【Java】已解决：org.apache.zookeeper.KeeperException.SessionExpiredException

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发布于 2025-05-24 10:25:33

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已解决：org.apache.zookeeper.KeeperException.SessionExpiredException

一、分析问题背景

在使用Apache ZooKeeper时，开发者可能会遇到org.apache.zookeeper.KeeperException.SessionExpiredException的报错。ZooKeeper是一个用于分布式系统的协调服务，SessionExpiredException通常出现在客户端与ZooKeeper服务器之间的会话过期时。这种情况通常发生在网络不稳定、客户端长时间没有发送请求或服务器端的问题导致会话超时。

场景：在一个分布式系统中，使用ZooKeeper来进行节点注册和管理。客户端在执行操作时，由于某些原因与ZooKeeper服务器的会话过期，从而抛出SessionExpiredException。

示例代码片段：

import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.KeeperException;

public class ZookeeperClient {

    private static final String CONNECT_STRING = "localhost:2181";
    private static final int SESSION_TIMEOUT = 5000;
    private ZooKeeper zooKeeper;

    public ZookeeperClient() throws Exception {
        zooKeeper = new ZooKeeper(CONNECT_STRING, SESSION_TIMEOUT, event -> {
            if (event.getState() == Watcher.Event.KeeperState.Expired) {
                System.out.println("Session expired");
            }
        });
    }

    public void createNode(String path, byte[] data) throws KeeperException, InterruptedException {
        zooKeeper.create(path, data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
    }
}

当客户端长时间不发送请求或网络中断时，可能会看到如下异常：

Exception in thread "main" org.apache.zookeeper.KeeperException$SessionExpiredException: KeeperErrorCode = Session expired

二、可能出错的原因

导致org.apache.zookeeper.KeeperException.SessionExpiredException报错的原因主要有以下几点：

网络不稳定：客户端与ZooKeeper服务器之间的网络连接不稳定，导致会话超时。
客户端长时间不活动：客户端长时间没有与ZooKeeper服务器进行通信，导致会话过期。
服务器端问题：ZooKeeper服务器由于负载过高或其他原因导致无法维持会话。

三、错误代码示例

以下是一个可能导致该报错的代码示例，并解释其错误之处：

import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.KeeperException;

public class ZookeeperClient {

    private static final String CONNECT_STRING = "localhost:2181";
    private static final int SESSION_TIMEOUT = 5000;
    private ZooKeeper zooKeeper;

    public ZookeeperClient() throws Exception {
        // 初始化ZooKeeper客户端
        zooKeeper = new ZooKeeper(CONNECT_STRING, SESSION_TIMEOUT, event -> {
            if (event.getState() == Watcher.Event.KeeperState.Expired) {
                System.out.println("Session expired");
            }
        });
    }

    public void createNode(String path, byte[] data) throws KeeperException, InterruptedException {
        // 尝试创建节点，但没有处理会话过期的情况
        zooKeeper.create(path, data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
    }
}

错误分析：

没有处理会话过期：在会话过期后，客户端没有重新连接ZooKeeper服务器，导致后续操作失败。

四、正确代码示例

为了解决该报错问题，我们需要在会话过期后重新连接ZooKeeper服务器，并重新执行操作。以下是正确的代码示例：

import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.CreateMode;

public class ZookeeperClient {

    private static final String CONNECT_STRING = "localhost:2181";
    private static final int SESSION_TIMEOUT = 5000;
    private ZooKeeper zooKeeper;

    public ZookeeperClient() throws Exception {
        connect();
    }

    private void connect() throws Exception {
        zooKeeper = new ZooKeeper(CONNECT_STRING, SESSION_TIMEOUT, event -> {
            if (event.getState() == Watcher.Event.KeeperState.Expired) {
                System.out.println("Session expired, reconnecting...");
                try {
                    connect();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public void createNode(String path, byte[] data) throws KeeperException, InterruptedException {
        try {
            zooKeeper.create(path, data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
        } catch (KeeperException.SessionExpiredException e) {
            System.out.println("Session expired, reconnecting and retrying...");
            connect();
            createNode(path, data);
        }
    }
}

通过上述代码，我们在会话过期后重新连接ZooKeeper服务器，并重新执行操作，避免了SessionExpiredException异常。