ZooKeeper與Curator註冊和監控
僅供參考,不保證正確性
Curator提供了對zookeeper客戶端的封裝,並監控連接狀態和會話session,特別是會話session過期後,curator能夠重新連接zookeeper,並且創建一個新的session。
對於zk的使用者來說,session的概念至關重要,如果想了解更多session的說明,請訪問:http://zookeeper.apache.org/doc/trunk/zookeeperProgrammers.html
zk客戶端和zk服務器間主要可能存在下面幾種異常情況:
1. 短暫失去連接:此時客戶端檢測到與服務端的連接已經斷開,但是服務端維護的客戶端session尚未過期,之後客戶端和服務端重新建立了連接;當客戶端重新連接後,由於session沒有過期,zookeeper能夠保證連接恢復後保持正常服務。
2. 失去連接時間很長:此時服務器相對於客戶端的session已經過期了,與先前session相關的watcher和ephemeral的路徑和數據都會消失;當Curator重新創建了與zk的連接後,會獲取到session expired異常,Curator會銷燬先前的session,並且會創建一個新的session,需要注意的是,與之前session相關的watcher和ephemeral類型的路徑和數據在新的session中也不會存在,需要開發者在CuratorFramework.getConnectionStateListenable().addListener()中添加狀態監聽事件,對ConnectionState.LOST事件進行監聽,當session過期後,使得之前的session狀態得以恢復。對於ephemeral類型,在客戶端應該保持數據的狀態,以便及時恢復。
3. 客戶端重新啓動:不論先前的zk session是否已經過期,都需要重新創建臨時節點、添加數據和watch事件,先前的session也會在稍後的一段時間內過期。
4. Zk服務器重新啓動:由於zk將session信息存放到了硬盤上,因此重啓後,先前未過期的session仍然存在,在zk服務器啓動後,客戶端與zk服務器創建新的連接,並使用先前的session,與1相同。
5. 需要注意的是,當session過期了,在session過期期間另外的客戶端修改了zk的值,那麼這個修改在客戶端重新連接到zk上時,zk客戶端不會接收到這個修改的watch事件(儘管添加了watch),如果需要嚴格的watch邏輯,就需要在curator的狀態監控中添加邏輯。
特別提示:watcher僅僅是一次性的,zookeeper通知了watcher事件後,就會將這個watcher從session中刪除,因此,如果想繼續監控,就要添加新的watcher。
下面提供了對persistent和ephemeral兩種類型節點的監控方法,其中get方法說明了persistent節點如何監控,而register方法說明了ephemeral類型的節點如何監控。
public class CuratorTest {
private CuratorFramework zkTools;
private ConcurrentSkipListSet watchers = newConcurrentSkipListSet();
private static Charset charset = Charset.forName("utf-8");
public CuratorTest() {
zkTools = CuratorFrameworkFactory
.builder()
.connectString("10.11.21.78:12306")
.namespace("zk/test")
.retryPolicy(new RetryNTimes(2000,20000))
.build();
zkTools.start();
}
public void addReconnectionWatcher(final String path,final ZookeeperWatcherType watcherType,final CuratorWatcher watcher){
synchronized (this) {
if(!watchers.contains(watcher.toString()))//不要添加重複的監聽事件
{
watchers.add(watcher.toString());
System.out.println("add new watcher " + watcher);
zkTools.getConnectionStateListenable().addListener(newConnectionStateListener() {
@Override
public void stateChanged(CuratorFramework client, ConnectionState newState) {
System.out.println(newState);
if(newState == ConnectionState.LOST){//處理session過期
try{
if(watcherType == ZookeeperWatcherType.EXITS){
zkTools.checkExists().usingWatcher(watcher).forPath(path);
}else if(watcherType == ZookeeperWatcherType.GET_CHILDREN){
zkTools.getChildren().usingWatcher(watcher).forPath(path);
}else if(watcherType == ZookeeperWatcherType.GET_DATA){
zkTools.getData().usingWatcher(watcher).forPath(path);
}else if(watcherType == ZookeeperWatcherType.CREATE_ON_NO_EXITS){
//ephemeral類型的節點session過期了,需要重新創建節點,並且註冊監聽事件,之後監聽事件中,
//會處理create事件,將路徑值恢復到先前狀態
Stat stat =zkTools.checkExists().usingWatcher(watcher).forPath(path);
if(stat == null){
System.err.println("to create");
zkTools.create()
.creatingParentsIfNeeded()
.withMode(CreateMode.EPHEMERAL)
.withACL(ZooDefs.Ids.OPEN_ACL_UNSAFE)
.forPath(path);
}
}
}catch (Exception e) {
e.printStackTrace();
}
}
}
});
}
}
}
public void create() throws Exception{
zkTools.create()//創建一個路徑
.creatingParentsIfNeeded()//如果指定的節點的父節點不存在,遞歸創建父節點
.withMode(CreateMode.PERSISTENT)//存儲類型(臨時的還是持久的)
.withACL(ZooDefs.Ids.OPEN_ACL_UNSAFE)//訪問權限
.forPath("zk/test");//創建的路徑
}
public void put() throws Exception{
zkTools.//對路徑節點賦值
setData().
