在Java和MySQL中生成流水号通常是为了确保数据的唯一性和顺序性。流水号可以用于订单号、交易号、日志号等各种需要唯一标识的场景。
CREATE TABLE orders (
id INT AUTO_INCREMENT PRIMARY KEY,
order_number VARCHAR(255),
-- 其他字段
);在Java中插入数据时,不需要指定id字段,MySQL会自动生成:
String sql = "INSERT INTO orders (order_number) VALUES (?)";
try (PreparedStatement pstmt = connection.prepareStatement(sql)) {
pstmt.setString(1, "ORDER-12345");
pstmt.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
}import java.util.UUID;
String orderNumber = UUID.randomUUID().toString();Snowflake算法生成的ID结构如下:
以下是一个简单的Snowflake实现示例:
public class SnowflakeIdGenerator {
private final long workerId;
private final long datacenterId;
private long sequence = 0L;
private final long workerIdBits = 5L;
private final long datacenterIdBits = 5L;
private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
private final long sequenceBits = 12L;
private final long workerIdShift = sequenceBits;
private final long datacenterIdShift = sequenceBits + workerIdBits;
private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
private final long sequenceMask = -1L ^ (-1L << sequenceBits);
private long lastTimestamp = -1L;
public SnowflakeIdGenerator(long workerId, long datacenterId) {
if (workerId > maxWorkerId || workerId < 0) {
throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
}
if (datacenterId > maxDataID || datacenterId < 0) {
throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
}
this.workerId = workerId;
this.datacenterId = datacenterId;
}
public synchronized long nextId() {
long timestamp = timeGen();
if (timestamp < lastTimestamp) {
throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
}
if (lastTimestamp == timestamp) {
sequence = (sequence + 1) & sequenceMask;
if (sequence == 0) {
timestamp = tilNextMillis(lastTimestamp);
}
} else {
sequence = 0L;
}
lastTimestamp = timestamp;
return ((timestamp - twepoch) << timestampLeftShift) |
(datacenterId << datacenterIdShift) |
(workerId << workerIdShift) |
sequence;
}
private long tilNextMillis(long lastTimestamp) {
long timestamp = timeGen();
while (timestamp <= lastTimestamp) {
timestamp = timeGen();
}
return timestamp;
}
private long timeGen() {
return System.currentTimeMillis();
}
}原因:
解决方法:
原因:
解决方法:
希望这些信息对你有所帮助!
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