将多个数组减少为列表

Question

我试图通过这样做来过滤并减少使用Java8新lambda 的List<Map<String, Object>>to List<String>:

List<Map<String, Object>> myObjects = new ArrayList<>();
myObjects.stream()
    .filter(myObject-> myObject.get("some integer value").equals(expectedValue))
    // myObject.get("some attribute") == ["some string", "maybe another string"]
    .map(myObject-> myObject.get("some attribute"))
    .collect(Collectors.toList());

结果是List,但我想将数组中的所有字符串组合到结果中List<String>.

为了澄清它,这是我现在得到的结果:

ArrayList{["some string"], ["another string"]}

但我想要这个:

ArrayList{"some string", "another string"}

有人可以给我一个提示,我必须将哪一部分减少String[]到一个String？我猜它本身,.map()但我不知道我会在那里改变什么.

编辑:

这就是如何List<Map<String, Object>> myObjects为测试目的生成的:

List<Map<String, Object>> myObjects = new ArrayList<>();
Map<String, Object> myObject = new HashMap<>();
myObject.put("some integer value", 1);
String[] theStringIWant = new String[1];
theStringIWant[0] = "Some important information I want";
myObject.put("some attribute", theStringIWant);
myObjects.add(myObject);

看起来像这样:

List<MyObject{"some attribute": 1}>

注意:这只是我的unittest的一个例子.列表规范包含多个元素,每个地图都有更多的属性,而不仅仅是some attribute.

Answer 1

您可能需要另一个过滤器，但这就是我的制作方法：

public static void main(String[] args) {
    List<Map<String, Object>> myObjects = new ArrayList<>();
    Map<String, Object> myObject1 = new HashMap<>();

    myObject1.put("some attribute", 1);
    myObject1.put("some string", new String[] { "Some important information I want"});
    myObjects.add(myObject1);

    Map<String, Object> myObject2 = new HashMap<>();
    myObject2.put("some attribute", 1);
    myObject2.put("some string", new String[] { "hello", "world" });
    myObjects.add(myObject2);

    Map<String, Object> myObject3 = new HashMap<>();
    myObject3.put("some attribute", 2);
    myObject3.put("some string", new String[] { "don't", "want", "this"});
    myObjects.add(myObject3);

    Map<String, Object> myObject4 = new HashMap<>();
    myObject4.put("some string", new String[] { "this", "one", "does", "not", "have", "some attribute"});
    myObjects.add(myObject4);

    List<String> list = myObjects.stream()
            .filter(map -> map.containsKey("some attribute"))
            .filter(map -> map.get("some attribute").equals(Integer.valueOf(1)))
            .flatMap(map -> Arrays.stream((String[])map.get("some string")))
            .collect(Collectors.toList());

        System.out.println(list);
    }

结果是[Some important information I want, hello, world]