案例-实现访问频率限制: 实现访问者 $ip 在一定的时间 $time 内只能访问 $limit 次.

• 非脚本实现

  private boolean accessLimit(String ip, int limit, int time, Jedis jedis) {
  boolean result = true;

  String key = "rate.limit:" + ip;
  if (jedis.exists(key)) {
      long afterValue = jedis.incr(key);
      if (afterValue > limit) {
          result = false;
      }
  } else {
      Transaction transaction = jedis.multi();
      transaction.incr(key);
      transaction.expire(key, time);
      transaction.exec();
  }
  return result;

  }

• 以上代码有两点缺陷 

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• Lua脚本实现 
  Redis 允许将 Lua 脚本传到 Redis 服务器中执行, 脚本内可以调用大部分 Redis 命令, 且 Redis 保证脚本的原子性:

  • 首先需要准备Lua代码: script.lua

  --
  -- Created by IntelliJ IDEA.
  -- User: jifang
  -- Date: 16/8/24

  -- Time: 下午6:11

  local key = "rate.limit:" .. KEYS[1]
  local limit = tonumber(ARGV[1])
  local expire_time = ARGV[2]

  local is_exists = redis.call("EXISTS", key)
  if is_exists == 1 then
  if redis.call("INCR", key) > limit then
  return 0
  else
  return 1
  end
  else
  redis.call("SET", key, 1)
  redis.call("EXPIRE", key, expire_time)
  return 1
  end

• Java

  private boolean accessLimit(String ip, int limit, int timeout, Jedis connection) throws IOException {
  List keys = Collections.singletonList(ip);
  List argv = Arrays.asList(String.valueOf(limit), String.valueOf(timeout));

  return 1 == (long) connection.eval(loadScriptString("script.lua"), keys, argv);

  }

  // 加载Lua代码
  private String loadScriptString(String fileName) throws IOException {
  Reader reader = new InputStreamReader(Client.class.getClassLoader().getResourceAsStream(fileName));
  return CharStreams.toString(reader);
  }

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• Lua 嵌入 Redis 优势: