How do I serialize an associated object differently using Jackson and annotations?

Question

Given the following class hierarchy, I would like Foo to be serialized differently depending on the context it is used in my class hierarchy.

public class Foo {
         


        

Answer 1

import static org.junit.Assert.*;

import java.io.IOException;
import java.io.StringWriter;
import java.lang.reflect.Type;

import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.JsonNode;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.SerializerProvider;
import org.codehaus.jackson.map.annotate.JsonSerialize;
import org.codehaus.jackson.map.ser.SerializerBase;
import org.junit.Test;

class Foo {
    public String bar;
    public String biz;
}

class FooContainer {
    public Foo fooA;
    @JsonSerialize(using = FooCustomSerializer.class)
    public Foo fooB;
}

class FooCustomSerializer extends SerializerBase {

    public FooCustomSerializer() {
        super(Foo.class);
    }

    @Override
    public void serialize(Foo foo, JsonGenerator generator, SerializerProvider provider) throws IOException, JsonGenerationException {
        generator.writeStartObject();
        generator.writeObjectField("bar", foo.bar);
        generator.writeEndObject();
    }

    @Override
    public JsonNode getSchema(SerializerProvider arg0, Type arg1) throws JsonMappingException {
        return null;
    }

}

public class JacksonTest {

    @Test
    public void customField() throws Exception {
        FooContainer object = new FooContainer();
        object.fooA = new Foo();
        object.fooA.bar = "asdf";
        object.fooA.biz = "fdsa";
        object.fooB = new Foo();
        object.fooB.bar = "qwer";
        object.fooB.biz = "test";
        ObjectMapper mapper = new ObjectMapper();
        StringWriter writer = new StringWriter();
        mapper.writeValue(writer, object);
        String expected = "{\"fooA\":{\"bar\":\"asdf\",\"biz\":\"fdsa\"},\"fooB\":{\"bar\":\"qwer\"}}";
        assertEquals(expected, writer.toString());
    }

}

Using @JsonSerialize(using = FooCustomSerializer.class) on the public Foo fooB; field.

http://jackson.codehaus.org/1.9.9/javadoc/org/codehaus/jackson/map/annotate/JsonSerialize.html