java zookeeper 使用_【分布式】Zookeeper使用--Java API
一、前言
上一篇博客我们通过命令行来操作Zookeper的客户端和服务端并进行相应的操作，这篇主要介绍如何通过API(JAVA)来操作Zookeeper。
二、开发环境配置
首先打开Zookeeper服务端(上一篇博客有具体的方法)，方便客户端连接。
配置开发环境环境可以有两种方式：① 直接下载相关的依赖Jar包，然后在IDE中添加依赖 ② 建立maven项目，使用maven进行依赖管理。
① 手动添加依赖至IDE
步骤一：点击这里下载对应版本的Jar包，包括(jar、javadoc.jar、sources.jar)，笔者对应下载的Zookeeper3.4.6版本。
步骤二：打开IDE(笔者使用eclispe)，新建名为zookeeper_examples_none_maven的java项目。由于需要单独添加依赖，为了方便管理，笔者在项目下新建了jar文件夹，用于存放本项目的jar包(将步骤一下载的3个jar包存放至此文件夹下)。
步骤三：在eclipse中添加依赖
步骤四：新建包、Java类进行测试
Zookeeper_Constructor_Usage_Simple.java
packagecom.hust.grid.leesf.examples;importjava.io.IOException;importjava.util.concurrent.CountDownLatch;importorg.apache.zookeeper.WatchedEvent;importorg.apache.zookeeper.Watcher;importorg.apache.zookeeper.Watcher.Event.KeeperState;importorg.apache.zookeeper.ZooKeeper;public class Zookeeper_Constructor_Usage_Simple implementsWatcher {private static CountDownLatch connectedSemaphore = new CountDownLatch(1);
@Overridepublic voidprocess(WatchedEvent event) {
System.out.println("Receive watched event : " +event);if (KeeperState.SyncConnected ==event.getState()) {
connectedSemaphore.countDown();
}
}public static void main(String[] args) throwsIOException {
ZooKeeper zookeeper= new ZooKeeper("127.0.0.1:2181", 5000, newZookeeper_Constructor_Usage_Simple());
System.out.println(zookeeper.getState());try{
connectedSemaphore.await();
}catch(InterruptedException e) {
e.printStackTrace();
}
System.out.println("Zookeeper session established");
}
}
View Code
运行结果如下
Exception in thread "main" java.lang.NoClassDefFoundError: org/slf4j/LoggerFactory
at org.apache.zookeeper.ZooKeeper.(ZooKeeper.java:94)
at com.hust.grid.leesf.examples.Zookeeper_Constructor_Usage_Simple.main(Zookeeper_Constructor_Usage_Simple.java:23)
Caused by: java.lang.ClassNotFoundException: org.slf4j.LoggerFactory
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
...2 more
结果表明缺失LoggerFactory类，经笔者查阅资料，只需将zookeeper的lib文件夹下log4j-1.2.16.jar、slf4j-api-1.6.1.jar放如zookeeper_examples_none_maven的jar文件夹下，然后再次将其添加至IDE即可。
再次运行结果如下
CONNECTING
Receive watched event : WatchedEvent state:SyncConnected type:None path:nullZookeeper session established
表示客户端已经成功连接至服务器了。
可以看到方法一相对而言比较麻烦，需要手动管理不同的依赖jar包，可以采用更成熟的依赖管理方法，即使用maven来管理Jar包。
② 使用maven管理依赖
步骤一：新建maven项目
步骤二：配置pom.xml文件如下
4.0.0
com.hust.grid.leesf
zookeeper_examples
0.0.1-SNAPSHOT
jar
zookeeper_examples
http://maven.apache.org
UTF-8
junit
junit
3.8.1
test
org.apache.zookeeper
zookeeper
3.4.6
log4j
log4j
1.2.16
org.slf4j
slf4j-api
1.6.1
View Code
步骤三：新建java类进行测试
Zookeeper_Constructor_Usage_Simple.java，代码同上。
运行结果如下
CONNECTING
Receive watched event : WatchedEvent state:SyncConnected type:None path:nullZookeeper session established
结果也表示客户端已经成功连接至服务器。
三、操作示例
3.1 创建节点
创建节点有异步和同步两种方式。无论是异步或者同步，Zookeeper都不支持递归调用，即无法在父节点不存在的情况下创建一个子节点，如在/zk-ephemeral节点不存在的情况下创建/zk-ephemeral/ch1节点；并且如果一个节点已经存在，那么创建同名节点时，会抛出NodeExistsException异常。
① 同步方式
packagecom.hust.grid.leesf.examples;importjava.util.concurrent.CountDownLatch;importorg.apache.zookeeper.CreateMode;importorg.apache.zookeeper.WatchedEvent;importorg.apache.zookeeper.Watcher;importorg.apache.zookeeper.Watcher.Event.KeeperState;importorg.apache.zookeeper.ZooDefs.Ids;importorg.apache.zookeeper.ZooKeeper;public class Zookeeper_Create_API_Sync_Usage implementsWatcher {private static CountDownLatch connectedSemaphore = new CountDownLatch(1);public static void main(String[] args) throwsException {
ZooKeeper zookeeper= new ZooKeeper("127.0.0.1:2181", 5000, newZookeeper_Create_API_Sync_Usage());
System.out.println(zookeeper.getState());
connectedSemaphore.await();
