I am trying to implement a custom JSON serializer class to display object BigInteger values as string in the JSON response.
I have implememented a custom serializer class
public class CustomCounterSerializer extends StdSerializer<BigInteger> {
private static final long serialVersionUID = 5440920327083673598L;
public CustomCounterSerializer() {
this(BigInteger.class);
}
public CustomCounterSerializer(Class<BigInteger> vc) {
super(vc);
}
#Override
public void serialize(BigInteger value, JsonGenerator jsonGenerator, SerializerProvider provider) throws IOException {
BigInteger valueJson = value==null ? BigInteger.valueOf(0) : value;
jsonGenerator.writeString(valueJson.toString());
}
}
The problem I have is that I want to handle the null object values using the overridden method and pass 0 to the JSON string and not null.
I have written a JUnit test for this:
public class CustomCounterSerializerTest {
private ObjectMapper objectMapper = new ObjectMapper();
#After
public void tearDown() {
objectMapper = null;
}
#Test
public void testCustomSerializerWithNullValues() throws JsonParseException, JsonMappingException, IOException {
MyObject obj = new MyObject();
obj.setNonNullValue(BigInteger.valueOf(1);
String obj_ = objectMapper.writeValueAsString(obj);
assertThat(obj_).isNotNull();
assertTrue(obj_.contains("\"nonNullValue\":\"" + BigInteger.valueOf(1).toString() + "\",\"nullValue\":\""+ BigInteger.valueOf(0).toString() +"\""));
}
}
It fails as it contains null and not nullValue:"0".
But the null value of the object always goes to no args constructor and even like this(BigInteger.class) does not use my method and prints null.
You need to tell Jackson that it should use your serializer
even for null values. You do this by using #JsonSerializer
also with the nullsUsing parameter.
In your MyObject class it would look like this:
#JsonSerialize(using = CustomCounterSerializer.class,
nullsUsing = CustomCounterSerializer.class)
private BigInteger nullValue;
Related
Is there a simple way to serialize an object using Jackson to base64 encoded JSON? (object -> JSON -> base64)
I tried using a custom StdSerializer, but this (of course) results in a endless loop:
class MySerializer extends StdSerializer<Foo> {
public void serialize(Foo value, JsonGenerator gen, SerializerProvider provider) {
StringWriter stringWriter = new StringWriter();
JsonGenerator newGen = gen.getCodec().getFactory().createGenerator(stringWriter);
gen.getCodec().getFactory().getCodec().writeValue(newGen, value);
String json = stringWriter.toString();
String base64 = new String(Base64.getEncoder().encode(json.getBytes()));
gen.writeString(base64);
}
}
A workaround is to copy all fields to another class and use that class for the intermediate representation:
class TmpFoo {
public String field1;
public int field2;
// ...
}
class MySerializer extends StdSerializer<Foo> {
public void serialize(Foo value, JsonGenerator gen, SerializerProvider provider) {
TmpFoo tmp = new TmpFoo();
tmp.field1 = value.field1;
tmp.field2 = value.field2;
// etc.
StringWriter stringWriter = new StringWriter();
JsonGenerator newGen = gen.getCodec().getFactory().createGenerator(stringWriter);
gen.getCodec().getFactory().getCodec().writeValue(newGen, tmp); // here "tmp" instead of "value"
String json = stringWriter.toString();
String base64 = new String(Base64.getEncoder().encode(json.getBytes()));
gen.writeString(base64);
}
}
Creating a new ObjectMapper is not desired, because I need all registered modules and serializers of the default ObjectMapper.
I was hoping for some easier way of achieving this.
EDIT: Example
Step 1: Java Object
class Foo {
String field1 = "foo";
int field2 = 42;
}
Step 2: JSON
{"field1":"foo","field2":42}
Step 3: Base64
eyJmaWVsZDEiOiJmb28iLCJmaWVsZDIiOjQyfQ==
According to this site, there is a workaround to avoid this recursion problem:
When we define a custom serializer, Jackson internally overrides the
original BeanSerializer instance [...] our SerializerProvider finds
the customized serializer every time, instead of the default one, and
this causes an infinite loop.
A possible workaround is using BeanSerializerModifier to store the
default serializer for the type Folder before Jackson internally
overrides it.
If I understood the workaround correctly, your Serializer should look like this:
class FooSerializer extends StdSerializer<Foo> {
private final JsonSerializer<Object> defaultSerializer;
public FooSerializer(JsonSerializer<Object> defaultSerializer) {
super(Foo.class);
this.defaultSerializer = defaultSerializer;
}
#Override
public void serialize(Foo value, JsonGenerator gen, SerializerProvider provider) throws IOException {
StringWriter stringWriter = new StringWriter();
JsonGenerator tempGen = provider.getGenerator().getCodec().getFactory().createGenerator(stringWriter);
defaultSerializer.serialize(value, tempGen, provider);
tempGen.flush();
String json = stringWriter.toString();
String base64 = new String(Base64.getEncoder().encode(json.getBytes()));
gen.writeString(base64);
}
}
In addition to the serializer, a modifier is needed:
public class FooBeanSerializerModifier extends BeanSerializerModifier {
#Override
public JsonSerializer<?> modifySerializer(
SerializationConfig config, BeanDescription beanDesc, JsonSerializer<?> serializer) {
if (beanDesc.getBeanClass().equals(Foo.class)) {
return new FooSerializer((JsonSerializer<Object>) serializer);
}
return serializer;
}
}
Example module:
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.setSerializerModifier(new FooBeanSerializerModifier());
mapper.registerModule(module);
EDIT:
I've added flush() to flush the JsonGenerator tempGen.
Also, I've created a minimal test enviroment with JUnit, which verifies your Example with Foo: The github repo can be found here.
EDIT: Alternative 2
Another (simple) option is using a wrapper class with generics:
public class Base64Wrapper<T> {
private final T wrapped;
private Base64Wrapper(T wrapped) {
this.wrapped = wrapped;
}
public T getWrapped() {
return this.wrapped;
}
public static <T> Base64Wrapper<T> of(T wrapped) {
return new Base64Wrapper<>(wrapped);
}
}
public class Base64WrapperSerializer extends StdSerializer<Base64Wrapper> {
public Base64WrapperSerializer() {
super(Base64Wrapper.class);
}
#Override
public void serialize(Base64Wrapper value, JsonGenerator gen, SerializerProvider provider) throws IOException {
StringWriter stringWriter = new StringWriter();
JsonGenerator tempGen = provider.getGenerator().getCodec().getFactory().createGenerator(stringWriter);
provider.defaultSerializeValue(value.getWrapped(), tempGen);
tempGen.flush();
String json = stringWriter.toString();
String base64 = new String(Base64.getEncoder().encode(json.getBytes()));
gen.writeString(base64);
}
}
An example usecase would be:
final ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addSerializer(new Base64WrapperSerializer());
mapper.registerModule(module);
final Foo foo = new Foo();
final Base64Wrapper<Foo> base64Wrapper = Base64Wrapper.of(foo);
final String base64Json = mapper.writeValueAsString(base64Wrapper);
This example can be found in this GitHub (branch: wrapper) repo, verifing you BASE64 String from your foo example with JUnit testing.
Instead of creating new object you may convert existing one into map. Like in the example below
import static java.nio.charset.StandardCharsets.UTF_8;
public class FooSerializer extends StdSerializer<Foo> {
public FooSerializer() {
super(Foo.class);
}
#Override
public void serialize(Foo foo, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) {
try {
ObjectMapper mapper = (ObjectMapper) jsonGenerator.getCodec();
var map = toMap(foo); // if you need class info for deserialization than use toMapWithClassInfo
String json = mapper.writeValueAsString(map);
jsonGenerator.writeString(Base64.getEncoder().encodeToString(json.getBytes(UTF_8)));
} catch (Exception e) {
throw new RuntimeException(e);
}
}
public static Map<String, Object> toMap(Object o) throws Exception {
Map<String, Object> result = new HashMap<>();
Field[] declaredFields = o.getClass().getDeclaredFields();
for (Field field : declaredFields) {
field.setAccessible(true);
result.put(field.getName(), field.get(o));
}
return result;
}
public static Map<String, Object> toMapWithClassInfo(Object obj) throws Exception {
Map<String, Object> result = new HashMap<>();
BeanInfo info = Introspector.getBeanInfo(obj.getClass());
for (PropertyDescriptor pd : info.getPropertyDescriptors()) {
Method reader = pd.getReadMethod();
if (reader != null)
result.put(pd.getName(), reader.invoke(obj));
}
return result;
}
}
I'm providing 2 ways of converting into map: with and without class info. Choose the one, applicable to your problem.
To serialize object jackson search #JsonValue method. You can add encodedJsonString method annotated by #JsonValue in Foo class.
Try with this:
#Getter
#Setter
public class Foo implements Serializable {
private static final long serialVersionUID = 1L;
public String field1;
public int field2;
#JsonValue
public String toEncodedJsonString() {
try {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
new ObjectOutputStream(baos).writeObject(this);
return org.apache.commons.codec.binary.Base64.encodeBase64String(baos.toByteArray());
}catch (Exception ex){
}
return null;
}
}
I'm trying to create a custom serializer for a class A's instance variable.
The problem is that the variable is of a "standard" built in type (List<List<String>>)
I found out that you can in theory create a custom serializer for a type to be used ONLY within your class using mix-ins; so in theory if I could create a custom serializer for List<List<String>>, I could mix-in it into class A that way.
But how do I create a custom serializer for List<List<String>>?
I think it can be something like this. I don't know the logic you want to use, when serialize, so I wrote simple json array[][]
private static class ListListSerializer extends StdSerializer<List<List<String>>>{
protected ListListSerializer(Class<List<List<String>>> t) {
super(t);
}
protected ListListSerializer(){
this(null);
}
#Override
public void serialize(List<List<String>> lists, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
jsonGenerator.writeStartArray();
for (List<String> strings : lists) {
jsonGenerator.writeStartArray();
for (String string : strings) {
jsonGenerator.writeString(string);
}
jsonGenerator.writeEndArray();
}
jsonGenerator.writeEndArray();
}
}
As example without mixIn
private static class YourObject {
private List<List<String>> myStrings = new ArrayList<>();
public YourObject() {
List<String> a = Arrays.asList("a","b","c");
List<String> b = Arrays.asList("d","f","g");
myStrings.add(a);
myStrings.add(b);
}
#JsonSerialize(using = ListListSerializer.class)
public Object getMyStrings(){
return myStrings;
}
}
public static void main(String[] args) throws IOException {
ObjectMapper mapper = new ObjectMapper();
System.out.println(mapper.writeValueAsString(new YourObject()));
}
The output is
{"myStrings":[["a","b","c"],["d","f","g"]]}
Is that what you are trying to do?
I am using Jackson to deserialize a number of different implementations of the Product interface. These product implementations have different fields, but all have an InsuredAmount field. This InsuredAmount class has a value field and an IAType field. The IAType is a marker interface with different enums as implementations.
Now here's the problem: The enum implementations of the IAType interface correspond to a certain implementation of the Product interface. How can I make a generic implementation and tell Jackson to find the correct implementation of thee IAType? Should I use a generic parameter on the Product and the IAType interface identifying the product implementation? Should I use a Productable functional interface on the classes identifying the product implementation? How can I tell Jackson to use that implementation?
I hope the code below clarifies the problem, I chose to implement a Productable interface here, but a bettere structure to handle this problem would also be welcome.
#JsonPropertyOrder({"type", "someInfo"})
public class InsuredAmount implements Productable, Serializable {
private static final long serialVersionUID = 1L;
private IAType type;
private String someInfo;
public InsuredAmount() {
}
public InsuredAmount(IAType typeA, String someInfo) {
this.type = typeA;
this.someInfo = someInfo;
}
/* This should be on the product level, but if I can solve this problem,
the next level will just be more of the same.
*/
#JsonIgnore
#Override
public Product getProduct() {
return Product.PROD_A;
}
// Getters, setters, equals, etc. omitted.
}
--
public interface Productable {
public Product getProduct();
}
--
public enum Product {
PROD_A, PROD_B;
}
--
#JsonDeserialize(using = IATypeDeserializer.class)
public interface IAType extends Productable {
}
--
public enum IATypeA implements IAType {
FOO, BAR;
#Override
public Product getProduct() {
return Product.PROD_A;
}
}
--
public class IATypeDeserializer extends StdDeserializer<IAType> {
private static final long serialVersionUID = 1L;
public IATypeDeserializer() {
this(null);
}
public IATypeDeserializer(Class<?> vc) {
super(vc);
}
#Override
public IAType deserialize(JsonParser parser, DeserializationContext context)
throws IOException, JsonProcessingException {
JsonNode node = parser.getCodec().readTree(parser);
/* How to find out that the class calling the deserialization is InsuredAmountA, which
has getProduct() method that returns PROD_A, and matches the IATypeA that also returns
PROD_A, so I know to deserialize IATypeA, instead of other implementations of the IAType
interface?
