Java中List使用stream流转成map的方法有哪些
这篇文章主要介绍了Java中List使用stream流转成map的方法有哪些的相关知识，内容详细易懂，操作简单快捷，具有一定借鉴价值，相信大家阅读完这篇Java中List使用stream流转成map的方法有哪些文章都会有所收获，下面我们一起来看看吧。
实体例子
public class Person {
private String name;
private String address;
public Person(String name, String address) {
this.name = name;
this.address = address;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
}
List 转成Map<String,Object>
List<Person> list = new ArrayList<>();
Person person1 = new Person("熊大","森林第一个小屋");
Person person2 = new Person("熊二","森林第二个小屋");
Person person3 = new Person("光头强","森林第三个小屋");
Person person4 = new Person("熊大","森林第四个小屋");
list.add(person1);
list.add(person2);
list.add(person3);
list.add(person4);
Map<String,Person> map = list.stream().collect(Collectors.toMap(Person::getName,each->each,(value1, value2) -> value1));
System.out.println(JSON.toJSONString(map));
控制台打印日志:
{“光头强”:{“address”:“森林第三个小屋”,“name”:“光头强”},“熊大”:{“address”:“森林第一个小屋”,“name”:“熊大”},“熊二”:{“address”:“森林第二个小屋”,“name”:“熊二”}}
List 转成Map<String,String>
List<Person> list = new ArrayList<>();
Person person1 = new Person("熊大","森林第一个小屋");
Person person2 = new Person("熊二","森林第二个小屋");
Person person3 = new Person("光头强","森林第三个小屋");
Person person4 = new Person("熊大","森林第四个小屋");
list.add(person1);
list.add(person2);
list.add(person3);
list.add(person4);
Map<String,String> map = list.stream().collect(Collectors.toMap(Person::getName,Person::getAddress,(value1, value2) -> value1));
System.out.println(JSON.toJSONString(map));
控制台打印日志:
{“光头强”:“森林第三个小屋”,“熊大”:“森林第一个小屋”,“熊二”:“森林第二个小屋”}
List 转成Map<String,List>
方法一:
List<Person> list = new ArrayList<>();
Person person1 = new Person("熊大","森林第一个小屋");
Person person2 = new Person("熊二","森林第二个小屋");
Person person3 = new Person("光头强","森林第三个小屋");
Person person4 = new Person("熊大","森林第四个小屋");
list.add(person1);
list.add(person2);
list.add(person3);
list.add(person4);
Map<String, List<Person>> map = list.stream().collect(Collectors.groupingBy(Person::getName));
System.out.println(JSON.toJSONString(map));
控制台打印日志:
{“光头强”:[{“address”:“森林第三个小屋”,“name”:“光头强”}],“熊大”:[{“address”:“森林第一个小屋”,“name”:“熊大”},{“address”:“森林第四个小屋”,“name”:“熊大”}],“熊二”:[{“address”:“森林第二个小屋”,“name”:“熊二”}]}
方法二:
List<Person> list = new ArrayList<>();
Person person1 = new Person("熊大","森林第一个小屋");
Person person2 = new Person("熊二","森林第二个小屋");
Person person3 = new Person("光头强","森林第三个小屋");
Person person4 = new Person("熊大","森林第四个小屋");
list.add(person1);
list.add(person2);
list.add(person3);
list.add(person4);
Map<String,List<Person>> map = list.stream().collect(Collectors.toMap(Person::getName,each->Collections.singletonList(each),(value1, value2) -> {
List<Person> union = new ArrayList<>(value1);
union.addAll(value2);
return union;
}));
System.out.println(JSON.toJSONString(map));
控制台打印日志:
{“光头强”:[{“address”:“森林第三个小屋”,“name”:“光头强”}],“熊大”:[{“address”:“森林第一个小屋”,“name”:“熊大”},{“address”:“森林第四个小屋”,“name”:“熊大”}],“熊二”:[{“address”:“森林第二个小屋”,“name”:“熊二”}]}
List 转成Map<String,List>
List<Person> list = new ArrayList<>();
Person person1 = new Person("熊大","森林第一个小屋");
Person person2 = new Person("熊二","森林第二个小屋");
Person person3 = new Person("光头强","森林第三个小屋");
Person person4 = new Person("熊大","森林第四个小屋");
list.add(person1);
list.add(person2);
list.add(person3);
list.add(person4);
Map<String,List<String>> map = list.stream().collect(Collectors.toMap(Person::getName,each->Collections.singletonList(each.getAddress()),(value1, value2) -> {
List<String> union = new ArrayList<>(value1);
union.addAll(value2);
return union;
}));
System.out.println(JSON.toJSONString(map));
控制台打印日志:
{“光头强”:[“森林第三个小屋”],“熊大”:[“森林第一个小屋”,“森林第四个小屋”],“熊二”:[“森林第二个小屋”]}
