Java操作Zookeeper原理及过程详解

<dependency>
  <groupId>org.apache.zookeeper</groupId>
  <artifactId>zookeeper</artifactId>
  <version>3.6.0</version>
</dependency>

<!-- Logger（log4j2） -->
<dependency>
  <groupId>org.apache.logging.log4j</groupId>
  <artifactId>log4j-core</artifactId>
  <version>2.11.2</version>
</dependency>
<!-- Log4j 1.x API Bridge -->
<dependency>
  <groupId>org.apache.logging.log4j</groupId>
  <artifactId>log4j-1.2-api</artifactId>
  <version>2.11.2</version>
</dependency>
<!-- SLF4J Bridge -->
<dependency>
  <groupId>org.apache.logging.log4j</groupId>
  <artifactId>log4j-slf4j-impl</artifactId>
  <version>2.11.2</version>
</dependency>

<dependency>
  <groupId>org.apache.zookeeper</groupId>
  <artifactId>zookeeper</artifactId>
  <version>3.6.0</version>
  <exclusions>
    <exclusion>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-log4j12</artifactId>
    </exclusion>
  </exclusions>
</dependency>

package com.zhi.test;

import java.util.List;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.Stat;
import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.MethodOrderer;
import org.junit.jupiter.api.Order;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestInstance;
import org.junit.jupiter.api.TestInstance.Lifecycle;
import org.junit.jupiter.api.TestMethodOrder;

/**
 * Zookeeper操作测试
 * 
 * @author 张远志
 * @since 2020年5月3日14:31:28
 *
 */
@TestInstance(Lifecycle.PER_CLASS)
@TestMethodOrder(MethodOrderer.OrderAnnotation.class)
public class ZookeeperTest {
  private final Logger logger = LogManager.getLogger(this.getClass());
  private ZooKeeper zooKeeper;
  private final String path = "/test";

  @BeforeAll
  public void init() throws Exception {
    zooKeeper = new ZooKeeper("192.168.59.131:2181", 60000, new Watcher() {
      public void process(WatchedEvent event) {
        logger.info("事件类型：{}，路径：{}", event.getType(), event.getPath());
      }
    });
  }

  /**
   * 添加数据，当路径已经存在时会报错，初始版本号为0。第三个参数是权限控制。 <br>
   * 第四个参数，CreateMode：
   * <li>PERSISTENT：持久化保存
   * <li>PERSISTENT_SEQUENTIAL：持久化保存，并且路径附加一个自动增长的序号
   * <li>EPHEMERAL：临时数据，客户端断开连接时自动删除数据（dubbo就是采用这种机制）
   * <li>EPHEMERAL_SEQUENTIAL：客户端断开连接时自动删除数据，并且路径会附加一个自动增长的序号
   * <li>CONTAINER：
   * <li>PERSISTENT_WITH_TTL：客户端断开连接时自动删除数据，当节点在指定时间没有被修改且没有子目录时，数据会被删除
   * <li>PERSISTENT_SEQUENTIAL_WITH_TTL：客户端断开连接时自动删除数据，路径会附加一个自动增长的序号，且当节点在指定时间没有被修改且没有子目录时，数据会被删除
   */
  @Order(1)
  @Test
  public void create() {
    try {
      String back = zooKeeper.create(path, "这是一个测试".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
      logger.info("添加一条数据成功，实际路径：{}", back);
    } catch (Exception e) {
      logger.error("调用create出错", e);
    }
  }

  /**
   * 判断路径是否存在，不存在时返回null
   */
  @Order(2)
  @Test
  public void exists() {
    try {
      Stat stat = zooKeeper.exists(path, false);
      logger.info("路径为{}的节点{}存在", path, stat == null ? "不" : "");
    } catch (Exception e) {
      logger.error("调用exists出错", e);
    }
  }

  /**
   * 查询数据，路径不存在时会报错
   */
  @Order(3)
  @Test
  public void find() {
    try {
      byte[] bits = zooKeeper.getData(path, false, new Stat()); // 路径不存在时会报错
      String data = new String(bits);
      logger.info("路径{}查询到数据：{}", path, data);
    } catch (Exception e) {
      logger.error("调用getData出错", e);
    }
  }

  /**
   * 获取子目录，结果为空时返回一个长度为0的ArrayList
   */
  @Order(3)
  @Test
  public void children() {
    try {
      List<String> list = zooKeeper.getChildren(path, false);
      logger.info("路径{}的子目录有：{}", path, String.join("、", list.toArray(new String[0])));
    } catch (Exception e) {
      logger.error("调用getChildren出错", e);
    }
  }

  /**
   * 修改数据，路径不存在时会报错，版本号与存储中不一致时也报错
   */
  @Order(4)
  @Test
  public void udpate() {
    try {
      Stat stat = zooKeeper.exists(path, false);
      if (stat != null) {
        stat = zooKeeper.setData(path, "这是一个修改测试".getBytes(), stat.getVersion()); // 版本号为-1时不做版本校验
        logger.info("数据修改成功，原版本号：{}，新版本号：{}", stat.getAversion(), stat.getVersion());
      }
    } catch (Exception e) {
      logger.error("调用setData出错", e);
    }
  }

  /**
   * 删除节点，路径不存在时报错，版本号不一致时也会报错
   */
  @Order(5)
  @Test
  public void delete() {
    try {
      zooKeeper.delete(path, -1); // -1表示不做版本校验
      logger.info("根据path删除数据成功");
    } catch (Exception e) {
      logger.error("调用delete出错", e);
    }
  }

  @AfterAll
  public void destory() throws Exception {
    if (zooKeeper != null) {
      zooKeeper.close();
    }
  }
}