今天寫程式碼的時候有一個service需要用到事務，故使用@Transactional註解

@Transactional
Map<String, Object> joinTeam(Long teamId, Long userId) throws Exception;

這裡丟擲自己定義的異常來實現事務回滾

介面實現類方法如下

 public Map<String, Object> joinTeam(Long teamId, Long userId) throws Exception {
        Map<String, Object> result = new
 
 HashMap<>();
        Team team = teamService.getTeamById(teamId);
        //新增組隊成員
        TeamMember member = new TeamMember();
        member.setUserId(userId);
        member.setTeamId(teamId);
        teamMemberDao.saveTeamMember(member);

        //更新組隊人數
        team.setCurrentSignup(team.getCurrentSignup() + 1
 
);
        Long count = teamService.updateTeamCurrentSignup(team);
        int i = 0;
        while (count == 0) {
            if (i >= 3) {
                throw new BaseException(BaseException.OPTIMISTIC_LOCK);
            }
            team = teamService.getTeamById(teamId);
            team.setCurrentSignup(team.getCurrentSignup() + 1
 
);
            count = teamService.updateTeamCurrentSignup(team);
            i++;
        }

        result.put("success", true);
        result.put("message", "加入成功!");
        throw new Exception(BaseException.OPTIMISTIC_LOCK);
    }

teamMemberDao.saveTeamMember(member) 與 count = teamService.updateTeamCurrentSignup(team) 、兩個修改庫操作，需要 teamService.updateTeamCurrentSignup(team) 拋異常來控制 teamMemberDao.saveTeamMember(member) 的資料回滾

但是結尾拋異常資料並不回滾，很是糟心。

於是檢視Spring的Transactional的API文件，發現下面這段：

If no rules are relevant to the exception, it will be treated like DefaultTransactionAttribute (rolling back on runtime exceptions).

所以Transactional預設異常回滾是runtimeexcetion才回滾

excetion是所有異常的總稱。
而runtimeexcetion是具體的某一個異常。

所以得將Transactional設定回滾異常為excetion

故將介面修改如下，這次再拋自定義異常就會回滾了

@Transactional(readOnly = false, propagation = Propagation.REQUIRED, rollbackFor = Exception.class)
Map<String, Object> joinTeam(Long teamId, Long userId) throws Exception;