Mybatis中如何生成全局主键ID

﹏ヽ暗。殇╰゛Y 2021-12-22 16:07 306阅读 0赞

## Mybatis中如何生成全局主键ID ##

上篇我讲了在mybatis中，新增数据时如何返回自增主键，依靠的是数据库可设置主键自动递增的机制，但是这种方法生成的主键扩展性比较差，如在一个分布式的系统中，会造成主键重复的问题。今天这篇文章讲下在分布式系统中如何生成全局唯一主键ID。

常见的解决方案大家可以参考下这篇文章，作者基于漫画的方式讲解的很清晰；

[漫画：什么是SnowFlake算法？][SnowFlake]

本文主要讲下在spring boot中如何集成SnowFlake算法，生成全局主键

SnowFlake算法github的网址: [https://github.com/twitter/snowflake][https_github.com_twitter_snowflake] 但貌似已经不维护了 ～～

好了在上一篇文章代码的基础上，开始撸代码～～

[源码地址][Link 1]

## １.第一步导入IdWorker.java ##

该类是SnowFlake算法的核心，这是我在网上找的一个java版本

/** * From: https://github.com/twitter/snowflake * An object that generates IDs. * This is broken into a separate class in case * we ever want to support multiple worker threads * per process */
    public class IdWorker { 
        // 时间起始标记点，作为基准，一般取系统的最近时间（一旦确定不能变动）2017/1/1 0:0:0
        private final static long twepoch = 1483200000000L;
        // 机器标识位数
        private final static long workerIdBits = 5L;
        // 数据中心标识位数
        private final static long datacenterIdBits = 5L;
        // 机器ID最大值
        private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
        // 数据中心ID最大值
        private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
        // 毫秒内自增位
        private final static long sequenceBits = 12L;
        // 机器ID偏左移12位
        private final static long workerIdShift = sequenceBits;
        // 数据中心ID左移17位
        private final static long datacenterIdShift = sequenceBits + workerIdBits;
        // 时间毫秒左移22位
        private final static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    
        private final static long sequenceMask = -1L ^ (-1L << sequenceBits);
        /* 上次生产id时间戳 */
        private static long lastTimestamp = -1L;
        // 0，并发控制
        private long sequence = 0L;
    
        private final long workerId;
        // 数据标识id部分
        private final long datacenterId;
    
        /** * @param workerId * 工作机器ID * @param datacenterId * 序列号 */
        public IdWorker(long workerId, long datacenterId) { 
            if (workerId > maxWorkerId || workerId < 0) { 
                throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
            }
            if (datacenterId > maxDatacenterId || datacenterId < 0) { 
                throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
            }
            this.workerId = workerId;
            this.datacenterId = datacenterId;
        }
        /** * 获取下一个ID * @return */
        public synchronized long nextId() { 
            long timestamp = timeGen();
            if (timestamp < lastTimestamp) { 
                throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
            }
    
            if (lastTimestamp == timestamp) { 
                // 当前毫秒内，则+1
                sequence = (sequence + 1) & sequenceMask;
                if (sequence == 0) { 
                    // 当前毫秒内计数满了，则等待下一秒
                    timestamp = tilNextMillis(lastTimestamp);
                }
            } else { 
                sequence = 0L;
            }
            lastTimestamp = timestamp;
            // ID偏移组合生成最终的ID，并返回ID
            long nextId = ((timestamp - twepoch) << timestampLeftShift)
                    | (datacenterId << datacenterIdShift)
                    | (workerId << workerIdShift) | sequence;
    
            return nextId;
        }
    
        private long tilNextMillis(final long lastTimestamp) { 
            long timestamp = this.timeGen();
            while (timestamp <= lastTimestamp) { 
                timestamp = this.timeGen();
            }
            return timestamp;
        }
    
        private long timeGen() { 
            return System.currentTimeMillis();
        }
    }

## 2.对算法参数进行配置 ##

导入idworker类后要想正常使用，肯定是要先配置一下：

首先在application.yml中新建如下2个配置参数，分别对应机器ID和序列号，多实例部署的话，不同实例该参数需配置不同值

util:
      #工作机器ID
      workerId: 5
      #序列号
      datacenterId: 10

然后创建配置类CustomerConfig，将IdWorker注入为bean

import lombok.Data;
    import org.springframework.boot.context.properties.ConfigurationProperties;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Configuration;
    
    @Configuration
    @ConfigurationProperties(prefix = "util")
    @Data
    public class CustomerConfig { 
        private Long workerId;
        private Long datacenterId;
        @Bean
        public IdWorker createIdWorker() { 
            IdWorker worker = new IdWorker(workerId, datacenterId);
            return worker;
        }
    
    }

## 3. 如何使用 ##

配置好IdWorker后，使用非常简单，只要每次在调用insert操作时，我们显示的调用idworker的nextId()方法获取一个全局ID，然后将生成的ID赋值给即将插入的对象即可，具体代码如下：

DepartmentController.java

@Api(description = "department")
    @RestController
    @RequestMapping("dept")
    public class DepartmentController { 
        @Autowired
        public DepartmentService departmentService;
        @Autowired
        public IdWorker idWorker;
        
        @ApiOperation(value = "新增部门")
        @PostMapping("new")
        public ResultMsg newDepartment(@RequestBody Department department)
        { 
            //每次插入数据时，调用nextId()获取一个全局ID
            department.setId(idWorker.nextId());
            int result = departmentService.insertDept(department);
            return ResultMsg.getMsg(result);
        }
    }

## 4.测试 ##

打开浏览器输入：http://localhost:9292/mybatis/swagger-ui.html 进入我们Swagger接口测试界面找到dept->new方法，输入测试参数，然后点击按钮try it out  
![format_png][]  
我们连续插入多条看看效果：  
![format_png 1][]  
[源码地址][Link 2]

## 5.总结 ##

相比较上篇文章中自增主键的方式，每条涉及插入的SQL语句都要设置useGeneratedKeys和keyProperty，全局获取ID的方式只要一次配置后，后边每次插入操作只需调用下idWorker.nextId()方法，简直不要太简单

建议大家在在实际开发过程中都采用这种方式来生成主键ID，可谓一劳永逸

[SnowFlake]: https://blog.csdn.net/bjweimengshu/article/details/80162731
[https_github.com_twitter_snowflake]: https://github.com/twitter/snowflake
[Link 1]: https://github.com/wanggang-git/Mybatis_demo
[format_png]: /images/20211220/a659c56b4fcf44888624145ffe9dcfae.png
[format_png 1]: /images/20211220/1b00b56c00f54ab499d1dfc1f1853258.png
[Link 2]: https://github.com/bdqx007/Mybatis_demo