大纲
1.基于Curator进行基本的zk数据操作
2.基于Curator实现集群元数据管理
3.基于Curator实现HA主备自动切换
4.基于Curator实现Leader选举
5.基于Curator实现分布式Barrier
6.基于Curator实现分布式计数器
7.基于Curator实现zk的节点和子节点监听机制
8.基于Curator创建客户端实例的源码分析
9.Curator在启动时是如何跟zk建立连接的
10.基于Curator进行增删改查节点的源码分析
11.基于Curator的节点监听回调机制的实现源码
12.基于Curator的Leader选举机制的实现源码
1.基于Curator进行基本的zk数据操作
Guava is to Java what Curator is to ZooKeeper，引入依赖如下：
<dependencies>
<dependency>
<groupId>org.apache.curator</groupId>
<artifactId>curator-framework</artifactId>
<version>2.12.0</version>
</dependency>
<dependency>
<groupId>org.apache.curator</groupId>
<artifactId>curator-recipes</artifactId>
<version>2.12.0</version>
</dependency>
</dependencies>Curator实现对znode进行增删改查的示例如下，其中CuratorFramework代表一个客户端实例。注意：可以通过creatingParentsIfNeeded()方法进行指定节点的级联创建。
public class CrudDemo {
public static void main(String[] args) throws Exception {
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
CuratorFramework client = CuratorFrameworkFactory.newClient("localhost:2181", 5000, 3000, retryPolicy);
client.start();//启动客户端并建立连接
System.out.println("已经启动Curator客户端");
client.create()
.creatingParentsIfNeeded()//进行级联创建
.withMode(CreateMode.PERSISTENT)//指定节点类型
.forPath("/my/path", "10".getBytes());//增
byte[] dataBytes = client.getData().forPath("/my/path");//查
System.out.println(new String(dataBytes));
client.setData().forPath("/my/path", "11".getBytes());//改
dataBytes = client.getData().forPath("/my/path");
System.out.println(new String(dataBytes));
List<String> children = client.getChildren().forPath("/my");//查
System.out.println(children);
client.delete().forPath("/my/path");//删
Thread.sleep(Integer.MAX_VALUE);
}
}2.基于Curator实现集群元数据管理
Curator可以操作zk。比如自研了一套分布式系统类似于Kafka、Canal，想把集群运行的核心元数据都放到zk里去。此时就可以通过Curator创建一些znode，往里面写入对应的值。
写入的值推荐用json格式，比如Kafka就是往zk写json格式数据。这样，其他客户端在需要的时候，就可以从里面读取出集群元数据了。
3.基于Curator实现HA主备自动切换
HDFS、Kafka、Canal都使用了zk进行Leader选举，所以可以基于Curator实现HA主备自动切换。
HDFS的NameNode是可以部署HA架构的，有主备两台机器。如果主机器宕机了，备用的机器可以感知到并选举为Leader，这样备用的机器就可以作为新的NameNode对外提供服务。
Kafka里的Controller负责管理整个集群的协作，Kafka中任何一个Broker都可以变成Controller，类似于Leader的角色。
Canal也会部署主备两台机器，主机器挂掉了，备用机器就可以跟上去。
4.基于Curator实现Leader选举
(1)Curator实现Leader选举的第一种方式之LeaderLatch
(2)Curator实现Leader选举的第二种方式之LeaderSelector
(1)Curator实现Leader选举的第一种方式之LeaderLatch
通过Curator的LeaderLatch来实现Leader选举：
public class LeaderLatchDemo {
public static void main(String[] args) throws Exception {
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
CuratorFramework client = CuratorFrameworkFactory.newClient("localhost:2181", 5000, 3000, retryPolicy);
client.start();
//"/leader/latch"这其实是一个znode顺序节点
LeaderLatch leaderLatch = new LeaderLatch(client, "/leader/latch");
leaderLatch.start();
leaderLatch.await();//直到等待他成为Leader再往后执行
//类似于HDFS里，两台机器，其中一台成为了Leader就开始工作
//另外一台机器可以通过await阻塞在这里，直到Leader挂了，自己就会成为Leader继续工作
Boolean hasLeaderShip = leaderLatch.hasLeadership();//判断是否成为Leader
System.out.println("是否成为leader：" + hasLeaderShip);
Thread.sleep(Integer.MAX_VALUE);
}
}(2)Curator实现Leader选举的第二种方式之LeaderSelector
通过Curator的LeaderSelector来实现Leader选举如下：其中，LeaderSelector有两个监听器，可以关注连接状态。
public class LeaderSelectorDemo {
public static void main(String[] args) throws Exception {
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
CuratorFramework client = CuratorFrameworkFactory.newClient("localhost:2181", 5000, 3000, retryPolicy);
client.start();
LeaderSelector leaderSelector = new LeaderSelector(
client,
"/leader/election",
new LeaderSelectorListener() {
