问题
Datatype for one of the column in cassandra table is timeuuid.
While creating my Mapper class as per docs, I am not sure of data type I should use for timeuuid column. I understand that it should be an equivalent Java data type and hence I tried java.util.Date. Refer column definition and Mapper class column definition as below
start timeuuid
@PartitionKey(1)
@Column(name="start")
private UUID start;
I get the below during CRUD operation
Codec not found for requested operation: [timeuuid -> java.util.Date]
回答1:
I have customize the UUIDs class of datastax to get TimeUUID from a Time Here is the Complete code with an exmaple
/*
* Copyright (C) 2012-2015 DataStax Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.datastax.driver.core.utils;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.nio.charset.Charset;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.*;
import java.util.concurrent.atomic.AtomicLong;
/**
* Utility methods to work with UUID and most specifically with time-based ones (version 1).
*/
public final class UUIDs {
private UUIDs() {
}
;
// http://www.ietf.org/rfc/rfc4122.txt
private static final long START_EPOCH = makeEpoch();
private static final long CLOCK_SEQ_AND_NODE = makeClockSeqAndNode();
/*
* The min and max possible lsb for a UUID.
* Note that his is not 0 and all 1's because Cassandra TimeUUIDType
* compares the lsb parts as a signed byte array comparison. So the min
* value is 8 times -128 and the max is 8 times +127.
*
* Note that we ignore the uuid variant (namely, MIN_CLOCK_SEQ_AND_NODE
* have variant 2 as it should, but MAX_CLOCK_SEQ_AND_NODE have variant 0)
* because I don't trust all uuid implementation to have correctly set
* those (pycassa don't always for instance).
*/
private static final long MIN_CLOCK_SEQ_AND_NODE = 0x8080808080808080L;
private static final long MAX_CLOCK_SEQ_AND_NODE = 0x7f7f7f7f7f7f7f7fL;
private static final AtomicLong lastTimestamp = new AtomicLong(0L);
private static long makeEpoch() {
// UUID v1 timestamp must be in 100-nanoseconds interval since 00:00:00.000 15 Oct 1582.
Calendar c = Calendar.getInstance(TimeZone.getTimeZone("GMT-0"));
c.set(Calendar.YEAR, 1582);
c.set(Calendar.MONTH, Calendar.OCTOBER);
c.set(Calendar.DAY_OF_MONTH, 15);
c.set(Calendar.HOUR_OF_DAY, 0);
c.set(Calendar.MINUTE, 0);
c.set(Calendar.SECOND, 0);
c.set(Calendar.MILLISECOND, 0);
return c.getTimeInMillis();
}
private static long makeNode() {
/*
* We don't have access to the MAC address (in pure JAVA at least) but
* need to generate a node part that identify this host as uniquely as
* possible.
* The spec says that one option is to take as many source that
* identify this node as possible and hash them together. That's what
* we do here by gathering all the ip of this host as well as a few
* other sources.
*/
try {
MessageDigest digest = MessageDigest.getInstance("MD5");
for (String address : getAllLocalAddresses()) {
update(digest, address);
}
Properties props = System.getProperties();
update(digest, props.getProperty("java.vendor"));
update(digest, props.getProperty("java.vendor.url"));
update(digest, props.getProperty("java.version"));
update(digest, props.getProperty("os.arch"));
update(digest, props.getProperty("os.name"));
update(digest, props.getProperty("os.version"));
byte[] hash = digest.digest();
long node = 0;
for (int i = 0; i < 6; i++) {
node |= (0x00000000000000ffL & (long) hash[i]) << (i * 8);
}
// Since we don't use the mac address, the spec says that multicast
// bit (least significant bit of the first byte of the node ID) must be 1.
return node | 0x0000010000000000L;
} catch (NoSuchAlgorithmException e) {
throw new RuntimeException(e);
}
}
private static void update(MessageDigest digest, String value) {
if (value != null) {
digest.update(value.getBytes(Charset.forName("utf-8")));
}
}
private static long makeClockSeqAndNode() {
long clock = new Random(System.currentTimeMillis()).nextLong();
long node = makeNode();
long lsb = 0;
lsb |= (clock & 0x0000000000003FFFL) << 48;
lsb |= 0x8000000000000000L;
lsb |= node;
return lsb;
}
/**
* Creates a new random (version 4) UUID.
