Stream API提供distinct()方法，该方法基于数据Object类的equals()方法返回列表的不同元素。下面先做一个数据Object类，用来发现重复数据：

public class LegacyObject {

private final UUID id;

private final String foo;

private final int bar;

public LegacyObject(UUID id, String foo, int bar) {

this.id = id;

this.foo = foo;

this.bar = bar;

}

@Override

public int hashCode() {

return Objects.hash(id);

}

// Implementation of equals() using only the id field

// Getters

}

public class DeduplicateWrapper {

private final LegacyObject object;

public DeduplicateWrapper(LegacyObject object) {

this.object = object;

}

public LegacyObject getObject() {

return object;

}

@Override

public int hashCode() {

return Objects.hash(object.getFoo());

}

// Implementation of equals() using only the foo field of the wrapped object

}

使用流API重复删除集合：

List duplicates = ...;

duplicates.stream()

.map(DeduplicateWrapper::new)

.distinct()

.map(DeduplicateWrapper::getObject);

不使用Stream的Java8之前代码

List deduplicated = new ArrayList<>();

Set wrappers = new HashSet<>();

for (LegacyObject duplicate: duplicates) {

wrappers.add(new DeduplicateWrapper(duplicate));

}

for (DeduplicateWrapper wrapper: wrappers) {

deduplicated.add(wrapper.getObject());

}

如果你足够幸运能够使用Kotlin:

val duplicates: List = ...

duplicates.distinctBy { it.foo }