英文:
How to throw an exception properly when do Flux processing?
问题
已有代码：
private Flux<Integer> testGetFluxTestData() {
return Flux.just(new TestData(1), new TestData(2))
.collectList()
.map(list -> list.stream()
.map(TestData::getId)
.collect(Collectors.toList()))
.flatMapMany(Flux::fromIterable);
}
我想要丰富现有的代码，在接收到某些不允许的数据时抛出异常，我做了以下更改：
private Flux<Integer> testGetFluxTestData2() {
return Flux.just(new TestData(1), new TestData(2))
.collectList()
.flatMapMany(list -> {
if (!list.contains(new TestData(1))) {
return Flux.fromIterable(list.stream()
.map(TestData::getId)
.collect(Collectors.toList()));
} else {
return Flux.error(new IllegalTestDataException("illegal test data 1"));
}
});
}
但是我的实现甚至因为以下这一行而无法编译通过：
Flux.error(new IllegalTestDataException("illegal test data 1"));
请问，您能否建议如何处理我特定情况下的异常抛出？
英文:
Existing code that I have:
private Flux<Integer> testGetFluxTestData() {
return Flux.just(new TestData(1), new TestData(2))
.collectList()
.map(list -> list.stream()
.map(TestData::getId)
.collect(Collectors.toList()))
.flatMapMany(Flux::fromIterable);
}
I want to enrich existing code and throw an exception when some not allowed data received, I made the following changes:
private Flux<Integer> testGetFluxTestData2() {
return Flux.just(new TestData(1), new TestData(2))
.collectList()
.map(list -> {
return !list.contains(new TestData(1)) ?
list.stream()
.map(TestData::getId)
.collect(Collectors.toList()) :
Flux.error(new IllegalTestDataException("illegal test data 1"));
})
.flatMapMany(Flux::fromIterable);
}
but my implementation even noncompilable due to the following line:
Flux.error(new IllegalTestDataException("illegal test data 1"));
Could you please suggest, how to handle exception throwing for my particular scenario?
答案1
得分: 1
你正在尝试从 List<TestData> 进行 map 操作，目标要么是 List<Integer>，要么是 Flux<?>（错误），这使得所需的结果类型不明确。在映射函数中返回响应式类型通常是不希望的（你应该在 flatMapping 函数中执行此操作）。
（顺便说一下：即使你在 flatMap 中，也不会起作用，因为在那时，由于 collectList，你已经在 Mono API 中，所以 Mono.flatMap 期望将结果返回给 Mono）。
请注意，map 操作符捕获来自 lambda 的异常并将它们转换为 onError 信号，因此从技术上讲，你可以用 throw 替换 Flux.error。
否则，你需要将 map 转换为 flatMap，并将 Flux.error 转换为 Mono.error，原因如上所述。
英文:
You are attempting to map from a List<TestData> to either a List<Integer> or a Flux<?> (error), which makes the desired result type ambiguous. Returning a reactive type in a mapping function is generally not desired (you'd want to do that in a flatmapping function).
(side note: even if you were in a flatMap, it wouldn't work either because at that point you're in Mono API due to collectList, so Mono.flatMap expects a Mono result to the Function).
Note that the map operator catches exceptions from the lambda and turn them into an onError signal, so technically you could replace the Flux.error with a throw.
Otherwise, you'd need to turn the map into a flatMap and the Flux.error into a Mono.error, for the reasons stated above.
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