public void takeLeadership(CuratorFramework curatorFramework) throws Exception {
System.out.println("你已经成为了Leader......");
//在这里干Leader所有的事情，此时方法不能退出
Thread.sleep(Integer.MAX_VALUE);
}
public void stateChanged(CuratorFramework curatorFramework, ConnectionState connectionState) {
System.out.println("连接状态的变化，已经不是Leader......");
if (connectionState.equals(ConnectionState.LOST)) {
throw new CancelLeadershipException();
}
}
}
);
leaderSelector.start();//尝试和其他节点在节点"/leader/election"上进行竞争成为Leader
Thread.sleep(Integer.MAX_VALUE);
}
}5.基于Curator实现的分布式Barrier
(1)分布式Barrier
(2)分布式双重Barrier
(1)分布式Barrier
很多台机器都可以创建一个Barrier，此时它们都被阻塞了。除非满足一个条件(setBarrier()或removeBarrier())，才能不再阻塞它们。
//DistributedBarrier
public class DistributedBarrierDemo {
public static void main(String[] args) throws Exception {
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
CuratorFramework client = CuratorFrameworkFactory.newClient("localhost:2181", 5000, 3000, retryPolicy);
client.start();
DistributedBarrier barrier = new DistributedBarrier(client, "/barrier");
barrier.waitOnBarrier();
}
}(2)分布式双重Barrier
//DistributedDoubleBarrier
public class DistributedDoubleBarrierDemo {
public static void main(String[] args) throws Exception {
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
CuratorFramework client = CuratorFrameworkFactory.newClient("localhost:2181", 5000, 3000, retryPolicy);
client.start();
DistributedDoubleBarrier doubleBarrier = new DistributedDoubleBarrier(client, "/barrier/double", 10);
doubleBarrier.enter();//每台机器都会阻塞在enter这里
//直到10台机器都调用了enter，就会从enter这里往下执行
//此时可以做一些计算任务
doubleBarrier.leave();//每台机器都会阻塞在leave这里，直到10台机器都调用了leave
//此时就可以继续往下执行
}
}6.基于Curator实现分布式计数器
如果真的要实现分布式计数器，最好用Redis来实现。因为Redis的并发量更高，性能更好，功能更加的强大，而且还可以使用lua脚本嵌入进去实现复杂的业务逻辑。但是Redis天生的异步同步机制，存在机器宕机导致的数据不同步风险。然而zk在ZAB协议下的数据同步机制，则不会出现宕机导致数据不同步的问题。
//SharedCount：通过一个节点的值来实现
public class SharedCounterDemo {
public static void main(String[] args) throws Exception {
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
CuratorFramework client = CuratorFrameworkFactory.newClient("localhost:2181", 5000, 3000, retryPolicy);
client.start();
SharedCount sharedCount = new SharedCount(client, "/shared/count", 0);
sharedCount.start();
sharedCount.addListener(new SharedCountListener() {
public void countHasChanged(SharedCountReader sharedCountReader, int i) throws Exception {
System.out.println("分布式计数器变化了......");
}
public void stateChanged(CuratorFramework curatorFramework, ConnectionState connectionState) {
System.out.println("连接状态变化了.....");
}
});
Boolean result = sharedCount.trySetCount(1);
System.out.println(sharedCount.getCount());
}
}7.基于Curator实现zk的节点和子节点监听机制
(1)基于Curator实现zk的子节点监听机制
(2)基于Curator实现zk的节点数据监听机制
我们使用zk主要用于：
一.对元数据进行增删改查、监听元数据的变化
二.进行Leader选举
有三种类型的节点可以监听：
一.子节点监听PathCache
二.节点监听NodeCache
三.整个节点以下的树监听TreeCache
(1)基于Curator实现zk的子节点监听机制
下面是PathCache实现的子节点监听示例：
public class PathCacheDemo {
public static void main(String[] args) throws Exception {
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
CuratorFramework client = CuratorFrameworkFactory.newClient("localhost:2181", 5000, 3000, retryPolicy);
client.start();
PathChildrenCache pathChildrenCache = new PathChildrenCache(client, "/cluster", true);
//cache就是把zk里的数据缓存到客户端里来
//可以针对这个缓存的数据加监听器，去观察zk里的数据的变化
pathChildrenCache.getListenable().addListener(new PathChildrenCacheListener() {
public void childEvent(CuratorFramework curatorFramework, PathChildrenCacheEvent pathChildrenCacheEvent) throws Exception {
