Java Stream进阶：将单一键映射至复合值对象以存储多属性信息

// 假设 futureList 是 CompletableFuture<Optional<UserProfile>> 的列表
Map<UserId, String> userIdToEmailMap = futureList.stream()
    .map(CompletableFuture::join) // 等待 CompletableFuture 完成并获取结果
    .filter(Optional::isPresent) // 过滤掉空的 Optional
    .map(Optional::get) // 获取 Optional 内部的 UserProfile 对象
    .collect(Collectors.toMap(
        UserProfile::getUserId, // 键：UserId
        UserProfile::getEmail   // 值：Email
    ));

import java.util.concurrent.CompletableFuture;
import java.util.Optional;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

// 假设 UserId 和 UserProfile 类已定义
// class UserId { /* ... */ }
// class UserProfile {
//     private UserId userId;
//     private String name;
//     private String email;
//     // 构造函数、getter方法等
//     public UserId getUserId() { return userId; }
//     public String getName() { return name; }
//     public String getEmail() { return email; }
// }

public class UserProfileMapper {

    public static Map<UserId, UserProfile> mapUserIdToUserProfile(
            java.util.List<CompletableFuture<Optional<UserProfile>>> futureList) {

        return futureList.stream()
            .map(CompletableFuture::join) // 等待所有 CompletableFuture 完成
            .filter(Optional::isPresent) // 过滤掉空的 Optional
            .map(Optional::get) // 从 Optional 中提取 UserProfile 对象
            .collect(Collectors.toMap(
                UserProfile::getUserId, // 键映射器：使用 UserProfile 的 userId 作为键
                Function.identity()     // 值映射器：使用 UserProfile 对象本身作为值
            ));
    }

    // 示例用法 (假设 UserId 和 UserProfile 类存在)
    public static void main(String[] args) {
        // 模拟数据
        UserId user1Id = new UserId("u001");
        UserId user2Id = new UserId("u002");

        UserProfile user1Profile = new UserProfile(user1Id, "Alice", "alice@example.com");
        UserProfile user2Profile = new UserProfile(user2Id, "Bob", "bob@example.com");

        java.util.List<CompletableFuture<Optional<UserProfile>>> futureList = java.util.Arrays.asList(
            CompletableFuture.completedFuture(Optional.of(user1Profile)),
            CompletableFuture.completedFuture(Optional.of(user2Profile)),
            CompletableFuture.completedFuture(Optional.empty()) // 模拟一个空结果
        );

        Map<UserId, UserProfile> userMap = mapUserIdToUserProfile(futureList);

        // 验证结果
        UserProfile retrievedUser1 = userMap.get(user1Id);
        if (retrievedUser1 != null) {
            System.out.println("User 1 Name: " + retrievedUser1.getName());
            System.out.println("User 1 Email: " + retrievedUser1.getEmail());
        }

        UserProfile retrievedUser2 = userMap.get(user2Id);
        if (retrievedUser2 != null) {
            System.out.println("User 2 Name: " + retrievedUser2.getName());
            System.out.println("User 2 Email: " + retrievedUser2.getEmail());
        }

        // 尝试获取不存在的用户
        System.out.println("Non-existent user: " + userMap.get(new UserId("u003")));
    }
}

// 辅助类定义 (为示例完整性)
class UserId {
    private String id;
    public UserId(String id) { this.id = id; }
    public String getId() { return id; }
    @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; UserId userId = (UserId) o; return id.equals(userId.id); }
    @Override public int hashCode() { return id.hashCode(); }
    @Override public String toString() { return "UserId{" + "id='" + id + '\'' + '}'; }
}

class UserProfile {
    private UserId userId;
    private String name;
    private String email;
    public UserProfile(UserId userId, String name, String email) {
        this.userId = userId;
        this.name = name;
        this.email = email;
    }
    public UserId getUserId() { return userId; }
    public String getName() { return name; }
    public String getEmail() { return email; }
    @Override public String toString() { return "UserProfile{userId=" + userId + ", name='" + name + '\'' + ", email='" + email + '\'' + '}'; }
}

UserProfile userProfile = userMap.get(someUserId);
if (userProfile != null) {
    String userName = userProfile.getName();
    String userEmail = userProfile.getEmail();
    System.out.println("Name: " + userName + ", Email: " + userEmail);
}