*/
return IATypeA.valueOf(node.asText());
}
}
--
public class InsuredAmountTest {
private final ObjectMapper mapper = new ObjectMapper();
#Test
public void test01() throws IOException {
InsuredAmount iaA = new InsuredAmount(IATypeA.FOO, "test it");
String json = mapper.writeValueAsString(iaA);
assertThat(json, is("{\"type\":\"FOO\",\"someInfo\":\"test it\"}"));
InsuredAmount iaA2 = mapper.readValue(json, InsuredAmount.class);
IAType type = iaA2.getType();
assertThat(type, is(IATypeA.FOO));
assertThat(type.getProduct(), is(Product.PROD_A));
assertThat(iaA, is(iaA2));
}
#Test
public void test02() throws IOException {
InsuredAmount iaA = new InsuredAmount(IATypeA.BAR, "test it");
String json = mapper.writeValueAsString(iaA);
assertThat(json, is("{\"type\":\"BAR\",\"someInfo\":\"test it\"}"));
InsuredAmount iaA2 = mapper.readValue(json, InsuredAmount.class);
assertThat(iaA, is(iaA2));
}
}
Jackson handles the serialization of enums with minimal fuss, so all you need to do is annotate the IAType field with #JsonTypeInfo:
#JsonTypeInfo(use = JsonTypeInfo.Id.MINIMAL_CLASS)
private IAType type;
Then a test:
public static void main(String[] args) throws IOException {
ObjectMapper mapper = new ObjectMapper();
String json = mapper.writeValueAsString(new InsuredAmount(IATypeA.FOO, "info"));
System.out.println(json);
InsuredAmount ia = mapper.readValue(json, InsuredAmount.class);
System.out.println("Type is: " + ia.getType());
}
results in the output:
{"type":[".IATypeA","FOO"],"someInfo":"info"}
Type is: FOO
To get a more compact representation you will have to use custom serialization. Assuming that there are no overlaps in your enum namespace, you can serialize the type field as the enum name.
The deserializer will need to know which types are available for construction, either by class path discovery or, as in the following example, simply hard-coding the references:
public class IATest {
public static class IATypeSerializer extends JsonSerializer<IAType> {
#Override
public void serialize(IAType value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
gen.writeString(((Enum) value).name());
}
}
public static class IATypeDeserializer extends JsonDeserializer<IAType> {
#Override
public IAType deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
String value = p.readValueAs(String.class);
try {
return IATypeA.valueOf(value);
} catch (IllegalArgumentException e) {
// fall through
}
try {
return IATypeB.valueOf(value);
} catch (IllegalArgumentException e) {
// fall through
}
throw new JsonMappingException(p, "Unknown type '" + value + "'");
}
}
public static void main(String[] args) throws IOException {
ObjectMapper mapper = new ObjectMapper();
// Register a module to handle serialization of IAType implementations
SimpleModule module = new SimpleModule();
module.addSerializer(IAType.class, new IATypeSerializer());
module.addDeserializer(IAType.class, new IATypeDeserializer());
mapper.registerModule(module);
// Test
String json = mapper.writeValueAsString(new InsuredAmount(IATypeA.FOO, "info"));
System.out.println(json);
InsuredAmount ia = mapper.readValue(json, InsuredAmount.class);
System.out.println("Type is: " + ia.getType());
}
}
Which outputs:
{"type":"FOO","someInfo":"info"}
Type is: FOO
I ended up with using JsonCreator annotation on a special constructor.
#JsonCreator
public InsuredAmountA(
#JsonProperty("type") String type,
#JsonProperty("someInfo") String someInfo) throws IOException {
switch (getProduct()) {
case PROD_A:
try {
this.type = IATypeA.valueOf(type);
break;
} catch (IllegalArgumentException ex) {
// Throw IOException in the default.
}
// case PROD_B:
// this.type = (IATypeB) typeA;
// break;
default:
throw new IOException(String.format("Cannot parse value %s as type.", type));
}
this.someInfo = someInfo;
}
You may look into direction of polymorphic deserialisation:
http://wiki.fasterxml.com/JacksonPolymorphicDeserialization
unsing custom type resolver
I am trying to serialize a complex object to string that somewhere contains bytebuffer inside by using ObjectMapper for logging the response.
This changes the cursor position inside the bytebuffer and simply corrupts the response.