}
});
pathChildrenCache.start();
}
}(2)基于Curator实现zk的节点数据监听机制
下面是NodeCache实现的节点监听示例：
public class NodeCacheDemo {
public static void main(String[] args) throws Exception {
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
final CuratorFramework client = CuratorFrameworkFactory.newClient("localhost:2181", 5000, 3000, retryPolicy);
client.start();
final NodeCache nodeCache = new NodeCache(client, "/cluster");
nodeCache.getListenable().addListener(new NodeCacheListener() {
public void nodeChanged() throws Exception {
Stat stat = client.checkExists().forPath("/cluster");
if (stat == null) {
} else {
nodeCache.getCurrentData();
}
}
});
nodeCache.start();
}
}8.基于Curator创建客户端实例的源码分析
(1)创建CuratorFramework实例使用了构造器模式
(2)创建CuratorFramework实例会初始化CuratorZooKeeperClient实例
(1)创建CuratorFramework实例使用了构造器模式
CuratorFrameworkFactory.newClient()方法使用了构造器模式。首先通过builder()方法创建出Builder实例对象，然后把参数都设置成Builder实例对象的属性，最后通过build()方法把Builder实例对象传入目标类的构造方法中。
public class Demo {
public static void main(String[] args) throws Exception {
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
CuratorFramework client = CuratorFrameworkFactory.newClient(
"127.0.0.1:2181",//zk的地址
5000,//客户端和zk的心跳超时时间，超过该时间没心跳，Session就会被断开
3000,//连接zk时的超时时间
retryPolicy
);
client.start();
System.out.println("已经启动Curator客户端");
}
}
public class CuratorFrameworkFactory {
//创建CuratorFramework实例使用了构造器模式
public static CuratorFramework newClient(String connectString, int sessionTimeoutMs, int connectionTimeoutMs, RetryPolicy retryPolicy) {
return builder().
connectString(connectString).
sessionTimeoutMs(sessionTimeoutMs).
connectionTimeoutMs(connectionTimeoutMs).
retryPolicy(retryPolicy).
build();
}
...
public static Builder builder() {
return new Builder();
}
public static class Builder {
...
private EnsembleProvider ensembleProvider;
private int sessionTimeoutMs = DEFAULT_SESSION_TIMEOUT_MS;
private int connectionTimeoutMs = DEFAULT_CONNECTION_TIMEOUT_MS;
private RetryPolicy retryPolicy;
...
public Builder connectString(String connectString) {
ensembleProvider = new FixedEnsembleProvider(connectString);
return this;
}
public Builder sessionTimeoutMs(int sessionTimeoutMs) {
this.sessionTimeoutMs = sessionTimeoutMs;
return this;
}
public Builder connectionTimeoutMs(int connectionTimeoutMs) {
this.connectionTimeoutMs = connectionTimeoutMs;
return this;
}
public Builder retryPolicy(RetryPolicy retryPolicy) {
this.retryPolicy = retryPolicy;
return this;
}
...
public CuratorFramework build() {
return new CuratorFrameworkImpl(this);
}
}
...
}
public class CuratorFrameworkImpl implements CuratorFramework {
...
public CuratorFrameworkImpl(CuratorFrameworkFactory.Builder builder) {
ZookeeperFactory localZookeeperFactory = makeZookeeperFactory(builder.getZookeeperFactory());
this.client = new CuratorZookeeperClient(
localZookeeperFactory,
builder.getEnsembleProvider(),
builder.getSessionTimeoutMs(),
builder.getConnectionTimeoutMs(),
builder.getWaitForShutdownTimeoutMs(),
new Watcher() {//这里注册了一个zk的watcher
@Override
public void process(WatchedEvent watchedEvent) {
CuratorEvent event = new CuratorEventImpl(CuratorFrameworkImpl.this, CuratorEventType.WATCHED, watchedEvent.getState().getIntValue(), unfixForNamespace(watchedEvent.getPath()), null, null, null, null, null, watchedEvent, null, null);
processEvent(event);
}
},
builder.getRetryPolicy(),
builder.canBeReadOnly(),
builder.getConnectionHandlingPolicy()
);
...
}
...
