Question

我在执行必须执行异步任务的操作时遇到问题。该操作返回CompletionStage，以便服务器不会被异步任务（doSearch（）方法）阻止，并且当任务完成时，我可以调用complete（）来响应客户端。这是控制器/ Application.java中的操作：

@BodyParser.Of(BodyParser.Json.class)
public static CompletionStage<Result> search(String secret) {
    CompletableFuture<Result> result = new CompletableFuture<>();
    if (!hasPermission(secret)) {
        result.complete(unauthorized("Secret is incorrect."));
        return result;
    }
    JsonNode json = request().body().asJson();
    if (json == null) {
        result.complete(badRequest("Expecting json data."));
        return result;
    }

    SearchRequestBody search = Json.fromJson(json, SearchRequestBody.class);
    doSearch(search.body).thenApply(searchResults -> {
        result.complete(ok(Json.toJson(searchResults)));
        return null;
    });
    return result;
}

路线档案：

# Home page
GET     /                           controllers.Application.index

# Map static resources from the /public folder to the /assets URL path
GET     /assets/*file               controllers.Assets.at(path="/public", file)

#PUT     /predict/:id                controllers.Application.predict()

GET    /search                     controllers.Application.search

错误：

[info] Compiling 1 Java source to C:\Users\senok\IdeaProjects\Culinars\target\scala-2.11\classes...
[info] Compiling 1 Scala source to C:\Users\senok\IdeaProjects\Culinars\target\scala-2.11\classes...
[error] C:\Users\senok\IdeaProjects\Culinars\conf\routes:13: Cannot use a method returning java.util.concurrent.CompletionStage[play.mvc.Result] as a Handler for requests
[error] GET    /search                     controllers.Application.search
[error] C:\Users\senok\IdeaProjects\Culinars\conf\routes:13: not enough arguments for method createInvoker: (implicit hif: play.core.routing.HandlerInvokerFactory[java.util.concurrent.CompletionStage[play.mvc.Result]])play.core.routing.HandlerInvoker[java.util.concurrent.CompletionStage[play.mvc.Result]].
[error] Unspecified value parameter hif.
[error] GET    /search                     controllers.Application.search
[error] two errors found
[error] (compile:compile) Compilation failed
[error] application - 

! @715l00c2i - Internal server error, for (GET) [/search] ->

play.sbt.PlayExceptions$CompilationException: Compilation error[Cannot use a method returning java.util.concurrent.CompletionStage[play.mvc.Result] as a Handler for requests]
    at play.sbt.PlayExceptions$CompilationException$.apply(PlayExceptions.scala:27) ~[na:na]
    at play.sbt.PlayExceptions$CompilationException$.apply(PlayExceptions.scala:27) ~[na:na]
    at scala.Option.map(Option.scala:145) ~[scala-library-2.11.7.jar:na]
    at play.sbt.run.PlayReload$$anonfun$taskFailureHandler$1.apply(PlayReload.scala:49) ~[na:na]
    at play.sbt.run.PlayReload$$anonfun$taskFailureHandler$1.apply(PlayReload.scala:44) ~[na:na]
    at scala.Option.map(Option.scala:145) ~[scala-library-2.11.7.jar:na]
    at play.sbt.run.PlayReload$.taskFailureHandler(PlayReload.scala:44) ~[na:na]
    at play.sbt.run.PlayReload$.compileFailure(PlayReload.scala:40) ~[na:na]
    at play.sbt.run.PlayReload$$anonfun$compile$1.apply(PlayReload.scala:17) ~[na:na]
    at play.sbt.run.PlayReload$$anonfun$compile$1.apply(PlayReload.scala:17) ~[na:na]

编辑：这里的doSearch：

private static CompletableFuture<List<SearchResult>> doSearch(Map<String, String>[] args) {
    CompletableFuture<List<SearchResult>> result = new CompletableFuture<>();
    List<SearchResult> results = new ArrayList<>();
    final int[] paramsLeft = new int[]{args.length};
    for (Map<String, String> param : args) {
        if (!param.containsKey("type")
                || !param.containsKey("uid")
                || !param.containsKey("importance")) {
            paramsLeft[0]--;
            if (paramsLeft[0] == 0)
                result.complete(results);
        } else {
            String nodeName = "";
            switch (param.get("type")) {
                case "ingredient":
                    nodeName = "ingredients";
                    break;
                case "tag":
                    nodeName = "tags";
                    break;
                case "keyword":
                    nodeName = "keywords";
                    break;
                default:
                    paramsLeft[0]--;
                    if (paramsLeft[0] == 0)
                        result.complete(results);
            }
            DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child(nodeName).child(param.get("uid"));
            ref.child("recipes").addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    if (!dataSnapshot.exists()) {
                        paramsLeft[0]--;
                        if (paramsLeft[0] == 0)
                            result.complete(results);
                        return;
                    }
                    for (DataSnapshot recipe : dataSnapshot.getChildren()) {
                        SearchResult searchResult = new SearchResult();
                        searchResult.uid = recipe.getKey();
                        searchResult.matching = Double.parseDouble(param.get("importance"));
                        int index = results.indexOf(searchResult);
                        if (index > -1)
                            results.get(index).combine(searchResult);
                        else
                            results.add(searchResult);
                    }
                    paramsLeft[0]--;
                    if (paramsLeft[0] == 0) {
                        result.complete(results);
                    }
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                    paramsLeft[0]--;
                    if (paramsLeft[0] == 0)
                        result.complete(results);
                }
            });
        }
    }
    return result;
}

Answer 1

只需将方法的最后一部分更改为：

SearchRequestBody search = Json.fromJson(json, SearchRequestBody.class);
return doSearch(search.body).thenApply(searchResults -> {
    return ok(Json.toJson(searchResults));
});

如果您仍然遇到编译错误，请发布doSearch

的代码

Answer 2

由于默认情况下所有操作都包含在自己的CompletionStage中，我们可以让它返回Result，但仍然保持异常。这是新的退货声明：

return result.get(); //Locks the thread until result.complete() is called.

编译错误：我们不能将一个方法返回CompetionStage作为请求的处理程序

2 个答案: