Serialization of constant value creates two entries

Serialization of one constant value creates two entries with different keys.

Steps to reproduce:

Given the following class (including test to reproduce issue):

@DisplayName( "Test constant value serialization" )
class ConstantTest {
   @Data
   class TestPojo {
      @JsonProperty("content-spec")
      private String CONTENT_SPEC = "This wont be changed";
   }

   @Test
   @DisplayName( "should contain content spec" )
   @SneakyThrows
   void shouldContainContentSpec() {
      TestPojo value = new TestPojo();
      String payload = new ObjectMapper().writeValueAsString( value );

      assertThat( payload ).isEqualTo( "{\"content-spec\":\"This wont be changed\"}" );
   }
}

Actual Behaviour

Results in the following output:

{
  "content_SPEC": "This wont be changed",
  "content-spec": "This wont be changed"
}

Note the two key/value pairs and that the word “SPEC” is uppercased while “content” is not.

Expected Behaviour

{
  "content-spec": "This wont be changed"
}

Additional hints:

• It works as expected when renaming the field to contentSpec.
• When removing the @JsonProperty annotation, only the content_SPEC key is left.
• Version 2.9.9.3

[cowtowncoder]

Thank you for fully documenting the work-around needed in this case; other users will probably find this useful as well!

Some more information just in case it might be useful…

Lower-casing or not of “CONTENT” is actually one aspect that is configurable: default one Jackson uses deviates from standard Bean naming convention I think. Setting to change is:

MapperFeature.USE_STD_BEAN_NAMING

which defaults to false for backwards-compatibility reasons. When enabled, inferred name would remain CONTENT_SPEC (because there is more than one capital letter starting name part), whereas legacy default setting would lower-case the continuous upper-case letter segment, to come up with content_SPEC (underscore ending the segment). It is actually possible to further re-configure aspects of casing with PropertyNamingStrategy, but that is more geared towards different style in JSON, not on POJO method naming.

[jwedel]

@cowtowncoder It’s a bit weird, that the word “CONTENT” is lower-cased but, OK. So, based on your valuable input, here is the fixed version with lombok (for anyone who is interested):

@DisplayName( "Test constant value serialization" )
class ConstantTest {
   @Data
   @Getter()
   class TestPojo {
      @JsonProperty( "content-spec" )
      @Getter( AccessLevel.NONE )
      @Setter( AccessLevel.NONE )
      private String CONTENT_SPEC = "This wont be changed";
   }

   @Test
   @DisplayName( "should contain content spec" )
   @SneakyThrows
   void shouldContainContentSpec() {
      TestPojo value = new TestPojo();
      String payload = new ObjectMapper().writeValueAsString( value );

      assertThat( payload ).isEqualTo( "{\"content-spec\":\"This wont be changed\"}" );
   }
}

This test actually succeeds. What did I do:

• I disabled getter/setter generation for the constant value. Obviously, it doesn’t make sense to annotate the class with @Data but usually, you have more fields that also requires to have getter/setter.

Now, there is no getter for CONTENT_SPEC and jackson will only pickup the @JsonProperty annotation and correctly serialize it.