String path1= zookeeper.create("/zk-test-ephemeral-", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
System.out.println("Success create znode: " +path1);
String path2= zookeeper.create("/zk-test-ephemeral-", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
System.out.println("Success create znode: " +path2);
}public voidprocess(WatchedEvent event) {if (KeeperState.SyncConnected ==event.getState()) {
connectedSemaphore.countDown();
}
}
}
View Code
运行结果如下
CONNECTING
Success create znode:/zk-test-ephemeral-Success create znode:/zk-test-ephemeral-0000000043
结果表明已经成功创建了临时节点和临时顺序节点，在创建顺序节点时，系统会在后面自动增加一串数字。
② 异步方式
使用异步方式于同步方式的区别在于节点的创建过程(包括网络通信和服务端的节点创建过程)是异步的，在同步接口调用过程中，开发者需要关注接口抛出异常的可能，但是在异步接口中，接口本身不会抛出异常，所有异常都会在回调函数中通过Result Code来体现。
packagecom.hust.grid.leesf.examples;importjava.util.concurrent.CountDownLatch;importorg.apache.zookeeper.AsyncCallback;importorg.apache.zookeeper.CreateMode;importorg.apache.zookeeper.WatchedEvent;importorg.apache.zookeeper.Watcher;importorg.apache.zookeeper.ZooKeeper;importorg.apache.zookeeper.Watcher.Event.KeeperState;importorg.apache.zookeeper.ZooDefs.Ids;public class Zookeeper_Create_API_ASync_Usage implementsWatcher {private static CountDownLatch connectedSemaphore = new CountDownLatch(1);public static void main(String[] args) throwsException {
ZooKeeper zookeeper= new ZooKeeper("127.0.0.1:2181", 5000, newZookeeper_Create_API_ASync_Usage());
System.out.println(zookeeper.getState());
connectedSemaphore.await();
zookeeper.create("/zk-test-ephemeral-", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL,new IStringCallback(), "I am context. ");
zookeeper.create("/zk-test-ephemeral-", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL,new IStringCallback(), "I am context. ");
zookeeper.create("/zk-test-ephemeral-", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL,new IStringCallback(), "I am context. ");
Thread.sleep(Integer.MAX_VALUE);
}public voidprocess(WatchedEvent event) {if (KeeperState.SyncConnected ==event.getState()) {
connectedSemaphore.countDown();
}
}
}class IStringCallback implementsAsyncCallback.StringCallback {public void processResult(intrc, String path, Object ctx, String name) {
System.out.println("Create path result: [" + rc + ", " + path + ", " + ctx + ", real path name: " +name);
}
}
View Code
运行结果如下
CONNECTING
Create path result: [0, /zk-test-ephemeral-, I am context. , real path name: /zk-test-ephemeral-Create path result: [-110, /zk-test-ephemeral-, I am context. , real path name: nullCreate path result: [0, /zk-test-ephemeral-, I am context. , real path name: /zk-test-ephemeral-0000000045
结果表明已经成功使用异步方式创建了相应节点。
3.2 删除节点
只允许删除叶子节点，即一个节点如果有子节点，那么该节点将无法直接删除，必须先删掉其所有子节点。同样也有同步和异步两种方式。
① 同步方式
packagecom.hust.grid.leesf.examples;importjava.util.concurrent.CountDownLatch;importorg.apache.zookeeper.CreateMode;importorg.apache.zookeeper.WatchedEvent;importorg.apache.zookeeper.Watcher;importorg.apache.zookeeper.Watcher.Event.EventType;importorg.apache.zookeeper.Watcher.Event.KeeperState;importorg.apache.zookeeper.ZooDefs.Ids;importorg.apache.zookeeper.ZooKeeper;public class Delete_API_Sync_Usage implementsWatcher {private static CountDownLatch connectedSemaphore = new CountDownLatch(1);private staticZooKeeper zk;public static void main(String[] args) throwsException {
String path= "/zk-book";
zk= new ZooKeeper("127.0.0.1:2181", 5000,newDelete_API_Sync_Usage());
connectedSemaphore.await();
zk.create(path,"".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
System.out.println("success create znode: " +path);
zk.create(path+ "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
System.out.println("success create znode: " + path + "/c1");try{
