zookeeper动态通知实现
转载请注明：@ni掌柜
本文重点围绕ZooKeeper的Watcher，介绍通知的状态类型和事件类型，以及这些事件通知的触发条件。
1、浅谈Watcher接口
在ZooKeeper中，接口类Watcher定义了事件通知相关的逻辑，包含了KeeperState和EventType两个枚举类，分别代表通知状态和事件类型。还有一个比较重要的接口方法：
- abstract public void process(WatchedEvent event);
这个方法用于处理事件通知，每个实现类都应该自己实现合适的处理逻辑。参数WatchedEvent类封装了上面提到的两个枚举类，以及触发事件对应的ZK节点path，当然，这个path不一定每次通知都有，例如会话建立，会话失效或连接断开等通知类型，就不是针对某一个单独path的。
2、如何注册Watcher
上面已经提到，Watcher接口已经提供了基本的回调方法用于处理来自服务器的通知。因此，我们只要在合适的地方实现这个接口，并传给服务器即可。下面来看看哪些是合适的地方：
A、构造方法
- ZooKeeper(String connectString, int sessionTimeout, Watcher watcher)
上面这个是ZooKeeper的一个构造方法，与ZK创建连接的时候会用到这个。这里我们重点关注第三个参数：Watcher，很显然在，这个就是一个注册Watcher的地方，传入的参数就是开发者自己Watcher接口实现。需要注意的是，这个地方注册的Watcher实现，会成为当前ZK会话的默认Watcher实现。也就是说，其它地方如果也想注册一个Watcher，那么是可以默认使用这个实现的。具体下面会涉及到。
B、API的读写接口中
- public Stat exists(String path, boolean watch)throws KeeperException, InterruptedException
- public List<String> getChildren(String path, boolean watch)throws KeeperException,InterruptedException
- public byte[] getData(String path,boolean watch,Stat stat)throws KeeperException,InterruptedException
- public void register(Watcher watcher)
3、通知的状态类型与事件类型
在Watcher接口类中，已经定义了所有的状态类型和事件类型，这里把各个状态和事件类型之间的关系整理一下。
3.1状态：KeeperState.Disconnected(0)
此时客户端处于断开连接状态，和ZK集群都没有建立连接。
3.1.1事件：EventType.None(-1)
触发条件：一般是在与服务器断开连接的时候，客户端会收到这个事件。
3.2状态：KeeperState. SyncConnected(3)
3.2.1事件：EventType.None(-1)
触发条件：客户端与服务器成功建立会话之后，会收到这个通知。
3.2.2事件：EventType. NodeCreated (1)
触发条件：所关注的节点被创建。
3.2.3事件：EventType. NodeDeleted (2)
触发条件：所关注的节点被删除。
3.2.4事件：EventType. NodeDataChanged (3)
触发条件：所关注的节点的内容有更新。注意，这个地方说的内容是指数据的版本号dataVersion。因此，即使使用相同的数据内容来更新，还是会收到这个事件通知的。无论如何，调用了更新接口，就一定会更新dataVersion的。
3.2.5事件：EventType. NodeChildrenChanged (4)
触发条件：所关注的节点的子节点有变化。这里说的变化是指子节点的个数和组成，具体到子节点内容的变化是不会通知的。
3.3状态 KeeperState. AuthFailed(4)
3.3.1事件：EventType.None(-1)
3.4状态 KeeperState. Expired(-112)
3.4.1事件：EventType.None(-1)
具体代码如下：
package
com
.
taobao
.
taokeeper
.
research
.
watcher
;
import
java.util.List
;
import
java.util.concurrent.CountDownLatch
;
import
java.util.concurrent.atomic.AtomicInteger
;
import
org.apache.log4j.PropertyConfigurator
;
import
org.apache.zookeeper.CreateMode
;
import
org.apache.zookeeper.WatchedEvent
;
import
org.apache.zookeeper.Watcher
;
import
org.apache.zookeeper.Watcher.Event.EventType
;
import
org.apache.zookeeper.Watcher.Event.KeeperState
;
import
org.apache.zookeeper.ZooDefs.Ids
;
import
org.apache.zookeeper.ZooKeeper
;
import
org.apache.zookeeper.data.Stat
;
import
org.slf4j.Logger
;
import
org.slf4j.LoggerFactory
;
import
common.toolkit.java.util.ObjectUtil
;
import
common.toolkit.java.util.ThreadUtil
;
/**
* 《ZooKeeper 事件类型详解》
* @author nileader/[email protected]
*
*/
public
class
AllZooKeeperWatcher
implements
Watcher
{
private
static
final
Logger
LOG
=
LoggerFactory
.
