如何使用流转换地图值

Question

我有一个任务：返回一个公司地图，其中键是它的名称，值是存储为String的员工列表，由firstName和lastName组成，用空格分隔。这是我的解决方案和它的工作罚款：

    Map<String, List<String>> getUserPerCompanyAsString() {
        return getCompanyStream()
                .collect(Collectors.toMap(Company::getName, company ->  getUserNames(company.getUsers())));
    }

    private List<String> getUserNames(List<User> users) {
        return users.stream()
                .map(user -> user.getFirstName() + " " + user.getLastName())
                .collect(Collectors.toList());
    }

public class Company {
    private final String name;
    private final List<User> users;
}

public class User {
    private final String firstName;
    private final String lastName;
    private final Sex sex;
    private final int age;
    private final List<Account> accounts;
    private final List<Permit> permits;
}

所以我的问题是，如何转换列表




Answer 1

我知道你想利用助手的方法。一种更简洁的方法是将getUserNames方法包含在公司中，这比将此逻辑挂在收集器中更有意义。

解决方案也会更具可读性

Map<String, List<String>> getUserPerCompanyAsString() {
    return getCompanyStream().collect(
        Collectors.toMap(
            Company::getName,
            Company::getUserNames
        )
    );
}



public class Company {
    private final String name;
    private final List<User> users;

    // Constructor making sure users is not null

    private List<String> getUserNames() {
        return this.users
                   .stream()
                   .map(User::getFullName)
                   .collect(Collectors.toList());
    }
}

public class User {
    private final String firstName;
    private final String lastName;
    
    // Etc.

    public String getFullName() {
        return firstName + " " + lastName;
    }
}

Answer 2

解决方案

多亏了托马斯的建议，我不需要助手就能解决这个问题：

    Map<String, List<String>> getUserPerCompanyAsString() {
        return getCompanyStream()
                .collect(Collectors.toMap(Company::getName, company -> company.getUsers().stream()
                                .map(user -> user.getFirstName() + " " + user.getLastName())
                                .collect(Collectors.toList())));