zk.delete(path,-1);
}catch(Exception e) {
System.out.println("fail to delete znode: " +path);
}
zk.delete(path+ "/c1", -1);
System.out.println("success delete znode: " + path + "/c1");
zk.delete(path,-1);
System.out.println("success delete znode: " +path);
Thread.sleep(Integer.MAX_VALUE);
}public voidprocess(WatchedEvent event) {if (KeeperState.SyncConnected ==event.getState()) {if (EventType.None == event.getType() && null ==event.getPath()) {
connectedSemaphore.countDown();
}
}
}
}
View Code
运行结果如下
success create znode: /zk-book
success create znode:/zk-book/c1
fail to delete znode:/zk-book
success delete znode:/zk-book/c1
success delete znode:/zk-book
结果表明若节点有子节点，则无法将其删除，必须先删除其所有子节点。
② 异步方式
packagecom.hust.grid.leesf.examples;importjava.util.concurrent.CountDownLatch;importorg.apache.zookeeper.AsyncCallback;importorg.apache.zookeeper.CreateMode;importorg.apache.zookeeper.WatchedEvent;importorg.apache.zookeeper.Watcher;importorg.apache.zookeeper.ZooKeeper;importorg.apache.zookeeper.Watcher.Event.EventType;importorg.apache.zookeeper.Watcher.Event.KeeperState;importorg.apache.zookeeper.ZooDefs.Ids;public class Delete_API_ASync_Usage implementsWatcher {private static CountDownLatch connectedSemaphore = new CountDownLatch(1);private staticZooKeeper zk;public static void main(String[] args) throwsException {
String path= "/zk-book";
zk= new ZooKeeper("127.0.0.1:2181", 5000,newDelete_API_ASync_Usage());
connectedSemaphore.await();
zk.create(path,"".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
System.out.println("success create znode: " +path);
zk.create(path+ "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
System.out.println("success create znode: " + path + "/c1");
zk.delete(path,-1, new IVoidCallback(), null);
zk.delete(path+ "/c1", -1, new IVoidCallback(), null);
zk.delete(path,-1, new IVoidCallback(), null);
Thread.sleep(Integer.MAX_VALUE);
}public voidprocess(WatchedEvent event) {if (KeeperState.SyncConnected ==event.getState()) {if (EventType.None == event.getType() && null ==event.getPath()) {
connectedSemaphore.countDown();
}
}
}
}class IVoidCallback implementsAsyncCallback.VoidCallback {public void processResult(intrc, String path, Object ctx) {
System.out.println(rc+ ", " + path + ", " +ctx);
}
}
View Code
运行结果如下
success create znode: /zk-book
success create znode:/zk-book/c1-111, /zk-book, null
0, /zk-book/c1, null
0, /zk-book, null
结果结果表明第一次删除/zk-book的时异常，ResultCode为-111。
3.3 子节点获取
读取节点的子节点列表，同样可以使用同步和异步的方式进行操作。
① 同步方式
packagecom.hust.grid.leesf.examples;importjava.util.List;importjava.util.concurrent.CountDownLatch;importorg.apache.zookeeper.CreateMode;importorg.apache.zookeeper.WatchedEvent;importorg.apache.zookeeper.Watcher;importorg.apache.zookeeper.ZooKeeper;importorg.apache.zookeeper.Watcher.Event.EventType;importorg.apache.zookeeper.Watcher.Event.KeeperState;importorg.apache.zookeeper.ZooDefs.Ids;public class Zookeeper_GetChildren_API_Sync_Usage implementsWatcher {private static CountDownLatch connectedSemaphore = new CountDownLatch(1);private static ZooKeeper zk = null;public static void main(String[] args) throwsException {
String path= "/zk-book-1";
zk= new ZooKeeper("127.0.0.1:2181", 5000, newZookeeper_GetChildren_API_Sync_Usage());
connectedSemaphore.await();
zk.create(path,"".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
System.out.println("success create znode: " +path);
zk.create(path+ "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
System.out.println("success create znode: " + path + "/c1");
List childrenList = zk.getChildren(path, true);
System.out.println(childrenList);
zk.create(path+ "/c2", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
