How to keep fields sequence in Gson serialization

user_1181103 0
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Seems like Gson.toJson(Object object) generates JSON code with randomly spread fields of the object. Is there way to fix fields order somehow?

public class Foo {
    public String bar;
    public String baz;
    public Foo( String bar, String baz ) {
        this.bar = bar;
        this.baz = baz;
    }
}
Gson gson = new Gson();
String jsonRequest = gson.toJson(new Foo("bar","baz"));

The string jsonRequest can be:

  • { "bar":"bar", "baz":"baz" } (correct)
  • { "baz":"baz", "bar":"bar" } (wrong sequence)
gson serialization json java
4 Answers

Actually Gson.toJson(Object object) doesn't generate fields in random order. The order of resulted json depends on literal sequence of the fields' names.

I had the same problem and it was solved by literal order of properties' names in the class.

The example in the question will always return the following jsonRequest:

{ "bar":"bar", "baz":"baz" }

In order to have a specific order you should modify fields' names, ex: if you want baz to be first in order then comes bar:

public class Foo {
    public String f1_baz;
    public String f2_bar;

    public Foo ( String f1_baz, String f2_bar ) {
        this.f1_baz = f1_baz;
        this.f2_bar = f2_bar;
    }
}

jsonRequest will be { "f1_baz ":"baz", "f2_bar":"bar" }

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