什麼是Zookeeper
Zookeeper是一個高性能的分佈式應用協調服務的框架。Zookeeper=Zoo+keeper,中文直譯是動物園的看守者。
為什麼要使用Zookeeper
Zookeeper可以用於解決很多分佈式系統遇到的問題，比如分佈式鎖，分佈式協調，分佈式消息隊列等。
安裝Zookeeper
在官網下載最新的Zookeeper穩定版，http://zookeeper.apache.org/releases.html#download,將下載的文件存放在本地目錄及安裝完畢，本文將Zookeeper安裝在/Developer/java/project目錄。本文下載的是zookeeper-3.4.9版本。
單機模式啟動Zookeeper
下載完之後，將conf目錄下的zoo_sample.cfg文件重命名成zoo.cfg文件。這個文件存放著Zookeeper的所有配置信息。
tickTime=2000initLimit=10syncLimit=5dataDir=/tmp/zookeeperclientPort=2181maxClientCnxns=60autopurge.snapRetainCount=3autopurge.purgeInterval=1
tickTime：客戶端和服務器端維持心跳的時間，單位為毫秒。
initLimit：
syncLimit：
dataDir：用來存放快照數據，官方建議不要使用/tmp目錄，可以使用/tmp/zookeeper。
clientPort；啟動Zookeeper服務的默認端口。
maxClientCnxns：最大客戶端連接數。如果客戶端的數量超過了指定的數量，則新連接的客戶端會拋出java.io.IOException: Connection reset by peer異常。
autopurge.snapRetainCount：
autopurge.purgeInterval：
通過zkServer.sh start命令啟動Zookeeper，啟動後默認端口是2181，啟動成功後命令行會回顯已經啟動成功的標示STARTED。
tengfeifangtf:bin tengfei.fangtf$ sh /Developer/java/project/zookeeper-3.4.9/bin/zkServer.sh startZooKeeper JMX enabled by defaultUsing config: /Developer/java/project/zookeeper-3.4.9/bin/../conf/zoo.cfg-n Starting zookeeper ...STARTED
通過命令行調用Zookeeper
連接Zookeeper
通過如下命令連接Zookeeper服務器端。如果服務器端不存在，則會拋出java.net.ConnectException: Connection refused異常
tengfeifangtf:bin tengfei.fangtf$ sh /Developer/java/project/zookeeper-3.4.9/bin/zkCli.sh -server 127.0.0.1:2181Connecting to 127.0.0.1:21812016-09-17 22:02:00,703 [myid:] - INFO [main:Environment@100] - Client environment:zookeeper.version=3.4.9-1757313, built on 08/23/2016 06:50 GMT2016-09-17 22:02:00,707 [myid:] - INFO [main:Environment@100] - Client environment:host.name=192.168.100.2242016-09-17 22:02:00,707 [myid:] - INFO [main:Environment@100] - Client environment:java.version=1.6.0_652016-09-17 22:02:00,710 [myid:] - INFO [main:Environment@100] - Client environment:java.vendor=Apple Inc.2016-09-17 22:02:00,710 [myid:] - INFO [main:Environment@100] - Client environment:java.home=/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home2016-09-17 22:02:00,710 [myid:] - INFO [main:Environment@100] - Client environment:java.class.path=/Developer/java/project/zookeeper-3.4.9/bin/../build/classes:/Developer/java/project/zookeeper-3.4.9/bin/../build/lib/*.jar:/Developer/java/project/zookeeper-3.4.9/bin/../lib/slf4j-log4j12-1.6.1.jar:/Developer/java/project/zookeeper-3.4.9/bin/../lib/slf4j-api-1.6.1.jar:/Developer/java/project/zookeeper-3.4.9/bin/../lib/netty-3.10.5.Final.jar:/Developer/java/project/zookeeper-3.4.9/bin/../lib/log4j-1.2.16.jar:/Developer/java/project/zookeeper-3.4.9/bin/../lib/jline-0.9.94.jar:/Developer/java/project/zookeeper-3.4.9/bin/../zookeeper-3.4.9.jar:/Developer/java/project/zookeeper-3.4.9/bin/../src/java/lib/*.jar:/Developer/java/project/zookeeper-3.4.9/bin/../conf:2016-09-17 