System.out.println("success create znode: " + path + "/c2");
Thread.sleep(1000);
zk.create(path+ "/c3", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
System.out.println("success create znode: " + path + "/c3");
Thread.sleep(Integer.MAX_VALUE);
}public voidprocess(WatchedEvent event) {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("ReGet Child:" + zk.getChildren(event.getPath(), true));
}catch(Exception e) {
}
}
}
}
}
View Code
运行结果如下
success create znode: /zk-book-1success create znode:/zk-book-1/c1
[c1]
success create znode:/zk-book-1/c2
ReGet Child:[c1, c2]
success create znode:/zk-book-1/c3
ReGet Child:[c3, c1, c2]
值得注意的是，Watcher通知是一次性的，即一旦触发一次通知后，该Watcher就失效了，因此客户端需要反复注册Watcher，即程序中在process里面又注册了Watcher，否则，将无法获取c3节点的创建而导致子节点变化的事件。
② 异步方式
packagecom.hust.grid.leesf.examples;importjava.util.List;importjava.util.concurrent.CountDownLatch;importorg.apache.zookeeper.AsyncCallback;importorg.apache.zookeeper.CreateMode;importorg.apache.zookeeper.WatchedEvent;importorg.apache.zookeeper.Watcher;importorg.apache.zookeeper.Watcher.Event.EventType;importorg.apache.zookeeper.Watcher.Event.KeeperState;importorg.apache.zookeeper.ZooDefs.Ids;importorg.apache.zookeeper.ZooKeeper;importorg.apache.zookeeper.data.Stat;public class Zookeeper_GetChildren_API_ASync_Usage implementsWatcher {private static CountDownLatch connectedSemaphore = new CountDownLatch(1);private static ZooKeeper zk = null;public static void main(String[] args) throwsException {
String path= "/zk-book";
zk= new ZooKeeper("127.0.0.1:2181", 5000, newZookeeper_GetChildren_API_ASync_Usage());
connectedSemaphore.await();
zk.create(path,"".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
System.out.println("success create znode: " +path);
zk.create(path+ "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
System.out.println("success create znode: " + path + "/c1");
zk.getChildren(path,true, new IChildren2Callback(), null);
zk.create(path+ "/c2", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
System.out.println("success create znode: " + path + "/c2");
Thread.sleep(Integer.MAX_VALUE);
}public voidprocess(WatchedEvent event) {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("ReGet Child:" + zk.getChildren(event.getPath(), true));
}catch(Exception e) {
}
}
}
}
}class IChildren2Callback implementsAsyncCallback.Children2Callback {public void processResult(int rc, String path, Object ctx, Listchildren, Stat stat) {
System.out.println("Get Children znode result: [response code: " + rc + ", param path: " + path + ", ctx: "
+ ctx + ", children list: " + children + ", stat: " +stat);
}
}
View Code
运行结果如下
success create znode: /zk-book
success create znode:/zk-book/c1
Get Children znode result: [response code:0, param path: /zk-book, ctx: null, children list: [c1], stat: 2901,2901,1478226062843,1478226062843,0,1,0,0,0,1,2902success create znode:/zk-book/c2
ReGet Child:[c1, c2]
结果表示通过异步的方式可以获取子节点信息。
3.4 数据节点获取
对于节点的数据获取，同样存在同步和异步两种方式。
① 同步方式
packagecom.hust.grid.leesf.examples;importjava.util.concurrent.CountDownLatch;importorg.apache.zookeeper.CreateMode;importorg.apache.zookeeper.WatchedEvent;importorg.apache.zookeeper.Watcher;importorg.apache.zookeeper.Watcher.Event.EventType;importorg.apache.zookeeper.Watcher.Event.KeeperState;importorg.apache.zookeeper.ZooDefs.Ids;importorg.apache.zookeeper.ZooKeeper;importorg.apache.zookeeper.data.Stat;public class GetData_API_Sync_Usage implementsWatcher {private static CountDownLatch connectedSemaphore = new CountDownLatch(1);private static ZooKeeper zk = null;private static Stat stat = newStat();public static void main(String[] args) throwsException {