forPath("zk/test","hello world".getBytes(Charset.forName("utf-8")));
}
public void get() throws Exception{
String path = "zk/test";
ZKWatch watch = new ZKWatch(path);
byte[] buffer = zkTools.
getData().
usingWatcher(watch).forPath(path);
System.out.println(new String(buffer,charset));
//添加session過期的監控
addReconnectionWatcher(path, ZookeeperWatcherType.GET_DATA, watch);
}
public void register() throws Exception{
String ip = InetAddress.getLocalHost().getHostAddress();
String registeNode = "zk/register/"+ip;//節點路徑
byte[] data = "disable".getBytes(charset);//節點值
CuratorWatcher watcher = new ZKWatchRegister(registeNode,data); //創建一個register watcher
Stat stat = zkTools.checkExists().forPath(registeNode);
if(stat != null){
zkTools.delete().forPath(registeNode);
}
zkTools.create()
.creatingParentsIfNeeded() .withMode(CreateMode.EPHEMERAL)
.withACL(ZooDefs.Ids.OPEN_ACL_UNSAFE)
.forPath(registeNode,data);//創建的路徑和值
//添加到session過期監控事件中
addReconnectionWatcher(registeNode, ZookeeperWatcherType.CREATE_ON_NO_EXITS,watcher);
data = zkTools.getData().usingWatcher(watcher).forPath(registeNode);
System.out.println("get path form zk : "+registeNode+":"+new String(data,charset));
}
public static void main(String[] args) throws Exception {
CuratorTest test = new CuratorTest();
test.get();
test.register();
Thread.sleep(10000000000L);
}
public class ZKWatch implements CuratorWatcher{
private final String path;
public String getPath() {
return path;
}
public ZKWatch(String path) {
this.path = path;
}
@Override
public void process(WatchedEvent event) throws Exception {
System.out.println(event.getType());
if(event.getType() == EventType.NodeDataChanged){
byte[] data = zkTools.
getData().
usingWatcher(this).forPath(path);
System.out.println(path+":"+new String(data,Charset.forName("utf-8")));
}
}
}
public class ZKWatchRegister implements CuratorWatcher{
private final String path;
private byte[] value;
public String getPath() {
return path;
}
public ZKWatchRegister(String path,byte[] value) {
this.path = path;
this.value = value;
}
@Override
public void process(WatchedEvent event) throws Exception {
System.out.println(event.getType());
if(event.getType() == EventType.NodeDataChanged){
//節點數據改變了,需要記錄下來,以便session過期後,能夠恢復到先前的數據狀態
byte[] data = zkTools.
getData().
usingWatcher(this).forPath(path);
value = data;
System.out.println(path+":"+new String(data,charset));
}else if(event.getType() == EventType.NodeDeleted){
//節點被刪除了,需要創建新的節點
System.out.println(path + ":" + path +" has been deleted.");
Stat stat = zkTools.checkExists().usingWatcher(this).forPath(path);
if(stat == null){
zkTools.create()
.creatingParentsIfNeeded()
.withMode(CreateMode.EPHEMERAL)
.withACL(ZooDefs.Ids.OPEN_ACL_UNSAFE)
.forPath(path);
}
}else if(event.getType() == EventType.NodeCreated){
//節點被創建時,需要添加監聽事件(創建可能是由於session過期後,curator的狀態監聽部分觸發的)
System.out.println(path + ":" +" has been created!" + "the current data is " + newString(value));
zkTools.setData().forPath(path, value);
zkTools.getData().usingWatcher(this).forPath(path);
}
}
}
public enum ZookeeperWatcherType{
GET_DATA,GET_CHILDREN,EXITS,CREATE_ON_NO_EXITS
}
}
轉載自:http://blog.sina.com.cn/s/blog_616e189f01018axz.html