JAVA LIST转换为MAP

List<ClassA> -> Map<Field, ClassA>
list.stream().collect(Collectors.toMap(ClassA::getField, value -> value));

 

List<ClassA> -> Map<Field, ClassB>

list.stream().collect(Collectors.toMap(ClassA::getField, value -> new ClassB()));

 

List<ClassA> -> Map<FieldA, FieldB>

list.stream().collect(Collectors.toMap(ClassA::getFieldA, ClassA::getFieldB));