Java 8 如何使用 lambda 表达式简化 for 循环

Question

我的代码中有此方法，需要使用 java 8 表达式来简化和减少代码行。 Lambda 可用于此但如果没有列表作为输入似乎是不可能的。

  public ResourceUsage[] filterResourceUsages(ResourceUsage[] resourceUsages, int role, int includeResourceType)
    throws SpiderException
  {
    ArrayList<ResourceUsage> filteredResourceUsages = new ArrayList<>();

    String[] ids = new String[resourceUsages.length];
    for (int i = 0; i < resourceUsages.length; i++)
    {
      ids[i] = resourceUsages[i].resource;
    }

    ResourceData[] resourceData = resourceToolkitAdapter.getData(ids);

    for (int i = 0; i < resourceData.length; i++)
    {
      if (resourceUsages[i].role == role && resourceData[i].basic.type == includeResourceType)
      {
        filteredResourceUsages.add(resourceUsages[i]);
      }
    }
    return filteredResourceUsages.toArray(new ResourceUsage[filteredResourceUsages.size()]);
  }

我试过使用resourceUsages.forEach(resourceUsages.resource-> do something); 但没有列表作为输入似乎是不可能的。

有什么办法可以简化这段代码吗？

Answer 1

这是原点 arrays 和批处理解决方案：

public ResourceUsage[] filterResourceUsages(ResourceUsage[] resourceUsages, int role, int includeResourceType)
        throws SpiderException {

    String[] ids = Stream.of(resourceUsages)
            .map(ResourceUsage::getResource)
            .toArray(String[]::new);
    Map<String, ResourceData> resourceDataMap = Stream.of(resourceToolkitAdapter.getData(ids))
            .collect(Collectors.toMap(ResourceData::id, Function.identity()));
    return Stream.of(resourceUsages)
            .filter(usage -> usage.role == usage)
            .filter(resourceDataMap::containsKey)
            .filter(usage -> resourceDataMap.get(usage.resource).basic.type == includeResourceType)
            .toArray(ResourceUsage[]::new);
}

Answer 2

您可以使用 arrays 这样做

Arrays.stream(resourceUsages) 
            .forEach(e->System.out.print(e));

Answer 3

最好使用List<ResourceUsage>而不是 arrays。

我还打算假装可以在每个资源上依次调用resourceToolkitAdapter.getData() ，而不是批量调用。

结果将是这样的：

    public List<ResourceUsage> filterResourceUsages(List<ResourceUsage> resourceUsages, int role, int includeResourceType)
            throws SpiderException
    {
        return resourceUsages.stream()
                .filter(r->r.role == role)
                .filter(r->resourceToolkitAdapter.getData(r.resource).basic.type == includeResourceType)
                .collect(Collectors.toList());
    }   

Answer 4

与 Matthew 的回答相反，我认为resourceToolkitAdapter.getData()应该用一批 id 来调用。

public ResourceUsage[] filterResourceUsages(ResourceUsage[] resourceUsages, int role, int includeResourceType)
  throws SpiderException
{
  ResourceData[] resourceData = resourceToolkitAdapter.getData(
    Arrays.stream(resourceUsages)
      .map(r -> r.resource)
      .toArray(String[]::new)
  );

  return IntStream
    .range(0, resourceData.length)
    .filter(i -> resourceUsages[i].role == role )
    .filter(i -> resourceData[i].basic.type == includeResourceType)
    .mapToObj(i -> resourceUsages[i])
    .toArray(ResourceUsage[]::new);
}