某分布式系统中，主节点可以有多台，可以动态上下线
任意一台客户端都能实时感知到主节点服务器的上下线
A、客户端实现
public class AppClient {
private String groupNode = "sgroup";
private ZooKeeper zk;
private Stat stat = new Stat();
private volatile List<String> serverList;
/**
* 连接zookeeper
*/
public void connectZookeeper() throws Exception {
zk
= new ZooKeeper("localhost:4180,localhost:4181,localhost:4182", 5000, new Watcher() {
public void process(WatchedEvent event) {
// 如果发生了"/sgroup"节点下的子节点变化事件, 更新server列表, 并重新注册监听
if (event.getType() == EventType.NodeChildrenChanged
&& ("/" + groupNode).equals(event.getPath())) {
try {
updateServerList();
} catch (Exception e) {
e.printStackTrace();
}
}
}
});
updateServerList();
}
/**
* 更新server列表
*/
private void updateServerList() throws Exception {
List<String> newServerList = new ArrayList<String>();
// 获取并监听groupNode的子节点变化
// watch参数为true, 表示监听子节点变化事件.
// 每次都需要重新注册监听, 因为一次注册, 只能监听一次事件, 如果还想继续保持监听, 必须重新注册
List<String> subList = zk.getChildren("/" + groupNode, true);
for (String subNode : subList) {
// 获取每个子节点下关联的server地址
byte[] data = zk.getData("/" + groupNode + "/" + subNode, false, stat);
newServerList.add(new String(data, "utf-8"));
}
// 替换server列表
serverList = newServerList;
System.out.println("server list updated: " + serverList);
}
/**
* client的工作逻辑写在这个方法中
* 此处不做任何处理, 只让client sleep
*/
public void handle() throws InterruptedException {
Thread.sleep(Long.MAX_VALUE);
}
public static void main(String[] args) throws Exception {
AppClient ac = new AppClient();
ac.connectZookeeper();
ac.handle();
}
}
B、服务器端实现
public class AppServer {
private String groupNode = "sgroup";
private String subNode = "sub";
/**
* 连接zookeeper
* @param address server的地址
*/
public void connectZookeeper(String address) throws Exception {
ZooKeeper zk = new ZooKeeper(
"localhost:4180,localhost:4181,localhost:4182",
5000, new Watcher() {
public void process(WatchedEvent event) {
// 不做处理
}
});
// 在"/sgroup"下创建子节点
// 子节点的类型设置为EPHEMERAL_SEQUENTIAL, 表明这是一个临时节点, 且在子节点的名称后面加上一串数字后缀
// 将server的地址数据关联到新创建的子节点上
String createdPath = zk.create("/" + groupNode + "/" + subNode, address.getBytes("utf-8"),
Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
System.out.println("create: " + createdPath);
}
/**
* server的工作逻辑写在这个方法中
* 此处不做任何处理, 只让server sleep
*/
public void handle() throws InterruptedException {
Thread.sleep(Long.MAX_VALUE);
}
public static void main(String[] args) throws Exception {
// 在参数中指定server的地址
if (args.length == 0) {
System.err.println("The first argument must be server address");
System.exit(1);
}
AppServer as = new AppServer();
as.connectZookeeper(args[0]);
as.handle();
}
}
3.7.2分布式共享锁的简单实现
客户端A
public class DistributedClient {
// 超时时间
private static final int SESSION_TIMEOUT = 5000;
// zookeeper server列表
private String hosts = "localhost:4180,localhost:4181,localhost:4182";
private String groupNode = "locks";
private String subNode = "sub";
private ZooKeeper zk;
// 当前client创建的子节点
private String thisPath;
// 当前client等待的子节点
private String waitPath;
private CountDownLatch latch = new CountDownLatch(1);
/**
* 连接zookeeper
*/
public void connectZookeeper() throws Exception {
zk = new ZooKeeper(hosts, SESSION_TIMEOUT, new Watcher() {
public void process(WatchedEvent event) {
try {
// 连接建立时, 打开latch, 唤醒wait在该latch上的线程
if (event.getState() == KeeperState.SyncConnected) {
latch.countDown();
}
// 发生了waitPath的删除事件
if (event.getType() == EventType.NodeDeleted && event.getPath().equals(waitPath)) {
doSomething();
}
} catch (Exception e) {
e.printStackTrace();
}
}
});
// 等待连接建立
latch.await();