22:02:00,711 [myid:] - INFO [main:Environment@100] - Client environment:java.library.path=.:/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java2016-09-17 22:02:00,711 [myid:] - INFO [main:Environment@100] - Client environment:java.io.tmpdir=/var/folders/6s/z6xt4ypn387239k7q1ty_rkc0000gn/T/2016-09-17 22:02:00,713 [myid:] - INFO [main:Environment@100] - Client environment:java.compiler=2016-09-17 22:02:00,713 [myid:] - INFO [main:Environment@100] - Client environment:os.name=Mac OS X2016-09-17 22:02:00,714 [myid:] - INFO [main:Environment@100] - Client environment:os.arch=x86_642016-09-17 22:02:00,714 [myid:] - INFO [main:Environment@100] - Client environment:os.version=10.11.62016-09-17 22:02:00,714 [myid:] - INFO [main:Environment@100] - Client environment:user.name=tengfei.fangtf2016-09-17 22:02:00,714 [myid:] - INFO [main:Environment@100] - Client environment:user.home=/Users/tengfei2016-09-17 22:02:00,714 [myid:] - INFO [main:Environment@100] - Client environment:user.dir=/Developer/java/project/zookeeper-3.4.9/bin2016-09-17 22:02:00,716 [myid:] - INFO [main:ZooKeeper@438] - Initiating client connection, connectString=127.0.0.1:2181 sessionTimeout=30000 watcher=org.apache.zookeeper.ZooKeeperMain$MyWatcher@3a21b220Welcome to ZooKeeper!2016-09-17 22:02:00,754 [myid:] - INFO [main-SendThread(127.0.0.1:2181):ClientCnxn$SendThread@1032] - Opening socket connection to server 127.0.0.1/127.0.0.1:2181. Will not attempt to authenticate using SASL (java.lang.SecurityException: Unable to locate a login configuration)JLine support is enabled2016-09-17 22:02:00,775 [myid:] - INFO [main-SendThread(127.0.0.1:2181):ClientCnxn$SendThread@876] - Socket connection established to 127.0.0.1/127.0.0.1:2181, initiating session[zk: 127.0.0.1:2181(CONNECTING) 0] 2016-09-17 22:02:01,075 [myid:] - INFO [main-SendThread(127.0.0.1:2181):ClientCnxn$SendThread@1299] - Session establishment complete on server 127.0.0.1/127.0.0.1:2181, sessionid = 0x157386e843d0004, negotiated timeout = 30000WATCHER::WatchedEvent state:SyncConnected type:None path:null
連接成功後會進入Zookeeper交互式窗口，命令行左邊顯示如下，然後你就可以使用Zookeeper提供的命令來創建，修改和刪除節點。
[zk: 127.0.0.1:2181(CONNECTED) 0]
創建節點
使用create參數創建節點，第一個參數是節點路徑，第二個參數是節點的數據。
[zk: 127.0.0.1:2181(CONNECTED) 1] create /dmcNode dataCreated /dmcNode
注意：節點路徑是大小寫敏感的。
查看節點
使用get命令查詢節點的數據，會顯示節點的數據長度，數據的版本
[zk: 127.0.0.1:2181(CONNECTED) 2] get /dmcNodedatacZxid = 0x54ctime = Sat Sep 17 22:07:49 CST 2016mZxid = 0x54mtime = Sat Sep 17 22:07:49 CST 2016pZxid = 0x54cversion = 0dataVersion = 0aclVersion = 0ephemeralOwner = 0x0dataLength = 4numChildren = 0
