Converting a List of POJO into List of some other POJO in Java Stream

Question

I have 2 POJO Foo and FooDBObj, I fetch List of FooDBObj from database and now I need to create List of Foo Objects. I need to set Id and name in FooDBObj into Foo's BarId and BarName respectively. If its in Java Stream it will be better

I have tried to get the list of Id's alone from below code.

List<String> fooIds =FooDBObjList.stream().map(FooDBObj::getId).collect(Collectors.toList());

The above code can give me only list of Id for Foo I need all the FooDBObj.id to be set in Foo.BarId and FooDBObj.name to be set in FooDBObj.BarName

I think that Link is usefull for you. https://stackoverflow.com/questions/19760590/how-to-copy-properties-from-a-bean-to-another-bean-in-different-class — Govind Sharma, Jun 12 '19 at 09:46
Because `FooDBObj::getId` don't create a different instance but just extract the ID. Use a method to create a `Foo` instance from a `FooDBObj`. — AxelH, Jun 12 '19 at 09:46

score 3 · Accepted Answer · answered Jun 12 '19 at 09:45

I guess you could simply write the mapping logic directly:

Stream<Foo> = fooDBObjList.stream()
  .map(db -> {
    Foo foo = new Foo();
    foo.setBarId(db.Id);
    foo.setBarName(db.name);

    return foo;
  });

If Foo already have an appropriate constructor (or a factory method like Foo.from(FooDbObj) it could be done via method reference:

Stream<Foo> = fooDbObjList.stream().map(Foo::from); // Factory method
….map(Foo::new) // if Foo(FooDbObj) constructor
….map(db -> new Foo(db.Id, db.name)) // if Foo(barId, barName) constructor

score 1 · Answer 2 · answered Jun 12 '19 at 09:56

1

Or you can go like this too,

fooDBObjList.stream().forEach(x -> {
            Foo foo = new Foo ();
            foo.setId(x.getid());
            foo.setName(x.getname());   
            foooList.add(foo);
        });

answered Jun 12 '19 at 09:56

Mak

1,068
8
19

erolkaya84 · Answer 3 · 2019-06-12T11:49:50.000

0

fooDBObjList.stream()
    .map(Foo:map)
    .collect(Collectors.toList());

in Foo class:

Foo map(FooDBObj dbObj) {
   return Foo.builder
              .id(dbObj.getId())
              .name(dbObj.getName())
              .build();
}

edited Jun 12 '19 at 11:49

answered Jun 12 '19 at 09:42

erolkaya84

1,769
21
28

score -1 · Answer 4 · answered Jun 12 '19 at 09:50

One can use below snippet:


  List foo = FooDBObjList.stream().map(fooDBObj -> { Foo f = new Foo();
                                                          f.setBarName(fooDBObj.getName());
                                                          f.setBarId(fooDBObj.getId()); 
                                                          return f;}).collect(Collectors.toList());

Converting a List of POJO into List of some other POJO in Java Stream

4 Answers4