leader选举

Curator 有两种选举 recipe（Leader Latch 和 Leader Election)，实现原理是通过分布式锁来实现。

Leader Latch

无

LeaderSelector

LeaderSelector 和 Leader Latch 最的差别在于，leader可以释放领导权以后，还可以继续参与竞争。

案例

public class LeaderSelectorClient extends LeaderSelectorListenerAdapter implements Closeable {

    private  String name;  //表示当前的进程
    private  LeaderSelector leaderSelector;  //leader选举的API
    private CountDownLatch countDownLatch=new CountDownLatch(1);

    public LeaderSelectorClient(){

    }

    public LeaderSelectorClient(String name) {
        this.name = name;
    }

    public LeaderSelector getLeaderSelector() {
        return leaderSelector;
    }

    public void setLeaderSelector(LeaderSelector leaderSelector) {
        this.leaderSelector = leaderSelector;
    }

    public void start(){
        leaderSelector.start(); //开始竞争leader
    }

    @Override
    public void takeLeadership(CuratorFramework client) throws Exception {
        //如果进入当前的方法，意味着当前的进程获得了锁。获得锁以后，这个方法会被回调
        //这个方法执行结束之后，表示释放leader权限
        System.out.println(name+"->现在是leader了");
//        countDownLatch.await(); //阻塞当前的进程防止leader丢失
    }

    @Override
    public void close() throws IOException {
        leaderSelector.close();
    }
    private static String CONNECTION_STR="192.168.13.102:2181";

    public static void main(String[] args) throws IOException {
        CuratorFramework curatorFramework = CuratorFrameworkFactory.builder().
                connectString(CONNECTION_STR).sessionTimeoutMs(50000000).
                retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();
        curatorFramework.start();

        LeaderSelectorClient leaderSelectorClient=new LeaderSelectorClient("ClientA");
        LeaderSelector leaderSelector=new LeaderSelector(curatorFramework,"/leader",leaderSelectorClient);
        leaderSelectorClient.setLeaderSelector(leaderSelector);
        leaderSelectorClient.start(); //开始选举
        System.in.read();
    }
}