Generate Distributed IDs with Zookeeper and Spring Boot

Zookeeper version: 3.6.2

Since Zookeeper 3.6, watches can be recursive, unlike earlier versions where a watch was removed after a change.

Create a sequential node via command line:

create /distributed/key/ids   # create a persistent node
Created /distributed/key/ids

create -s /distributed/key/ids/  # create sequential node under ids
Created /distributed/key/ids/0000000000

# Repeating the command continues the sequence even after deletion.

Next, implement with Java.

Environment: Spring Boot 2.2.10.RELEASE, JDK 1.8, Zookeeper 3.6.2

pom.xml

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
  </dependency>
  <dependency>
    <groupId>org.apache.zookeeper</groupId>
    <artifactId>zookeeper</artifactId>
    <version>3.6.2</version>
  </dependency>
</dependencies>

application.yml configuration

server:
  port: 9881
---
zk:
  connectString: localhost:2181,localhost:2182,localhost:2183
  timeout: 3000

Zookeeper connection configuration

@Configuration
public class ZKConfig {
    private static Logger logger = LoggerFactory.getLogger(ZKConfig.class);

    @Value("${zk.connectString}")
    private String connectString;

    @Value("${zk.timeout}")
    private Integer timeout;

    @Bean
    public ZooKeeper zookeeper() {
        ZooKeeper zookeeper = null;
        try {
            CountDownLatch cdl = new CountDownLatch(1);
            logger.info("zk准备连接: {}", connectString);
            zookeeper = new ZooKeeper(connectString, timeout, event -> {
                if (event.getState() == Event.KeeperState.SyncConnected) {
                    logger.info("zk服务器连接成功");
                    cdl.countDown();
                }
            });
            cdl.await();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return zookeeper;
    }
}

Implementation

public interface DistributedIdModel {
    Long getId(String key);
}

@Service
public class DistributedIdZK implements DistributedIdModel {
    private static final String PATH = "/distributed/key/ids/";
    @Resource
    private ZooKeeper zk;

    @Override
    public Long getId(String key) {
        try {
            String res = zk.create(PATH, null, Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT_SEQUENTIAL);
            zk.delete(res, 0);
            if (res != null && res.length() > PATH.length()) {
                return Long.valueOf(res.substring(PATH.length()));
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

zk.create returns the full path; the node is then deleted to avoid accumulation.

Test

@SpringBootTest
@RunWith(SpringRunner.class)
public class SpringDistributedIdApplicationTests {
    @Resource
    private DistributedIdModel distId;
    private final int COUNT = 100;
    private CountDownLatch cdl = new CountDownLatch(COUNT);
    private CountDownLatch state = new CountDownLatch(COUNT);
    private Thread[] threads = new Thread[COUNT];

    @Before
    public void before() {
        for (int i = 0; i < COUNT; i++) {
            threads[i] = new Thread(() -> {
                cdl.countDown();
                System.out.println(Thread.currentThread().getName() + ", 到达");
                try {
                    cdl.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                Long id = distId.getId(null);
                System.out.println(Thread.currentThread().getName() + ", 获取到ID = " + id);
                state.countDown();
            }, "线程-" + i);
        }
    }

    @Test
    public void testGetRedisId() {
        for (int i = 0; i < COUNT; i++) {
            threads[i].start();
        }
        try {
            state.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

This simulates 100 concurrent threads obtaining IDs.

Done!