只要你调用contains, containsAll, equals, hashCode, remove, retainAll, size或toArray，你就必须遍历元素。

如果您偶尔只调用isEmpty或clear等方法，我认为您最好是惰性地创建集合。例如，你可以有一个支持数组列表来存储先前迭代的元素。

我不知道任何一个库中有这样的类，但是编写它应该是一个相当简单的练习。

来自common -collections的IteratorUtils可能会有所帮助(尽管它们在最新的稳定版本3.2.1中不支持泛型):

@SuppressWarnings("unchecked")
Collection<Type> list = IteratorUtils.toList(iterable.iterator());

4.0版本(目前在SNAPSHOT中)支持泛型，您可以去掉@SuppressWarnings。

更新:检查IterableAsList从仙人掌。

在JDK 8+中，不使用任何额外的库:

Iterator<T> source = ...;
List<T> target = new ArrayList<>();
source.forEachRemaining(target::add);

编辑:上面的是迭代器。如果你在处理Iterable，

iterable.forEach(target::add);

当你从Spring Data中获得你的Iterable时，你有两个额外的选择。

You can override the method that returns the Iterable in the repository with a version that returns a List, Set or Streamable. This way Spring Data is doing the conversion for you. You may do so in a super interface of your repositories so you don't have to repeat the override in all your repository interfaces. If you happen to use Spring Data JPA this is already done for you in JpaRepository You may do the conversion using the just mentioned Streamable yourself: Iterable<X> iterable = repo.findAll(); List<X> list = Streamable.of(iterable).toList();

既然你提到了沮丧，也许还有一些决定使用Iterable帮助的背景。

It is expected that it is actually fairly rare to actually require a Collection so in many cases it shouldn't make a difference. Using the overriding mechanics one can return different types which wouldn't be possible with a more specific return type like Collection. This would make it impossible to return a Streamable which is intended for cases where a store may decide to return a result before all elements have been fetched. Streamable would actually be a flexible return type, since it offers easy conversions to List, Set, Stream and is itself an Iterable. But this would require you to use a Spring Data specific type in your application which many users wouldn't like.

在参考文档中有关于这方面的章节。

从CollectionUtils:

List<T> targetCollection = new ArrayList<T>();
CollectionUtils.addAll(targetCollection, iterable.iterator())

下面是这个实用方法的完整源代码:

public static <T> void addAll(Collection<T> collection, Iterator<T> iterator) {
    while (iterator.hasNext()) {
        collection.add(iterator.next());
    }
}

我在试图获取项目列表时遇到了类似的情况，而不是在CrudRepository接口中声明的默认Iterable<T> findAll()。因此，在我的ProjectRepository接口(从CrudRepository扩展而来)中，我简单地声明了findAll()方法来返回一个List<Project>而不是Iterable<Project>。

package com.example.projectmanagement.dao;

import com.example.projectmanagement.entities.Project;
import org.springframework.data.repository.CrudRepository;
import java.util.List;

public interface ProjectRepository extends CrudRepository<Project, Long> {

    @Override
    List<Project> findAll();
}

我认为这是最简单的解决方案，不需要转换逻辑或使用外部库。