String path= "/zk-book";
zk= new ZooKeeper("127.0.0.1:2181", 5000,newGetData_API_Sync_Usage());
connectedSemaphore.await();
zk.create(path,"123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
System.out.println("success create znode: " +path);
System.out.println("the data of znode " + path + " is : " + new String(zk.getData(path, true, stat)));
System.out.println("czxID: " + stat.getCzxid() + ", mzxID: " + stat.getMzxid() + ", version: " +stat.getVersion());
zk.setData(path,"123".getBytes(), -1);
Thread.sleep(Integer.MAX_VALUE);
}public voidprocess(WatchedEvent event) {if (KeeperState.SyncConnected ==event.getState()) {if (EventType.None == event.getType() && null ==event.getPath()) {
connectedSemaphore.countDown();
}else if (event.getType() ==EventType.NodeDataChanged) {try{
System.out.println("the data of znode " + event.getPath() + " is : " + new String(zk.getData(event.getPath(), true, stat)));
System.out.println("czxID: " + stat.getCzxid() + ", mzxID: " + stat.getMzxid() + ", version: " +stat.getVersion());
}catch(Exception e) {
}
}
}
}
}
View Code
运行结果如下
success create znode: /zk-book
the data of/zk-book is : 123czxID:2924, mzxID: 2924, version: 0the data of/zk-book is : 123czxID:2924, mzxID: 2925, version: 1
结果表明可以使用getData函数获取节点的数据。
② 异步方式
packagecom.hust.grid.leesf.examples;importjava.util.concurrent.CountDownLatch;importorg.apache.zookeeper.AsyncCallback;importorg.apache.zookeeper.CreateMode;importorg.apache.zookeeper.WatchedEvent;importorg.apache.zookeeper.Watcher;importorg.apache.zookeeper.Watcher.Event.EventType;importorg.apache.zookeeper.Watcher.Event.KeeperState;importorg.apache.zookeeper.ZooDefs.Ids;importorg.apache.zookeeper.ZooKeeper;importorg.apache.zookeeper.data.Stat;public class GetData_API_ASync_Usage implementsWatcher {private static CountDownLatch connectedSemaphore = new CountDownLatch(1);private staticZooKeeper zk;public static void main(String[] args) throwsException {
String path= "/zk-book";
zk= new ZooKeeper("127.0.0.1:2181", 5000,newGetData_API_ASync_Usage());
connectedSemaphore.await();
zk.create(path,"123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
System.out.println("success create znode: " +path);
zk.getData(path,true, new IDataCallback(), null);
zk.setData(path,"123".getBytes(), -1);
Thread.sleep(Integer.MAX_VALUE);
}public voidprocess(WatchedEvent event) {if (KeeperState.SyncConnected ==event.getState()) {if (EventType.None == event.getType() && null ==event.getPath()) {
connectedSemaphore.countDown();
}else if (event.getType() ==EventType.NodeDataChanged) {try{
zk.getData(event.getPath(),true, new IDataCallback(), null);
}catch(Exception e) {
}
}
}
}
}class IDataCallback implementsAsyncCallback.DataCallback {public void processResult(int rc, String path, Object ctx, byte[] data, Stat stat) {
System.out.println("rc: " + rc + ", path: " + path + ", data: " + newString(data));
System.out.println("czxID: " + stat.getCzxid() + ", mzxID: " + stat.getMzxid() + ", version: " +stat.getVersion());
}
}
View Code
运行结果如下
success create znode: /zk-book
rc:0, path: /zk-book, data: 123czxID:2932, mzxID: 2932, version: 0rc:0, path: /zk-book, data: 123czxID:2932, mzxID: 2933, version: 1
结果表明采用异步方式同样可方便获取节点的数据。
3.5 更新数据
在更新数据时，setData方法存在一个version参数，其用于指定节点的数据版本，表明本次更新操作是针对指定的数据版本进行的，但是，在getData方法中，并没有提供根据指定数据版本来获取数据的接口，那么，这里为何要指定数据更新版本呢，这里方便理解，可以等效于CAS(compare and swap)，对于值V，每次更新之前都会比较其值是否是预期值A，只有符合预期，才会将V原子化地更新到新值B。Zookeeper的setData接口中的version参数可以对应预期值，表明是针对哪个数据版本进行更新，假如一个客户端试图进行更新操作，它会携带上次获取到的version值进行更新，而如果这段时间内，Zookeeper服务器上该节点的数据已经被其他客户端更新，那么其数据版本也会相应更新，而客户端携带的version将无法匹配，无法更新成功，因此可以有效地避免分布式更新的并发问题。
① 同步方式
