zookeeper事務

zookeeper事物操作，其實只是其multi操作的簡單封裝：

public List<OpResult> multi(Iterable<Op> ops)

基本操作：new Transaction(zk).create(...).setData(...)... .commit();

因為每次返回  this 可以串行操作，最后執行commit()，提交批量事務操作，並返回List<OpResult>結果。

package org.apache.zookeeper;

import org.apache.zookeeper.data.ACL;
import java.util.ArrayList;
import java.util.List;

/**
 * Provides a builder style interface for doing multiple updates.  This is
 * really just a thin layer on top of Zookeeper.multi().
 *
 * @since 3.4.0
 *
 */
public class Transaction {
    private ZooKeeper zk;
    private List<Op> ops = new ArrayList<Op>();

    protected Transaction(ZooKeeper zk) {
        this.zk = zk;
    }

    public Transaction create(final String path, byte data[], List<ACL> acl,
                              CreateMode createMode) {
        ops.add(Op.create(path, data, acl, createMode.toFlag()));
        return this;
    }

    public Transaction delete(final String path, int version) {
        ops.add(Op.delete(path, version));
        return this;
    }

    public Transaction check(String path, int version) {
        ops.add(Op.check(path, version));
        return this;
    }

    public Transaction setData(final String path, byte data[], int version) {
        ops.add(Op.setData(path, data, version));
        return this;
    }

    public List<OpResult> commit() throws InterruptedException, KeeperException {
        return zk.multi(ops);
    }
}