getLogger
(
NodeDataChangedEvent
.
class
);
AtomicInteger
seq
=
new
AtomicInteger
();
private
static
final
int
SESSION_TIMEOUT
=
10000
;
private
static
final
String
CONNECTION_STRING
=
"test.zookeeper.connection_string:2181,"
+
"test.zookeeper.connection_string2:2181,"
+
"test.zookeeper.connection_string3:2181"
;
private
static
final
String
ZK_PATH
=
"/nileader"
;
private
static
final
String
CHILDREN_PATH
=
"/nileader/ch"
;
private
static
final
String
LOG_PREFIX_OF_MAIN
=
"【Main】"
;
private
ZooKeeper
zk
=
null
;
private
CountDownLatch
connectedSemaphore
=
new
CountDownLatch
(
1
);
/**
* 创建ZK连接
* @param connectString ZK服务器地址列表
* @param sessionTimeout Session超时时间
*/
public
void
createConnection
(
String
connectString
,
int
sessionTimeout
)
{
this
.
releaseConnection
();
try
{
zk
=
new
ZooKeeper
(
connectString
,
sessionTimeout
,
this
);
LOG
.
info
(
LOG_PREFIX_OF_MAIN
+
"开始连接ZK服务器"
);
connectedSemaphore
.
await
();
}
catch
(
Exception
e
)
{}
}
/**
* 关闭ZK连接
*/
public
void
releaseConnection
()
{
if
(
!
ObjectUtil
.
isBlank
(
this
.
zk
)
)
{
try
{
this
.
zk
.
close
();
}
catch
(
InterruptedException
e
)
{}
}
}
/**
* 创建节点
* @param path 节点path
* @param data 初始数据内容
* @return
*/
public
boolean
createPath
(
String
path
,
String
data
)
{
try
{
this
.
zk
.
exists
(
path
,
true
);
LOG
.
info
(
LOG_PREFIX_OF_MAIN
+
"节点创建成功, Path: "
+
this
.
zk
.
create
(
path
,
//
data
.
getBytes
(),
//
Ids
.
OPEN_ACL_UNSAFE
,
//
CreateMode
.
PERSISTENT
)
+
", content: "
+
data
);
}
catch
(
Exception
e
)
{}
return
true
;
}
/**
* 读取指定节点数据内容
* @param path 节点path
* @return
*/
public
String
readData
(
String
path
,
boolean
needWatch
)
{
try
{
return
new
String
(
this
.
zk
.
getData
(
path
,
needWatch
,
null
)
);
}
catch
(
Exception
e
)
{
return
""
;
}
}
/**
* 更新指定节点数据内容
* @param path 节点path
* @param data 数据内容
* @return
*/
public
boolean
writeData
(
String
path
,
String
data
)
{
try
{
LOG
.
info
(
LOG_PREFIX_OF_MAIN
+
"更新数据成功，path："
+
path
+
", stat: "
+
this
.
zk
.
setData
(
path
,
data
.
getBytes
(),
-
1
)
);
}
catch
(
Exception
e
)
{}
return
false
;
}
/**
* 删除指定节点
* @param path 节点path
*/
public
void
deleteNode
(
String
path
)
{
try
{
this
.
zk
.
delete
(
path
,
-
1
);
LOG
.
info
(
LOG_PREFIX_OF_MAIN
+
"删除节点成功，path："
+
path
);
}
catch
(
Exception
e
)
{
//TODO
}
}
/**
* 删除指定节点
* @param path 节点path
*/
public
Stat
exists
(
String
path
,
boolean
needWatch
)
{
try
{
return
this
.
zk
.
exists
(
path
,
needWatch
);
}
catch
(
Exception
e
)
{
return
null
;}
}
/**
* 获取子节点
* @param path 节点path
*/
private
List
<
String
>
getChildren
(
String
path
,
boolean
needWatch
)
{
try
{
return
this
.
zk
.
getChildren
(
path
,
needWatch
);
}
catch
(
Exception
e
)
{
return
null
;}
}
public
void
deleteAllTestPath
(){
this
.
deleteNode
(
CHILDREN_PATH
);
this
.