}(2)创建CuratorFramework实例会初始化CuratorZooKeeperClient实例
CuratorFramework实例代表了一个zk客户端，CuratorFramework初始化时会初始化一个CuratorZooKeeperClient实例。
CuratorZooKeeperClient是Curator封装ZooKeeper的客户端。
初始化CuratorZooKeeperClient时会传入一个Watcher监听器。
所以CuratorFrameworkFactory的newClient()方法的主要工作是：初始化CuratorFramework -> 初始化CuratorZooKeeperClient -> 初始化ZookeeperFactory + 注册一个Watcher。
客户端发起与zk的连接，以及注册Watcher监听器，则是由CuratorFramework的start()方法触发的。
9.Curator启动时是如何跟zk建立连接的
ConnectionStateManager的start()方法会启动一个线程处理eventQueue。eventQueue里存放了与zk的网络连接变化事件，eventQueue收到这种事件便会通知ConnectionStateListener。
CuratorZookeeperClient的start()方法会初始化好原生zk客户端，和zk服务器建立一个TCP长连接，而且还会注册一个ConnectionState类型的Watcher监听器，以便能收到zk服务端发送的通知事件。
public class CuratorFrameworkImpl implements CuratorFramework {
private final CuratorZookeeperClient client;
private final ConnectionStateManager connectionStateManager;
private volatile ExecutorService executorService;
...
public CuratorFrameworkImpl(CuratorFrameworkFactory.Builder builder) {
...
this.client = new CuratorZookeeperClient(...);
connectionStateManager = new ConnectionStateManager(this, builder.getThreadFactory(),
builder.getSessionTimeoutMs(),
builder.getConnectionHandlingPolicy().getSimulatedSessionExpirationPercent(),
builder.getConnectionStateListenerDecorator()
);
...
}
...
@Override
public void start() {
log.info("Starting");
if (!state.compareAndSet(CuratorFrameworkState.LATENT, CuratorFrameworkState.STARTED)) {
throw new IllegalStateException("Cannot be started more than once");
}
...
//1.启动一个线程监听和zk网络连接的变化事件
connectionStateManager.start();
//2.添加一个监听器监听和zk网络连接的变化
final ConnectionStateListener listener = new ConnectionStateListener() {
@Override
public void stateChanged(CuratorFramework client, ConnectionState newState) {
if (ConnectionState.CONNECTED == newState || ConnectionState.RECONNECTED == newState) {
logAsErrorConnectionErrors.set(true);
}
}
@Override
public boolean doNotDecorate() {
return true;
}
};
this.getConnectionStateListenable().addListener(listener);
//3.创建原生zk客户端
client.start();
//4.创建一个线程池，执行后台的操作
executorService = Executors.newSingleThreadScheduledExecutor(threadFactory);
executorService.submit(new Callable<Object>() {
@Override
public Object call() throws Exception {
backgroundOperationsLoop();
return null;
}
});
if (ensembleTracker != null) {
ensembleTracker.start();
}
log.info(schemaSet.toDocumentation());
}
...
}
public class ConnectionStateManager implements Closeable {
private final ExecutorService service;
private final BlockingQueue<ConnectionState> eventQueue = new ArrayBlockingQueue<ConnectionState>(QUEUE_SIZE);
...
public ConnectionStateManager(CuratorFramework client, ThreadFactory threadFactory, int sessionTimeoutMs, int sessionExpirationPercent, ConnectionStateListenerDecorator connectionStateListenerDecorator) {
...
service = Executors.newSingleThreadExecutor(threadFactory);
...
}
...
public void start() {
Preconditions.checkState(state.compareAndSet(State.LATENT, State.STARTED), "Cannot be started more than once");
//启动一个线程
service.submit(
new Callable<Object>() {
@Override
public Object call() throws Exception {
processEvents();
return null;
}
}
);
}
private void processEvents() {
while (state.get() == State.STARTED) {
int useSessionTimeoutMs = getUseSessionTimeoutMs();
long elapsedMs = startOfSuspendedEpoch == 0 ? useSessionTimeoutMs / 2 : System.currentTimeMillis() - startOfSuspendedEpoch;
long pollMaxMs = useSessionTimeoutMs - elapsedMs;
final ConnectionState newState = eventQueue.poll(pollMaxMs, TimeUnit.MILLISECONDS);
if (newState != null) {
if (listeners.size() == 0) {
log.warn("There are no ConnectionStateListeners registered.");
}
listeners.forEach(listener -> listener.stateChanged(client, newState));
} else if (sessionExpirationPercent > 0) {
synchronized(this) {
checkSessionExpiration();
}
}
}
}
...
}
public class CuratorZookeeperClient implements Closeable {
private final ConnectionState state;
...
public CuratorZookeeperClient(ZookeeperFactory zookeeperFactory, EnsembleProvider ensembleProvider,
int sessionTimeoutMs, int connectionTimeoutMs, int waitForShutdownTimeoutMs, Watcher watcher,
RetryPolicy retryPolicy, boolean canBeReadOnly, ConnectionHandlingPolicy connectionHandlingPolicy) {
...
state = new ConnectionState(zookeeperFactory, ensembleProvider, sessionTimeoutMs, connectionTimeoutMs, watcher, tracer, canBeReadOnly, connectionHandlingPolicy);
...
