我想知道如何在条件下选择使用流过滤器。也就是说,我是否可以使用fiter来决定变量。
我原来的代码是:
if (keyword == null) {
return list.parallelStream()
//not using filter
.map(...)
.collect(Collectors.toList());
}
return list.parallelStream()
.filter(dto -> dto.getString().contains(keyword))
.map(...)
.collect(Collectors.toList());
那么我可以将两个return语句混合成一个吗?喜欢
return list.parallelStream()
.filterIfKeywordNonNull(dto -> dto.getString().contains(keyword))
.map(...)
.collect(Collectors.toList());
提前谢谢。
答案 0 :(得分:3)
您只需将keyword
测试添加到过滤器即可。像,
return list.parallelStream()
.filter(dto -> keyword == null || dto.getString().contains(keyword))
.map(...)
.collect(Collectors.toList());
为了提高效率,还可以构建Stream
一次,并使用三元组保存临时变量。像,
Stream<T> stream = (keyword == null) ? list.parallelStream() :
list.parallelStream().filter(dto -> dto.getString().contains(keyword));
return stream.map(...).collect(Collectors.toList());
您可以在回复中使用三元组,但是您必须重复map
和collect
来电。
答案 1 :(得分:1)
.filter(getFilter(dto));
和
private static Predicate getFilter(String dto){
// logic here. either return Filter A's singleton instance or return Null filter (that allows to pass everything i.e. `(dto)-> true`)
}
答案 2 :(得分:0)
因为过滤器不是结束流条件。你可以随时添加它。那么,这个怎么样?
public class ConditionalStreams {
//send your stream, a boolean, and the filter condition
public static Stream<Integer> filterFun(Stream<Integer> stream, boolean needToFilter, Predicate<Integer> filterStream){
if(needToFilter)
return stream.filter(filterStream);
else
return stream;
}
public static void main(String[] args) {
List<Integer> numbers = Arrays.asList(1,2,3,4,5,6);
// create your filter condition
Predicate<Integer> filterStream = (num)->num%2==0;
System.out.println("without filter: ");
//call the function, pass parameters and return the right stream and process it.
filterFun(numbers.parallelStream(),false,filterStream)
.forEach(System.out::println);
System.out.println("with filter : ");
filterFun(numbers.parallelStream(),true,filterStream)
.forEach(System.out::println);
}
}