Java實現ZooKeeper的zNode監控
1 場景設計
目的是體驗ZooKeeper的Watcher功能。程序監控ZooKeeper的/watcher節點數據變化，當創建或修改數據時，控制檯打印當前的數據內容和版本號；當/watcher被刪除時，程序退出。
/watcher的創建、修改和刪除操作，使用控制檯或zkui操作。
2 搭建Maven項目
代碼相對比較簡單，就不用SpringBoot這個大殺器了，使用一個普通的Maven項目即可。
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缺省使用的是log4j V1，因此在引入的時候需要excludes。另外，使用了lombok來簡化一些代碼。
以下是pom.xml的內容
<?xml version="1.0" encoding="UTF-8"?>
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
4.0.0
tech.codestory.research
zookeeper
1.0.0-SNAPSHOT
<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>
3 log4j2.xml
在項目的 src/main/resources 下創建一個文件 log4j2.xml，內容爲
<?xml version="1.0" encoding="UTF-8"?>
<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>
<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>
4 創建ZooKeeper連接
創建連接代碼比較簡單，只需要創建 ZooKeeper對象就行，
ZooKeeper構造函數的定義
/**
- 創建一個 ZooKeeper 客戶端對象
- @param connectString 逗號分隔的 host:port 字符串，
- 單點如 127.0.0.1:2181，
- 集羣如 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 毫秒爲單位的超時時間
- @param watcher Watcher對象，用於接收 MatcherEvent
- @throws IOException 網絡錯誤時拋出異常
- @throws IllegalArgumentException 如果Root路徑設置錯誤
*/
public ZooKeeper(String connectString, int sessionTimeout, Watcher watcher)
throws IOException;
寫一段測試代碼，創建zk對象後判斷某一個zNode是否存在。
public class ZooKeeperWatcher implements Watcher {
/* ZooKeeper的客戶端連接 /
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);
}
}
}
運行這段代碼，發現會拋異常
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的字面意思是連接還沒有創建好，網絡搜索了一下，建立連接需要一些時間，創建zk對象後馬上調用exists命令，這時候連接還沒有創建好，就會拋異常。ZooKeeper在連接建立成功之後，會發送一個WatchedEvent事件，我們可以利用這個事件完成建立連接的過程。修改後的代碼如下，順便添加了slf4j-ext中的Profiler，用於記錄所消耗的時間。
public class ZooKeeperWatcher implements Watcher {
/* 等待連接建立成功的信號 /
private CountDownLatch connectedSemaphore = new CountDownLatch(1);
/* ZooKeeper的客戶端連接 /
ZooKeeper zk;
public ZooKeeperWatcher(String hostPort, String zNode) throws KeeperException, IOException {
Profiler profiler = new Profiler("連接到ZooKeeper");
profiler.start("開始鏈接");
zk = new ZooKeeper(hostPort, 3000, this);
try {
profiler.start("等待連接成功的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())) {
// 連接狀態發生變化
if (Event.KeeperState.SyncConnected.equals(event.getState())) {
// 連接建立成功
connectedSemaphore.countDown();
}
}
}
}
修改代碼之後的執行記錄日誌如下，可以看到等待連接成功的Event耗時9秒多。網絡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之後重新執行程序，仍然需要9秒多。
[INFO] - ZooKeeperWatcher.process(61) - event = WatchedEvent state:SyncConnected type:None path:null
[DEBUG] - ZooKeeperWatcher.log(201) -
- Profiler [連接到ZooKeeper]
|-- elapsed time [開始鏈接] 78.912 milliseconds.
|-- elapsed time [等待連接成功的Event] 9330.606 milliseconds.
|-- Total [連接到ZooKeeper] 9409.926 milliseconds.
[INFO] - ZooKeeperWatcher.readNodeData(95) - /watcher 不存在
5 讀取WatchedEvent
前面的代碼，只是處理了建立連接成功時的Event，下面再來看看讀取數據的過程。關鍵代碼如下：
if (Event.EventType.NodeDataChanged.equals(event.getType())
|| Event.EventType.NodeCreated.equals(event.getType())) {
String path = event.getPath();
if (path != null && path.equals(zNode)) {
// 節點數據被修改
readNodeData();
}
}
/* 讀節點數據 /
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);
}
}
當接收到創建節點和修改節點的WatchedEvent，都會將數據讀出並打印在控制檯。
6 調整後的完整程序清單
對前面的代碼做了部分調整，同時添加了退出系統的機制：節點被刪除。
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 {
/* 等待連接建立成功的信號 /
private CountDownLatch connectedSemaphore = new CountDownLatch(1);
/* 退出系統的信號 /
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("連接到ZooKeeper");
profiler.start("開始鏈接");
zk = new ZooKeeper(hostPort, 3000, this);
try {
profiler.start("等待連接成功的Event");
connectedSemaphore.await();
} catch (InterruptedException e) {
log.error("InterruptedException", e);
}
profiler.stop();
profiler.setLogger(log);
profiler.log();
// 先讀當前的數據
readNodeData();
}
/* 收到ZooKeeper的WatchedEvent /
@Override
public void process(WatchedEvent event) {
log.info("event = {}", event);
if (Event.EventType.None.equals(event.getType())) {
// 連接狀態發生變化
if (Event.KeeperState.SyncConnected.equals(event.getState())) {
// 連接建立成功
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)) {
// 節點數據被修改
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，通知退出線程
quitSemaphore.notify();
}
}
}
}
/* 讀節點數據 /
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 {
// 目的是添加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);
}
}
/* 主程序，代碼中寫死了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，應用啓動後創建節點，修改多次節點，最後刪除節點，日誌輸出如下：
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 [連接到ZooKeeper]
|-- elapsed time [開始鏈接] 210.193 milliseconds.
|-- elapsed time [等待連接成功的Event] 9385.467 milliseconds.
|-- Total [連接到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