java synchronize如何处理分布式锁-乐工具技术知识

在Java中，处理分布式锁通常需要使用一些额外的工具和技术，因为Java内置的synchronized关键字只能在单个JVM实例中使用。在分布式系统中，你需要确保多个节点之间的同步和互斥访问共享资源。以下是几种常见的处理分布式锁的方法：

1. 使用数据库

通过在数据库中创建一个锁表，可以使用SQL语句来实现分布式锁。例如：

CREATE TABLE distributed_lock (
    lock_id VARCHAR(255) PRIMARY KEY,
    owner VARCHAR(255),
    acquire_time TIMESTAMP,
    release_time TIMESTAMP,
    UNIQUE (lock_id)
);

然后，你可以使用JDBC或ORM框架（如Hibernate）来执行锁的获取和释放操作。

public boolean tryLock(String lockId, String owner) {
    String sql = "SELECT * FROM distributed_lock WHERE lock_id = ? AND owner = ? AND release_time IS NULL";
    try (Connection conn = dataSource.getConnection();
         PreparedStatement ps = conn.prepareStatement(sql)) {
        ps.setString(1, lockId);
        ps.setString(2, owner);
        ResultSet rs = ps.executeQuery();
        if (rs.next()) {
            return false; // Lock already held by another owner
        }
        sql = "INSERT INTO distributed_lock (lock_id, owner, acquire_time) VALUES (?, ?, NOW())";
        ps = conn.prepareStatement(sql);
        ps.setString(1, lockId);
        ps.setString(2, owner);
        ps.executeUpdate();
        return true;
    } catch (SQLException e) {
        throw new RuntimeException("Failed to acquire lock", e);
    }
}

public void releaseLock(String lockId, String owner) {
    String sql = "UPDATE distributed_lock SET release_time = NOW() WHERE lock_id = ? AND owner = ?";
    try (Connection conn = dataSource.getConnection();
         PreparedStatement ps = conn.prepareStatement(sql)) {
        ps.setString(1, lockId);
        ps.setString(2, owner);
        ps.executeUpdate();
    } catch (SQLException e) {
        throw new RuntimeException("Failed to release lock", e);
    }
}

2. 使用Redis

Redis是一个高性能的内存数据存储系统，可以用来实现分布式锁。你可以使用Redis的SETNX命令来尝试获取锁，并使用EXPIRE命令设置锁的过期时间。

public boolean tryLock(String lockKey, String requestId, int expireTime) {
    Boolean result = jedis.set(lockKey, requestId, "NX", "EX", expireTime);
    return result != null && result;
}

public void releaseLock(String lockKey, String requestId) {
    if (requestId.equals(jedis.get(lockKey))) {
        jedis.del(lockKey);
    }
}

3. 使用Zookeeper

Apache ZooKeeper是一个分布式协调服务，可以用来实现分布式锁。你可以使用ZooKeeper的临时顺序节点来实现锁。

public boolean tryLock(String lockPath) throws Exception {
    InterProcessMutex lock = new InterProcessMutex(curatorFramework, lockPath);
    return lock.acquire(0, TimeUnit.MILLISECONDS);
}

public void releaseLock(String lockPath) throws Exception {
    InterProcessMutex lock = new InterProcessMutex(curatorFramework, lockPath);
    lock.release();
}