Zookeeper应用案例-实现分布式应用的(主节点HA)及客户端动态更新主节点状态

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();
}
}

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();
}
}