ZooKeeper

　　ZooKeeper是客戶端操作ZooKeeper服務端的核心類。當用戶向ZooKeeperMain執行相關命令時，最終會交給ZooKeeper執行，其會將用戶請求封裝成對象，然後發送到服務端。內部使用ClientCnxn來提供與服務端的通信。 請求數據會被封裝成RequestHeader、Request對象，相應的返回結果會存儲在Response，ReplyHeader對象。

public String create(final String path, byte data[], List<ACL> acl,
            CreateMode createMode)
        
 
throws KeeperException, InterruptedException
    {
        final String clientPath = path;
        PathUtils.validatePath(clientPath, createMode.isSequential());
        final String serverPath = prependChroot(clientPath);
        RequestHeader h = new RequestHeader();
        h.setType(ZooDefs.OpCode.create);
        CreateRequest request 
 
= new CreateRequest();
        CreateResponse response = new CreateResponse();
        request.setData(data);
        request.setFlags(createMode.toFlag());
        request.setPath(serverPath);
        if (acl != null && acl.size() == 0) {
            throw new KeeperException.InvalidACLException();
        }
        request.setAcl(acl);
        ReplyHeader r 
 
= cnxn.submitRequest(h, request, response, null);
        if (r.getErr() != 0) {
            throw KeeperException.create(KeeperException.Code.get(r.getErr()),
                    clientPath);
        }
        if (cnxn.chrootPath == null) {
            return response.getPath();
        } else {
            return response.getPath().substring(cnxn.chrootPath.length());
        }
    }

zookeeper總結之客戶端執行核心模塊