packagecom.hust.grid.leesf.examples;importjava.util.concurrent.CountDownLatch;importorg.apache.zookeeper.CreateMode;importorg.apache.zookeeper.KeeperException;importorg.apache.zookeeper.WatchedEvent;importorg.apache.zookeeper.Watcher;importorg.apache.zookeeper.Watcher.Event.EventType;importorg.apache.zookeeper.Watcher.Event.KeeperState;importorg.apache.zookeeper.ZooDefs.Ids;importorg.apache.zookeeper.ZooKeeper;importorg.apache.zookeeper.data.Stat;public class SetData_API_Sync_Usage implementsWatcher {private static CountDownLatch connectedSemaphore = new CountDownLatch(1);private staticZooKeeper zk;public static void main(String[] args) throwsException {
String path= "/zk-book";
zk= new ZooKeeper("127.0.0.1:2181", 5000, newSetData_API_Sync_Usage());
connectedSemaphore.await();
zk.create(path,"123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
System.out.println("success create znode: " +path);
zk.getData(path,true, null);
Stat stat= zk.setData(path, "456".getBytes(), -1);
System.out.println("czxID: " + stat.getCzxid() + ", mzxID: " + stat.getMzxid() + ", version: " +stat.getVersion());
Stat stat2= zk.setData(path, "456".getBytes(), stat.getVersion());
System.out.println("czxID: " + stat2.getCzxid() + ", mzxID: " + stat2.getMzxid() + ", version: " +stat2.getVersion());try{
zk.setData(path,"456".getBytes(), stat.getVersion());
}catch(KeeperException e) {
System.out.println("Error: " + e.code() + "," +e.getMessage());
}
Thread.sleep(Integer.MAX_VALUE);
}public voidprocess(WatchedEvent event) {if (KeeperState.SyncConnected ==event.getState()) {if (EventType.None == event.getType() && null ==event.getPath()) {
connectedSemaphore.countDown();
}
}
}
}
View Code
运行结果如下
success create znode: /zk-book
czxID:2936, mzxID: 2937, version: 1czxID:2936, mzxID: 2938, version: 2Error: BADVERSION,KeeperErrorCode= BadVersion for /zk-book
结果表明由于携带的数据版本不正确，而无法成功更新节点。其中，setData中的version参数设置-1含义为客户端需要基于数据的最新版本进行更新操作。
② 异步方式
packagecom.hust.grid.leesf.examples;importjava.util.concurrent.CountDownLatch;importorg.apache.zookeeper.AsyncCallback;importorg.apache.zookeeper.CreateMode;importorg.apache.zookeeper.WatchedEvent;importorg.apache.zookeeper.Watcher;importorg.apache.zookeeper.Watcher.Event.EventType;importorg.apache.zookeeper.Watcher.Event.KeeperState;importorg.apache.zookeeper.ZooDefs.Ids;importorg.apache.zookeeper.ZooKeeper;importorg.apache.zookeeper.data.Stat;public class SetData_API_ASync_Usage implementsWatcher {private static CountDownLatch connectedSemaphore = new CountDownLatch(1);private staticZooKeeper zk;public static void main(String[] args) throwsException {
String path= "/zk-book";
zk= new ZooKeeper("127.0.0.1:2181", 5000, newSetData_API_ASync_Usage());
connectedSemaphore.await();
zk.create(path,"123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
System.out.println("success create znode: " +path);
zk.setData(path,"456".getBytes(), -1, new IStatCallback(), null);
Thread.sleep(Integer.MAX_VALUE);
}public voidprocess(WatchedEvent event) {if (KeeperState.SyncConnected ==event.getState()) {if (EventType.None == event.getType() && null ==event.getPath()) {
connectedSemaphore.countDown();
}
}
}
}class IStatCallback implementsAsyncCallback.StatCallback {public void processResult(intrc, String path, Object ctx, Stat stat) {
System.out.println("rc: " + rc + ", path: " + path + ", stat: " +stat);
}
}
View Code
运行结果如下
success create znode: /zk-book
rc:0, path: /zk-book, stat: 2942,2943,1478228414526,1478228414545,1,0,0,96876700808708136,3,0,2942
rc(ResultCode)为0，表明成功更新节点数据。
3.6 检测节点是否存在
在调用接口时注册Watcher的话，还可以对节点是否存在进行监听，一旦节点被创建、被删除、数据更新，都会通知客户端。
① 同步方式
