I need to create a custom serializer that conditionally skips fields. In contrast to the case described in Skip objects conditionally when serializing with jackson my class contains a POJO member. A PersonalInfo has a Address as member. In case the Address is hidden the resulting JSON still has the "address" tag, but without value. I could not figure out how to fix this.
Creating a custom serializer on the ObjectMapper (see 3. at http://www.baeldung.com/jackson-custom-serialization) leads to the exact same result.
Here is the adapted code from the referenced question that shows the problem:
public class JacksonHide {
@JsonIgnoreProperties("hidden")
public static interface IHideable {
boolean isHidden();
}
public static class Address implements IHideable {
public final String city;
public final String street;
public final boolean hidden;
public Address(String city, String street, boolean hidden) {
this.city = city;
this.street = street;
this.hidden = hidden;
}
@Override
public boolean isHidden() {
return hidden;
}
}
public static class PersonalInfo implements IHideable {
public final String name;
public final int age;
public final Address address;
public final boolean hidden;
public PersonalInfo(String name, int age, Address address, boolean hidden) {
this.name = name;
this.age = age;
this.address = address;
this.hidden = hidden;
}
@Override
public boolean isHidden() {
return hidden;
}
}
private static class MyBeanSerializerModifier extends BeanSerializerModifier {
@Override
public JsonSerializer<?> modifySerializer(SerializationConfig config, BeanDescription beanDesc, JsonSerializer<?> serializer) {
if (IHideable.class.isAssignableFrom(beanDesc.getBeanClass())) {
return new MyIHideableJsonSerializer((JsonSerializer<IHideable>) serializer);
}
return super.modifySerializer(config, beanDesc, serializer);
}
private static class MyIHideableJsonSerializer extends JsonSerializer<IHideable> {
private final JsonSerializer<IHideable> serializer;
public MyIHideableJsonSerializer(JsonSerializer<IHideable> serializer) {
this.serializer = serializer;
}
@Override
public void serialize(IHideable value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
if (!value.isHidden()) {
serializer.serialize(value, jgen, provider);
}
}
}
}
public static void main(String[] args) throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.setSerializerModifier(new MyBeanSerializerModifier());
mapper.registerModule(module);
PersonalInfo p1 = new PersonalInfo("John", 30, new Address("A", "B", false), false);
PersonalInfo p2 = new PersonalInfo("Ivan", 20, new Address("C", "D", true), true);
PersonalInfo p3 = new PersonalInfo("Mary", 40, new Address("C", "D", true), false);
Address a1 = new Address("A", "B", false);
Address a2 = new Address("C", "D", true);
System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(Arrays.asList(p1, p2, p3, a1, a2)));
}
}
UPDATE: Thanks to the feedback I have now a version based on @JSONFilter that gives me at least valid JSON. Unfortunately the nodes are still there, but are empty now ({}). How can I completely get rid of them?
public class JacksonFilterHide {
@JsonFilter("HiddenFilter")
@JsonIgnoreProperties("hidden")
public static interface IHideable {
boolean isHidden();
}
public static class Address implements IHideable {
public final String city;
public final String street;
public final boolean hidden;
public Address(String city, String street, boolean hidden) {
this.city = city;
this.street = street;
this.hidden = hidden;
}
@Override
public boolean isHidden() {
return hidden;
}
}
public static class PersonalInfo implements IHideable {
public final String name;
public final int age;
public final Address address;
public final boolean hidden;
public PersonalInfo(String name, int age, Address address, boolean hidden) {
this.name = name;
this.age = age;
this.address = address;
this.hidden = hidden;
}
@Override
public boolean isHidden() {
return hidden;
}
}
static final PropertyFilter hiddenFilter = new SimpleBeanPropertyFilter() {
@Override
public void serializeAsField(Object pojo, JsonGenerator jgen, SerializerProvider provider, PropertyWriter writer) throws Exception {
if (include(writer)) {
if (pojo instanceof IHideable && ((IHideable) pojo).isHidden()) {
return;
} else {
writer.serializeAsField(pojo, jgen, provider);
return;
}
} else if (!jgen.canOmitFields()) { // since 2.3
writer.serializeAsOmittedField(pojo, jgen, provider);
}
}
@Override
protected boolean include(BeanPropertyWriter writer) {
return true;
}
@Override
protected boolean include(PropertyWriter writer) {
return true;
}
};
public static void main(String[] args) throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
// ObjectMapper mapper = UserInteractionModel.getMapper();
FilterProvider filters = new SimpleFilterProvider().addFilter("HiddenFilter", hiddenFilter);
mapper.setFilters(filters);
mapper.enable(SerializationFeature.INDENT_OUTPUT);
PersonalInfo p1 = new PersonalInfo("John", 30, new Address("A", "B", false), false);
PersonalInfo p2 = new PersonalInfo("Ivan", 20, new Address("C", "D", true), true);
PersonalInfo p3 = new PersonalInfo("Mary", 40, new Address("C", "D", true), false);
Address a1 = new Address("A", "B", false);
Address a2 = new Address("C", "D", true);
System.out.println(mapper.writeValueAsString(Arrays.asList(p1, p2, p3, a1, a2)));
}
}
Output now is:
[ { "name" : "John", "age" : 30, "address" : { "city" : "A", "street" : "B" } }, { }, { "name" : "Mary", "age" : 40, "address" : { } }, { "city" : "A", "street" : "B" }, { } ]
Expected:
[ { "name" : "John", "age" : 30, "address" : { "city" : "A", "street" : "B" } }, { "name" : "Mary", "age" : 40, }, { "city" : "A", "street" : "B" } ]
Update2 Temporary fix by traversing the tree and removing empty nodes. Ugly, but works for now. Still looking for a better answer.
private void removeEmptyNodes(JSONObject json) {
Iterator<String> iter = json.keys();
while (iter.hasNext()) {
String key = iter.next();
JSONObject node;
try {
node = json.getJSONObject(key);
} catch (JSONException e) {
continue;
}
if (node.length() == 0) {
iter.remove();
} else {
removeEmptyNodes(node);
}
}
}
Solution inspired by this question: How do I remove empty json nodes in Java with Jackson?
