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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

深入Jedis

  • 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;
    }
    }
  • 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。

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。

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