How do you customize the java JSON serialization done by Google Cloud Endpoints?

Question

Below is the relevant method. One of the properties is of LocalDate (Joda).

@ApiMethod(
    name = "taxforms.get",
    path = "tax-forms",
    httpMethod = ApiMethod.HttpMethod.GET
)
public TaxDataList retrieveTaxDataList(
    HttpServletRequest httpServletRequest
) {

    TaxDataList taxDataList = new TaxDataList( );
    TaxData taxData = SampleTax.sampleTaxData( "Tax1098" );
    taxDataList.addFormsItem( taxData );

    return taxDataList;

}

If I do my own serialization, my code includes this:

 ObjectMapper objectMapper = new ObjectMapper( );

 // Special handling for dates
 objectMapper.registerModule( new JodaModule( ) );
 objectMapper.disable( SerializationFeature.WRITE_DATES_AS_TIMESTAMPS );

 objectMapper.writeValue( sw, data );

 json = sw.toString( );

How can I customize the way the framework does the serialization?

Answer 1

This is a close sample code to what you want and which uses transforms java LocalDate and Instant classes into strings and numbers:

package com.company.example;
 
import com.google.api.server.spi.config.Api;
import com.google.api.server.spi.config.ApiMethod;
import com.google.api.server.spi.config.Transformer;
 
import java.time.Instant;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
 
@Api(
  name="myApi",
  version="v1",
  transformers={
    MyApi.MyInstantTransformer.class,
    MyApi.MyLocalDateTransformer.class,
  }
)
public class MyApi {
 
  @ApiMethod(name="getStuff")
  public MyStuff getStuff() {
    return new MyStuff();
  }
 
  public static class MyStuff {
    private final LocalDate date;
    private final Instant instant;
    MyStuff() {
      date = LocalDate.now();
      instant = Instant.now();
    }
    public LocalDate getDate() { return date; }
    public Instant getInstant() { return instant; }
  }
 
  public static class MyInstantTransformer implements Transformer<Instant, Long> {
    public Instant transformFrom(Long input) {
      return Instant.ofEpochMilli(input);
    }
    public Long transformTo(Instant input) {
      return input.toEpochMilli();
    }
  }
 
  public static class MyLocalDateTransformer implements Transformer<LocalDate, String> {
    public LocalDate transformFrom(String input) {
      return LocalDate.parse(input, DateTimeFormatter.ISO_LOCAL_DATE);
    }
    public String transformTo(LocalDate input) {
      return input.format(DateTimeFormatter.ISO_LOCAL_DATE);
    }
  }
 
}