上一篇文章已經完成了ZooKeeper的基本搭建和使用的介紹，現在開始用程式碼說話。參考 https://zookeeper.apache.org/doc/current/javaExample.html ，但對場景和程式碼都做了簡化，只實現基本的Watcher功能。
1 場景設計
目的是體驗ZooKeeper的Watcher功能。程式監控ZooKeeper的/watcher節點資料變化，當建立或修改資料時，控制檯列印當前的資料內容和版本號；當/watcher被刪除時，程式退出。
/watcher的建立、修改和刪除操作，使用控制檯或zkui操作。
2 搭建Maven專案
程式碼相對比較簡單，就不用SpringBoot這個大殺器了，使用一個普通的Maven專案即可。
ZooKeeper客戶端使用官方提供的Java庫，org.apache.zookeeper: zookeeper: 3.5.5。日誌框架使用習慣的slf4j+log4j2，ZooKeeper預設使用的是log4j V1，因此在引入的時候需要excludes。另外，使用了lombok來簡化一些程式碼。
以下是pom.xml的內容
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<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>tech.codestory.research</groupId> <artifactId>zookeeper</artifactId> <version>1.0.0-SNAPSHOT</version> <dependencies> <dependency> <groupId>org.apache.zookeeper</groupId> <artifactId>zookeeper</artifactId> <version>3.5.5</version> <exclusions> <exclusion> <groupId>log4j</groupId> <artifactId>log4j</artifactId> </exclusion> <exclusion> <groupId>org.slf4j</groupId> <artifactId>slf4j-log4j12</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-core</artifactId> <version>2.12.1</version> </dependency> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-api</artifactId> <version>2.12.1</version> </dependency> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-web</artifactId> <version>2.12.1</version> </dependency> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-slf4j-impl</artifactId> <version>2.12.1</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-api</artifactId> <version>1.7.28</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-ext</artifactId> <version>1.7.28</version> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.18.8</version> <scope>provided</scope> </dependency> </dependencies> </project> |
3 log4j2.xml
在專案的 src/main/resources 下建立一個檔案 log4j2.xml，內容為
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<?xml version="1.0" encoding="UTF-8"?> <configuration status="DEBUG" name="codeStoryLogger"> <appenders> <Console name="stdout"> <ThresholdFilter level="TRACE" onMatch="ACCEPT" onMismatch="DENY"/> <PatternLayout pattern="%d{HH:mm:ss:SSS} [%p] - %c{1}.%M(%L) - %m%n"/> </Console> </appenders> <ThresholdFilter level="TRACE"/> <loggers> <logger name="org.apache.zookeeper.ClientCnxn" level="ERROR" additivity="false"> <appender-ref ref="stdout" /> </logger> <logger name="org.apache.zookeeper" level="TRACE" additivity="false"> <appender-ref ref="stdout"/> </logger> <logger name="tech.codestory" level="TRACE" additivity="false"> <appender-ref ref="stdout"/> </logger> <root level="WARN"> <appender-ref ref="stdout"/> </root> </loggers> </configuration> |
4 建立ZooKeeper連線
建立連線程式碼比較簡單，只需要建立 ZooKeeper物件就行，
ZooKeeper建構函式的定義
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/** * 建立一個 ZooKeeper 客戶端物件 * @param connectString 逗號分隔的 host:port 字串， * 單點如 127.0.0.1:2181， * 叢集如 192.168.5.128:2181,192.168.5.129:2181,192.168.5.130:2181， * 還可以指定根節點，如 127.0.0.1:2181/foo/bar * @param sessionTimeout 毫秒為單位的超時時間 * @param watcher Watcher物件，用於接收 MatcherEvent * @throws IOException 網路錯誤時丟擲異常 * @throws IllegalArgumentException 如果Root路徑設定錯誤 */ public ZooKeeper(String connectString, int sessionTimeout, Watcher watcher) throws IOException; |