}
...
public void start() throws Exception {
log.debug("Starting");
if (!started.compareAndSet(false, true)) {
throw new IllegalStateException("Already started");
}
state.start();
}
...
}
class ConnectionState implements Watcher, Closeable {
private final HandleHolder zooKeeper;
ConnectionState(ZookeeperFactory zookeeperFactory, EnsembleProvider ensembleProvider,
int sessionTimeoutMs, int connectionTimeoutMs, Watcher parentWatcher,
AtomicReference<TracerDriver> tracer, boolean canBeReadOnly, ConnectionHandlingPolicy connectionHandlingPolicy) {
this.ensembleProvider = ensembleProvider;
this.sessionTimeoutMs = sessionTimeoutMs;
this.connectionTimeoutMs = connectionTimeoutMs;
this.tracer = tracer;
this.connectionHandlingPolicy = connectionHandlingPolicy;
if (parentWatcher != null) {
parentWatchers.offer(parentWatcher);
}
//把自己作为Watcher注册给HandleHolder
zooKeeper = new HandleHolder(zookeeperFactory, this, ensembleProvider, sessionTimeoutMs, canBeReadOnly);
}
...
void start() throws Exception {
log.debug("Starting");
ensembleProvider.start();
reset();
}
synchronized void reset() throws Exception {
log.debug("reset");
instanceIndex.incrementAndGet();
isConnected.set(false);
connectionStartMs = System.currentTimeMillis();
//创建客户端与zk的连接
zooKeeper.closeAndReset();
zooKeeper.getZooKeeper();//initiate connection
}
...
}
class HandleHolder {
private final ZookeeperFactory zookeeperFactory;
private final Watcher watcher;
private final EnsembleProvider ensembleProvider;
private final int sessionTimeout;
private final boolean canBeReadOnly;
private volatile Helper helper;
...
HandleHolder(ZookeeperFactory zookeeperFactory, Watcher watcher, EnsembleProvider ensembleProvider, int sessionTimeout, boolean canBeReadOnly) {
this.zookeeperFactory = zookeeperFactory;
this.watcher = watcher;
this.ensembleProvider = ensembleProvider;
this.sessionTimeout = sessionTimeout;
this.canBeReadOnly = canBeReadOnly;
}
private interface Helper {
ZooKeeper getZooKeeper() throws Exception;
String getConnectionString();
int getNegotiatedSessionTimeoutMs();
}
ZooKeeper getZooKeeper() throws Exception {
return (helper != null) ? helper.getZooKeeper() : null;
}
void closeAndReset() throws Exception {
internalClose(0);
helper = new Helper() {
private volatile ZooKeeper zooKeeperHandle = null;
private volatile String connectionString = null;
@Override
public ZooKeeper getZooKeeper() throws Exception {
synchronized(this) {
if (zooKeeperHandle == null) {
connectionString = ensembleProvider.getConnectionString();
//创建和zk的连接，初始化变量zooKeeperHandle
zooKeeperHandle = zookeeperFactory.newZooKeeper(connectionString, sessionTimeout, watcher, canBeReadOnly);
}
...
return zooKeeperHandle;
}
}
@Override
public String getConnectionString() {
return connectionString;
}
@Override
public int getNegotiatedSessionTimeoutMs() {
return (zooKeeperHandle != null) ? zooKeeperHandle.getSessionTimeout() : 0;
}
};
}
...
}
//创建客户端与zk的连接
public class DefaultZookeeperFactory implements ZookeeperFactory {
@Override
public ZooKeeper newZooKeeper(String connectString, int sessionTimeout, Watcher watcher, boolean canBeReadOnly) throws Exception {
return new ZooKeeper(connectString, sessionTimeout, watcher, canBeReadOnly);
}
}10.基于Curator进行增删改查节点的源码分析
(1)基于Curator创建znode节点
(2)基于Curator查询znode节点
(3)基于Curator修改znode节点
(4)基于Curator删除znode节点
Curator的CURD操作，底层都是通过调用zk原生的API来完成的。
(1)基于Curator创建znode节点
创建节点也使用了构造器模式：首先通过CuratorFramework的create()方法创建一个CreateBuilder实例，然后通过CreateBuilder的withMode()等方法设置CreateBuilder的变量，最后通过CreateBuilder的forPath()方法 + 重试调用来创建znode节点。
创建节点时会调用CuratorFramework的getZooKeeper()方法获取zk客户端实例，之后就是通过原生zk客户端的API去创建节点了。
public class Demo {
public static void main(String[] args) throws Exception {
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
CuratorFramework client = CuratorFrameworkFactory.newClient(
"127.0.0.1:2181",//zk的地址
5000,//客户端和zk的心跳超时时间，超过该时间没心跳，Session就会被断开
3000,//连接zk时的超时时间
retryPolicy
);
client.start();
System.out.println("已经启动Curator客户端");
//创建节点
client.create().creatingParentsIfNeeded().withMode(CreateMode.PERSISTENT).forPath("/my/path", "100".getBytes());
}
}
public class CuratorFrameworkImpl implements CuratorFramework {
...
