在 RxJava 中实现并行异步调用时,我需要一些帮助。我选择了一个简单的用例,其中 FIRST 调用获取(相当搜索)要显示的产品列表(平铺)。随后的调用出去并获取(A)评论和(B)产品图像
经过几次尝试,我到达了这个地方。
1 Observable<Tile> searchTile = searchServiceClient.getSearchResults(searchTerm);
2 List<Tile> allTiles = new ArrayList<Tile>();
3 ClientResponse response = new ClientResponse();
4 searchTile.parallel(oTile -> {
5 return oTile.flatMap(t -> {
6 Observable<Reviews> reviews = reviewsServiceClient.getSellerReviews(t.getSellerId());
7 Observable<String> imageUrl = reviewsServiceClient.getProductImage(t.getProductId());
8 return Observable.zip(reviews, imageUrl, (r, u) -> {
9 t.setReviews(r);
10 t.setImageUrl(u);
11 return t;
12 });
13 });
14 }).subscribe(e -> {
15 allTiles.add((Tile) e);
16 });
第 1 行:取出要显示的产品(Tile)
第 4 行:我们获取 Observable 的列表并对其进行 SHARD 以获取评论和 imageUrls
谎言 6,7:获取 Observable 评论和 Observable url
第 8 行:最后 2 个 observable 被压缩以返回更新后的 Observable
第 15 行:最后第 15 行整理了所有要显示在集合中的单个产品,该集合可以返回给调用层
虽然 Observable 已被分片并且在我们的测试中运行了 4 个不同的线程;获取评论和图像似乎是一个接一个。我怀疑第 8 行的 zip 步骤基本上导致了 2 个 observables(reviews 和 url)的顺序调用。
这个小组对并行获取评论和图片网址有什么建议吗?本质上,上面附加的瀑布图应该看起来更垂直堆叠。对评论和图像的调用应该是并行的
谢谢 阿南德拉曼
最佳答案
并行运算符被证明是几乎所有用例的问题,并且没有达到大多数人的预期,因此在 1.0.0.rc.4 版本中将其删除:https://github.com/ReactiveX/RxJava/pull/1716
可以看到 here 的一个很好的例子来说明如何执行这种类型的行为并获得并行执行。 .
在您的示例代码中,不清楚 searchServiceClient
是同步的还是异步的。它会稍微影响如何解决问题,就好像它已经是异步的,不需要额外的调度。如果需要同步额外调度。
首先这里有一些显示同步和异步行为的简单示例:
import rx.Observable;
import rx.Subscriber;
import rx.schedulers.Schedulers;
public class ParallelExecution {
public static void main(String[] args) {
System.out.println("------------ mergingAsync");
mergingAsync();
System.out.println("------------ mergingSync");
mergingSync();
System.out.println("------------ mergingSyncMadeAsync");
mergingSyncMadeAsync();
System.out.println("------------ flatMapExampleSync");
flatMapExampleSync();
System.out.println("------------ flatMapExampleAsync");
flatMapExampleAsync();
System.out.println("------------");
}
private static void mergingAsync() {
Observable.merge(getDataAsync(1), getDataAsync(2)).toBlocking().forEach(System.out::println);
}
private static void mergingSync() {
// here you'll see the delay as each is executed synchronously
Observable.merge(getDataSync(1), getDataSync(2)).toBlocking().forEach(System.out::println);
}
private static void mergingSyncMadeAsync() {
// if you have something synchronous and want to make it async, you can schedule it like this
// so here we see both executed concurrently
Observable.merge(getDataSync(1).subscribeOn(Schedulers.io()), getDataSync(2).subscribeOn(Schedulers.io())).toBlocking().forEach(System.out::println);
}
private static void flatMapExampleAsync() {
Observable.range(0, 5).flatMap(i -> {
return getDataAsync(i);
}).toBlocking().forEach(System.out::println);
}
private static void flatMapExampleSync() {
Observable.range(0, 5).flatMap(i -> {
return getDataSync(i);
}).toBlocking().forEach(System.out::println);
}
// artificial representations of IO work
static Observable<Integer> getDataAsync(int i) {
return getDataSync(i).subscribeOn(Schedulers.io());
}
static Observable<Integer> getDataSync(int i) {
return Observable.create((Subscriber<? super Integer> s) -> {
// simulate latency
try {
Thread.sleep(1000);
} catch (Exception e) {
e.printStackTrace();
}
s.onNext(i);
s.onCompleted();
});
}
}
以下是尝试提供与您的代码更匹配的示例:
import java.util.List;
import rx.Observable;
import rx.Subscriber;
import rx.schedulers.Schedulers;
public class ParallelExecutionExample {
public static void main(String[] args) {
final long startTime = System.currentTimeMillis();
Observable<Tile> searchTile = getSearchResults("search term")
.doOnSubscribe(() -> logTime("Search started ", startTime))
.doOnCompleted(() -> logTime("Search completed ", startTime));
Observable<TileResponse> populatedTiles = searchTile.flatMap(t -> {
Observable<Reviews> reviews = getSellerReviews(t.getSellerId())
.doOnCompleted(() -> logTime("getSellerReviews[" + t.id + "] completed ", startTime));
Observable<String> imageUrl = getProductImage(t.getProductId())
.doOnCompleted(() -> logTime("getProductImage[" + t.id + "] completed ", startTime));
return Observable.zip(reviews, imageUrl, (r, u) -> {
return new TileResponse(t, r, u);
}).doOnCompleted(() -> logTime("zip[" + t.id + "] completed ", startTime));
});
List<TileResponse> allTiles = populatedTiles.toList()
.doOnCompleted(() -> logTime("All Tiles Completed ", startTime))
.toBlocking().single();
}
private static Observable<Tile> getSearchResults(String string) {
return mockClient(new Tile(1), new Tile(2), new Tile(3));
}
private static Observable<Reviews> getSellerReviews(int id) {
return mockClient(new Reviews());
}
private static Observable<String> getProductImage(int id) {
return mockClient("image_" + id);
}
private static void logTime(String message, long startTime) {
System.out.println(message + " => " + (System.currentTimeMillis() - startTime) + "ms");
}
private static <T> Observable<T> mockClient(T... ts) {
return Observable.create((Subscriber<? super T> s) -> {
// simulate latency
try {
Thread.sleep(1000);
} catch (Exception e) {
}
for (T t : ts) {
s.onNext(t);
}
s.onCompleted();
}).subscribeOn(Schedulers.io());
// note the use of subscribeOn to make an otherwise synchronous Observable async
}
public static class TileResponse {
public TileResponse(Tile t, Reviews r, String u) {
// store the values
}
}
public static class Tile {
private final int id;
public Tile(int i) {
this.id = i;
}
public int getSellerId() {
return id;
}
public int getProductId() {
return id;
}
}
public static class Reviews {
}
}
这个输出:
Search started => 65ms
Search completed => 1094ms
getProductImage[1] completed => 2095ms
getSellerReviews[2] completed => 2095ms
getProductImage[3] completed => 2095ms
zip[1] completed => 2096ms
zip[2] completed => 2096ms
getProductImage[2] completed => 2096ms
getSellerReviews[1] completed => 2096ms
zip[3] completed => 2096ms
All Tiles Completed => 2097ms
getSellerReviews[3] completed => 2097ms
我已将每个 IO 调用模拟为花费 1000 毫秒,因此很明显延迟在哪里并且它是并行发生的。它以经过的毫秒数打印出进度。
这里的技巧是 flatMap 会合并异步调用,所以只要被合并的 Observable 是异步的,它们都会被并发执行。
如果像 getProductImage(t.getProductId())
这样的调用是同步的,可以像这样异步调用:getProductImage(t.getProductId()).subscribeOn(Schedulers.io)。
这是上面示例的重要部分,没有所有的日志记录和样板类型:
Observable<Tile> searchTile = getSearchResults("search term");;
Observable<TileResponse> populatedTiles = searchTile.flatMap(t -> {
Observable<Reviews> reviews = getSellerReviews(t.getSellerId());
Observable<String> imageUrl = getProductImage(t.getProductId());
return Observable.zip(reviews, imageUrl, (r, u) -> {
return new TileResponse(t, r, u);
});
});
List<TileResponse> allTiles = populatedTiles.toList()
.toBlocking().single();
我希望这会有所帮助。
关于java - RxJava 并行获取 Observables,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/26249030/