To overcome serializing properties with null values using Jackson >2.0, you can configure the ObjectMapper instantly, or make use of the @JsonInclude annotation:
Alternatively, you could use @JsonInclude in a getter so that the property would be shown if the value is not null.
To handle the null Map keys, some custom serialization is required, as best I understand.
A simple method to serialize null keys as empty strings (including complete examples of previously mentioned configurations):
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import com.fasterxml.jackson.annotation.JsonInclude.Include;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.SerializerProvider;
public class JacksonFoo
{
public static void main(String[] args) throws Exception
{
Map<String, Foo> foos = new HashMap<String, Foo>();
foos.put("foo1", new Foo("foo1"));
foos.put("foo2", new Foo(null));
foos.put("foo3", null);
foos.put(null, new Foo("foo4"));
// System.out.println(new ObjectMapper().writeValueAsString(foos));
// Exception: A null key for a Map isn't allowed in JSON (use a converting NullKeySerializer?)
ObjectMapper mapper = new ObjectMapper();
mapper.configure(SerializationFeature.WRITE_NULL_MAP_VALUES, false);
mapper.setSerializationInclusion(Include.NON_NULL);
mapper.getSerializerProvider().setNullKeySerializer(new MyNullKeySerializer()); System.out.println(mapper.writeValueAsString(foos));
// output:
// {"":{"bar":"foo4"},"foo2":{},"foo1":{"bar":"foo1"}}
}
class MyNullKeySerializer extends JsonSerializer<Object>
{
@Override
public void serialize(Object nullKey, JsonGenerator jsonGenerator, SerializerProvider unused)
throws IOException, JsonProcessingException
{ jsonGenerator.writeFieldName("");
}
}
class Foo
{
public String bar;
Foo(String bar)
{
this.bar = bar;
}
}