英文:
Optionally call .distinct() in the middle of a Streams API function call chain
问题
我找不到同时使用Streams API和在聚合操作的“pipeline”中进行简短条件添加（例如.distinct()调用）的方法。
以下代码显示了我在条件性的.distinct()调用后不得不重复.filter调用，使代码比我想要的更冗长：
AtomicInteger index = new AtomicInteger();
Supplier<Stream<NodeXType>> nodexSupplier = () -> myXMLPayload.getNodeXs().stream();
// 避免BUG，其中NodeXs在影响测试的情况下在Payload XML中重复。
if (NODE_X.length < nodexSupplier.get().filter(e -> e.getSubTypeofNode_X().equalsIgnoreCase("myTargetValue")).count()){
LOGGER.log(Level.WARNING, "had more sub-type values than expected, so removed duplicates");
nodexSupplier.get()
.distinct()
.filter(e -> e.getSubTypeofNode_X().equalsIgnoreCase("myTargetValue"))
.forEachOrdered(e -> {
assertEquals(" myTargetValue nodes not updated to expected value",
e.getSubTypeofNode_X().getNewValue().toString(), NODE_X[index.getAndIncrement()]);
});
} else {
nodexSupplier.get()
.filter(e -> e.getSubTypeofNode_X().equalsIgnoreCase("myTargetValue"))
.forEachOrdered(e -> {
assertEquals(" myTargetValue nodes not updated to expected value",
e.getSubTypeofNode_X().getNewValue().toString(), NODE_X[index.getAndIncrement()]);
});
}
是否有一种方法可以避免这种情况，而不违反Streams的规则？
像这样：
pipelineObj = Source.stream()
if (condition) {pipelineObj.distinct}
pipelineObj.filter{}...
英文:
I cannot find a way to use the Streams API and to have a short conditional addition to the 'pipeline' of an aggregate operation like a .distinct() call.
The following code shows how I have to duplicate the .filter call after the conditional .distinct() call, making the code more verbose than I'd like:
AtomicInteger index = new AtomicInteger();
Supplier<Stream<NodeXType>> nodexSupplier = () -> myXMLPayload.getNodeXs().stream();
// Avoid BUG where the NodeXs are duplicated in the Payload XML impacting tests.
if (NODE_X.length < nodexSupplier.get().filter(e -> e.getSubTypeofNode_X().equalsIgnoreCase("myTargetValue")).count()){
LOGGER.log(Level.WARNING, "had more sub-type values than expected, so removed duplicates");
nodexSupplier.get()
.distinct()
.filter(e -> e.getSubTypeofNode_X().equalsIgnoreCase("myTargetValue"))
.forEachOrdered(e -> {
assertEquals(" myTargetValue nodes not updated to expected value",
e.getSubTypeofNode_X().getNewValue().toString(), NODE_X[index.getAndIncrement()]);
});
} else {
nodexSupplier.get()
.filter(e -> e.getSubTypeofNode_X().equalsIgnoreCase("myTargetValue"))
.forEachOrdered(e -> {
assertEquals(" myTargetValue nodes not updated to expected value",
e.getSubTypeofNode_X().getNewValue().toString(), NODE_X[index.getAndIncrement()]);
});
}
Is there a way to avoid this, without breaking the Streams rules?
like:
pipelineObj = Source.stream()
if (condition) {pipelineObj.distinct}
pipelineObj.filter{}...
答案1
得分: 5
只要在单个流上不多次执行终端操作，将流放入变量中是可以的：
Stream<NodeXType> pipelineObj = nodexSupplier.get();
if (NODE_X.length < pipelineObj.filter(e -> e.getSubTypeofNode_X().equalsIgnoreCase("myTargetValue")).count()) {
pipelineObj = pipelineObj.distinct();
}
pipelineObj
.filter(e -> e.getSubTypeofNode_X().equalsIgnoreCase("myTargetValue"))
.forEachOrdered(e -> {
assertEquals(" myTargetValue节点未更新为预期值",
e.getSubTypeofNode_X().getNewValue().toString(), NODE_X[index.getAndIncrement()]);
});
不过，你可能想要解决关于两次调用nodexSupplier.get()的问题...
英文:
As long as you don't do terminal operations multiple times on a single stream, it's okay to put the stream into a variable:
Stream<NodeXType> pipelineObj = nodexSupplier.get();
if (NODE_X.length < nodexSupplier.get().filter(e -> e.getSubTypeofNode_X().equalsIgnoreCase("myTargetValue")).count()) {
pipelineObj = pipelineObj.distinct();
}
pipelineObj
.filter(e -> e.getSubTypeofNode_X().equalsIgnoreCase("myTargetValue"))
.forEachOrdered(e -> {
assertEquals(" myTargetValue nodes not updated to expected value",
e.getSubTypeofNode_X().getNewValue().toString(), NODE_X[index.getAndIncrement()]);
});
However, you might want to do something about calling nodexSupplier.get() twice...
答案2
得分: 2
写一个实用方法：
```java
static <T> Stream<T> distinctIf(Stream<T> s, boolean b) {
return b ? s.distinct() : s;
}
英文:
Write a utility method:
static <T> Stream<T> distinctIf(Stream<T> s, boolean b) {
return b ? s.distinct() : s;
}
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