Context attributes are not passed/available to custom serializer if object is in POJO

[dletin]

Below is a test case where I create a custom serializer and use it to serialize an object 1) in a HashMap and 2) in an ObjectNode. In both cases I pass attribute to the serializer like this:
mapper.writer().withAttribute("myAttr", "Hello!")
Serializing HashMap works as expected, but during ObjectNode serialization the attribute is null . It seems that in both cases the custom serializer should get access to the passed attribute and so both lines in the output should contain "Hello!"

Produced output from running testCase.test()

{"data":{"aStr":"The value is: Hello!"}}
{"data":{"aStr":"The value is: NULL"}}

Test case:

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import com.fasterxml.jackson.databind.node.ObjectNode;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

public class TestCase {
  public final static ObjectMapper mapper = new ObjectMapper();

  @JsonSerialize(using = TestCase.CustomSer.class)
  public static class Data {
    public String aStr;
  }

  public static class CustomSer extends StdSerializer<Data> {
    public CustomSer() {
      super(Data.class);
    }

    @Override
    public void serialize(Data value, JsonGenerator gen, SerializerProvider provider) throws IOException {
      String attrStr = (String) provider.getAttribute("myAttr");
      gen.writeStartObject();
      gen.writeObjectField("aStr", "The value is: " + (attrStr == null ? "NULL" : attrStr));
      gen.writeEndObject();
    }
  }

  public static void test() throws IOException {
    Data data = new Data();
    data.aStr = "Hello";

    Map<String, Object> mapTest = new HashMap<>();
    mapTest.put("data", data);

    ObjectNode treeTest = mapper.createObjectNode();
    treeTest.putPOJO("data", data);

    String mapOut = mapper.writer().withAttribute("myAttr", "Hello!").writeValueAsString(mapTest);
    System.out.println(mapOut);

    String treeOut = mapper.writer().withAttribute("myAttr", "Hello!").writeValueAsString(treeTest);
    System.out.println(treeOut);
  }
}

[dletin]

Version 2.9.5

[cowtowncoder]

Thank you for reporting this. I agree in that context should be retained and attributes available.

There may be technical problems in achieving that with 2.x since there is unfortunately no way to pass them through methods in JsonGenerator. This is something that is solved in 3.x (master), but is not something that can be retrofitted easily.

But I hope to see if there might something simple to do; it really depends on how delegation works for POJONodes and serialization.

[SrinivasKothuri]

A hack that worked for me is to use writeValue(Writer, Object) that allows you to pass on a custom Writer that can carry context.
Example:

class MyWriter extends StringWriter {
    MyWriter(Object context) {
        this.context = context;
    }
    Object getContext() {
        return context;
    }
}

In the custom serializer, you can get hold of the context through the Writer

public void serialize(Data value, JsonGenerator gen, SerializerProvider provider) throws IOException {
    Object context = ((MyWriter) get.getOutputTarget()).getContext();
    ........
}

And use it as below

      Writer writer = new MyWriter(WHAT_EVER);
      mapper.writer().writeValue(writer, mapTest);
      String serializedStr = writer.toString();

[cowtowncoder]

@SrinivasKothuri Thank you for sharing this interesting technique! Yes, that allows passing of information. :)