packagecom.hust.grid.leesf.examples;importjava.util.concurrent.CountDownLatch;importorg.apache.zookeeper.CreateMode;importorg.apache.zookeeper.WatchedEvent;importorg.apache.zookeeper.Watcher;importorg.apache.zookeeper.Watcher.Event.EventType;importorg.apache.zookeeper.Watcher.Event.KeeperState;importorg.apache.zookeeper.ZooDefs.Ids;importorg.apache.zookeeper.ZooKeeper;public class Exist_API_Sync_Usage implementsWatcher {private static CountDownLatch connectedSemaphore = new CountDownLatch(1);private staticZooKeeper zk;public static void main(String[] args) throwsException {
String path= "/zk-book";
zk= new ZooKeeper("127.0.0.1:2181", 5000, // newExist_API_Sync_Usage());
connectedSemaphore.await();
zk.exists(path,true);
zk.create(path,"".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
zk.setData(path,"123".getBytes(), -1);
zk.create(path+ "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
System.out.println("success create znode: " + path + "/c1");
zk.delete(path+ "/c1", -1);
zk.delete(path,-1);
Thread.sleep(Integer.MAX_VALUE);
}public voidprocess(WatchedEvent event) {try{if (KeeperState.SyncConnected ==event.getState()) {if (EventType.None == event.getType() && null ==event.getPath()) {
connectedSemaphore.countDown();
}else if (EventType.NodeCreated ==event.getType()) {
System.out.println("success create znode: " +event.getPath());
zk.exists(event.getPath(),true);
}else if (EventType.NodeDeleted ==event.getType()) {
System.out.println("success delete znode: " +event.getPath());
zk.exists(event.getPath(),true);
}else if (EventType.NodeDataChanged ==event.getType()) {
System.out.println("data changed of znode: " +event.getPath());
zk.exists(event.getPath(),true);
}
}
}catch(Exception e) {
}
}
}
View Code
运行结果如下
success create znode: /zk-book
data changed of znode:/zk-book
success create znode:/zk-book/c1
success delete znode:/zk-book
结果表明：
· 无论节点是否存在，都可以通过exists接口注册Watcher。
· 注册的Watcher，对节点创建、删除、数据更新事件进行监听。
· 对于指定节点的子节点的各种变化，不会通知客户端。
② 异步方式
packagecom.hust.grid.leesf.examples;importjava.util.concurrent.CountDownLatch;importorg.apache.zookeeper.AsyncCallback;importorg.apache.zookeeper.CreateMode;importorg.apache.zookeeper.WatchedEvent;importorg.apache.zookeeper.Watcher;importorg.apache.zookeeper.Watcher.Event.EventType;importorg.apache.zookeeper.Watcher.Event.KeeperState;importorg.apache.zookeeper.ZooDefs.Ids;importorg.apache.zookeeper.ZooKeeper;importorg.apache.zookeeper.data.Stat;public class Exist_API_ASync_Usage implementsWatcher {private static CountDownLatch connectedSemaphore = new CountDownLatch(1);private staticZooKeeper zk;public static void main(String[] args) throwsException {
String path= "/zk-book";
zk= new ZooKeeper("127.0.0.1:2181", 5000,newExist_API_ASync_Usage());
connectedSemaphore.await();
zk.exists(path,true, new IIStatCallback(), null);
zk.create(path,"".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
zk.setData(path,"123".getBytes(), -1);
zk.create(path+ "/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
System.out.println("success create znode: " + path + "/c1");
zk.delete(path+ "/c1", -1);
zk.delete(path,-1);
Thread.sleep(Integer.MAX_VALUE);
}public voidprocess(WatchedEvent event) {try{if (KeeperState.SyncConnected ==event.getState()) {if (EventType.None == event.getType() && null ==event.getPath()) {
connectedSemaphore.countDown();
}else if (EventType.NodeCreated ==event.getType()) {
System.out.println("success create znode: " +event.getPath());
zk.exists(event.getPath(),true, new IIStatCallback(), null);
}else if (EventType.NodeDeleted ==event.getType()) {
System.out.println("success delete znode: " +event.getPath());
