Java 8 在java 8流的收集阶段,是否可以过滤/忽略对象?
这个问题与我不久前发表的文章有关 我找到了一种方法,可以按照我想要的方式对数据进行分组。但由于我需要对对象进行分组/映射,所以在收集过程中,当我需要应用一些过滤时,我已经关闭了流。我有以下代码:Java 8 在java 8流的收集阶段,是否可以过滤/忽略对象?,java-8,java-stream,collectors,Java 8,Java Stream,Collectors,这个问题与我不久前发表的文章有关 我找到了一种方法,可以按照我想要的方式对数据进行分组。但由于我需要对对象进行分组/映射,所以在收集过程中,当我需要应用一些过滤时,我已经关闭了流。我有以下代码: final Map<TeamDetails, List<Player>> teamDetailsPlayerListMap = dbRows.stream().map(row -> mapDbRowToTeamPlayerPair(row))
final Map<TeamDetails, List<Player>> teamDetailsPlayerListMap =
dbRows.stream().map(row -> mapDbRowToTeamPlayerPair(row))
.collect(Collectors.groupingBy(TeamPlayerPair::getKey,
Collectors.mapping(TeamPlayerPair::getValue, Collectors.toList())));
final List<Team> teams = teamDetailsPlayerListMap.entrySet().stream()
.map(teamPlayerList -> mapTeamPlayerListToTeam(teamPlayerList))
.collect(Collectors.toList());
其中MyCollectors.toFilteredLinkedList()是:
public class MyCollectors {
public static <T, A extends Collection<T>> Collector<T, ?, A> toFilteredCollection(Supplier<A> collectionFactory, Function<T, Boolean> filter) {
return Collector.of(
collectionFactory,
(acc, entry) -> {
if (filter.apply(entry)) {
acc.add(entry);
}
},
(left, right) -> { left.addAll(right); return left; }
);
}
public static <T> Collector<T, ?, List<T>> toFilteredLinkedList(Function<T, Boolean> filter) {
return toFilteredCollection(LinkedList<T>::new, filter);
}
}
公共类MyCollector{
公共静态收集器ToFiltedCollection(供应商收集工厂、函数过滤器){
返回收集器(
收藏工厂,
(acc,条目)->{
如果(筛选应用(条目)){
acc.add(条目);
}
},
(左,右)->{left.addAll(右);返回左;}
);
}
公共静态收集器toFilteredLinkedList(函数筛选器){
返回到FilteredCollection(LinkedList::new,filter);
}
}
似乎您需要一个过滤
收集器,它类似于映射
,但执行过滤。它已经出现在Java-9中,但在Java-8中不存在。您可以将其放入项目中的某个实用程序类中:
public static <T, A, R> Collector<T, A, R> filtering(
Predicate<? super T> filter, Collector<T, A, R> downstream) {
BiConsumer<A, T> accumulator = downstream.accumulator();
Set<Characteristics> characteristics = downstream.characteristics();
return Collector.of(downstream.supplier(), (acc, t) -> {
if(filter.test(t)) accumulator.accept(acc, t);
}, downstream.combiner(), downstream.finisher(),
characteristics.toArray(new Collector.Characteristics[0]));
}
公共静态收集器筛选(
谓语
public static <T, A, R> Collector<T, A, R> filtering(
Predicate<? super T> filter, Collector<T, A, R> downstream) {
BiConsumer<A, T> accumulator = downstream.accumulator();
Set<Characteristics> characteristics = downstream.characteristics();
return Collector.of(downstream.supplier(), (acc, t) -> {
if(filter.test(t)) accumulator.accept(acc, t);
}, downstream.combiner(), downstream.finisher(),
characteristics.toArray(new Collector.Characteristics[0]));
}
final Map<TeamDetails, List<Player>> teamDetailsPlayerListMap =
dbRows.stream()
.map(row -> mapDbRowToTeamPlayerPair(row))
.collect(Collectors.groupingBy(TeamPlayerPair::getKey,
Collectors.mapping(TeamPlayerPair::getValue,
filtering(player -> player != null && player.getName() != null
&& !player.getName().isEmpty(), Collectors.toList()))));