zookeeper的Java客户端API

zookeeper作为一个分布式服务框架，主要用来解决分布式数据一致性问题，对多种语言提供了API。这里主要记录下JAVA客户端API的使用。

1.创建会话

客户端可以通过创建一个ZooKeeper实例来连接zookeeper服务器

ZooKeeper的4个构造函数如下：

ZooKeeper(connectString, sessionTimeout, watcher);
ZooKeeper(connectString, sessionTimeout, watcher,canBeReadOnly);
ZooKeeper(connectString, sessionTimeout, watcher, sessionId, sessionPasswd);
ZooKeeper(connectString, sessionTimeout, watcher, sessionId, sessionPasswd, canBeReadOnly);

参数说明：

connectString: 连接字符串例如 "127.0.0.1:2181"

sessionTimeout: 会话超时时间以毫秒为单位的整型值在sessionTimeout时间内服务端与客户端没有有效的心跳检测则会话失效

watcher: 默认的事件通知处理器

sessionId: 会话ID

sessionPasswd: 会话秘钥

canBeReadOnly: 是否是只读

public class ZookeeperSampleTest implements Watcher {
private static CountDownLatch connectedSemaphore = new CountDownLatch(1);
public static void main(String args[]) throws IOException, InterruptedException{
ZooKeeper zk = new ZooKeeper("192.168.1.138:2181",5000,new ZookeeperSampleTest());
System.out.println(zk.getState());
try {
connectedSemaphore.await();
} catch (Exception e) {
// TODO: handle exception
}
Long sessionId = zk.getSessionId();
byte[] password = zk.getSessionPasswd();
zk = new ZooKeeper("192.168.1.138:2181",5000,new ZookeeperSampleTest(),1L,"test".getBytes());
zk = new ZooKeeper("192.168.1.138:2181",5000,new ZookeeperSampleTest(),sessionId,password);
Thread.sleep(Integer.MAX_VALUE);
//System.out.println("ZooKeeper session established");
}
@Override
public void process(WatchedEvent event) {
// TODO Auto-generated method stub
System.out.println("Receive watched event :" + event);
if(event.getState()==KeeperState.SyncConnected){
connectedSemaphore.countDown();
}
}
}

2.创建节点

创建节点的方式分为同步和异步，构造函数如下：

zk.create(path, data, acl, createMode);
, data, acl, createMode, cb, ctx);

参数说明：

path: 创建节点的路径如：/zk-test

data[]: 字节数组，节点数据

acl: 权限

createMode: 节点类型分为4种：持久性节点，持久性有序节点，临时节点，临时有序节点

cb: 回调函数需要实现StringCallback接口

ctx: 上下文一般用于回调函数时候使用

public class ZookeeperSampleCreateTest implements Watcher {
public static CountDownLatch connectedSemaphore = new CountDownLatch(1);
public static void main(String[] args) throws IOException, InterruptedException, KeeperException{
ZooKeeper zk = new ZooKeeper("192.168.1.138:2181",5000,new ZookeeperSampleCreateTest());
connectedSemaphore.await();
/*同步的方式*/
/*String path1 = zk.create("/zk-test-ephemeral-", "test-ephemeral".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
System.out.println("Success create node :" + path1);
String path2 = zk.create("/zk-test-ephemeral-", "test-ephemeral-sequential".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
System.out.println("Success create node :" + path2);*/
/*异步的方式*/
zk.create("/zk-test-ephemeral-", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL,new IStringCallback(),"i am context");
zk.create("/zk-test-ephemeral-", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL,new IStringCallback(),"i am context");
zk.create("/zk-test-ephemeral-", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL,new IStringCallback(),"i am context");
Thread.sleep(Integer.MAX_VALUE);
}
@Override
public void process(WatchedEvent event) {
// TODO Auto-generated method stub
if(KeeperState.SyncConnected == event.getState()){
connectedSemaphore.countDown();
}
}
}
class IStringCallback implements AsyncCallback.StringCallback{
@Override
public void processResult(int rc, String path, Object ctx, String name) {
// TODO Auto-generated method stub
System.out.println("Create path result: [" + rc + "," + path + "," + ctx + ", real path name " + name);
}
}

3.删除节点

zk.delete(path,version);
zk.delete(path,version,cb,ctx);

参数说明：

path：节点路径

version：版本号

cb: 回调函数

ctx: 上下文

4.获取子节点

getChildren有8个重载方法

zk.getChildren(path, watch);
zk.getChildren(path, watcher);
zk.getChildren(path, watch, stat);
zk.getChildren(path, watcher, stat);
zk.getChildren(path, watch, cb, ctx);
zk.getChildren(path, watcher, cb, ctx);

其中回调函数有两种 ChildrenCallback Children2Callback

参数说明：

path：节点路径

watch: boolean类型如果为true 表示使用默认的Watcher 为false表示不需要Watcher

watcher: 通知处理器在本次获取子节点以后一旦子节点有变化机会收到服务端传来的通知

stat: 指定数据节点的节点状态信息，传入一个旧的stat对象，当执行方法后 stat会被服务器响应的新stat替换

cb:回调函数有两种类型上面已经说过

ctx: 上下文

5.获取节点数据

获取节点数据有4个重载方法

zk.getData(path, watch, stat);
zk.getData(path, watcher, stat);
zk.getData(path, watch, cb, ctx);
zk.getData(path, watcher, cb, ctx);

