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Java中List使用stream流转成map的几种方式详解

作者:小小小米fly

Stream是Java8中处理集合的关键抽象概念,它可以指定你希望对集合进行的操作,可以执行非常复杂的查找、过滤和映射数据等操作,下面这篇文章主要给大家介绍了关于Java中List使用stream流转成map的几种方式,需要的朋友可以参考下

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”}

总结

到此这篇关于Java中List使用stream流转成map的几种方式的文章就介绍到这了,更多相关Java List用stream流转map内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家!

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