Jedis cluster 源码解读

1、底层结构分析
我们从JedisCluster类入手

public class JedisCluster extends BinaryJedisCluster implements JedisCommands,
    MultiKeyJedisClusterCommands, JedisClusterScriptingCommands

这个类继承了BinaryJedisCluster，实现了JedisCommands,
MultiKeyJedisClusterCommands, JedisClusterScriptingCommands，而这三个接口，主要是redis的命令。可以不用关注。
JedisCluster的构造器最终调用了父类BinaryJedisCluster的构造器方法

public JedisCluster(Set jedisClusterNode, int timeout, int maxAttempts,
      final GenericObjectPoolConfig poolConfig) {
    super(jedisClusterNode, timeout, maxAttempts, poolConfig);
  }

  public JedisCluster(Set jedisClusterNode, int connectionTimeout, int soTimeout,
      int maxAttempts, final GenericObjectPoolConfig poolConfig) {
    super(jedisClusterNode, connectionTimeout, soTimeout, maxAttempts, poolConfig);
  }

BinaryJedisCluster类有两个属性，分别是

protected int maxAttempts;
protected JedisClusterConnectionHandler connectionHandler;

构造器方法主要是初始化这俩属性。所以一步一步看进去，就要看这个方法

this.connectionHandler = new JedisSlotBasedConnectionHandler(jedisClusterNode, poolConfig,
        timeout);

JedisSlotBasedConnectionHandler类是JedisClusterConnectionHandler的子类
而关于槽点、redis请求时根据key计算槽点然后到哪个节点请求数据都是在这两个类里做的。
先看基类JedisClusterConnectionHandler

public abstract class JedisClusterConnectionHandler implements Closeable {
  protected final JedisClusterInfoCache cache;

  public JedisClusterConnectionHandler(Set nodes,
                                       final GenericObjectPoolConfig poolConfig, int connectionTimeout, int soTimeout) {
    this.cache = new JedisClusterInfoCache(poolConfig, connectionTimeout, soTimeout);
    initializeSlotsCache(nodes, poolConfig);
  }

  abstract Jedis getConnection();

  abstract Jedis getConnectionFromSlot(int slot);

  public Jedis getConnectionFromNode(HostAndPort node) {
    return cache.setupNodeIfNotExist(node).getResource();
  }
  
  public Map getNodes() {
    return cache.getNodes();
  }
	//初始化槽点缓存
  private void initializeSlotsCache(Set startNodes, GenericObjectPoolConfig poolConfig) {
    for (HostAndPort hostAndPort : startNodes) {
      Jedis jedis = new Jedis(hostAndPort.getHost(), hostAndPort.getPort());
      try {
        cache.discoverClusterNodesAndSlots(jedis);
        break;
      } catch (JedisConnectionException e) {
        // try next nodes
      } finally {
        if (jedis != null) {
          jedis.close();
        }
      }
    }
  }

  public void renewSlotCache() {
    cache.renewClusterSlots(null);
  }

  public void renewSlotCache(Jedis jedis) {
    cache.renewClusterSlots(jedis);
  }

  @Override
  public void close() {
    cache.reset();
  }
}

这个类里主要做了两件事，初始化JedisClusterInfoCache类，然后调用initializeSlotsCache(nodes, poolConfig);
再来看下JedisClusterInfoCache类是做什么的。

public class JedisClusterInfoCache {
  private final Map nodes = new HashMap();
  private final Map slots = new HashMap();

nodes变量存放的是节点信息，key是hnp.getHost() + “:” + hnp.getPort()，

public JedisPool setupNodeIfNotExist(HostAndPort node) {
    w.lock();
    try {
      String nodeKey = getNodeKey(node);
      JedisPool existingPool = nodes.get(nodeKey);
      if (existingPool != null) return existingPool;

      JedisPool nodePool = new JedisPool(poolConfig, node.getHost(), node.getPort(),
              connectionTimeout, soTimeout, null, 0, null);
      nodes.put(nodeKey, nodePool);
      return nodePool;
    } finally {
      w.unlock();
    }
  }

上述代码是用来存储nodes信息的
再来说slots变量，是用来存放槽点对应的节点信息。

public void discoverClusterNodesAndSlots(Jedis jedis) {
    w.lock();

    try {
      reset();
      //获取节点的槽点信息
      List