LeaderTransaction.java

package org.apache.curator.framework.recipes.leader;

import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.api.transaction.CuratorOp;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.data.Stat;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.Objects;

public class LeaderTransaction
{
    private final Logger log = LoggerFactory.getLogger(getClass());
    private final CuratorFramework client;
    private final String coordinationPath;
    private volatile int savedVersion;

    public LeaderTransaction(CuratorFramework client, String coordinationPath)
    {
        this.client = Objects.requireNonNull(client, "client cannot be null");
        this.coordinationPath = Objects.requireNonNull(coordinationPath, "coordinationPath cannot be null");
    }

    public boolean setLeader()
    {
        try
        {
            Stat stat = client.checkExists().forPath(coordinationPath);
            if ( stat == null )
            {
                client.create().creatingParentContainersIfNeeded().forPath(coordinationPath);
                savedVersion = 0;
            }
            else
            {
                savedVersion = stat.getVersion();
            }
            stat = client.setData().withVersion(savedVersion).forPath(coordinationPath);
            savedVersion = stat.getVersion();
        }
        catch ( KeeperException.BadVersionException e )
        {
            log.debug("setLeader failed due to bad version", e);
            return false;
        }
        catch ( Exception e )
        {
            log.debug("setLeader failed", e);
            return false;
        }
        return true;
    }

    public CuratorOp transactionOp()
    {
        try
        {
            return client.transactionOp().check().withVersion(savedVersion).forPath(coordinationPath);
        }
        catch ( Exception e )
        {
            // should never happen
            throw new RuntimeException(e);
        }
    }
}