这是ZooKeeper客户端库的主要类。使用一个ZooKeeper服务，应用程序必须首先实例化ZooKeeper类的对象。所有的迭代都将通过调用ZooKeeper类的方法来完成。除非另有说明，该类的方法是线程安全的。
构造函数：
public ZooKeeper(String connectString, int sessionTimeout, Watcher watcher)
throws IOException
{
this(connectString, sessionTimeout, watcher, false);
}
public ZooKeeper(String connectString, int sessionTimeout, Watcher watcher,
boolean canBeReadOnly)
throws IOException{
LOG.info("Initiating client connection, connectString=" + connectString
+ " sessionTimeout=" + sessionTimeout + " watcher=" + watcher); watchManager.defaultWatcher = watcher; ConnectStringParser connectStringParser = new ConnectStringParser(
connectString);
HostProvider hostProvider = new StaticHostProvider(
connectStringParser.getServerAddresses());
cnxn = new ClientCnxn(connectStringParser.getChrootPath(),
hostProvider, sessionTimeout, this, watchManager,
getClientCnxnSocket(), canBeReadOnly);
cnxn.start();
}
public ZooKeeper(String connectString, int sessionTimeout, Watcher watcher,
long sessionId, byte[] sessionPasswd)
throws IOException{
this(connectString, sessionTimeout, watcher, sessionId, sessionPasswd, false);
}
public ZooKeeper(String connectString, int sessionTimeout, Watcher watcher,
long sessionId, byte[] sessionPasswd, boolean canBeReadOnly)
throws IOException{
LOG.info("Initiating client connection, connectString=" + connectString
+ " sessionTimeout=" + sessionTimeout
+ " watcher=" + watcher
+ " sessionId=" + Long.toHexString(sessionId)
+ " sessionPasswd="
+ (sessionPasswd == null ? "<null>" : "<hidden>")); watchManager.defaultWatcher = watcher; ConnectStringParser connectStringParser = new ConnectStringParser(
connectString);
HostProvider hostProvider = new StaticHostProvider(
connectStringParser.getServerAddresses());
cnxn = new ClientCnxn(connectStringParser.getChrootPath(),
hostProvider, sessionTimeout, this, watchManager,
getClientCnxnSocket(), sessionId, sessionPasswd, canBeReadOnly);
cnxn.seenRwServerBefore = true; // since user has provided sessionId
cnxn.start();
}