心得：
项目中使用 for update 来控制业务逻辑，实际上 for update 是不推荐开发中使用的一种锁，原因是非常容易产生死锁。
还要注意的是锁的级别，因为InnoDB 的锁是建立在索引上，如果你没有使用索引查询数据，那么锁的级别就是表，否则就是索引数据也就是行级锁
个人觉得，尽量使用数据校验+数据回滚的方式来避免业务上的控制，比如库存数量，我们可以通过最后库存数的大小判断是否需要回滚。
日志：
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLTransactionRollbackException: Deadlock found when trying to get lock; try restarting transaction
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[?:1.8.0_65]
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[?:1.8.0_65]
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[?:1.8.0_65]
at java.lang.reflect.Constructor.newInstance(Constructor.java:422) ~[?:1.8.0_65]
at com.mysql.jdbc.Util.handleNewInstance(Util.java:404) ~[mysql-connector-java-5.1.38.jar:5.1.38]
at com.mysql.jdbc.Util.getInstance(Util.java:387) ~[mysql-connector-java-5.1.38.jar:5.1.38]
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:946) ~[mysql-connector-java-5.1.38.jar:5.1.38]
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3878) ~[mysql-connector-java-5.1.38.jar:5.1.38]
at com.mysql.jdbc.MysqlIO.nextRowFast(MysqlIO.java:2090) ~[mysql-connector-java-5.1.38.jar:5.1.38]
at com.mysql.jdbc.MysqlIO.nextRow(MysqlIO.java:1964) ~[mysql-connector-java-5.1.38.jar:5.1.38]
at com.mysql.jdbc.MysqlIO.readSingleRowSet(MysqlIO.java:3306) ~[mysql-connector-java-5.1.38.jar:5.1.38]
at com.mysql.jdbc.MysqlIO.getResultSet(MysqlIO.java:463) ~[mysql-connector-java-5.1.38.jar:5.1.38]
at com.mysql.jdbc.MysqlIO.readResultsForQueryOrUpdate(MysqlIO.java:3040) ~[mysql-connector-java-5.1.38.jar:5.1.38]
at com.mysql.jdbc.MysqlIO.readAllResults(MysqlIO.java:2288) ~[mysql-connector-java-5.1.38.jar:5.1.38]
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2681) ~[mysql-connector-java-5.1.38.jar:5.1.38]
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2551) ~[mysql-connector-java-5.1.38.jar:5.1.38]
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1861) ~[mysql-connector-java-5.1.38.jar:5.1.38]
at com.mysql.jdbc.PreparedStatement.execute(PreparedStatement.java:1192) ~[mysql-connector-java-5.1.38.jar:5.1.38]