* <p/>
* This method is just a convenience for {@code UUID.randomUUID()}.
*
* @return a newly generated, pseudo random, version 4 UUID.
*/
public static UUID random() {
return UUID.randomUUID();
}
/**
* Creates a new time-based (version 1) UUID.
* <p/>
* UUID generated by this method are suitable for use with the {@code timeuuid} Cassandra type. In particular the generated UUID includes the timestamp of its generation.
*
* @return a new time-based UUID.
*/
public static UUID timeBased() {
return new UUID(makeMSB(getCurrentTimestamp()), CLOCK_SEQ_AND_NODE);
}
public static UUID getTimeUUID(long tstamp) {
long timestamp = (tstamp - START_EPOCH) * 10000;
long msb = 0L;
msb |= (0x00000000ffffffffL & timestamp) << 32;
msb |= (0x0000ffff00000000L & timestamp) >>> 16;
msb |= (0x0fff000000000000L & timestamp) >>> 48;
msb |= 0x0000000000001000L; // sets the version to 1.
return new UUID(msb, CLOCK_SEQ_AND_NODE);
}
/**
* Creates a "fake" time-based UUID that sorts as the smallest possible version 1 UUID generated at the provided timestamp.
* <p/>
* Such created UUID are useful in queries to select a time range of a {@code timeuuid} column.
* <p/>
* The UUID created by this method <b>are not unique</b> and as such are
* <b>not</b> suitable for anything else than querying a specific time range. In particular, you should not insert such UUID.
* <p/>
* Also, the timestamp to provide as parameter must be a unix timestamp (as returned by {@link System#currentTimeMillis} or {@link java.util.Date#getTime}), not a UUID 100-nanoseconds intervals since 15 October 1582. In other words, given a UUID {@code uuid}, you should never do {@code startOf(uuid.timestamp())} but rather {@code startOf(unixTimestamp(uuid.timestamp()))}.
* <p/>
* Lastly, please note that Cassandra's timeuuid sorting is not compatible with {@link UUID#compareTo} and hence the UUID created by this method are not necessarily lower bound for that latter method.
*
* @param timestamp the unix timestamp for which the created UUID must be a lower bound.
* @return the smallest (for Cassandra timeuuid sorting) UUID of {@code timestamp}.
*/
public static UUID startOf(long timestamp) {
return new UUID(makeMSB(fromUnixTimestamp(timestamp)), MIN_CLOCK_SEQ_AND_NODE);
}
/**
* Creates a "fake" time-based UUID that sorts as the biggest possible version 1 UUID generated at the provided timestamp.
* <p/>
* Such created UUID are useful in queries to select a time range of a {@code timeuuid} column.
* <p/>
* The UUID created by this method <b>are not unique</b> and as such are
* <b>not</b> suitable for anything else than querying a specific time range. In particular, you should not insert such UUID.
* <p/>
* Also, the timestamp to provide as parameter must be a unix timestamp (as returned by {@link System#currentTimeMillis} or {@link java.util.Date#getTime}), not a UUID 100-nanoseconds intervals since 15 October 1582. In other words, given a UUID {@code uuid}, you should never do {@code startOf(uuid.timestamp())} but rather {@code startOf(unixTimestamp(uuid.timestamp()))}.
* <p/>
* Lastly, please note that Cassandra's timeuuid sorting is not compatible with {@link UUID#compareTo} and hence the UUID created by this method are not necessarily upper bound for that latter method.
*
* @param timestamp the unix timestamp for which the created UUID must be an upper bound.
* @return the biggest (for Cassandra timeuuid sorting) UUID of {@code timestamp}.
*/
public static UUID endOf(long timestamp) {
long uuidTstamp = fromUnixTimestamp(timestamp + 1) - 1;
return new UUID(makeMSB(uuidTstamp), MAX_CLOCK_SEQ_AND_NODE);
}
/**
* Return the unix timestamp contained by the provided time-based UUID.
