SpringBoot+Mybatis实现分表

基本思路

• 根据创建时间字段按年进行分表，比如日志表log可以分为log_2024、log_2025

• 在需要进行插入、更新操作的地方利用threadlocal将数据表对应的Entity和创建时间放入当前的线程中，利用mybatis提供的拦截器在sql执行前进行拦截，将threadlocal中的Entity类取出，根据类上标注的注解获取要操作的表名，再利用创建时间获得最终要操作的实际表名，最后更换sql中的表名让拦截器继续执行

创建拦截器

@Component
@Intercepts({@Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class,Integer.class})})
public class ShardingInterceptor implements Interceptor {

    @Autowired
    private ShardingStrategy shardingStrategy;

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
        BoundSql boundSql = statementHandler.getBoundSql();
        String originalSql =  boundSql.getSql();

        ShardingContext context = ShardingContext.getContext(); // 获取当前操作的实体类
        if (context != null){
            Class<?> entityClass = context.getEntityClass();
            Date date = context.getDate();
            ShardedTable annotation = entityClass.getAnnotation(ShardedTable.class);
            if (annotation != null) {
                String baseTableName = annotation.prefix(); // 设置新的sql,替换表名
                String actualTableName = shardingStrategy.getTableName(User.class, date);
                String modifiedSql = originalSql.replace(baseTableName, actualTableName);
                setSql(boundSql, modifiedSql);
            }
        }

        return invocation.proceed();
    }

    private void setSql(BoundSql boundSql, String sql) throws Exception {
        Field field = BoundSql.class.getDeclaredField("sql");
        field.setAccessible(true);
        field.set(boundSql, sql);
    }

    @Override
    public Object plugin(Object target) {
        // 判断是否为StatementHandler类型
        if (target instanceof StatementHandler){
            return Plugin.wrap(target, this);
        }else {
            return target;
        }
    }

    @Override
    public void setProperties(Properties properties) {
    }
}

获取表名

@Component
public class ShardingStrategy {

    public String getTableName(Class<?> entityClass, Date date) {
        ShardedTable annotation = entityClass.getAnnotation(ShardedTable.class);
        if (annotation == null) {
            throw new RuntimeException("实体类必须使用@ShardedTable注解");
        }
        // 获取分表前缀
        String tablePrefix = annotation.prefix();
        if (tablePrefix == null || tablePrefix.isEmpty()) {
            throw new RuntimeException("分表前缀不能为空");
        }
        // 获取当前日期所在的年份
        int year = DateUtil.year(date);
        return tablePrefix + "_" + year;
    }
}

业务处理

在需要进行业务处理的地方，将数据表对应的Entity.class和创建时间通过threadlocal放入当前线程中，后面要根据这些信息获取实际要操作的表名

public void insert(ServiceOrderLogEntity serviceOrderLogEntity) {
    ShardingContext.setContext(ServiceOrderLogEntity.class, serviceOrderLogEntity.getTime() == null ? new Date() : serviceOrderLogEntity.getTime());
    
    int result = serviceOrderLogMapper.insert(serviceOrderLogEntity);
    
    ShardingContext.clearContext();
}

定义注解

定义注解@ShardedTable，将该注解标注在数据表对应的Entity类上，比如User类上

/**
 * 分表注解
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface ShardedTable {

    // 表名前缀
    String prefix();

}

@ShardedTable(prefix = "user")
@TableName("user")
public class User {

    @TableId(type = IdType.AUTO)
    private Integer id;

    private String name;

    private Integer age;

    public User(String name, Integer age) {
        this.name = name;
        this.age = age;
    }
}

创建ThreadLocal

public class ShardingContext{
    private static final ThreadLocal<ShardingContext> CONTEXT = new ThreadLocal<>();

    private Class<?> entityClass; // 数据表对应的实体类
    private Date date;

    public static void setContext(Class<?> entityClass, Date date) {
        ShardingContext context = new ShardingContext();
        context.entityClass = entityClass;
        context.date = date;
        CONTEXT.set(context);
    }

    public static ShardingContext getContext() {
        return CONTEXT.get();
    }

    public static void clearContext() {
        CONTEXT.remove();
    }

    public Class<?> getEntityClass() {
        return entityClass;
    }

    public Date getDate() {
        return date;
    }
}