@XmlRootElement(name = "graph") @XmlAccessorType(XmlAccessType.NONE) public class Class1 { public List<Integer> i1; public Class1(Integer... i1) { if (this.i1 == null) { this.i1 = new ArrayList<>(); } for (Integer Int : i1) { this.i1.add(Int); } } public Class1() { } @XmlElement public List<Integer> getI1() { return i1; } public void setI1(List<Integer> i1) { if (this.i1 == null) { this.i1 = new ArrayList<>(); } System.out.println("before: " + this.i1); this.i1 = i1.stream().map(arg -> arg*2).collect(Collectors.toList()); System.out.println("after: " + this.i1); } @Override public String toString() { return "Class1{" + "i1=" + i1 + '}'; } }

Omitting JAXB initialization. Here is what class we will marshall, and then unmarshallit (omit the details): new Class1 (1,2,3)

result:

 before: [ ] after: [ ] Class1{i1=[ ]}

replace setter with:

  public void setI1(List<Integer> i1) { if (this.i1 == null) { this.i1 = new ArrayList<>(); } System.out.println("before: " + this.i1); this.i1 = i1; System.out.println("after: " + this.i1); }

result:

 before: [ ] after: [ ] Class1{i1=[1, 2, 3]}

The question is, what is this hellish magic? And is it possible to somehow handle the values ​​coming into the setter / getter?

    1 answer 1

    When the setter is called, an empty list that JAXB created is passed to it. And you see this after: [ ] . But then JAXB begins to fill this list with elements. But since in the first case you create a new list, the completed list just disappears somewhere in the depths of JAXB, in the second case you save the link to that list, which will then be full and as a result you see Class1{i1=[1, 2, 3]}