一、環境準備及創建會話實例
-
JAR包
使用JAVA API調用ZooKeeper時必須要導入對應的jar包
對應的jar包:ZooKeeper-3.x.x.jar（其中的x需要依據版本而定。注意：使用3.4.14版本的ZooKeeper時，如何使用3.4.14的jar包，創建連接時需要把session超時時間設置長一點否則會報錯，改用3.4.10版本的jar包則無此問題）
在lib目錄下的jar包也是需要導入的
2. 創建會話實例
需要訪問ZooKeeper的第一步是需要先保證可以創建會話實例
創建會話實例的方法
ZooKeeper(String connectString,int sessionTimeout,Watcher watcher)
connectString：表示連接到哪一個Zookeeper，如192.168.2.2:2181
sessionTimeout：表示會話過期時間，單位是毫秒
watcher：通過註冊Watcher來實現對節點的狀態變化監聽
關於ZooKeeper的構造方法還有如下幾個：
ZooKeeper(String connectString,int sessionTimeout,Watcher watcher,boolean canBeReadOnly)
ZooKeeper(String connectString,int sessionTimeout,Watcher watcher,long sessionId,boolean canBeReadOnly)
ZooKeeper(String connectString,int sessionTimeout,Watcher watcher,long sessionId,byte[] sessionPasswd,boolean canBeReadOnly)
canBeReadOnly：表示當前會話是否支持read-only
sessionId：表示會話的ID
sessionPasswd：密鑰
關於watcher
watcher是org.apache.Zookeeper.Watcher類型的對象，當客戶端和服務器建立連接後會調用Watcher中的process方法，這個方法中會有一個WatchedEvent類型的參數，它用來標識發生了哪一種事件
WatchedEvent主要包含以下兩個方面的信息：
watchedEvent.getState()：取得與服務器連接狀態，這裏的連接狀態包含（SyncConnected、Disconnected、connectedReadOnly、AuthFailed等）
watchedEvent.getType()：取得節點事件類型，通過它可以獲得具體的事件類型，這裏事件類型的取值包含（None、NodeCreated、NodeDeleted、 NodeDataChanged、NodeChildrenChanged）
注意：Watcher通知是一次性的，當一旦觸發一次通知後，這個Watcher就無效了，客戶端需要再次註冊Watcher,否則無法再次監聽到節點的狀態變化
二、使用JAVA API調用ZooKeeper
使用JAVA API創建節點
public class ZooKeeperDemo implements Watcher{
private static final int SESSION_TIMEOUT = 3000;
public static ZooKeeper ZooKeeper;
public static void main(String[] args) {
String path = "/mynode";
try {
ZooKeeper = new ZooKeeper("192.168.2.2:2181",SESSION_TIMEOUT,new ZooKeeperDemo());
ZooKeeper.exists(path,true);
ZooKeeper.create(path,"mycontent 1".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
Thread.sleep(3000);
} catch (Exception e) {
e.printStackTrace();
}
}
@Override
public void process(WatchedEvent event) {
if(Event.KeeperState.SyncConnected == event.getState()){
if(Event.EventType.NodeCreated == event.getType()){
//創建成功時在此處進行回調
System.out.println("node創建成功！");
try {
ZooKeeper.exists(event.getPath(),true);
} catch (KeeperException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}
創建節點語句：
ZooKeeper.create(path,"mycontent 1".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
第一個參數：path，是一個局部變量“/mynode”
第二個參數："mycontent 1".getBytes(),指的是創建節點的數據值
第三個參數：ZooDefs.Ids.OPEN_ACL_UNSAFE,指的是這個節點的訪問權限爲任何人可以訪問
第四個參數：CreateMode.PERSISTENT，指的是創建節點的類型，這裏指的是在會話重啓後節點仍然存在
節點的創建、取值、修改、刪除操作
public class ZookeeperDemo01 implements Watcher {
//定義sessioTimeout常量
private static final int SESSION_TIMEOUT = 30000;
public static ZooKeeper zooKeeper;
public static void main(String[] args) {
createNode("/zknode1");
getContent("/zknode1");
setContent("/zknode1","你好!");
getContent("/zknode1");
deleteNode("/zknode1");
closeConnect(zooKeeper);
}
@Override
public void process(WatchedEvent watchedEvent) {
if (Event.KeeperState.SyncConnected == watchedEvent.getState()) {
if (Event.EventType.NodeCreated == watchedEvent.getType()) {
//創建節點的消息通知
System.out.println("創建節點成功! 時間：" + new SimpleDateFormat("yyyy-mm-dd HH:mm:ss").format(new Date()));
try {
zooKeeper.exists(watchedEvent.getPath(), true);
} catch (KeeperException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
} else if(Event.EventType.NodeDeleted == watchedEvent.getType()){
try {
zooKeeper.exists(watchedEvent.getPath(),true);
} catch (KeeperException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("節點被刪除! 時間：" + new SimpleDateFormat("yyyy-mm-dd HH:mm:ss").format(new Date()));
} else if(Event.EventType.NodeDataChanged == watchedEvent.getType()){
try {
zooKeeper.exists(watchedEvent.getPath(),true);
} catch (KeeperException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("節點被修改! 時間：" + new SimpleDateFormat("yyyy-mm-dd HH:mm:ss").format(new Date()));
}
}
}
/**
* 創建節點
*
* @param path
*/
public static void createNode(String path) {
try {
zooKeeper = new ZooKeeper("192.168.2.4:2181", SESSION_TIMEOUT, new ZookeeperDemo01());
zooKeeper.exists(path, true);
//創建節點
zooKeeper.create(path, "xiesheng".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
Thread.sleep(3000);
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* 獲取節點的內容
*
* @param path
* @return
*/
public static String getContent(String path) {
try {
if (zooKeeper == null) {
zooKeeper = new ZooKeeper("192.168.2.4:2181", SESSION_TIMEOUT, new ZookeeperDemo01());
}
byte[] rb = zooKeeper.getData(path, null, null);
System.out.println("獲取節點【" + path + "】的內容爲：" + new String(rb));
Thread.sleep(3000);
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
/**
* 設置節點的內容
* @param path
* @param content
*/
public static void setContent(String path,String content) {
try {
if (zooKeeper == null) {
zooKeeper = new ZooKeeper("192.168.2.4:2181", SESSION_TIMEOUT, new ZookeeperDemo01());
}
zooKeeper.setData(path, content.getBytes(), -1);
Thread.sleep(3000);
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* 刪除節點
* @param path
*/
public static void deleteNode(String path){
try {
if (zooKeeper == null) {
zooKeeper = new ZooKeeper("192.168.2.4:2181", SESSION_TIMEOUT, new ZookeeperDemo01());
}
zooKeeper.delete(path,-1);
Thread.sleep(3000);
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* 關閉連接
* @param zooKeeper
*/
public static void closeConnect(ZooKeeper zooKeeper){
if(zooKeeper == null){
System.out.println("未連接，無需關閉！");
} else {
try {
zooKeeper.close();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("連接關閉成功！");
}
}
}
進行以上測試後控制檯打印結果如下：
創建節點成功! 時間：2020-13-04 11:13:11
獲取節點【/zknode1】的內容爲：xiesheng
節點被修改! 時間：2020-13-04 11:13:17
獲取節點【/zknode1】的內容爲：你好!
節點被刪除! 時間：2020-13-04 11:13:23
連接關閉成功！