* <p/>
* This method is not equivalent to {@code uuid.timestamp()}. More precisely, a version 1 UUID stores a timestamp that represents the number of 100-nanoseconds intervals since midnight, 15 October 1582 and that is what {@code uuid.timestamp()} returns. This method however converts that timestamp to the equivalent unix timestamp in milliseconds, i.e. a timestamp representing a number of milliseconds since midnight, January 1, 1970 UTC. In particular the timestamps returned by this method are comparable to the timestamp returned by {@link System#currentTimeMillis}, {@link java.util.Date#getTime}, etc.
*
* @param uuid the UUID to return the timestamp of.
* @return the unix timestamp of {@code uuid}.
* @throws IllegalArgumentException if {@code uuid} is not a version 1 UUID.
*/
public static long unixTimestamp(UUID uuid) {
if (uuid.version() != 1) {
throw new IllegalArgumentException(String.format("Can only retrieve the unix timestamp for version 1 uuid (provided version %d)", uuid.version()));
}
long timestamp = uuid.timestamp();
return (timestamp / 10000) + START_EPOCH;
}
/*
* Note that currently we use System.currentTimeMillis() for a base time in
* milliseconds, and then if we are in the same milliseconds that the
* previous generation, we increment the number of nanoseconds.
* However, since the precision is 100-nanoseconds intervals, we can only
* generate 10K UUID within a millisecond safely. If we detect we have
* already generated that much UUID within a millisecond (which, while
* admittedly unlikely in a real application, is very achievable on even
* modest machines), then we stall the generator (busy spin) until the next
* millisecond as required by the RFC.
*/
private static long getCurrentTimestamp() {
while (true) {
long now = fromUnixTimestamp(System.currentTimeMillis());
long last = lastTimestamp.get();
if (now > last) {
if (lastTimestamp.compareAndSet(last, now)) {
return now;
}
} else {
long lastMillis = millisOf(last);
// If the clock went back in time, bail out
if (millisOf(now) < millisOf(last)) {
return lastTimestamp.incrementAndGet();
}
long candidate = last + 1;
// If we've generated more than 10k uuid in that millisecond,
// we restart the whole process until we get to the next millis.
// Otherwise, we try use our candidate ... unless we've been
// beaten by another thread in which case we try again.
if (millisOf(candidate) == lastMillis && lastTimestamp.compareAndSet(last, candidate)) {
return candidate;
}
}
}
}
// Package visible for testing
static long fromUnixTimestamp(long tstamp) {
return (tstamp - START_EPOCH) * 10000;
}
private static long millisOf(long timestamp) {
return timestamp / 10000;
}
// Package visible for testing
static long makeMSB(long timestamp) {
long msb = 0L;
msb |= (0x00000000ffffffffL & timestamp) << 32;
msb |= (0x0000ffff00000000L & timestamp) >>> 16;
msb |= (0x0fff000000000000L & timestamp) >>> 48;
msb |= 0x0000000000001000L; // sets the version to 1.
return msb;
}
private static Set<String> getAllLocalAddresses() {
Set<String> allIps = new HashSet<String>();
try {
InetAddress localhost = InetAddress.getLocalHost();
allIps.add(localhost.toString());
// Also return the hostname if available, it won't hurt (this does a dns lookup, it's only done once at startup)
allIps.add(localhost.getCanonicalHostName());
InetAddress[] allMyIps = InetAddress.getAllByName(localhost.getCanonicalHostName());
if (allMyIps != null) {
for (int i = 0; i < allMyIps.length; i++) {
allIps.add(allMyIps[i].toString());
}
}
} catch (UnknownHostException e) {
// Ignore, we'll try the network interfaces anyway
}
try {
Enumeration<NetworkInterface> en = NetworkInterface.getNetworkInterfaces();
if (en != null) {
while (en.hasMoreElements()) {
Enumeration<InetAddress> enumIpAddr = en.nextElement().getInetAddresses();
while (enumIpAddr.hasMoreElements()) {
allIps.add(enumIpAddr.nextElement().toString());
}
}
}
} catch (SocketException e) {
// Ignore, if we've really got nothing so far, we'll throw an exception
}
return allIps;
}
public static void main(String[] args) {
long time = System.currentTimeMillis();
System.out.println(UUIDs.getTimeUUID(time));
}
}
来源：https://stackoverflow.com/questions/40459001/what-should-be-datatype-for-timeuuid-in-datastax-mapper-class