How to convert a list into a map in Java 8 Map function in chain

See the English answer > java 8 grouping using custom collector? 3

class Passenger {
   String type;
   String firstName;
   String lastName;

   //getter,setter
   public String getName() {
     return firstName + " " + lastName
 } 
}

Now I want to convert the passenger list into a map, where the key is "type" and the value is "name"

I try to achieve the following,

passengerList.stream().map(w -> w.getName()).collect(groupBy( getType() ));

But in After the map function, the passenger has been mapped to firstname, and the type is no longer available. I don't know how to do this

Solution

You must first group and then use the mapping to get a list of names for each type:

Map<String,List<String>> namesByType = 
    passengerList.stream()
                 .collect(Collectors.groupingBy(Passenger::getType,Collectors.mapping(Passenger::getName,Collectors.toList())));