz.updateByWhereSql(catalogPlayRecord, sql.toString());} else {catalogPlayRecord.setUserId(courseLearnFlow.getUserId());// 保存播放记录coursePlayRecordBiz.save(catalogPlayRecord);}}}

正文

方法一
但是运行起来好像是锁不住，debug了一下看了一下，因为userId是Intefer类型的所以每次获取到的userId的地址值都是不一样的，所以根本没法锁。
然后我就想到了把Integer类型转换成String类型来使用，后来一弄还是不行，然后研究了研究发现好像新建的String类型是在堆中的，并不是在字符串常量池，这个时候我就想到了使用intern()方法，使其返回字符串常量池中的地址,然后就成功的锁住了

 /*** 保存课程播放记录更新学习记录** @param courseLearnFlow 课程学习记录明细*/@Transactional(rollbackFor = Exception.class)public void saveFlowAndUpdateRecord(CourseLearnFlow courseLearnFlow) {CoursePlayRecord userCatalogPlayRecord = coursePlayRecordBiz.findUserCatalogPlayRecord(courseLearnFlow.getUserId(), courseLearnFlow.getBuyCourseId(), courseLearnFlow.getCourseId(), courseLearnFlow.getCatalogId());CoursePlayRecord catalogPlayRecord = new CoursePlayRecord();synchronized(String.ValueOf(courseLearnFlow.getUserId()).intern()){if (ObjectUtils.isNotEmpty(userCatalogPlayRecord)) {catalogPlayRecord.setUserId(courseLearnFlow.getUserId());catalogPlayRecord.setId(userCatalogPlayRecord.getId());// 拼接字符串，更新（CoursePlayRecord）StringBuilder sql = new StringBuilder("id =");sql.append(catalogPlayRecord.getId());sql.append(" and userId = ");sql.append(courseLearnFlow.getUserId());// 更新播放记录coursePlayRecordBiz.updateByWhereSql(catalogPlayRecord, sql.toString());} else {catalogPlayRecord.setUserId(courseLearnFlow.getUserId());// 保存播放记录coursePlayRecordBiz.save(catalogPlayRecord);}}}

方法二
其实还有一种方法，就是用Integer的valueof方法，但是这个方法只能在[-128, 127]这个范围使用，这个范围内使用的话，返回的Integer类型的地址是也是相同的，由于我此处的UserId已经远远超出了这个超出这个范围，所以返回的地址值不同，所以说也就锁不住。

 /*** 保存课程播放记录更新学习记录** @param courseLearnFlow 课程学习记录明细*/@Transactional(rollbackFor = Exception.class)public void saveFlowAndUpdateRecord(CourseLearnFlow courseLearnFlow) {CoursePlayRecord userCatalogPlayRecord = coursePlayRecordBiz.findUserCatalogPlayRecord(courseLearnFlow.getUserId(), courseLearnFlow.getBuyCourseId(), courseLearnFlow.getCourseId(), courseLearnFlow.getCatalogId());CoursePlayRecord catalogPlayRecord = new CoursePlayRecord();synchronized(Integer.valueOf(courseLearnFlow.getUserId())){if (ObjectUtils.isNotEmpty(userCatalogPlayRecord)) {catalogPlayRecord.setUserId(courseLearnFlow.getUserId());catalogPlayRecord.setId(userCatalogPlayRecord.getId());// 拼接字符串，更新（CoursePlayRecord）StringBuilder sql = new StringBuilder("id =");sql.append(catalogPlayRecord.getId());sql.append(" and userId = ");sql.append(courseLearnFlow.getUserId());// 更新播放记录coursePlayRecordBiz.updateByWhereSql(catalogPlayRecord, sql.toString());} else {catalogPlayRecord.setUserId(courseLearnFlow.getUserId());// 保存播放记录coursePlayRecordBiz.save(catalogPlayRecord);}}}

ok，就这么多，毕竟是新手，如果有说的不对的，希望大家多多指教。