zookeeper典型應(yīng)用場(chǎng)景之一就是利用發(fā)布訂閱模式實(shí)現(xiàn)配置動(dòng)態(tài)管理尸昧≠诵校基本原理就是將配置信息存在zk的某個(gè)節(jié)點(diǎn)中枉层，客戶端啟動(dòng)時(shí)從這個(gè)節(jié)點(diǎn)讀取配置信息啸臀，并Watcher届宠，一旦配置發(fā)生變化，客戶端會(huì)接收到變化通知，便可以再次讀取節(jié)點(diǎn)內(nèi)容席揽。
樣例
/**
* A simple example program to use DataMonitor to start and
* stop executables based on a znode. The program watches the
* specified znode and saves the data that corresponds to the
* znode in the filesystem. It also starts the specified program
* with the specified arguments when the znode exists and kills
* the program if the znode goes away.
*/
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
public class Executor
implements Watcher, Runnable, DataMonitor.DataMonitorListener
{
String znode;
DataMonitor dm;
ZooKeeper zk;
String filename;
String exec[];
Process child;
public Executor(String hostPort, String znode, String filename,
String exec[]) throws KeeperException, IOException {
this.filename = filename;
this.exec = exec;
zk = new ZooKeeper(hostPort, 3000, this);
dm = new DataMonitor(zk, znode, null, this);
}
/**
* @param args
*/
public static void main(String[] args) {
if (args.length < 4) {
System.err
.println("USAGE: Executor hostPort znode filename program [args ...]");
System.exit(2);
}
String hostPort = args[0];
String znode = args[1];
String filename = args[2];
String exec[] = new String[args.length - 3];
System.arraycopy(args, 3, exec, 0, exec.length);
try {
new Executor(hostPort, znode, filename, exec).run();
} catch (Exception e) {
e.printStackTrace();
}
}
/***************************************************************************
* We do process any events ourselves, we just need to forward them on.
*
* @see org.apache.zookeeper.Watcher#process(org.apache.zookeeper.proto.WatcherEvent)
*/
@Override
public void process(WatchedEvent event) {
dm.process(event);
}
@Override
public void run() {
try {
synchronized (this) {
while (!dm.dead) {
wait();
}
}
} catch (InterruptedException e) {
}
}
public void closing(int rc) {
synchronized (this) {
notifyAll();
}
}
static class StreamWriter extends Thread {
OutputStream os;
InputStream is;
StreamWriter(InputStream is, OutputStream os) {
this.is = is;
this.os = os;
start();
}
public void run() {
byte b[] = new byte[80];
int rc;
try {
while ((rc = is.read(b)) > 0) {
os.write(b, 0, rc);
}
} catch (IOException e) {
}
}
}
public void exists(byte[] data) {
if (data == null) {
if (child != null) {
System.out.println("Killing process");
child.destroy();
try {
child.waitFor();
} catch (InterruptedException e) {
}
}
child = null;
} else {
if (child != null) {
System.out.println("Stopping child");
child.destroy();
try {
child.waitFor();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
try {
FileOutputStream fos = new FileOutputStream(filename);
fos.write(data);
fos.close();
} catch (IOException e) {
e.printStackTrace();
}
try {
System.out.println("Starting child");
child = Runtime.getRuntime().exec(exec);
new StreamWriter(child.getInputStream(), System.out);
new StreamWriter(child.getErrorStream(), System.err);
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
/**
* A simple class that monitors the data and existence of a ZooKeeper
* node. It uses asynchronous ZooKeeper APIs.
*/
import java.util.Arrays;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.AsyncCallback.StatCallback;
import org.apache.zookeeper.KeeperException.Code;
import org.apache.zookeeper.data.Stat;
public class DataMonitor implements Watcher, StatCallback {
ZooKeeper zk;
String znode;
Watcher chainedWatcher;
boolean dead;
DataMonitorListener listener;
byte prevData[];
public DataMonitor(ZooKeeper zk, String znode, Watcher chainedWatcher,
DataMonitorListener listener) {
this.zk = zk;
this.znode = znode;
this.chainedWatcher = chainedWatcher;
this.listener = listener;
// Get things started by checking if the node exists. We are going
// to be completely event driven
zk.exists(znode, true, this, null);
}
/**
* Other classes use the DataMonitor by implementing this method
*/
public interface DataMonitorListener {
/**
* The existence status of the node has changed.