寫一段測試程式碼，建立zk物件後判斷某一個zNode是否存在。
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public class ZooKeeperWatcher implements Watcher { /** ZooKeeper的客戶端連線 */ ZooKeeper zk;
public ZooKeeperWatcher(String hostPort, String zNode) throws KeeperException, IOException { zk = new ZooKeeper(hostPort, 3000, this); try { Stat exists = zk.exists(zNode, true); if(exists == null){ log.info(“{} 不存在”, zNode) } } catch (InterruptedException e) { log.error("InterruptedException", e); } } } |
執行這段程式碼，發現會拋異常
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java.net.SocketException: Socket is not connected at sun.nio.ch.Net.translateToSocketException(Net.java:162) ~[?:?] at sun.nio.ch.Net.translateException(Net.java:196) ~[?:?] at sun.nio.ch.Net.translateException(Net.java:202) ~[?:?] at sun.nio.ch.SocketAdaptor.shutdownInput(SocketAdaptor.java:400) ~[?:?] at org.apache.zookeeper.ClientCnxnSocketNIO.cleanup(ClientCnxnSocketNIO.java:198) [zookeeper-3.5.5.jar:3.5.5] at org.apache.zookeeper.ClientCnxn$SendThread.cleanup(ClientCnxn.java:1338) [zookeeper-3.5.5.jar:3.5.5] at org.apache.zookeeper.ClientCnxn$SendThread.cleanAndNotifyState(ClientCnxn.java:1276) [zookeeper-3.5.5.jar:3.5.5] at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1254) [zookeeper-3.5.5.jar:3.5.5] Caused by: java.nio.channels.NotYetConnectedException at sun.nio.ch.SocketChannelImpl.shutdownInput(SocketChannelImpl.java:917) ~[?:?] at sun.nio.ch.SocketAdaptor.shutdownInput(SocketAdaptor.java:398) ~[?:?] ... 4 more |
NotYetConnectedException的字面意思是連線還沒有建立好，網路搜尋了一下，建立連線需要一些時間，建立zk物件後馬上呼叫exists命令，這時候連線還沒有建立好，就會拋異常。ZooKeeper在連線建立成功之後，會傳送一個WatchedEvent事件，我們可以利用這個事件完成建立連線的過程。修改後的程式碼如下，順便新增了slf4j-ext中的Profiler，用於記錄所消耗的時間。
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public class ZooKeeperWatcher implements Watcher { /** 等待連線建立成功的訊號 */ private CountDownLatch connectedSemaphore = new CountDownLatch(1);
/** ZooKeeper的客戶端連線 */ ZooKeeper zk;
public ZooKeeperWatcher(String hostPort, String zNode) throws KeeperException, IOException { Profiler profiler = new Profiler("連線到ZooKeeper"); profiler.start("開始連結"); zk = new ZooKeeper(hostPort, 3000, this); try { profiler.start("等待連線成功的Event"); connectedSemaphore.await(); Stat exists = zk.exists(zNode, true); if(exists == null){ log.info(“{} 不存在”, zNode) } } catch (InterruptedException e) { log.error("InterruptedException", e); } profiler.stop(); profiler.setLogger(log); profiler.log(); }
/** 收到ZooKeeper的WatchedEvent */ @Override public void process(WatchedEvent event) { log.info("event = {}", event); if (Event.EventType.None.equals(event.getType())) { // 連線狀態發生變化 if (Event.KeeperState.SyncConnected.equals(event.getState())) { // 連線建立成功 connectedSemaphore.countDown(); } } } } |
修改程式碼之後的執行記錄日誌如下，可以看到等待連線成功的Event耗時9秒多。網路上有文章說關閉防火牆可以秒連，但我測試過，沒發現有什麼變化，使用systemctl stop firewalld之後重新執行程式，仍然需要9秒多。
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[INFO] - ZooKeeperWatcher.process(61) - event = WatchedEvent state:SyncConnected type:None path:null [DEBUG] - ZooKeeperWatcher.log(201) - + Profiler [連線到ZooKeeper] |-- elapsed time [開始連結] 78.912 milliseconds. |-- elapsed time [等待連線成功的Event] 9330.606 milliseconds. |-- Total [連線到ZooKeeper] 9409.926 milliseconds.