zk.exists(event.getPath(),true, new IIStatCallback(), null);
}else if (EventType.NodeDataChanged ==event.getType()) {
System.out.println("data changed of znode: " +event.getPath());
zk.exists(event.getPath(),true, new IIStatCallback(), null);
}
}
}catch(Exception e) {
}
}
}class IIStatCallback implementsAsyncCallback.StatCallback {public void processResult(intrc, String path, Object ctx, Stat stat) {
System.out.println("rc: " + rc + ", path: " + path + ", stat: " +stat);
}
}
View Code
运行结果如下
rc: -101, path: /zk-book, stat: nullsuccess create znode:/zk-book
rc:0, path: /zk-book, stat: 2974,2974,1478229717889,1478229717889,0,0,0,0,0,0,2974data changed of znode:/zk-book
rc:0, path: /zk-book, stat: 2974,2975,1478229717889,1478229717922,1,0,0,0,3,0,2974success create znode:/zk-book/c1
success delete znode:/zk-book
rc:-101, path: /zk-book, stat: null
结果表明当节点不存在时，其rc(ResultCode)为-101。
3.7 权限控制
通过设置Zookeeper服务器上数据节点的ACL控制，就可以对其客户端对该数据节点的访问权限：如果符合ACL控制，则可以进行访问，否则无法访问。
① 使用无权限信息的Zookeeper会话访问含权限信息的数据节点
packagecom.hust.grid.leesf.examples;importorg.apache.zookeeper.CreateMode;importorg.apache.zookeeper.ZooDefs.Ids;importorg.apache.zookeeper.ZooKeeper;public classAuthSample_Get {final static String PATH = "/zk-book-auth_test";public static void main(String[] args) throwsException {
ZooKeeper zookeeper1= new ZooKeeper("127.0.0.1:2181", 5000, null);
zookeeper1.addAuthInfo("digest", "foo:true".getBytes());
zookeeper1.create(PATH,"init".getBytes(), Ids.CREATOR_ALL_ACL, CreateMode.EPHEMERAL);
System.out.println("success create znode: " +PATH);
ZooKeeper zookeeper2= new ZooKeeper("127.0.0.1:2181", 5000, null);
zookeeper2.getData(PATH,false, null);
}
}
View Code
运行结果如下
success create znode: /zk-book-auth_test
Exception in thread"main" org.apache.zookeeper.KeeperException$NoAuthException: KeeperErrorCode = NoAuth for /zk-book-auth_test
at org.apache.zookeeper.KeeperException.create(KeeperException.java:113)
at org.apache.zookeeper.KeeperException.create(KeeperException.java:51)
at org.apache.zookeeper.ZooKeeper.getData(ZooKeeper.java:1155)
at org.apache.zookeeper.ZooKeeper.getData(ZooKeeper.java:1184)
at com.hust.grid.leesf.examples.AuthSample_Get.main(AuthSample_Get.java:17)
表示权限不够，不能进行操作。
② 删除带权限控制的节点
packagecom.hust.grid.leesf.examples;importorg.apache.zookeeper.CreateMode;importorg.apache.zookeeper.ZooDefs.Ids;importorg.apache.zookeeper.ZooKeeper;public classAuthSample_Delete {final static String PATH = "/zk-book-auth_test";final static String PATH2 = "/zk-book-auth_test/child";public static void main(String[] args) throwsException {
ZooKeeper zookeeper1= new ZooKeeper("127.0.0.1:2181", 5000, null);
zookeeper1.addAuthInfo("digest", "foo:true".getBytes());
zookeeper1.create(PATH,"init".getBytes(), Ids.CREATOR_ALL_ACL, CreateMode.PERSISTENT);
zookeeper1.create(PATH2,"init".getBytes(), Ids.CREATOR_ALL_ACL, CreateMode.EPHEMERAL);try{
ZooKeeper zookeeper2= new ZooKeeper("127.0.0.1:2181", 5000, null);
zookeeper2.delete(PATH2,-1);
}catch(Exception e) {
System.out.println("fail to delete: " +e.getMessage());
}
ZooKeeper zookeeper3= new ZooKeeper("127.0.0.1:2181", 5000, null);
zookeeper3.addAuthInfo("digest", "foo:true".getBytes());
zookeeper3.delete(PATH2,-1);
System.out.println("success delete znode: " +PATH2);
ZooKeeper zookeeper4= new ZooKeeper("127.00.1:2181", 5000, null);
zookeeper4.delete(PATH,-1);
System.out.println("success delete znode: " +PATH);
}
}
View Code
运行结果如下
fail to delete: KeeperErrorCode = NoAuth for /zk-book-auth_test/child
success delete znode:/zk-book-auth_test/child
success delete znode:/zk-book-auth_test
结果表明若没有权限，则无法删除节点。
四、总结
基于原生态的JAVA API的调用相对较简单，笔者后续会对源码进行分析。本博客的所有代码也同步上传至github，也谢谢各位园友的观看～