@Override
public CreateBuilder create() {
checkState();
return new CreateBuilderImpl(this);
}
...
}
public class CreateBuilderImpl implements CreateBuilder, CreateBuilder2, BackgroundOperation<PathAndBytes>, ErrorListenerPathAndBytesable<String> {
private final CuratorFrameworkImpl client;
private CreateMode createMode;
private Backgrounding backgrounding;
private boolean createParentsIfNeeded;
...
CreateBuilderImpl(CuratorFrameworkImpl client) {
this.client = client;
createMode = CreateMode.PERSISTENT;
backgrounding = new Backgrounding();
acling = new ACLing(client.getAclProvider());
createParentsIfNeeded = false;
createParentsAsContainers = false;
compress = false;
setDataIfExists = false;
storingStat = null;
ttl = -1;
}
@Override
public String forPath(final String givenPath, byte[] data) throws Exception {
if (compress) {
data = client.getCompressionProvider().compress(givenPath, data);
}
final String adjustedPath = adjustPath(client.fixForNamespace(givenPath, createMode.isSequential()));
List<ACL> aclList = acling.getAclList(adjustedPath);
client.getSchemaSet().getSchema(givenPath).validateCreate(createMode, givenPath, data, aclList);
String returnPath = null;
if (backgrounding.inBackground()) {
pathInBackground(adjustedPath, data, givenPath);
} else {
//创建节点
String path = protectedPathInForeground(adjustedPath, data, aclList);
returnPath = client.unfixForNamespace(path);
}
return returnPath;
}
private String protectedPathInForeground(String adjustedPath, byte[] data, List<ACL> aclList) throws Exception {
return pathInForeground(adjustedPath, data, aclList);
}
private String pathInForeground(final String path, final byte[] data, final List<ACL> aclList) throws Exception {
OperationTrace trace = client.getZookeeperClient().startAdvancedTracer("CreateBuilderImpl-Foreground");
final AtomicBoolean firstTime = new AtomicBoolean(true);
//重试调用
String returnPath = RetryLoop.callWithRetry(
client.getZookeeperClient(),
new Callable<String>() {
@Override
public String call() throws Exception {
boolean localFirstTime = firstTime.getAndSet(false) && !debugForceFindProtectedNode;
protectedMode.checkSetSessionId(client, createMode);
String createdPath = null;
if (!localFirstTime && protectedMode.doProtected()) {
debugForceFindProtectedNode = false;
createdPath = findProtectedNodeInForeground(path);
}
if (createdPath == null) {
//在创建znode节点的时候，首先会调用CuratorFramework.getZooKeeper()获取zk客户端实例
//之后就是通过原生zk客户端的API去创建节点了
try {
if (client.isZk34CompatibilityMode()) {
createdPath = client.getZooKeeper().create(path, data, aclList, createMode);
} else {
createdPath = client.getZooKeeper().create(path, data, aclList, createMode, storingStat, ttl);
}
} catch (KeeperException.NoNodeException e) {
if (createParentsIfNeeded) {
//这就是级联创建节点的实现
ZKPaths.mkdirs(client.getZooKeeper(), path, false, acling.getACLProviderForParents(), createParentsAsContainers);
if (client.isZk34CompatibilityMode()) {
createdPath = client.getZooKeeper().create(path, data, acling.getAclList(path), createMode);
} else {
createdPath = client.getZooKeeper().create(path, data, acling.getAclList(path), createMode, storingStat, ttl);
}
} else {
throw e;
}
} catch (KeeperException.NodeExistsException e) {
if (setDataIfExists) {
Stat setStat = client.getZooKeeper().setData(path, data, setDataIfExistsVersion);
if (storingStat != null) {
DataTree.copyStat(setStat, storingStat);
}
createdPath = path;
} else {
throw e;
}
}
}
if (failNextCreateForTesting) {
failNextCreateForTesting = false;
throw new KeeperException.ConnectionLossException();
}
return createdPath;
}
}
);
trace.setRequestBytesLength(data).setPath(path).commit();
return returnPath;
}
...
}
public class CuratorFrameworkImpl implements CuratorFramework {
private final CuratorZookeeperClient client;
public CuratorFrameworkImpl(CuratorFrameworkFactory.Builder builder) {
ZookeeperFactory localZookeeperFactory = makeZookeeperFactory(builder.getZookeeperFactory());
this.client = new CuratorZookeeperClient(
localZookeeperFactory,
builder.getEnsembleProvider(),
builder.getSessionTimeoutMs(),
builder.getConnectionTimeoutMs(),
builder.getWaitForShutdownTimeoutMs(),
new Watcher() {
...