deleteNode
(
ZK_PATH
);
}
public
static
void
main
(
String
[]
args
)
{
PropertyConfigurator
.
configure
(
"src/main/resources/log4j.properties"
);
AllZooKeeperWatcher
sample
=
new
AllZooKeeperWatcher
();
sample
.
createConnection
(
CONNECTION_STRING
,
SESSION_TIMEOUT
);
//清理节点
sample
.
deleteAllTestPath
();
if
(
sample
.
createPath
(
ZK_PATH
,
System
.
currentTimeMillis
()+
""
)
)
{
ThreadUtil
.
sleep
(
3000
);
//读取数据
sample
.
readData
(
ZK_PATH
,
true
);
//读取子节点
sample
.
getChildren
(
ZK_PATH
,
true
);
//更新数据
sample
.
writeData
(
ZK_PATH
,
System
.
currentTimeMillis
()+
""
);
ThreadUtil
.
sleep
(
3000
);
//创建子节点
sample
.
createPath
(
CHILDREN_PATH
,
System
.
currentTimeMillis
()+
""
);
}
ThreadUtil
.
sleep
(
3000
);
//清理节点
sample
.
deleteAllTestPath
();
ThreadUtil
.
sleep
(
3000
);
sample
.
releaseConnection
();
}
/**
* 收到来自Server的Watcher通知后的处理。
*/
@Override
public
void
process
(
WatchedEvent
event
)
{
ThreadUtil
.
sleep
(
200
);
if
(
ObjectUtil
.
isBlank
(
event
)
)
{
return
;
}
// 连接状态
KeeperState
keeperState
=
event
.
getState
();
// 事件类型
EventType
eventType
=
event
.
getType
();
// 受影响的path
String
path
=
event
.
getPath
();
String
logPrefix
=
"【Watcher-"
+
this
.
seq
.
incrementAndGet
()
+
"】"
;
LOG
.
info
(
logPrefix
+
"收到Watcher通知"
);
LOG
.
info
(
logPrefix
+
"连接状态:\t"
+
keeperState
.
toString
()
);
LOG
.
info
(
logPrefix
+
"事件类型:\t"
+
eventType
.
toString
()
);
if
(
KeeperState
.
SyncConnected
==
keeperState
)
{
// 成功连接上ZK服务器
if
(
EventType
.
None
==
eventType
)
{
LOG
.
info
(
logPrefix
+
"成功连接上ZK服务器"
);
connectedSemaphore
.
countDown
();
}
else
if
(
EventType
.
NodeCreated
==
eventType
)
{
LOG
.
info
(
logPrefix
+
"节点创建"
);
this
.
exists
(
path
,
true
);
}
else
if
(
EventType
.
NodeDataChanged
==
eventType
)
{
LOG
.
info
(
logPrefix
+
"节点数据更新"
);
LOG
.
info
(
logPrefix
+
"数据内容: "
+
this
.
readData
(
ZK_PATH
,
true
)
);
}
else
if
(
EventType
.
NodeChildrenChanged
==
eventType
)
{
LOG
.
info
(
logPrefix
+
"子节点变更"
);
LOG
.
info
(
logPrefix
+
"子节点列表："
+
this
.
getChildren
(
ZK_PATH
,
true
)
);
}
else
if
(
EventType
.
NodeDeleted
==
eventType
)
{
LOG
.
info
(
logPrefix
+
"节点 "
+
path
+
" 被删除"
);
}
}
else
if
(
KeeperState
.
Disconnected
==
keeperState
)
{
LOG
.
info
(
logPrefix
+
"与ZK服务器断开连接"
);
}
else
if
(
KeeperState
.
AuthFailed
==
keeperState
)
{
LOG
.
info
(
logPrefix
+
"权限检查失败"
);
}
else
if
(
KeeperState
.
