Howto serialize java.util.Optional and final members

[Sven Rathgeber]

Hello,

I'm looking for a way to serialize (to yaml) such a class:

public class Person
{
  public final int age;
  public final Optional< String > hairColor;


  public Person(
    int age,
    Optional< String > hairColor )
  {
    this.age = age;
    this.hairColor = hairColor;
  }

}

Is there a way to do that with snakeyaml.

Regards.

Sven

[Andrey Somov]

Hi Sven,

you can check the test to see how to work with Optional: https://bitbucket.org/asomov/snakeyaml/src/default/src/test/java8/org/yaml/snakeyaml/issues/issue310/

See BeanAccess.FIELD for the variables.

Andrey

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[Sven Rathgeber]

Hi Andrey,

thanks for the quick help.

I tried this, but that fails. What am I missing ? I experimented with loadAs(dump, Person.class), but still no success.

 @Test
  void testYamlSerializationAndDeserialization()
  {
    Yaml yaml = new Yaml( new OptionalRepresenter() );
    yaml.setBeanAccess( BeanAccess.FIELD );
    Person person = new Person( 101, Optional.of( "green" ) );
    String dump = yaml.dump(person);
    System.out.println( dump );
    Person loadedPerson = yaml.load( dump);
    assertEquals( person, loadedPerson );
  }

I get an Exception:

Can't construct a java object for tag:yaml.org,2002:org.yamlstuff.Person; exception=java.lang.InstantiationException: NoSuchMethodException:org.yamlstuff.Person.<init>()
 in 'string', line 1, column 1:
    !!org.yamlstuff.Person

I interpret this, that there is no constructor given. Does snakeyaml expect a default constructor and setter, hmm, but that wouldn't work with final variables.

Do you have any suggestions ?

Regards.

Sven

PS: You can find the complete code here: https://github.com/svenrathgeber/YamlStuff

Am Freitag, 12. April 2019 16:30:22 UTC+2 schrieb Andrey Somov:

Hi Sven,

you can check the test to see how to work with Optional: https://bitbucket.org/asomov/snakeyaml/src/default/src/test/java8/org/yaml/snakeyaml/issues/issue310/

See BeanAccess.FIELD for the variables.

Andrey

On Fri, Apr 12, 2019 at 2:37 PM Sven Rathgeber <sven.r...@web.de> wrote:

Hello,

I'm looking for a way to serialize (to yaml) such a class:

public class Person
{
  public final int age;
  public final Optional< String > hairColor;


  public Person(
    int age,
    Optional< String > hairColor )
  {
    this.age = age;
    this.hairColor = hairColor;
  }

}

Is there a way to do that with snakeyaml.

Regards.

Sven

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Andrey Somov

[maslovalex]

Hi Sven,

I think at the moment you would need to have Representer which looks like

public class MyRepresenter extends Representer {
    public MyRepresenter() {
        this.representers.put(Optional.class, new RepresentOptional());
        this.representers.put(Person.class, new RepresentPerson());
    }

    private class RepresentOptional implements Represent {

        @Override
        public Node representData(Object data) {
            Optional<?> opt = (Optional<?>) data;
            List<Object> seq = new ArrayList<>(1);
            seq.add(opt.get());
            return representSequence(Tag.SEQ, seq, DumperOptions.FlowStyle.FLOW);
        }
    }

    private class RepresentPerson implements Represent {

        @Override
        public Node representData(Object data) {
            Person person = (Person) data;
            List<Object> seq = new ArrayList<>(2);
            seq.add(person.age);
            seq.add(person.hairColor);
            return representSequence(Tag.SEQ, seq, DumperOptions.FlowStyle.FLOW);
        }
    }
}

If you change your test to use this representer it should work.

-alex

[Sven Rathgeber]

Hi Alex,

thanks for working on a solution.

I tried it and it basically works. Still have to convert List<Object> to Person.

But the main flaw, I see, I'd have to implement each class twice. The class + its Representer.

Whenever class changes I'd have to change the Representer as well. Furthermore this solution

would nail me to snakeyaml and make a library change pretty hard.

That would not work as a general solution for - let's say 1000 classes.

Again, thanks for your help.

Sven