实现商品秒杀之——Redis Watch机制

Watch命令

       watch命令可以监控一个或多个键，一旦其中有一个键被修改或删除，之后的事务就不会执行。监控一直持续到exec命令，事务中的命令是在exec之后才执行的，所以在multi命令后可以修改watch监控的键值。假设我们通过watch命令在事务执行之前监控了多个Key，这时在watch之后有任何Key的值发生了变化，exec命令执行的事务都将被放弃。

在业务中的应用

1.创建Redis操作工具类

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONArray;

import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
 
@Service
public class RedisService {
	
	@Autowired
	private JedisPool jedisPool;
	
	/**
	 * 获取对象
	 */
	public <T> T get(String key,Class<T> clazz){
	    Jedis jedis = null;
	    try {
		jedis = jedisPool.getResource();
		String sval = jedis.get(key);
		//将String转换为Bean
		T t = stringToBean(sval,clazz);
		return t;
	    }finally {
		if(jedis != null) {	
		    jedis.close();
		}
	    }
        }
	
	/**
	 * 设置对象
	 */					
	public <T> boolean set(String key,T value){
	    Jedis jedis = null;
	    try {
	    	jedis = jedisPool.getResource();
		//将Bean转换为String
		String s = beanToString(value);
		if(s == null || s.length() <= 0) {
		    return false;
		}
		jedis.set(key, s);
		return true;
	    }finally {
	        if(jedis != null) {	
	    	    jedis.close();
	        }
	    }
        }
	
	/**
	 * 减少值
	 */
	public <T> Long decr(String key){
	    Jedis jedis = null;
	    try {
	    	jedis = jedisPool.getResource();
	    	//返回value减1后的值
	    	return jedis.decr(key);
	    }finally {
	    	if(jedis != null) {	
	    	    jedis.close();
	    	}
	    }
        }
	
	/**
	 * 将字符串转换为Bean对象
	 */
	@SuppressWarnings("unchecked")
	public static <T> T stringToBean(String str,Class<T> clazz) {
	    if(str == null || str.length() == 0 || clazz == null) {
	    	return null;
	    }		
	    if(clazz == int.class || clazz == Integer.class) {
	    	return ((T) Integer.valueOf(str));
	    }else if(clazz == String.class) {
	    	return (T) str;
	    }else if(clazz == long.class || clazz == Long.class) {
	    	return (T) Long.valueOf(str);
	    }else if(clazz == List.class) {
	    	return JSON.toJavaObject(JSONArray.parseArray(str), clazz);
	    }else {
	    	return JSON.toJavaObject(JSON.parseObject(str), clazz);
	    }		
        }
	
	/**
	 * 将Bean对象转换为字符串类型
	 */
	public static <T> String beanToString(T value) {
	    if(value == null){
	    	return null;
	    }
	    Class<?> clazz = value.getClass();
	    if(clazz == int.class || clazz == Integer.class) {
	    	return ""+value;
	    }else if(clazz == String.class) {
	    	return (String)value;
	    }else if(clazz == long.class || clazz == Long.class) {
	    	return ""+value;
	    }else {
	    	return JSON.toJSONString(value);
	    }		
	}
	
}

2.秒杀业务调用

import java.util.HashMap;
import java.util.List;
import java.util.UUID;

import javax.servlet.http.HttpServletRequest;

import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
import redis.clients.jedis.Response;
import redis.clients.jedis.Transaction;
import cn.com.app.redis.RedisService;

@Controller
public class RedisWatchController implements InitializingBean {
	
    @Autowired
    private RedisService redisService;
    @Autowired
    private JedisPool jedisPool;
	
    //内存标记，减少redis访问
    private HashMap<String, Boolean> localOverMap =  new HashMap<String, Boolean>();
    
	/**
	 * 系统初始化的时把商品库存加入到缓存中
	 */
	@Override
	public void afterPropertiesSet() throws Exception {
	    //设置默认商品库存
	    redisService.set("goodsStock", "10");
            //添加内存标记
	    localOverMap.put("goodsStock", false);
	}
    
	/**
         * 请求秒杀,redis watch事务方式
         */
	@RequestMapping(value="/miaoshawatch")
	@ResponseBody
        public String miaoshawatch(HttpServletRequest request,@RequestParam("userid")String userid){
    	    boolean over = localOverMap.get("goodsStock");
    	    if(over) {
    		System.out.println("秒杀结束");
    		return "秒杀结束";
    	    }
    	    Jedis jedis = null;
	    try {
	        jedis = jedisPool.getResource();
		//监视商品库存key和订单key
		jedis.watch("goodsStock","order"+userid);
	    	int count = redisService.get("goodsStock",Integer.class);
	    	if(count <= 0){
	    	    localOverMap.put("goodsStock", true);
	    	    System.out.println("库存不足");
	    	    return "库存不足";
	    	}
	    	String orderInfo = redisService.get("order"+userid,String.class);
		if(orderInfo != null){
		    System.out.println("重复下单");
		    return "重复下单";
		}
		//开启事务    
		Transaction transaction = jedis.multi();
		//保存订单
		transaction.set("order"+userid, userid+"_"+UUID.randomUUID().toString());
	        //扣减库存
		Response<Long> v = transaction.decrBy("goodsStock",1);
	        List<Object> result = transaction.exec();
		if(result == null || result.isEmpty()){
	            System.out.println("秒杀失败");
	            return "秒杀失败";
	        }
	        System.out.println("秒杀成功,剩余：" + v.get().intValue());
	        /**
        	 * 数据库操作减少库存,下订单,在一个事务中
        	 */        
	}finally {
	    if(jedis != null) {	
		jedis.close();
	    }
	}
	return "秒杀成功";
    }
}