通過get命令我們可以看到Zookeeper節點的數據結構
cxxid：當前節點事務的xxid。
ctime：當前節點的創建時間。
mxxid: 當前節點最近修改的xxid。
pZxid ： 子節點的最後版本
cversion：這個節點的子節點變化次數，創建一個子節點會加1。
dataVersion：數據的版本，每次修改會加一。
aclVersion：這個節點的ACL變化次數。
ephemeralOwner ：如果這個節點是臨時節點，表示創建者的會話id。如果不是臨時節點，這個值是0。
dataLength：這個節點存放的數據長度。
numChildren：這個節點的子節點個數。
mtime：這個節點的最後修改時間。
這些屬性可以參考《Zookeeper官方文檔》Zookeeper tatStructure章節https://zookeeper.apache.org/doc/r3.4.6/zookeeperProgrammers.html#sc_zkStatStructure
修改節點
可以發現dataVersion從剛才的0變成了1，數據長度也變化了。
[zk: 127.0.0.1:2181(CONNECTED) 3] set /dmcNode data1cZxid = 0x54ctime = Sat Sep 17 22:07:49 CST 2016mZxid = 0x55mtime = Sat Sep 17 22:10:46 CST 2016pZxid = 0x54cversion = 0dataVersion = 1aclVersion = 0ephemeralOwner = 0x0dataLength = 5numChildren = 0
刪除節點
通過delete [path]命令刪除節點
[zk: 127.0.0.1:2181(CONNECTED) 12] delete /dmcNode
help命令
我們通過help命令可以看下Zookeeper提供哪些操作命令。
[zk: 127.0.0.1:2181(CONNECTED) 0] helpZooKeeper -server host:port cmd args connect host:port get path [watch] ls path [watch] set path data [version] rmr path delquota [-n|-b] path quit printwatches on|off create [-s] [-e] path data acl stat path [watch] close ls2 path [watch] history listquota path setAcl path acl getAcl path sync path redo cmdno addauth scheme auth delete path [version] setquota -n|-b val path
quit：退出連接。
history：查看當前連接歷史執行命令。
關閉Zookeeper
如果先關閉了Zookeeper服務端，而客戶端沒有關閉，則客戶端會不斷的重連服務器端，並拋出異常closing socket connection and attempting reconnect。
sh /Developer/java/project/zookeeper-3.4.9/bin/zkServer.sh stop
通過Java API調用Zookeeper
1：引入POM
org.apache.zookeeper zookeeper 3.4.7
2：Java測試代碼
演示了ZooKeeper節點的創建，修改和刪除操作。
import java.io.IOException;import org.apache.zookeeper.CreateMode;import org.apache.zookeeper.KeeperException;import org.apache.zookeeper.ZooDefs;import org.apache.zookeeper.ZooKeeper;/**** @author tengfei.fangtf* @version $Id: TestZookeeper.java, v 0.1 Sep 14, 2016 5:05:07 PM tengfei.fangtf Exp $*/public class TestZookeeper { public static void main(String[] args) throws IOException, InterruptedException, KeeperException { //創建ZooKeeper實例 ZooKeeper zk = new ZooKeeper("127.0.0.1:2181", 100, null); String path = "/dmc"; //創建一個節點,模式是PERSISTENT zk.create(path, "1".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT); System.out.println("創建節點" + path + ",數據為：" + new String(zk.getData(path, null, null))); //修改節點數據 zk.setData(path, "2".getBytes(), -1); System.out.println("修改節點" + path + ",數據為：" + new String(zk.getData(path, null, null))); //刪除一個節點 System.out.println(zk.exists(path, null)); zk.delete(path, -1); //節點是否存在 System.out.println(zk.exists(path, null)); }}輸出的結果如下：
創建節點/dmc,數據為：1修改節點/dmc,數據為：278,79,1474120607561,1474120607575,1,0,0,0,1,0,78null
閱讀更多 JAVA技術開發 的文章
