使用单个流收集映射的多个属性

Question

public class TeamMates{

    private String playerFirstName;
    private String playerLastName;
    private String playerMaidenName;

    //Constructors , getters and Setters    
}

(playerFirstName,("John","Bob"));
(playerLastName,("Joe","Henry"));
(playerMaidenName,("H","K"));

由于我不想多次使用流来单独收集每个属性，也不想使用foreach来收集每个属性，是否有任何方法可以用单个流来获得上述属性。

Answer 1

首先，创建一个生成值的getter方法和它们各自的字段名的映射。

// Map.of is available from Java 9. 
// If you are using java 8 you could create the below using a normal HashMap.
Map<String, Function<TeamMates, String>> mapper 
    = Map.of("playerFirstName", TeamMates::getPlayerFirstName,
             "playerLastName", TeamMates::getPlayerLastName,
             "playerMaidenName", TeamMates::getPlayerMaidenName);

现在迭代这个映射器函数，并将每个映射应用到队友列表

// applies getter method on each teammate object and returns the list of strings.
Function<Function<TeamMates, String>, List<String>> listMapper 
    = fn -> list.stream().map(fn::apply).collect(Collectors.toList());

// assume static import of Collectors.toMap
Map<String, List<String>> map = mapper.entrySet().stream()
                                      .collect(toMap(Entry::getKey,
                                                     e -> listMapper.apply(e.getValue())));

我还建议将您的类命名为Teammate而不是Teammate，因为该类代表一个团队成员实体。