在Java的映射列表中按键查找值

Question

我有以下方式的地图列表：

List<Map<String,String>> input = 
[{AddressField=AddressUsageType, AddressValue=PRINCIPAL},  {AddressField=StreetNumber, AddressValue=2020}, {AddressField=StreetName, AddressValue=Some street}]

我想从地址字段的值中获取地址值。例如，

我想从键值"AddressUsageType"中获取值"PRINCIPAL"

我尝试过使用过滤器和许多其他MAP函数，但最终没有找到合适的解决方案。

这是我的代码片段，获取第一个键值对的值：

DataTable table;
List<Map<String,String>> input= table.asMaps(String.class, String.class);

    String AddressField = input.get(0).get("AddressField");
    String AddressValue = input.get(0).get("AddressValue");
    System.out.println("AddressField " +AddressField);
    System.out.println("AddressValue " +AddressValue);

以下是上述片段的输出：

AddressField AddressUsageType
AddressValue PRINCIPAL

Answer 1

过滤输入以仅保留包含AddressField=AddressUsageType的映射。然后使用提取地址值条目。映射函数并将其收集到结果列表中。

public static void main(String[] args) {
    List<Map<String, String>> input = new ArrayList<>();
    Map<String, String> map = new HashMap<>();
    map.put("AddressField", "AddressUsageType");
    map.put("AddressValue", "PRINCIPAL");
    input.add(map);

    map = new HashMap<>();
    map.put("AddressField", "StreetNumber");
    map.put("AddressValue", "2020");
    input.add(map);
    map = new HashMap<>();
    map.put("AddressField", "StreetName");
    map.put("AddressValue", "Some street");
    input.add(map);

    map = new HashMap<>();
    map.put("AddressField", "AddressUsageType");
    map.put("AddressValue", "NOT_PRINCIPAL");
    input.add(map);
    
    List<String> collect = input.stream().filter(e -> e.get("AddressField").equals("AddressUsageType"))
            .map(e -> e.get("AddressValue")).collect(Collectors.toList());
    System.out.println(input);
    System.out.println(collect);
}

输出是

[{地址字段=地址用户类型，地址值=PRINCIPAL}，{地址字段=街道号，地址值=2020}，{地址字段=街道名称，地址值=一些街道}，{地址字段=地址用户类型，地址值=NOT_PRINCIPAL}]

[校长，NOT_PRINCIPAL]

Answer 2

我想这就是你想要的：

Map<String, String> map = data.stream()
        .filter(m -> m.values().contains("AddressUsageType"))
        .findFirst()
        .orElse(null);

if (map != null) {
    System.out.println("AddressField " + map.get("AddressField"));
    System.out.println("AddressValue " + map.get("AddressValue"));
}

这里还有一条测试主线

public class Test {
    public static void main(String[] args) {
        List<Map<String, String>> data = new ArrayList<>();

        Map<String, String> map1 = new HashMap<>();
        map1.put("AddressField", "AddressUsageType");
        map1.put("AddressValue", "PRINCIPAL");
        data.add(map1);

        Map<String, String> map2 = new HashMap<>();
        map2.put("AddressField", "StreetNumber");
        map2.put("AddressValue", "2020");
        data.add(map2);

        Map<String, String> map3 = new HashMap<>();
        map3.put("AddressField", "StreetName");
        map3.put("AddressValue", "Some street");
        data.add(map3);

        Map<String, String> map = data.stream()
                .filter(m -> m.values().contains("AddressUsageType"))
                .findFirst()
                .orElse(null);

        if (map != null) {
            System.out.println("AddressField " + map.get("AddressField"));
            System.out.println("AddressValue " + map.get("AddressValue"));
        }
    }
}

Answer 3

在这里，您对映射的使用有点奇怪，因为您的实际键“AddressUsageType”是映射中的一个值，而每个映射只是存储在静态键后面的一对键和值。如果你不能改变这一点，你可以这样做：

String key = "AddressUsageType";
String result = "";

for (Map<String,String> map : input)
{
    if (map.containsValue(key))
    {
        result = map.get("AddressValue");
        break;
    }
}

System.out.println(key + " is " + result);