Java幂等性的4种解决方案实战讲解(附通俗案例)

-- 用户表
CREATE TABLE t_user (
    id VARCHAR(50) PRIMARY KEY,
    name VARCHAR(50),
    coupon_count INT DEFAULT 0
);

-- 订单表
CREATE TABLE t_order (
    id VARCHAR(50) PRIMARY KEY,
    user_id VARCHAR(50),
    status VARCHAR(20), -- "待收货"、"已完成"
    version BIGINT DEFAULT 0
);

-- 用户张三，没有优惠券
INSERT INTO t_user VALUES ('u1', '张三', 0);

-- 一笔待收货订单
INSERT INTO t_order VALUES ('o1', 'u1', '待收货', 0);

@Transactional
public String confirmOrder(String orderId) {
    // 查询订单状态
    Order order = orderMapper.selectById(orderId);
    if ("已完成".equals(order.getStatus())) {
        return "SUCCESS";
    }

    // 核心：只更新待收货的订单
    int rows = orderMapper.updateStatusIfUnfinished(orderId, "已完成", "待收货");

    if (rows == 1) {
        // 发优惠券
        userMapper.addCoupon(order.getUserId(), 1);
        return "SUCCESS";
    } else {
        throw new RuntimeException("系统繁忙，请稍后重试");
    }
}

@Transactional(rollbackFor = Exception.class)
public String handleRecharge(String rechargeId) {
    // 根据rechargeId去找充值记录，如果已处理过，则直接返回成功
    RechargePO rechargePo = rechargeMapper.selectById(rechargeId);
    if (rechargePo == null) {
        throw new IllegalArgumentException("充值记录不存在");
    }

    // 充值记录已处理过，直接返回成功
    if (rechargePo.getStatus() == 1) {
        return "SUCCESS";
    }

    // 开启Spring事务（由 @Transactional 控制）

    // 在where后面要加 status = 0 这个条件；count表示影响行数
    int count = rechargeMapper.updateStatusToProcessed(rechargeId, 0, 1);

    // count = 1，表示上面sql执行成功
    if (count != 1) {
        // 走到这里，说明有并发，直接抛出异常
        throw new RuntimeException("系统繁忙，请重试");
    } else {
        // 给账户加钱
        accountMapper.increaseBalance(rechargePo.getAccountId(), rechargePo.getPrice());
    }

    // 提交Spring事务（由 @Transactional 控制）

    return "SUCCESS";
}

CREATE TABLE t_idempotent (
    id VARCHAR(50) PRIMARY KEY,
    idempotent_key VARCHAR(100) NOT NULL,
    UNIQUE KEY uq_idempotent_key (idempotent_key)
);

@Transactional
public String confirmOrderWithUniqueKey(String orderId) {
    String idempotentKey = "order_confirm:" + orderId;

    try {
        idempotentMapper.insert(idempotentKey);
    } catch (DuplicateKeyException e) {
        return "SUCCESS";
    }

    Order order = orderMapper.selectById(orderId);
    if ("已完成".equals(order.getStatus())) return "SUCCESS";

    orderMapper.updateStatus(orderId, "已完成");
    userMapper.addCoupon(order.getUserId(), 1);
    return "SUCCESS";
}

public String confirmOrderWithRedisLock(String orderId) {
    String lockKey = "lock:order:confirm:" + orderId;

    if (!redisLock.tryLock(lockKey, 5秒)) {
        throw new RuntimeException("系统繁忙，请稍后重试");
    }

    try {
        // 幂等处理逻辑
        ...
    } finally {
        redisLock.release(lockKey);
    }
}