SpringDataRedis事务处理
ZoiSkerst
9年前
来自： http://segmentfault.com/a/1190000004393573
序
本文主要讲述如何在java里头使用redis进行cas操作。其实呢，redis不像memcached那样显示地支持cas操作，不过它有事务的概念。
准备
redis的乐观锁支持
Redis通过使用WATCH, MULTI, and EXEC组成的事务来实现乐观锁( 注意没有用DISCARD ),Redis事务没有回滚操作。在SpringDataRedis当中通过RedisTemplate的SessionCallback中来支持( 否则事务不生效 )。discard的话不需要自己代码处理，callback返回null，成的话，返回非null，依据这个来判断事务是否成功( 没有抛异常 )。
实例
@Test public void cas() throws InterruptedException, ExecutionException { String key = "test-cas-1"; ValueOperations<String, String> strOps = redisTemplate.opsForValue(); strOps.set(key, "hello"); ExecutorService pool = Executors.newCachedThreadPool(); List<Callable<Object>> tasks = new ArrayList<>(); for(int i=0;i<5;i++){ final int idx = i; tasks.add(new Callable() { @Override public Object call() throws Exception { return redisTemplate.execute(new SessionCallback() { @Override public Object execute(RedisOperations operations) throws DataAccessException { operations.watch(key); String origin = (String) operations.opsForValue().get(key); operations.multi(); operations.opsForValue().set(key, origin + idx); Object rs = operations.exec(); System.out.println("set:"+origin+idx+" rs:"+rs); return rs; } }); } }); } List<Future<Object>> futures = pool.invokeAll(tasks); for(Future<Object> f:futures){ System.out.println(f.get()); } pool.shutdown(); pool.awaitTermination(1000, TimeUnit.MILLISECONDS); } 输出
set:hello2 rs:null set:hello3 rs:[] set:hello1 rs:null set:hello4 rs:null set:hello0 rs:null
查看该值
127.0.0.1:6379> get test-cas-1 "\"hello3\""
坑
SessionCallback
没有在SessionCallback里头执行watch、multi、exec，而是自己单独写
与数据库事务的混淆
template.setEnableTransactionSupport(true);
这个应该是支持数据库的事务成功才执行的意思。
/** * Gets a Redis connection. Is aware of and will return any existing corresponding connections bound to the current * thread, for example when using a transaction manager. Will create a new Connection otherwise, if * {@code allowCreate} is <tt>true</tt>. * * @param factory connection factory for creating the connection * @param allowCreate whether a new (unbound) connection should be created when no connection can be found for the * current thread * @param bind binds the connection to the thread, in case one was created * @param enableTransactionSupport * @return an active Redis connection */ public static RedisConnection doGetConnection(RedisConnectionFactory factory, boolean allowCreate, boolean bind, boolean enableTransactionSupport) { Assert.notNull(factory, "No RedisConnectionFactory specified"); RedisConnectionHolder connHolder = (RedisConnectionHolder) TransactionSynchronizationManager.getResource(factory); if (connHolder != null) { if (enableTransactionSupport) { potentiallyRegisterTransactionSynchronisation(connHolder, factory); } return connHolder.getConnection(); } if (!allowCreate) { throw new IllegalArgumentException("No connection found and allowCreate = false"); } if (log.isDebugEnabled()) { log.debug("Opening RedisConnection"); } RedisConnection conn = factory.getConnection(); if (bind) { RedisConnection connectionToBind = conn; if (enableTransactionSupport && isActualNonReadonlyTransactionActive()) { connectionToBind = createConnectionProxy(conn, factory); } connHolder = new RedisConnectionHolder(connectionToBind); TransactionSynchronizationManager.bindResource(factory, connHolder); if (enableTransactionSupport) { potentiallyRegisterTransactionSynchronisation(connHolder, factory); } return connHolder.getConnection(); } return conn; } 不要跟本文的乐观锁说的事务混淆在一起。