[INFO] - ZooKeeperWatcher.readNodeData(95) - /watcher 不存在 |
5 讀取WatchedEvent
前面的程式碼，只是處理了建立連線成功時的Event，下面再來看看讀取資料的過程。關鍵程式碼如下：
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if (Event.EventType.NodeDataChanged.equals(event.getType()) || Event.EventType.NodeCreated.equals(event.getType())) { String path = event.getPath(); if (path != null && path.equals(zNode)) { // 節點資料被修改 readNodeData(); } }
/** 讀節點資料 */ private void readNodeData() { try { Stat stat = new Stat(); byte[] data = zk.getData(zNode, true, stat); if (data != null) { log.info("{}, value={}, version={}", zNode, new String(data), stat.getVersion()); } } catch (KeeperException e) { log.info("{} 不存在", zNode); } catch (InterruptedException e) { log.error("InterruptedException", e); } } |
當接收到建立節點和修改節點的WatchedEvent，都會將資料讀出並列印在控制檯。
6 調整後的完整程式清單
對前面的程式碼做了部分調整，同時新增了退出系統的機制：節點被刪除。
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package tech.codestory.zookeeper.watcher;
import java.io.IOException; import java.util.concurrent.CountDownLatch; import org.apache.zookeeper.*; import org.apache.zookeeper.data.Stat; import org.slf4j.profiler.Profiler; import lombok.extern.slf4j.Slf4j;
/** * 用於測試 ZooKeeper的 WatchedEvent用法 * @author code story * @date 2019/8/13 */ @Slf4j public class ZooKeeperWatcher implements Watcher, Runnable { /** 等待連線建立成功的訊號 */ private CountDownLatch connectedSemaphore = new CountDownLatch(1); /** 退出系統的訊號 */ static Integer quitSemaphore = Integer.valueOf(-1);
String zNode; ZooKeeper zk;
public ZooKeeperWatcher(String hostPort, String zNode) throws KeeperException, IOException { this.zNode = zNode;
Profiler profiler = new Profiler("連線到ZooKeeper"); profiler.start("開始連結"); zk = new ZooKeeper(hostPort, 3000, this); try { profiler.start("等待連線成功的Event"); connectedSemaphore.await(); } catch (InterruptedException e) { log.error("InterruptedException", e); } profiler.stop(); profiler.setLogger(log); profiler.log();
// 先讀當前的資料 readNodeData(); }
/** 收到ZooKeeper的WatchedEvent */ @Override public void process(WatchedEvent event) { log.info("event = {}", event); if (Event.EventType.None.equals(event.getType())) { // 連線狀態發生變化 if (Event.KeeperState.SyncConnected.equals(event.getState())) { // 連線建立成功 connectedSemaphore.countDown(); } } else if (Event.EventType.NodeDataChanged.equals(event.getType()) || Event.EventType.NodeCreated.equals(event.getType())) { String path = event.getPath(); if (path != null && path.equals(zNode)) { // 節點資料被修改 readNodeData(); } } else if (Event.EventType.NodeDeleted.equals(event.getType())) { String path = event.getPath(); if (path != null && path.equals(zNode)) { synchronized (quitSemaphore) { // 節點被刪除，通知退出執行緒 quitSemaphore.notify(); } } } }
/** 讀節點資料 */ private void readNodeData() { try { Stat stat = new Stat(); byte[] data = zk.getData(zNode, true, stat); if (data != null) { log.info("{}, value={}, version={}", zNode, new String(data), stat.getVersion()); } } catch (KeeperException e) { log.info("{} 不存在", zNode); try { // 目的是新增Watcher zk.exists(zNode, true); } catch (KeeperException ex) { } catch (InterruptedException ex) { } } catch (InterruptedException e) { log.error("InterruptedException", e); } }
