如果您能够使用Java
8，则可以
parallelStream对表列表进行操作，并使用lambda将表名扩展为每个表的唯一ID对应列表，然后将结果合并为一个表哈希。
没有Java 8，我将使用Google Guava的可监听期货和类似以下内容的执行服务：
public static Set<String> fetchFromTable(int table) { String sql = "select * from testkeyspace.test_table_" + table + ";"; Set<String> result = new HashSet<String>(); // populate result with your SQL statements // ... return result;}public static Set<String> fetchFromAllTables() throws InterruptedException, ExecutionException { // Create a ListeningExecutorService (Guava) by wrapping a // normal ExecutorService (Java) ListeningExecutorService executor = MoreExecutors.listeningDecorator(Executors.newCachedThreadPool()); List<ListenableFuture<Set<String>>> list = new ArrayList<ListenableFuture<Set<String>>>(); // For each table, create an independent thread that will // query just that table and return a set of user IDs from it for (int i = 0; i < 10; i++) { final int table = i; ListenableFuture<Set<String>> future = executor.submit(new Callable<Set<String>>() { public Set<String> call() throws Exception { return fetchFromTable(table); } }); // Add the future to the list list.add(future); } // We want to know when ALL the threads have completed, // so we use a Guava function to turn a list of ListenableFutures // into a single ListenableFuture ListenableFuture<List<Set<String>>> combinedFutures = Futures.allAsList(list); // The get on the combined ListenableFuture will now block until // ALL the individual threads have completed work. List<Set<String>> tableSets = combinedFutures.get(); // Now all we have to do is combine the individual sets into a // single result Set<String> userList = new HashSet<String>(); for (Set<String> tableSet: tableSets) { userList.addAll(tableSet); } return userList;}Executors和Futures的使用都是Java的核心。番石榴唯一要做的就是让我将Future变成ListenableFutures。请参阅此处以讨论为何后者更好。
可能仍有改善这种方法并行性的方法，但是如果您花费大量时间等待数据库响应或处理网络流量，则此方法可能会有所帮助。