// 创建子节点
thisPath = zk.create("/" + groupNode + "/" + subNode, null, Ids.OPEN_ACL_UNSAFE,
CreateMode.EPHEMERAL_SEQUENTIAL);
// wait一小会, 让结果更清晰一些
Thread.sleep(10);
// 注意, 没有必要监听"/locks"的子节点的变化情况
List<String> childrenNodes = zk.getChildren("/" + groupNode, false);
// 列表中只有一个子节点, 那肯定就是thisPath, 说明client获得锁
if (childrenNodes.size() == 1) {
doSomething();
} else {
String thisNode = thisPath.substring(("/" + groupNode + "/").length());
// 排序
Collections.sort(childrenNodes);
int index = childrenNodes.indexOf(thisNode);
if (index == -1) {
// never happened
} else if (index == 0) {
// inddx == 0, 说明thisNode在列表中最小, 当前client获得锁
doSomething();
} else {
// 获得排名比thisPath前1位的节点
this.waitPath = "/" + groupNode + "/" + childrenNodes.get(index – 1);
// 在waitPath上注册监听器, 当waitPath被删除时, zookeeper会回调监听器的process方法
zk.getData(waitPath, true, new Stat());
}
}
}
private void doSomething() throws Exception {
try {
System.out.println("gain lock: " + thisPath);
Thread.sleep(2000);
// do something
} finally {
System.out.println("finished: " + thisPath);
// 将thisPath删除, 监听thisPath的client将获得通知
// 相当于释放锁
zk.delete(this.thisPath, -1);
}
}
public static void main(String[] args) throws Exception {
for (int i = 0; i < 10; i++) {
new Thread() {
public void run() {
try {
DistributedClient dl = new DistributedClient();
dl.connectZookeeper();
} catch (Exception e) {
e.printStackTrace();
}
}
}.start();
}
Thread.sleep(Long.MAX_VALUE);
}
}
分布式多进程模式实现：
public class DistributedClientMy {
// 超时时间
private static final int SESSION_TIMEOUT = 5000;
// zookeeper server列表
private String hosts = "spark01:2181,spark02:2181,spark03:2181";
private String groupNode = "locks";
private String subNode = "sub";
private boolean haveLock = false;
private ZooKeeper zk;
// 当前client创建的子节点
private volatile String thisPath;
/**
* 连接zookeeper
*/
public void connectZookeeper() throws Exception {
zk = new ZooKeeper("spark01:2181", SESSION_TIMEOUT, new Watcher() {
public void process(WatchedEvent event) {
try {
// 子节点发生变化
if (event.getType() == EventType.NodeChildrenChanged && event.getPath().equals("/" + groupNode)) {
// thisPath是否是列表中的最小节点
List<String> childrenNodes = zk.getChildren("/" + groupNode, true);
String thisNode = thisPath.substring(("/" + groupNode + "/").length());
// 排序
Collections.sort(childrenNodes);
if (childrenNodes.indexOf(thisNode) == 0) {
doSomething();
thisPath = zk.create("/" + groupNode + "/" + subNode, null, Ids.OPEN_ACL_UNSAFE,
CreateMode.EPHEMERAL_SEQUENTIAL);
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
});
// 创建子节点
thisPath = zk.create("/" + groupNode + "/" + subNode, null, Ids.OPEN_ACL_UNSAFE,
CreateMode.EPHEMERAL_SEQUENTIAL);
// wait一小会, 让结果更清晰一些
Thread.sleep(new Random().nextInt(1000));
// 监听子节点的变化
List<String> childrenNodes = zk.getChildren("/" + groupNode, true);
// 列表中只有一个子节点, 那肯定就是thisPath, 说明client获得锁
if (childrenNodes.size() == 1) {
doSomething();
thisPath = zk.create("/" + groupNode + "/" + subNode, null, Ids.OPEN_ACL_UNSAFE,
CreateMode.EPHEMERAL_SEQUENTIAL);
}
}
/**
* 共享资源的访问逻辑写在这个方法中
*/
private void doSomething() throws Exception {
try {
System.out.println("gain lock: " + thisPath);
Thread.sleep(2000);
// do something
} finally {
System.out.println("finished: " + thisPath);
// 将thisPath删除, 监听thisPath的client将获得通知
// 相当于释放锁
zk.delete(this.thisPath, -1);
}
}
public static void main(String[] args) throws Exception {
DistributedClientMy dl = new DistributedClientMy();
dl.connectZookeeper();
Thread.sleep(Long.MAX_VALUE);
}
}
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