看代碼：Collection<MyDto> col = ...MyBuilder builder = new MyBuilder(); for (MyDto dto: col) { switch (dto.getType()) { case FIELD1: builder.field1(dto.getValue()); break: case FIELD2: builder.field2(dto.getValue()); break: } }Some result = builder.build();有沒(méi)有辦法用流來(lái)做到這一點(diǎn)，比如：Some result = col.stream().collect(...)請(qǐng)注意，所有流值都被收集到單個(gè) pojo 中，而不是集合、流或映射。
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慕尼黑8549860
TA貢獻(xiàn)1818條經(jīng)驗(yàn) 獲得超11個(gè)贊
假設(shè)兩個(gè)MyBuilder實(shí)例能夠合并/合并，那么您可以使用Collector.
public class MyCollector implements Collector<MyDto, MyBuilder, Result> {
@Override
public Supplier<MyBuilder> supplier() {
return MyBuilder::new;
}
@Override
public BiConsumer<MyBuilder, MyDto> accumulator() {
return (builder, dto) -> {
// Add "dto" to "builder" based on type
};
}
@Override
public BinaryOperator<MyBuilder> combiner() {
return (left, right) -> left.merge(right);
}
@Override
public Function<MyBuilder, Result> finisher() {
return MyBuilder::build;
}
@Override
public Set<Characteristics> characteristics() {
return Set.of();
}
}
那么你可以這樣做：
Collection<MyDto> col = ...;
Result r = col.stream().collect(new MyCollector());
如果您不想自定義實(shí)現(xiàn)，Collector可以使用Collector.of(...).
另一種可能更易于維護(hù)的方法是讓構(gòu)建器完成所有工作。這樣所有的映射邏輯都集中在一個(gè)地方。
public class ResultBuilder {
public static Collector<MyDto, ?, Result> resultCollector() {
return Collector.of(ResultBuilder::new, ResultBuilder::add,
ResultBuilder::merge, ResultBuilder::build);
}
public ResultBuilder add(MyDto dto) {
// Do what is needed based on the type of "dto"
return this;
}
public ResultBuilder merge(ResultBuilder other) {
// Merge "other" into "this"
return this;
}
public Result build() {
// Build result and return it
}
}
然后您可以使用帶或不帶流的構(gòu)建器。使用流與之前非常相似：
Collection<MyDto> col = ...;
Result r = col.stream().collect(ResultBuilder.resultCollector());
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