相关疑难解决方法(0)

拥有键值列表:

public class KeyValue {

    private Long key;

    private Long value;

    public KeyValue(long key, long value) {
        this.key = key;
        this.value = value;
    } 

    //getters, setters, toStrings...
}

...

    List<KeyValue> values = new ArrayList<>();
    values.add(new KeyValue(15, 10));
    values.add(new KeyValue(15, 12));
    values.add(new KeyValue(25, 13));
    values.add(new KeyValue(25, 15));

如何使用Java 8 API将其转换为Multimap？

程序方式:

    Map<Long, List<Long>> keyValsMap = new HashMap<>();
    for (KeyValue dto : values) {
        if (keyValsMap.containsKey(dto.getKey())) {
            keyValsMap.get(dto.getKey()).add(dto.getValue());
        } else {
            List<Long> list = new ArrayList<>();
            list.add(dto.getValue());
            keyValsMap.put(dto.getKey(), list);
        }
    }

结果: …