参数说明：

path: 节点路径

watch: boolean类型如果为true 表示使用默认的Watcher 为false表示不需要Watcher

stat: 指定数据节点的节点状态信息，传入一个旧的stat对象，当执行方法后 stat会被服务器响应的新stat替换

cb:回调函数有两种类型上面已经说过

ctx: 上下文

在获取节点数据时候如果注册watcher 在节点数据发送变化的时候会通知客户端,当客户端收到通知以后，如果想下次数据发送变化再次收到通知，

需要重新注册watcher,获取子节点机制也如此

6.更新节点数据

更新节点数据也分为同步异步两个方法

zk.setData(path, data, version);
zk.setData(path, data, version, cb, ctx);

参数说明：同上

public class ZookeeperSampleGetDataTest implements Watcher {
public static CountDownLatch connectedSemaphore = new CountDownLatch(1);
public static Stat stat = new Stat();
public static ZooKeeper zk = null;
public static void main(String[] args) throws IOException, KeeperException, InterruptedException{
String path = "/zk-test";
zk = new ZooKeeper("192.168.1.138:2181", 5000, new ZookeeperSampleGetDataTest());
connectedSemaphore.await();
//获取子节点
/*zk.delete(path, 0);
zk.create(path, "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
zk.create(path+"/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
//同步方法获取children
//List<String> childs = zk.getChildren(path, true);
//System.out.println(childs);
//异步方法获取children
zk.getChildren(path, true, new IChildren2Callback(), null);
zk.create(path+"/c2", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
Thread.sleep(Integer.MAX_VALUE);*/
//获取节点数据
zk.delete(path, 0);
zk.create(path, "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
System.out.println(new String(zk.getData(path, true, stat)));
/** czxid: 创建该节点的事务ID mzxid: 更新该节点的事务ID version：数据版本*/
System.out.println("Czxid: " + stat.getCzxid() + "Mzxid: " + stat.getMzxid() + "Version: " + stat.getVersion());
zk.setData(path, "123".getBytes(), -1);
Thread.sleep(Integer.MAX_VALUE);
}
@Override
public void process(WatchedEvent event) {
// TODO Auto-generated method stub
if(KeeperState.SyncConnected==event.getState()){
if(EventType.None==event.getType() && null==event.getPath()){
connectedSemaphore.countDown();
}else if(event.getType()==EventType.NodeChildrenChanged){
try {
System.out.println("Get Child :" + zk.getChildren(event.getPath(), true));
} catch (KeeperException | InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}else if(event.getType()==EventType.NodeDataChanged){
try {
System.out.println(new String(zk.getData(event.getPath(), true, stat)));
System.out.println("Czxid: " + stat.getCzxid() + "Mzxid: " + stat.getMzxid() + "Version: " + stat.getVersion());
} catch (KeeperException | InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}
class IChildren2Callback implements AsyncCallback.Children2Callback{
@Override
public void processResult(int rc, String path, Object ctx,
List<String> childrens, Stat stat) {
// TODO Auto-generated method stub
System.out.println("Get Children znode result: [response code: " + rc + ", param path: " + path + ", ctx " + ctx
+ ", childrens :" + childrens + ", stat: " + stat);
}
}

其中更新节点数据版本version问题 -1表示基于数据的最新版本更新这里可以作为分布式锁的一个思路如果客户端参入的version不是数据最新版本则会更新失败

比如目前节点"/zk-test"的数据版本为 2 而某个客户端尝试执行 setData("/zk-test","test".getBytes(),1) 由于传入version为1 < 服务器目前版本2 这样就会更新失败

7.检测节点是否存在

zk.exists(path, watch);
zk.exists(path, watcher);
zk.exists(path, watch, cb, ctx);
zk.exists(path, watcher, cb, ctx);

如果判断节点是否存在是注册watcher 会对节点是否存在进行监听--创建节点，删除节点，节点数据更新都会通知客户端

8.权限控制

zookeeper提供了ACL的权限控制机制，简单来说就是通过控制zookeeper服务器上数据节点的ACL，来控制客户端对节点的访问权限

addAuthInfo(String scheme,byte[] auth);

参数说明：

scheme: 权限控制模式分为： world ,auth,digest,ip和super

auth: 具体的权限信息类似于shiro的权限字符串

如下代码：

<span style="white-space:pre;"> </span>ZooKeeper zk1 = new ZooKeeper("192.168.1.138:2181",5000,new ZookeeperSampleCreateTest());
zk1.addAuthInfo("digest", "test:true".getBytes());
zk1.create("/zk-test-auth", "123".getBytes(), Ids.CREATOR_ALL_ACL, CreateMode.EPHEMERAL);
ZooKeeper zk2 = new ZooKeeper("192.168.1.138:2181",5000,new ZookeeperSampleCreateTest());
zk2.addAuthInfo("digest", "test:true".getBytes());
System.out.println(new String(zk2.getData("/zk-test-auth", false, null)));
ZooKeeper zk3 = new ZooKeeper("192.168.1.138:2181",5000,new ZookeeperSampleCreateTest());
zk3.addAuthInfo("digest", "test:false".getBytes());
zk3.getData("/zk-test-auth", false, null);

zk2设置了正确的权限所以可以获取到节点数据 zk3则会抛异常

org.apache.zookeeper.KeeperException$NoAuthException: KeeperErrorCode = NoAuth for /zk-test-auth

巴特西

zookeeper的Java客户端API

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