Expired
==
keeperState
)
{
LOG
.
info
(
logPrefix
+
"会话失效"
);
}
LOG
.
info
(
"--------------------------------------------"
);
}
}
4、程序实例
这里有一个可以用来演示“触发事件通知”和“如何处理这些事件通知”的程序AllZooKeeperWatcher.java。
在这里：https://github.com/alibaba/taokeeper/blob/master/taokeeper-research/src/main/java/com/taobao/taokeeper/research/watcher/AllZooKeeperWatcher.java
运行结果如下：
- 2012-08-05 06:35:23,779 - 【Main】开始连接ZK服务器
- 2012-08-05 06:35:24,196 - 【Watcher-1】收到Watcher通知
- 2012-08-05 06:35:24,196 - 【Watcher-1】连接状态: SyncConnected
- 2012-08-05 06:35:24,196 - 【Watcher-1】事件类型: None
- 2012-08-05 06:35:24,196 - 【Watcher-1】成功连接上ZK服务器
- 2012-08-05 06:35:24,196 - --------------------------------------------
- 2012-08-05 06:35:24,354 - 【Main】节点创建成功, Path: /nileader, content: 1353337464279
- 2012-08-05 06:35:24,554 - 【Watcher-2】收到Watcher通知
- 2012-08-05 06:35:24,554 - 【Watcher-2】连接状态: SyncConnected
- 2012-08-05 06:35:24,554 - 【Watcher-2】事件类型: NodeCreated
- 2012-08-05 06:35:24,554 - 【Watcher-2】节点创建
- 2012-08-05 06:35:24,582 - --------------------------------------------
- 2012-08-05 06:35:27,471 - 【Main】更新数据成功，path：/nileader,
- 2012-08-05 06:35:27,667 - 【Watcher-3】收到Watcher通知
- 2012-08-05 06:35:27,667 - 【Watcher-3】连接状态: SyncConnected
- 2012-08-05 06:35:27,667 - 【Watcher-3】事件类型: NodeDataChanged
- 2012-08-05 06:35:27,667 - 【Watcher-3】节点数据更新
- 2012-08-05 06:35:27,696 - 【Watcher-3】数据内容: 1353337467434
- 2012-08-05 06:35:27,696 - --------------------------------------------
- 2012-08-05 06:35:30,534 - 【Main】节点创建成功, Path: /nileader/ch, content: 1353337470471
- 2012-08-05 06:35:30,728 - 【Watcher-4】收到Watcher通知
- 2012-08-05 06:35:30,728 - 【Watcher-4】连接状态: SyncConnected
- 2012-08-05 06:35:30,728 - 【Watcher-4】事件类型: NodeCreated
- 2012-08-05 06:35:30,728 - 【Watcher-4】节点创建
- 2012-08-05 06:35:30,758 - --------------------------------------------
- 2012-08-05 06:35:30,958 - 【Watcher-5】收到Watcher通知
- 2012-08-05 06:35:30,958 - 【Watcher-5】连接状态: SyncConnected
- 2012-08-05 06:35:30,958 - 【Watcher-5】事件类型: NodeChildrenChanged
- 2012-08-05 06:35:30,958 - 【Watcher-5】子节点变更
- 2012-08-05 06:35:30,993 - 【Watcher-5】子节点列表：[ch]
- 2012-08-05 06:35:30,993 - --------------------------------------------
- 2012-08-05 06:35:33,618 - 【Main】删除节点成功，path：/nileader/ch
- 2012-08-05 06:35:33,756 - 【Main】删除节点成功，path：/nileader
- 2012-08-05 06:35:33,817 - 【Watcher-6】收到Watcher通知
- 2012-08-05 06:35:33,817 - 【Watcher-6】连接状态: SyncConnected
- 2012-08-05 06:35:33,817 - 【Watcher-6】事件类型: NodeDeleted
- 2012-08-05 06:35:33,817 - 【Watcher-6】节点 /nileader/ch 被删除
- 2012-08-05 06:35:33,817 - --------------------------------------------
- 2012-08-05 06:35:34,017 - 【Watcher-7】收到Watcher通知
- 2012-08-05 06:35:34,017 - 【Watcher-7】连接状态: SyncConnected
- 2012-08-05 06:35:34,017 - 【Watcher-7】事件类型: NodeChildrenChanged
- 2012-08-05 06:35:34,017 - 【Watcher-7】子节点变更
- 2012-08-05 06:35:34,109 - 【Watcher-7】子节点列表：null
- 2012-08-05 06:35:34,109 - --------------------------------------------
- 2012-08-05 06:35:34,309 - 【Watcher-8】收到Watcher通知
- 2012-08-05 06:35:34,309 - 【Watcher-8】连接状态: SyncConnected
- 2012-08-05 06:35:34,309 - 【Watcher-8】事件类型: NodeDeleted
- 2012-08-05 06:35:34,309 - 【Watcher-8】节点 /nileader 被删除
- 2012-08-05 06:35:34,309 - --------------------------------------------