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。
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