@Override public void run() { try { synchronized (quitSemaphore) { quitSemaphore.wait(); log.info("{} 被刪除，退出", zNode); } } catch (InterruptedException e) { log.error("InterruptedException", e); } }
/** 主程式，程式碼中寫死了Server地址和zNode名，也可以改成從args中讀取 */ public static void main(String[] args) { String hostPort = "192.168.5.128:2181"; String zNode = "/watcher"; try { new ZooKeeperWatcher(hostPort, zNode).run(); } catch (Exception e) { log.error("new ZooKeeperExecutor()", e); } } } |
做一個測試，應用啟動後建立節點，修改多次節點，最後刪除節點，日誌輸出如下：
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10:13:31:979 [INFO] - ZooKeeperWatcher.process(50) - event = WatchedEvent state:SyncConnected type:None path:null 10:13:31:982 [DEBUG] - ZooKeeperWatcher.log(201) - + Profiler [連線到ZooKeeper] |-- elapsed time [開始連結] 210.193 milliseconds. |-- elapsed time [等待連線成功的Event] 9385.467 milliseconds. |-- Total [連線到ZooKeeper] 9596.196 milliseconds.
10:13:31:996 [INFO] - ZooKeeperWatcher.readNodeData(84) - /watcher 不存在 10:15:43:451 [INFO] - ZooKeeperWatcher.process(50) - event = WatchedEvent state:SyncConnected type:NodeCreated path:/watcher 10:15:43:463 [INFO] - ZooKeeperWatcher.readNodeData(81) - /watcher, value=hello zk 00, version=0 10:15:50:906 [INFO] - ZooKeeperWatcher.process(50) - event = WatchedEvent state:SyncConnected type:NodeDataChanged path:/watcher 10:15:50:910 [INFO] - ZooKeeperWatcher.readNodeData(81) - /watcher, value=hello zk 01, version=1 10:15:56:004 [INFO] - ZooKeeperWatcher.process(50) - event = WatchedEvent state:SyncConnected type:NodeDataChanged path:/watcher 10:15:56:007 [INFO] - ZooKeeperWatcher.readNodeData(81) - /watcher, value=hello zk 02, version=2 10:16:00:246 [INFO] - ZooKeeperWatcher.process(50) - event = WatchedEvent state:SyncConnected type:NodeDataChanged path:/watcher 10:16:00:249 [INFO] - ZooKeeperWatcher.readNodeData(81) - /watcher, value=hello zk 03, version=3 10:16:06:399 [INFO] - ZooKeeperWatcher.process(50) - event = WatchedEvent state:SyncConnected type:NodeDataChanged path:/watcher 10:16:06:402 [INFO] - ZooKeeperWatcher.readNodeData(81) - /watcher, value=hello zk 10, version=4 10:16:10:217 [INFO] - ZooKeeperWatcher.process(50) - event = WatchedEvent state:SyncConnected type:NodeDataChanged path:/watcher 10:16:10:220 [INFO] - ZooKeeperWatcher.readNodeData(81) - /watcher, value=hello zk 11, version=5 10:16:14:444 [INFO] - ZooKeeperWatcher.process(50) - event = WatchedEvent state:SyncConnected type:NodeDataChanged path:/watcher 10:16:14:447 [INFO] - ZooKeeperWatcher.readNodeData(81) - /watcher, value=hello zk 12, version=6 10:16:20:118 [INFO] - ZooKeeperWatcher.process(50) - event = WatchedEvent state:SyncConnected type:NodeDeleted path:/watcher 10:16:20:118 [INFO] - ZooKeeperWatcher.run(101) - /watcher 被刪除，退出 |