java8集合互相转换
数组转Map
String[] str = {"aaa,bbb,ccc,ddd","aa,bb,cc,dd","a,b,c,d"};
Map<String,String> mapMsg = Arrays.stream(str).map(i -> i.split(",")).collect(Collectors.toMap(i->(String)i[1], i->(String)i[3]));
System.out.println(mapMsg.toString());
List<String> moidList = Arrays.stream(str).map(i -> i.split(",")[1]).collect(Collectors.toList());
System.out.println(moidList.toString());
{bb=dd, b=d, bbb=ddd}
[bbb, bb, b]
数组转List
String[] str = {"aaa,bbb,ccc,ddd","aa,bb,cc,dd","a,b,c,d"};
List<String> collect1 = Arrays.stream(str).map(i -> i.split(",")).flatMap(Arrays::stream).collect(Collectors.toList());
List<String> collect2 = Arrays.stream(str).map(i -> i.split(",")).flatMap(str1 -> Arrays.asList(str1).stream()).collect(Collectors.toList());
System.out.println(collect1.toString());
[aaa, bbb, ccc, ddd, aa, bb, cc, dd, a, b, c, d]
List转Map
1.list转map
Map<String,Integer> map = list.stream().collect(Collectors.toMap(Person::getName,Person::getAge));
2.在转换过程中, key重复的情况的处理方式
Map<String,Integer> map = list.stream().collect(Collectors.toMap(Person::getName,Person::getAge,(key1,key2) -> key2));
(key1,key2) -> key2是一种表达式, 表示转换map时,如果有两个相同的key,则取后面的key2替换前面的key1,key1,key2两个关键字可以随意修改.
3.key重复时,将前面的value和后面的value相加
Map<String,Integer> map = list.stream().collect(Collectors.toMap(Person::getName,Person::getAge,(key1,key2) -> key1 + key2));
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