[英]Java 8 Stream API Collector - addAll not applicable for argument Object, addAll is undefined for type Object
我的代码没有编译,我不太清楚为什么。 这是代码:
ArrayList<ClassificationData> classifications = productData
.stream()
.filter(p -> CollectionUtils.isNotEmpty(p.getClassifications()))
.flatMap(p -> p.getClassifications().stream())
.collect(groupingBy(ClassificationData::getName,
mapping(ClassificationData::getFeatures,
Collector.of(LinkedHashSet<FeatureData>::new,
(a,b) -> b.addAll(a),
(a,b) -> {
b.addAll(a);
return b;
})
)))
.entrySet()
.stream()
.map(e -> {
ClassificationData c = new ClassificationData();
c.setName(e.getKey());
c.setFeatures(e.getValue());
return c;
})
.collect(Collectors.toCollection(ArrayList::new));
而错误:
(a,b) -> b.addAll(a),
The method addAll(Collection<? extends FeatureData>) in the type Collection<FeatureData> is not applicable for the arguments (Object)
b.addAll(a);
The method addAll(Object) is undefined for the type Object
c.setFeatures(e.getValue());
The method setFeatures(Collection<FeatureData>) in the type ClassificationData is not applicable for the arguments (Object)
我也试过Set :: add和Set :: addAll,结果非常相似。
编辑:
我最终得到了这段代码。 请告诉我是否有更干净的方法来做到这一点,还是可以的?
ArrayList<ClassificationData> classifications = productData
.stream()
.filter(p -> CollectionUtils.isNotEmpty(p.getClassifications()))
.flatMap(p -> p.getClassifications().stream())
.collect(groupingBy(ClassificationData::getName,
mapping(ClassificationData::getFeatures,
toCollection(LinkedHashSet::new)
)))
.entrySet()
.stream()
.map(e -> {
ClassificationData c = new ClassificationData();
c.setCode(e.getKey());
c.setName(e.getKey());
c.setFeatures(e.getValue()
.stream()
.filter(CollectionUtils::isNotEmpty)
.flatMap(p -> p.stream())
.filter(distinctByKey(FeatureData::getName))
.collect(toCollection(ArrayList::new)));
return c;
})
.collect(toCollection(ArrayList::new));
我认为你在第一个lambda中搞乱了参数的顺序; 它应该是
(set, a) -> set.add(a)
......但坦率地说,用更换整个收藏家创作会更好
toCollection(LinkedHashSet::new)
这相当于。
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