*/
void exists(byte data[]);
/**
* The ZooKeeper session is no longer valid.
*
* @param rc
* the ZooKeeper reason code
*/
void closing(int rc);
}
public void process(WatchedEvent event) {
String path = event.getPath();
if (event.getType() == Event.EventType.None) {
// We are are being told that the state of the
// connection has changed
switch (event.getState()) {
case SyncConnected:
// In this particular example we don't need to do anything
// here - watches are automatically re-registered with
// server and any watches triggered while the client was
// disconnected will be delivered (in order of course)
break;
case Expired:
// It's all over
dead = true;
listener.closing(KeeperException.Code.SessionExpired);
break;
}
} else {
if (path != null && path.equals(znode)) {
// Something has changed on the node, let's find out
zk.exists(znode, true, this, null);
}
}
if (chainedWatcher != null) {
chainedWatcher.process(event);
}
}
public void processResult(int rc, String path, Object ctx, Stat stat) {
boolean exists;
switch (rc) {
case Code.Ok:
exists = true;
break;
case Code.NoNode:
exists = false;
break;
case Code.SessionExpired:
case Code.NoAuth:
dead = true;
listener.closing(rc);
return;
default:
// Retry errors
zk.exists(znode, true, this, null);
return;
}
byte b[] = null;
if (exists) {
try {
b = zk.getData(znode, false, null);
} catch (KeeperException e) {
// We don't need to worry about recovering now. The watch
// callbacks will kick off any exception handling
e.printStackTrace();
} catch (InterruptedException e) {
return;
}
}
if ((b == null && b != prevData)
|| (b != null && !Arrays.equals(prevData, b))) {
listener.exists(b);
prevData = b;
}
}
}
測(cè)試
以上兩個(gè)類(lèi)來(lái)自zookeeper官網(wǎng)顽馋，下面測(cè)試一下這兩個(gè)類(lèi)是如何工作的。
-
創(chuàng)建zk節(jié)點(diǎn)
設(shè)置初始值為Hello_world
[zk: localhost:2181(CONNECTED) 0] create /zk_tutorials Hello_world
Created /zk_tutorials
[zk: localhost:2181(CONNECTED) 1] get /zk_tutorials
Hello_world
cZxid = 0x300000017
ctime = Mon May 22 08:28:10 CST 2017
mZxid = 0x300000017
mtime = Mon May 22 08:28:10 CST 2017
pZxid = 0x300000017
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 11
numChildren = 0
```
- 創(chuàng)建測(cè)試腳本count.sh
output.txt保存的是/zk_tutorials的值幌羞，所以這個(gè)腳本的作用是每5秒輸出一次此節(jié)點(diǎn)的值寸谜。
count=0
while [ true ]; do
let count+=1
echo Count: $count using cat output.txt
sleep 5
done
```
-
編譯
Executor.java和DataMonitor
javac Executor.java DataMonitor.java -classpath /usr/hdp/2.5.0.0-1245/zookeeper/zookeeper-3.4.6.2.5.0.0-1245.jar
```
-
運(yùn)行測(cè)試
export ZK_HOME=/usr/hdp/2.5.0.0-1245/zookeeper export CLASSPATH=.:$ZK_HOME/zookeeper-3.4.6.2.5.0.0-1245.jar:$ZK_HOME/lib/slf4j-api-1.6.1.jar:$ZK_HOME/lib/slf4j-log4j12-1.6.1.jar:$ZK_HOME/lib/log4j-1.2.16.jar:$ZK_HOME/conf java Executor localhost:3181 /zk_tutorials output.txt ./count.sh會(huì)看到每5秒輸出一次結(jié)果
Count: 1 using Hello_world Count: 2 using Hello_world Count: 3 using Hello_world這時(shí)在另一終端修改
/zk_tutorials的值set /zk_tutorials Hello_zk可以看到結(jié)果已經(jīng)發(fā)生了改變
Count: 43 using Hello_world
Stopping child
Starting child
Count: 1 using Hello_zk
Count: 2 using Hello_zk
Count: 3 using Hello_zk
Count: 4 using Hello_zk
Count: 5 using Hello_zk
```
總結(jié)
通過(guò)上面的方法，利用zookeeper可以實(shí)現(xiàn)配置的動(dòng)態(tài)管理属桦，更多內(nèi)容請(qǐng)參考zookeeper-v3.4.10官網(wǎng)
