深入Jedis

huangy 8年前

来自: https://blog.huachao.me/2016/2/深入Jedis/

RESP(REdis Serialization Protocol)是redis server与redis client的通信协议。

  • TCP Port 6379
  • Request-Response模型。2个例外,1)pipeline;2)pub/sub
  • 5种DataType,Simple String(+);Errors(-);Integers(:);Bulk String($);Arrays(*)
  • \r\n (CRLF)是结束符
  • Simple String 例子: "+OK\r\n"
  • Errors 例子: -WRONGTYPE Operation against a key holding the wrong kind of value
  • Integer 例子: ":1000\r\n"
  • Bulk String 例子: "$6\r\nfoobar\r\n" 6表示后面有6个byte的长度
  • Null 例子: "$-1\r\n"
  • Arrays 例子: "*2\r\n$3\r\nfoo\r\n$3\r\nbar\r\n" 2表示有2个元素; "*0\r\n" 表示空数组
  • 客户端发送命令:就是Bulk String。例子: llen mylist -> *2\r\n$4\r\nllen\r\n$6\r\nmylist\r\n
  • redis服务器回答RESP DataType。例子: :48293\r\n

Jedis对RESP协议的抽象

  • Protocol是实现上述RESP协议的主要类,其中可以看到 sendCommand(final RedisOutputStream os, final byte[] command, final byte[]... args) 是如何根据协议拼接字符串发送到redis server, Object read(final RedisInputStream is) 是如何接收redis server的返回,并且转换为Java Object。
  • BinaryXxxCommands <- BinaryJedis, XxxCommands <- Jedis 用来抽象所有通过二进制流来发送的Redis命令
  • XxxCommands <- Jedis 用来抽象类似ClusterCommands的命令,最终都是走的二进制流,去掉Binary一层估计是作者觉得厌烦了。不对之处还请赐教。
  • Commands, Connection <- BinaryClient <- Client 抽象了网络发送命令和接收回复,其中Client将参数encode为byte[],然后调用BinaryClient的方法;BinaryClient调用Connection#sendCommand;sendCommand调用connect(),构造RedisInputStream和RedisOutputStream,用Protocol.sendCommand来发送命令;client.getXxxReply()首先将outputstream中的内容flush出去,然后调用Protocol.read来处理接收到的返回值。

    /* 发送命令 Connection.java */  protected Connection sendCommand(final ProtocolCommand cmd, final byte[]... args) {      try {        connect();        Protocol.sendCommand(outputStream, cmd, args);        pipelinedCommands++;        return this;      } catch (JedisConnectionException ex) {        // Any other exceptions related to connection?        broken = true;        throw ex;      }  }    public void connect() {      if (!isConnected()) {        try {          socket = new Socket();          // ->@wjw_add          socket.setReuseAddress(true);          socket.setKeepAlive(true); // Will monitor the TCP connection is          // valid          socket.setTcpNoDelay(true); // Socket buffer Whetherclosed, to          // ensure timely delivery of data          socket.setSoLinger(true, 0); // Control calls close () method,          // the underlying socket is closed          // immediately          // <-@wjw_add            socket.connect(new InetSocketAddress(host, port), connectionTimeout);          socket.setSoTimeout(soTimeout);          outputStream = new RedisOutputStream(socket.getOutputStream());          inputStream = new RedisInputStream(socket.getInputStream());        } catch (IOException ex) {          broken = true;          throw new JedisConnectionException(ex);        }      }  }    /* 接收回复 */  public String getBulkReply() {      final byte[] result = getBinaryBulkReply();      if (null != result) {        return SafeEncoder.encode(result);      } else {        return null;      }  }    public byte[] getBinaryBulkReply() {      flush();      pipelinedCommands--;      return (byte[]) readProtocolWithCheckingBroken();  }    protected Object readProtocolWithCheckingBroken() {      try {        return Protocol.read(inputStream);      } catch (JedisConnectionException exc) {        broken = true;        throw exc;      }  }
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  • Jedis通过Pipeline这个类来对redis的pipeline进行抽象, jedis.pipelined() 返回一个Pipeline实例,并且这个Pipeline实例的client就是当前jedis实例的client;调用 pipeline.a_redis_command() 的时候会有一个 responseList ,用来记录每个command应该对应的response; pipeline.syncAndReturnAll() 会调用 client.getAll() 将所有command一次 flush() 出去,然后拿回List<Object>,再将这些Object填充到responseList中。

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    Jedis使用注意事项

    • Jedis instance本身不是线程安全的!要用JedisPool

      //将JedisPool定义为spring单例  JedisPool pool = new JedisPool(new JedisPoolConfig(), "localhost");    Jedis jedis = null;  try {    jedis = pool.getResource();    /// ... do stuff here ... for example    jedis.set("foo", "bar");    String foobar = jedis.get("foo");    jedis.zadd("sose", 0, "car"); jedis.zadd("sose", 0, "bike");     Set<String> sose = jedis.zrange("sose", 0, -1);  } finally {    if (jedis != null) {      jedis.close();    }  }  /// ... when closing your application:  pool.destroy();
    • JedisPool是一个包装模式,内部就是Apache Common Pool 2, Pool里面装的是Jedis。Jedis之所以不是线程安全的主要是由于Jedis类中的fields(client, pipeline, transaction)没有做同步。如果每个thread都有一份Jedis实例,其实也不存在线程安全问题,就是要注意使用完了需要 jedis.close() 。JedisPool和DBCP的Pool一样,就是用来创建Jedis实例,然后提供给线程使用,Pool技术能够复用已经标记为IDLE的Jedis,以此来提供内存利用率和减小开销。

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