黑马点评：秒杀 Lua 与数据库唯一约束

RedisScript<Long> script = RedisScript.of(luaText, Long.class);
List<String> keys = List.of("stock:{v1}", "buyers:{v1}"); // 所有脚本访问键显式传入，同活动键使用相同hash tag。
Long result = template.execute(script, keys, authenticatedUserId); // 身份来自认证上下文，参数序列化要与Lua约定一致。
if (result == null) throw new IllegalStateException("no direct script result"); // 流水线或事务模式返回语义不能当普通同步调用。
recordReservationOutcome(result); // 这里只记录预扣结果，不能标记MySQL订单已提交。

import java.util.*;
public class Main {
    enum State {RESERVED,CONFIRMED,CANCELED}
    record Order(String user,State state){}
    static class Ledger {
        final int initial;int available;Map<String,Order> orders=new HashMap<>();Map<String,String> active=new HashMap<>();
        Ledger(int stock){if(stock<0)throw new IllegalArgumentException("stock");initial=available=stock;}
        State reserve(String id,String user){
            if(id==null||id.isBlank()||user==null||user.isBlank())throw new IllegalArgumentException("identity");Order old=orders.get(id);
            if(old!=null){if(!old.user().equals(user))throw new IllegalArgumentException("id conflict");return old.state();} // 稳定订单号重放不再次扣库存。
            if(active.containsKey(user)||available==0)throw new IllegalStateException("not eligible");
            available--;orders.put(id,new Order(user,State.RESERVED));active.put(user,id);return State.RESERVED;
        }
        void confirm(String id){Order o=required(id);if(o.state()==State.CANCELED)throw new IllegalStateException("canceled");orders.put(id,new Order(o.user(),State.CONFIRMED));} // 确认不再扣减。
        void cancel(String id){Order o=required(id);if(o.state()==State.CONFIRMED)throw new IllegalStateException("confirmed");if(o.state()==State.CANCELED)return;
            orders.put(id,new Order(o.user(),State.CANCELED));active.remove(o.user());available++; // 只释放一次未确认预扣。
        }
        Order required(String id){Order o=orders.get(id);if(o==null)throw new IllegalArgumentException("unknown");return o;}
        void audit(){long held=orders.values().stream().filter(o->o.state()!=State.CANCELED).count();if(available<0||available+held!=initial||active.size()!=held)throw new AssertionError("conservation");}
    }
    public static void main(String[] args){
        Ledger l=new Ledger(1);if(l.reserve("o1","A")!=State.RESERVED||l.reserve("o1","A")!=State.RESERVED||l.available!=0)throw new AssertionError();l.audit();
        try{l.reserve("o2","B");throw new AssertionError();}catch(IllegalStateException expected){}
        l.cancel("o1");l.cancel("o1");if(l.available!=1||l.reserve("o1","A")!=State.CANCELED)throw new AssertionError();l.audit();
        l.reserve("o2","A");l.confirm("o2");l.confirm("o2");if(l.available!=0)throw new AssertionError();l.audit();
        try{l.cancel("o2");throw new AssertionError();}catch(IllegalStateException expected){}
        try{l.reserve("o2","B");throw new AssertionError();}catch(IllegalArgumentException expected){}
        Ledger empty=new Ledger(0);empty.audit();try{empty.reserve("x","X");throw new AssertionError();}catch(IllegalStateException expected){}
        System.out.println("PASS 7 scenarios");
    }
}