服务器动态上下线监听案例
需求
在分布式系统中，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。
需求分析
客户端能实时洞察到服务器上下线的变化
基本流程：
1.服务端启动时去注册信息（创建的都是临时节点）
2.客户端获取到当前在线服务器列表，并注册监听
3.当服务器节点下线
4.服务器节点上下线的通知
5.process()重新再去获取服务器列表，并注册监听
具体实现
环境准备
在pom.xml添加相关依赖
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>RELEASE</version>
</dependency>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-core</artifactId>
<version>2.8.2</version>
</dependency>
<dependency>
<groupId>org.apache.zookeeper</groupId>
<artifactId>zookeeper</artifactId>
<version>3.6.1</version>
</dependency>
</dependencies>
1、启动zookeeper集群，在集群上创建/servers节点
[root@kk01 ~]# xzk.sh start # zk集群启动脚本
# 如果没有脚本，使用下面命令去集群的每台机器收到启动zkServer也可以
zkServer.sh start
# 进入zk客户端
[root@kk01 ~]# zkCli.sh -server
# 创建servers节点
[zk: localhost:2181(CONNECTED) 3] ls /
[zookeeper]
[zk: localhost:2181(CONNECTED) 4] create /servers "servers"
Created /servers
2.服务器端向zookeeper注册代码
public class DistributeServer {
private String connectString = "kk01:2181,kk02:2181,kk01:2181";
private int sessionTimeout = 2000;
private ZooKeeper zk;
public static void main(String[] args) {
DistributeServer server = new DistributeServer();
try {
// 1.获取zk连接
server.getConnect();
// 2.注册服务器到zk集群
server.regist(args[0]);
// 3.业务逻辑（因为是演示，所以睡眠即可）
server.business();
} catch (IOException e) {
e.printStackTrace();
} catch (KeeperException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
private void business() throws InterruptedException {
// 模拟业务逻辑
Thread.sleep(Long.MAX_VALUE);
}
private void regist(String hostname) throws KeeperException, InterruptedException {
zk.create("/servers/"+hostname, hostname.getBytes(),
// CreateMode.EPHEMERAL_SEQUENTIAL 表示创建的是临时顺序节点
ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
System.out.println(hostname + " is online");
}
private void getConnect() throws IOException {
zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
@Override
public void process(WatchedEvent event) {
}
});
}
}
3.客户端获取到当前在线服务器列表，并注册监听，代码如下
public class DistributeClient {
private String connectString = "kk01:2181,kk02:2181,kk01:2181";
private int sessionTimeout = 2000;
private ZooKeeper zk;
public static void main(String[] args) {
DistributeClient client = new DistributeClient();
try {
// 1.获取zk连接
client.getConnect();
// 2.监听 /server 下面子节点的增加和删除
client.getServerList();
// 3.业务逻辑（因为是演示，所以睡眠即可）
client.business();
} catch (IOException e) {
e.printStackTrace();
} catch (KeeperException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
private void business() throws InterruptedException {
// 模拟业务逻辑
Thread.sleep(Long.MAX_VALUE);
}
private void getServerList() throws KeeperException, InterruptedException {
List<String> children = zk.getChildren("/servers", true);
List<String> servers = new ArrayList<>();
for (String child : children) {
byte[] data = zk.getData("/servers/" + child, false, null);
servers.add(new String(data));
}
// 打印
System.out.println(servers);
}
private void getConnect() throws IOException {
zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
@Override
public void process(WatchedEvent event) {
try {
getServerList();
} catch (KeeperException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
}
}
测试
1、在Linux上（zk客户端）命令行增加减少服务器
1）启动 DistributeClient 客户端
即在idea上运行
2）在kk01上的zk客户端 /servers 目录下创建 临时带序号节点
[zk: localhost:2181(CONNECTED) 11] create -e -s /servers/hadoop100 "hadoop100"
Created /servers/hadoop1000000000000
[zk: localhost:2181(CONNECTED) 12] create -e -s /servers/hadoop101 "hadoop101"
Created /servers/hadoop1010000000001
[zk: localhost:2181(CONNECTED) 13] create -e -s /servers/hadoop103 "hadoop103"
Created /servers/hadoop1030000000002
[zk: localhost:2181(CONNECTED) 18] ls /servers
[hadoop1000000000000, hadoop1010000000001, hadoop1030000000002]
3）观察idea控制台变化
[]
[]
[hadoop100]
[hadoop101, hadoop100]
[hadoop101, hadoop100, hadoop103]
4）执行删除操作，删除部分节点
[zk: localhost:2181(CONNECTED) 19] delete /servers/hadoop1030000000002
[zk: localhost:2181(CONNECTED) 20] ls /servers
[hadoop1000000000000, hadoop1010000000001]
5）再次观察idea控制台变化
[hadoop101, hadoop100]
2、在idea上操作增加减少服务器
1）启动 DistributeClient客户端（如果前面已经启动过了，则忽略此步骤）
2）启动DistributeServer服务
在args[]数组传入 hadoop103
3）观察idea控制台发现打印了如下信息
hadoop103 is online
4）在zkClient查询节点信息，如下
[zk: localhost:2181(CONNECTED) 33] ls /servers
[hadoop1000000000000, hadoop1010000000001, hadoop1030000000003]