MyBatis-Plus主键策略（雪花算法16位长度的整型id，解决默认雪花算法生成19位长度id导致JS精度丢失问题）

js表达的最大整数2的53次方减1，精度丢失后面几位全是0！

主键策略

如果内置支持不满足你的需求，可实现 IKeyGenerator 接口来进行扩展.

举个栗子

@KeySequence(value = "SEQ_ORACLE_STRING_KEY", clazz = String.class)
public class YourEntity {

    @TableId(value = "ID_STR", type = IdType.INPUT)
    private String idStr;

}

#Spring-Boot

#方式一：使用配置类

@Bean
public IKeyGenerator keyGenerator() {
    return new H2KeyGenerator();
}

#方式二：通过 MybatisPlusPropertiesCustomizer 自定义

@Bean
public MybatisPlusPropertiesCustomizer plusPropertiesCustomizer() {
    return plusProperties -> plusProperties.getGlobalConfig().getDbConfig().setKeyGenerator(new H2KeyGenerator());
}

#Spring

#方式一: XML 配置

<bean id="globalConfig" class="com.baomidou.mybatisplus.core.config.GlobalConfig">
   <property name="dbConfig" ref="dbConfig"/>
</bean>

<bean id="dbConfig" class="com.baomidou.mybatisplus.core.config.GlobalConfig.DbConfig">
   <property name="keyGenerator" ref="keyGenerator"/>
</bean>

<bean id="keyGenerator" class="com.baomidou.mybatisplus.extension.incrementer.H2KeyGenerator"/>

#方式二：注解配置

@Bean
public GlobalConfig globalConfig() {
	GlobalConfig conf = new GlobalConfig();
	conf.setDbConfig(new GlobalConfig.DbConfig().setKeyGenerator(new H2KeyGenerator()));
	return conf;
}

官方示例

官方id generator示例https://gitee.com/baomidou/mybatis-plus-samples/tree/master/mybatis-plus-sample-id-generator

工程中16位长度的long整型id示例

@Component
public class CustomerIdGenerator implements IdentifierGenerator {
    @Override
    public Long nextId(Object entity) {
        // 填充自己的Id生成器，
        return IdGenerator.generateId();
    }
}

import java.util.Date;
import java.util.UUID;

/**
 * compressed id generator, result id not great than 53bits before 2318-06-04.
 */
public class IdGenerator {

    private static IdGenerator instance = new IdGenerator(0);

    public static IdGenerator initDefaultInstance(int machineId) {
        instance = new IdGenerator(machineId);
        return instance;
    }

    public static IdGenerator getInstance() {
        return instance;
    }

    public static long generateId() {
        return instance.nextId();
    }

    // total bits=53(max 2^53-1：9007199254740992-1)

    // private final static long TIME_BIT = 40; // max: 2318-06-04
    private final static long MACHINE_BIT = 5; // max 31
    private final static long SEQUENCE_BIT = 8; // 256/10ms

    /**
     * mask/max value
     */
    private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long TIMESTMP_LEFT = MACHINE_BIT + SEQUENCE_BIT;

    private long machineId;
    private long sequence = 0L;
    private long lastStmp = -1L;

    private IdGenerator(long machineId) {
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException(
                    "machineId can't be greater than " + MAX_MACHINE_NUM + " or less than 0");
        }
        this.machineId = machineId;
    }

    /**
     * generate new ID
     *
     * @return
     */
    public synchronized long nextId() {
        long currStmp = getTimestamp();
        if (currStmp < lastStmp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currStmp == lastStmp) {
            sequence = (sequence + 1) & MAX_SEQUENCE;
            if (sequence == 0L) {
                currStmp = getNextTimestamp();
            }
        } else {
            sequence = 0L;
        }

        lastStmp = currStmp;

        return currStmp << TIMESTMP_LEFT //
                | machineId << MACHINE_LEFT //
                | sequence;
    }

    private long getNextTimestamp() {
        long mill = getTimestamp();
        while (mill <= lastStmp) {
            mill = getTimestamp();
        }
        return mill;
    }

    private long getTimestamp() {
        // per 10ms
        return System.currentTimeMillis() / 10;// 10ms
    }

    public static Date parseIdTimestamp(long id) {
        return new Date((id >>> TIMESTMP_LEFT) * 10);
    }

    public static String uuid() {
        return UUID.randomUUID().toString().replaceAll("-", "");
    }
}

实体类还是直接使用

@TableId(value = "id", type = IdType.ASSIGN_ID)

@TableId(value = "id", type = IdType.ASSIGN_ID)
private Long id;