Vesta发号器源码解析——DbMachineIdProvider

数据库持有machineId的模式

相关字段和构造方法

    //日志记录
    private static final Logger log = LoggerFactory
            .getLogger(DbMachineIdProvider.class);
    
    //machineId的记录
    private long machineId;
    //jdbcTemplate
    private JdbcTemplate jdbcTemplate;
    //构造方法记录日志
    public DbMachineIdProvider() {
        //这个地方源代码中错了，应修改
        //原始：
        //log.debug("IpConfigurableMachineIdProvider constructed.");
        //改为：
        log.debug("DbMachineIdProvider constructed.");
    }

初始化方法

    public void init() {
        //利用工具类读取主机IP
        String ip = IpUtils.getHostIp();
        //判断是否正确读取了IP，如果失败了，停止初始化，抛出异常
        if (StringUtils.isEmpty(ip)) {
            String msg = "Fail to get host IP address. Stop to initialize the DbMachineIdProvider provider.";

            log.error(msg);
            throw new IllegalStateException(msg);
        }
        
        //查询数据库
        Long id = null;
        try {
            id = jdbcTemplate.queryForObject(
                    "select ID from DB_MACHINE_ID_PROVIDER where IP = ?",
                    new Object[]{ip}, Long.class);

        } catch (EmptyResultDataAccessException e) {
            // 记录日志忽略这个异常
            log.error("No allocation before for ip {}.", ip);
        }
        
        //id查找成功，赋值后初始化完成，返回
        if (id != null) {
            machineId = id;
            return;
        }
        //记录日志，失败，没能获取到ip对应的id
        log.info(
                "Fail to get ID from DB for host IP address {}. Next step try to allocate one.",
                ip);
        //分配一个id
        int count = jdbcTemplate
                .update("update DB_MACHINE_ID_PROVIDER set IP = ? where IP is null limit 1",
                        ip);
        //如果更新条数大于1或者小于等于0，说明出现不合法状态，记录日志后抛异常失败，返回
        if (count <= 0 || count > 1) {
            String msg = String
                    .format("Fail to allocte ID for host IP address {}. The {} records are updated. Stop to initialize the DbMachineIdProvider provider.",
                            ip, count);

            log.error(msg);
            throw new IllegalStateException(msg);
        }
        
        //重新查询一次
        try {
            id = jdbcTemplate.queryForObject(
                    "select ID from DB_MACHINE_ID_PROVIDER where IP = ?",
                    new Object[]{ip}, Long.class);

        } catch (EmptyResultDataAccessException e) {
            //忽略异常
            log.error("Fail to do allocation for ip {}.", ip);
        }

        //仍然没有找到，抛出异常记录日之后结束初始化
        if (id == null) {
            String msg = String
                    .format("Fail to get ID from DB for host IP address {} after allocation. Stop to initialize the DbMachineIdProvider provider.",
                            ip);

            log.error(msg);
            throw new IllegalStateException(msg);
        }
        //赋值，初始化完成
        machineId = id;
    }

字段的getter和setter

    public long getMachineId() {
        return machineId;
    }

    public void setMachineId(long machineId) {
        this.machineId = machineId;
    }

    public JdbcTemplate getJdbcTemplate() {
        return jdbcTemplate;
    }

    public void setJdbcTemplate(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;