SpringDataRedis事务处理

ZoiSkerst 8年前

来自: http://segmentfault.com/a/1190000004393573

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\""

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。

参考