1.for循环

import com.google.common.base.Function;import com.google.common.collect.Maps;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;public class ListToMap { public static void main(String[] args) { List<User> userList = new ArrayList<>(); User user1 = new User(); user1.setId(1L); user1.setAge("12"); User user2 = new User(); user2.setId(2L); user2.setAge("13"); userList.add(user1); userList.add(user2); Map<Long, User> maps = new HashMap<>(); for (User user : userList) { maps.put(user.getId(), user); } System.out.println(maps); } public static class User { private Long id; private String age; public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getAge() { return age; } public void setAge(String age) { this.age = age; } @Override public String toString() { return "User{" + "id=" + id + ", age='" + age + '\'' + '}'; } }}

2.使用guava

Map<Long, User> maps = Maps.uniqueIndex(userList, new Function<User, Long>() { @Override public Long apply(User user) { return user.getId(); }});

3.使用JDK1.8

Map<Long, User> maps = userList.stream().collect(Collectors.toMap(User::getId, user -> user));

看来还是使用JDK 1.8方便一些。

总结

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