List<Map<String,Object>> 转成Map<String,Map<String,Object>>
List<Map<String,Object>> list = new ArrayList<>();
Person person1 = new Person("熊大","森林第一个小屋");
Person person2 = new Person("熊二","森林第二个小屋");
Person person3 = new Person("光头强","森林第三个小屋");
Map<String,Object> map1 = new HashMap<>();
map1.put("id","1");
map1.put("person",person1);
Map<String,Object> map2 = new HashMap<>();
map2.put("id","2");
map2.put("person",person2);
Map<String,Object> map3 = new HashMap<>();
map3.put("id","3");
map3.put("person",person3);
list.add(map1);
list.add(map2);
list.add(map3);
Map<String,Map<String,Object>> map = list.stream().collect(Collectors.toMap(each->Objects.toString(each.get("id"),""),each->each,(key1,key2)->key1));
System.out.println(JSON.toJSONString(map));
控制台打印日志:
{“1”:{“person”:{“address”:“森林第一个小屋”,“name”:“熊大”},“id”:“1”},“2”:{“person”:{“address”:“森林第二个小屋”,“name”:“熊二”},“id”:“2”},“3”:{“person”:{“address”:“森林第三个小屋”,“name”:“光头强”},“id”:“3”}}
List<Map<String,Object>> 转成Map<String,Object>
List<Map<String,Object>> list = new ArrayList<>();
Person person1 = new Person("熊大","森林第一个小屋");
Person person2 = new Person("熊二","森林第二个小屋");
Person person3 = new Person("光头强","森林第三个小屋");
Map<String,Object> map1 = new HashMap<>();
map1.put("id","1");
map1.put("person",person1);
Map<String,Object> map2 = new HashMap<>();
map2.put("id","2");
map2.put("person",person2);
Map<String,Object> map3 = new HashMap<>();
map3.put("id","3");
map3.put("person",person3);
list.add(map1);
list.add(map2);
list.add(map3);
Map<String,Object> map = list.stream().collect(Collectors.toMap(each->Objects.toString(each.get("id"),""),each->each.get("person"),(key1,key2)->key1));
System.out.println(JSON.toJSONString(map));
控制台打印日志:
{“1”:{“address”:“森林第一个小屋”,“name”:“熊大”},“2”:{“address”:“森林第二个小屋”,“name”:“熊二”},“3”:{“address”:“森林第三个小屋”,“name”:“光头强”}}
List<Map<String,String>> 转成Map<String,Map<String,String>>
List<Map<String,String>> list = new ArrayList<>();
Map<String,String> map1 = new HashMap<>();
map1.put("id","1");
map1.put("name","熊大");
map1.put("address","森林第一个小屋");
Map<String,String> map2 = new HashMap<>();
map2.put("id","2");
map2.put("name","熊二");
map2.put("address","森林第二个小屋");
Map<String,String> map3 = new HashMap<>();
map3.put("id","3");
map3.put("name","光头强");
map3.put("address","森林第三个小屋");
list.add(map1);
list.add(map2);
list.add(map3);
Map<String,Map<String,String>> map = list.stream().collect(Collectors.toMap(each->each.get("id"),each->each,(key1,key2)->key1));
System.out.println(JSON.toJSONString(map));
控制台打印日志:
{“1”:{“address”:“森林第一个小屋”,“name”:“熊大”,“id”:“1”},“2”:{“address”:“森林第二个小屋”,“name”:“熊二”,“id”:“2”},“3”:{“address”:“森林第三个小屋”,“name”:“光头强”,“id”:“3”}}
List<Map<String,String>> 转成Map<String,String>
List<Map<String,String>> list = new ArrayList<>();
Map<String,String> map1 = new HashMap<>();
map1.put("id","1");
map1.put("name","熊大");
map1.put("address","森林第一个小屋");
Map<String,String> map2 = new HashMap<>();
map2.put("id","2");
map2.put("name","熊二");
map2.put("address","森林第二个小屋");
Map<String,String> map3 = new HashMap<>();
map3.put("id","3");
map3.put("name","光头强");
map3.put("address","森林第三个小屋");
list.add(map1);
list.add(map2);
list.add(map3);
Map<String,String> map = list.stream().collect(Collectors.toMap(each->each.get("id"),each->each.get("name"),(key1,key2)->key1));
System.out.println(JSON.toJSONString(map));
控制台打印日志:
{“1”:“熊大”,“2”:“熊二”,“3”:“光头强”}
关于“Java中List使用stream流转成map的方法有哪些”这篇文章的内容就介绍到这里，感谢各位的阅读！相信大家对“Java中List使用stream流转成map的方法有哪些”知识都有一定的了解，大家如果还想学习更多知识，欢迎关注蜗牛博客行业资讯频道。
免责声明：本站发布的内容（图片、视频和文字）以原创、转载和分享为主，文章观点不代表本网站立场，如果涉及侵权请联系站长邮箱：niceseo99@gmail.com进行举报，并提供相关证据，一经查实，将立刻删除涉嫌侵权内容。
版权声明：如无特殊标注，文章均为本站原创，转载时请以链接形式注明文章出处。
评论