java生成分布式随机文件名

可以使用Snowflake算法生成分布式随机文件名，示例代码如下：

import java.io.File;
import java.io.IOException;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.node.ObjectNode;

public class DistributedRandomFileNameGenerator {
    private static final long EPOCH = 1420041600000L; // 2015-01-01
    private static final int NODE_ID_BITS = 10;
    private static final int SEQUENCE_BITS = 12;
    private static final long MAX_NODE_ID = (1L << NODE_ID_BITS) - 1;
    private static final long MAX_SEQUENCE = (1L << SEQUENCE_BITS) - 1;

    private final long nodeId;
    private long lastTimestamp = -1L;
    private long sequence = 0L;

    public DistributedRandomFileNameGenerator(long nodeId) {
        if (nodeId < 0 || nodeId > MAX_NODE_ID) {
            throw new IllegalArgumentException(String.format("NodeId must be between 0 and %d", MAX_NODE_ID));
        }
        this.nodeId = nodeId;
    }

    public synchronized String generate() {
        long timestamp = System.currentTimeMillis() - EPOCH;
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }
        if (timestamp == lastTimestamp) {
            sequence = (sequence + 1) & MAX_SEQUENCE;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }
        lastTimestamp = timestamp;
        long id = ((timestamp << (NODE_ID_BITS + SEQUENCE_BITS)) | (nodeId << SEQUENCE_BITS) | sequence) & Long.MAX_VALUE;
        return Long.toString(id, 36);
    }

    private long tilNextMillis(long lastTimestamp) {
        long timestamp = System.currentTimeMillis() - EPOCH;
        while (timestamp <= lastTimestamp) {
            timestamp = System.currentTimeMillis() - EPOCH;
        }
        return timestamp;
    }

    public static void main(String[] args) throws IOException {
        DistributedRandomFileNameGenerator generator = new DistributedRandomFileNameGenerator(1);
        String fileName = generator.generate();
        System.out.println(fileName);

        // Save nodeId and lastTimestamp to file for recovery
        ObjectMapper mapper = new ObjectMapper();
        mapper.enable(SerializationFeature.INDENT_OUTPUT);
        ObjectNode node = mapper.createObjectNode();
        node.put("nodeId", generator.nodeId);
        node.put("lastTimestamp", generator.lastTimestamp);
        mapper.writeValue(new File("generator.json"), node);
    }
}

上述代码中，`DistributedRandomFileNameGenerator`类使用Snowflake算法生成分布式随机文件名。在构造函数中指定节点ID，然后调用`generate()`方法即可生成随机文件名。为了防止时钟回拨等问题，需要在生成文件名时保证时间戳单调递增。如果需要在重启程序后恢复生成器状态，可以将节点ID和上一次生成文件名的时间戳保存到文件中，然后在程序启动时读取该文件，恢复生成器状态。