},
builder.getRetryPolicy(),
builder.canBeReadOnly(),
builder.getConnectionHandlingPolicy()
);
...
}
...
ZooKeeper getZooKeeper() throws Exception {
return client.getZooKeeper();
}
...
}
public class CuratorZookeeperClient implements Closeable {
private final ConnectionState state;
...
public ZooKeeper getZooKeeper() throws Exception {
Preconditions.checkState(started.get(), "Client is not started");
return state.getZooKeeper();
}
...
}
class ConnectionState implements Watcher, Closeable {
private final HandleHolder zooKeeper;
...
ZooKeeper getZooKeeper() throws Exception {
if (SessionFailRetryLoop.sessionForThreadHasFailed()) {
throw new SessionFailRetryLoop.SessionFailedException();
}
Exception exception = backgroundExceptions.poll();
if (exception != null) {
new EventTrace("background-exceptions", tracer.get()).commit();
throw exception;
}
boolean localIsConnected = isConnected.get();
if (!localIsConnected) {
checkTimeouts();
}
//通过HandleHolder获取ZooKeeper实例
return zooKeeper.getZooKeeper();
}
...
}(2)基于Curator查询znode节点
查询节点也使用了构造器模式：首先通过CuratorFramework的getData()方法创建一个GetDataBuilder实例，然后通过GetDataBuilder的forPath()方法 + 重试调用来查询znode节点。
public class Demo {
public static void main(String[] args) throws Exception {
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
CuratorFramework client = CuratorFrameworkFactory.newClient(
"127.0.0.1:2181",//zk的地址
5000,//客户端和zk的心跳超时时间，超过该时间没心跳，Session就会被断开
3000,//连接zk时的超时时间
retryPolicy
);
client.start();
System.out.println("已经启动Curator客户端");
//查询节点
byte[] dataBytes = client.getData().forPath("/my/path");
System.out.println(new String(dataBytes));
//查询子节点
List<String> children = client.getChildren().forPath("/my");
System.out.println(children);
}
}
public class CuratorFrameworkImpl implements CuratorFramework {
...
@Override
public GetDataBuilder getData() {
checkState();
return new GetDataBuilderImpl(this);
}
@Override
public GetChildrenBuilder getChildren() {
checkState();
return new GetChildrenBuilderImpl(this);
}
...
}
public class GetDataBuilderImpl implements GetDataBuilder, BackgroundOperation<String>, ErrorListenerPathable<byte[]> {
private final CuratorFrameworkImpl client;
...
@Override
public byte[] forPath(String path) throws Exception {
client.getSchemaSet().getSchema(path).validateWatch(path, watching.isWatched() || watching.hasWatcher());
path = client.fixForNamespace(path);
byte[] responseData = null;
if (backgrounding.inBackground()) {
client.processBackgroundOperation(new OperationAndData<String>(this, path, backgrounding.getCallback(), null, backgrounding.getContext(), watching), null);
} else {
//查询节点
responseData = pathInForeground(path);
}
return responseData;
}
private byte[] pathInForeground(final String path) throws Exception {
OperationTrace trace = client.getZookeeperClient().startAdvancedTracer("GetDataBuilderImpl-Foreground");
//重试调用
byte[] responseData = RetryLoop.callWithRetry(
client.getZookeeperClient(),
new Callable<byte[]>() {
@Override
public byte[] call() throws Exception {
byte[] responseData;
//通过CuratorFramework获取原生zk客户端实例，然后调用其getData()获取节点
if (watching.isWatched()) {
responseData = client.getZooKeeper().getData(path, true, responseStat);
} else {
responseData = client.getZooKeeper().getData(path, watching.getWatcher(path), responseStat);
watching.commitWatcher(KeeperException.NoNodeException.Code.OK.intValue(), false);
}
return responseData;
}
}
);
trace.setResponseBytesLength(responseData).setPath(path).setWithWatcher(watching.hasWatcher()).setStat(responseStat).commit();
return decompress ? client.getCompressionProvider().decompress(path, responseData) : responseData;
}
...
}(3)基于Curator修改znode节点
修改节点也使用了构造器模式：首先通过CuratorFramework的setData()方法创建一个SetDataBuilder实例，然后通过SetDataBuilder的forPath()方法 + 重试调用来修改znode节点。
public class Demo {
public static void main(String[] args) throws Exception {
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
CuratorFramework client = CuratorFrameworkFactory.newClient(
"127.0.0.1:2181",//zk的地址
5000,//客户端和zk的心跳超时时间，超过该时间没心跳，Session就会被断开
3000,//连接zk时的超时时间
retryPolicy
);
client.start();
System.out.println("已经启动Curator客户端");
//修改节点
client.setData().forPath("/my/path", "110".getBytes());
byte[] dataBytes = client.getData().forPath("/my/path");
System.out.println(new String(dataBytes));
}
}
public class CuratorFrameworkImpl implements CuratorFramework {
...
@Override
public SetDataBuilder setData() {
checkState();
return new SetDataBuilderImpl(this);
}
...
}
public class SetDataBuilderImpl implements SetDataBuilder, BackgroundOperation<PathAndBytes>, ErrorListenerPathAndBytesable<Stat> {
private final CuratorFrameworkImpl client;
...
@Override
public Stat forPath(String path, byte[] data) throws Exception {
client.getSchemaSet().getSchema(path).validateGeneral(path, data, null);
if (compress) {
data = client.getCompressionProvider().compress(path, data);
}
path = client.fixForNamespace(path);
Stat resultStat = null;
if (backgrounding.inBackground()) {
client.processBackgroundOperation(new OperationAndData<>(this, new PathAndBytes(path, data), backgrounding.getCallback(), null, backgrounding.getContext(), null), null);
} else {
//修改节点
resultStat = pathInForeground(path, data);
}
return resultStat;
}
private Stat pathInForeground(final String path, final byte[] data) throws Exception {
OperationTrace trace = client.getZookeeperClient().startAdvancedTracer("SetDataBuilderImpl-Foreground");
//重试调用
Stat resultStat = RetryLoop.callWithRetry(
client.getZookeeperClient(),
new Callable<Stat>() {
@Override
public Stat call() throws Exception {
//通过CuratorFramework获取原生zk客户端实例，然后调用其setData()修改节点
return client.getZooKeeper().setData(path, data, version);
}
}
);
trace.setRequestBytesLength(data).setPath(path).setStat(resultStat).commit();
return resultStat;
}
...
}(4)基于Curator删除znode节点
删除节点也使用了构造器模式：首先通过CuratorFramework的delete()方法创建一个DeleteBuilder实例，然后通过DeleteBuilder的forPath()方法 + 重试调用来删除znode节点。
public class Demo {
public static void main(String[] args) throws Exception {
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
CuratorFramework client = CuratorFrameworkFactory.newClient(
"127.0.0.1:2181",//zk的地址
5000,//客户端和zk的心跳超时时间，超过该时间没心跳，Session就会被断开
3000,//连接zk时的超时时间
retryPolicy
);
client.start();
System.out.println("已经启动Curator客户端");
//删除节点
client.delete().forPath("/my/path");
}
}
public class CuratorFrameworkImpl implements CuratorFramework {
...
@Override
public DeleteBuilder delete() {
checkState();
return new DeleteBuilderImpl(this);
}
...
}
public class DeleteBuilderImpl implements DeleteBuilder, BackgroundOperation<String>, ErrorListenerPathable<Void> {
private final CuratorFrameworkImpl client;
...
@Override
public Void forPath(String path) throws Exception {
client.getSchemaSet().getSchema(path).validateDelete(path);
final String unfixedPath = path;
path = client.fixForNamespace(path);
if (backgrounding.inBackground()) {
OperationAndData.ErrorCallback<String> errorCallback = null;
if (guaranteed) {
errorCallback = new OperationAndData.ErrorCallback<String>() {
@Override
public void retriesExhausted(OperationAndData<String> operationAndData) {
client.getFailedDeleteManager().addFailedOperation(unfixedPath);
}
};
}
client.processBackgroundOperation(new OperationAndData<String>(this, path, backgrounding.getCallback(), errorCallback, backgrounding.getContext(), null), null);
} else {
//删除节点
pathInForeground(path, unfixedPath);
}
return null;
}
private void pathInForeground(final String path, String unfixedPath) throws Exception {
OperationTrace trace = client.getZookeeperClient().startAdvancedTracer("DeleteBuilderImpl-Foreground");
//重试调用
RetryLoop.callWithRetry(
client.getZookeeperClient(),
new Callable<Void>() {
@Override
public Void call() throws Exception {
try {
//通过CuratorFramework获取原生zk客户端实例，然后调用其delete()删除节点
client.getZooKeeper().delete(path, version);
} catch (KeeperException.NoNodeException e) {
if (!quietly) {
throw e;
}
} catch (KeeperException.NotEmptyException e) {
if (deletingChildrenIfNeeded) {
ZKPaths.deleteChildren(client.getZooKeeper(), path, true);
} else {
throw e;
}
}
return null;
}
}
);
trace.setPath(path).commit();
}
}
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