Code snippet that i am using:
import org.codehaus.jackson.map.ObjectMapper;
private static final ObjectMapper MAPPER = new ObjectMapper();
public static String serializeToString(final Object obj) {
Preconditions.checkArgument(obj != null, "Object to be serialized is null");
try {
final String str = MAPPER.writeValueAsString(obj);
if (Strings.isNullOrEmpty(str)) {
log.warn("Serialized to null/empty string");
}
return str;
} catch (final JsonGenerationException e) {
throw new IllegalArgumentException("Json generation exception occured in de-serializing obj", e);
} catch (final JsonMappingException e) {
throw new IllegalArgumentException("Json mapping exception occured in de-serializing obj", e);
} catch (final IOException e) {
throw new IllegalArgumentException("IO exception occured in de-serializing obj", e);
}
}
I passed above method a complex object having bytebuffer inside.
I printed bytebuffer before and after calling above method.
public static void main(final String[] args) throws SecurityException, NoSuchMethodException {
final String x =
"Random data i am using for this test for byte buffer. Random data i am using for this test for byte buffer";
final byte[] byteArr = x.getBytes();
final ByteBuffer bb = ByteBuffer.wrap(byteArr);
System.out.println("before bytebuffer :" + bb);
String stringData = SerializerUtil.serializeToString(bb); // In real i am passing a complex structure having
// bytebuffer inside
System.out.println(stringData);
System.out.println("after bytebuffer :" + bb);
}
Output:
before bytebuffer :java.nio.HeapByteBuffer[pos=0 lim=106 cap=106]
{"short":21089,"char":"\u6e64","int":1869422692,"long":7022344510808023405,"float":2.0790493E-19,"double":6.687717052371733E223,"direct":false,"readOnly":false}
after bytebuffer :java.nio.HeapByteBuffer[pos=28 lim=106 cap=106]
This change in (pos=0 to pos=28)position simply corrupts the response sent. Do we have any way to convert this complex object to string without affecting the byteBuffer?
Any help much appreciated.
Obviously, you don't want to serialize the ByteBuffer property as another structured class, but just the content, as a string. One way to do that is to use a #JsonProperty annotation on a method to tell the mapper to use that method instead of trying to serialize the field directly. Assuming you have a bean like this:
class Stuff {
private ByteBuffer data;
public Stuff() {
}
public Stuff(ByteBuffer data) {
super();
this.data = data;
}
public ByteBuffer getData() {
return data;
}
public void setData(ByteBuffer data) {
this.data = data;
}
#JsonProperty(value = "data")
public String convertData() {
return new String(data.array());
}
#JsonProperty("data")
public void convertData(String s) {
data = ByteBuffer.wrap(s.getBytes());
}
}
The mapper will now use the convertData methods for serializeing and deserializing the ByteBuffer data property, and you can still use normal java bean property methods.
Update:
Since the serialized class cannot be changed, here is an alternative method using som advanced JACKSON stuff. First, create custom serializer and deserializer:
static class ByteBufferSerializer extends JsonSerializer<ByteBuffer> {
#Override
public void serialize(ByteBuffer value, JsonGenerator jgen,
SerializerProvider provider) throws IOException,
JsonProcessingException {
jgen.writeString(new String(value.array()));
}
}
static class ByteBufferDeserializer extends JsonDeserializer<ByteBuffer> {
#Override
public ByteBuffer deserialize(JsonParser jp,
DeserializationContext context) throws IOException,
JsonProcessingException {
return ByteBuffer.wrap(jp.getText().getBytes());
}
}
Then, create a Mixin interface to provide the annotations for the properties that we cannot provide in the real target class:
static interface Mixin {
#JsonSerialize(using = ByteBufferSerializer.class, contentAs = String.class)
ByteBuffer getData();
#JsonDeserialize(using = ByteBufferDeserializer.class, contentAs = String.class)
void setData(ByteBuffer data);
}
Further, create a Module used to configure the object mapper, and add the mixin interface:
static class MyModule extends SimpleModule {
public MyModule() {
super("ByteBuffer wrangling");
}
#Override
public void setupModule(SetupContext context) {
context.setMixInAnnotations(Stuff.class, Mixin.class);
}
}
And, finally, register the module with the mapper:
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new MyModule());
Voilà, piece of cake! :-)
I would like serialize an object such that one of the fields will be named differently based on the type of the field. For example:
public class Response {
private Status status;
private String error;
private Object data;
[ getters, setters ]
}
Here, I would like the field data to be serialized to something like data.getClass.getName() instead of always having a field called data which contains a different type depending on the situation.
How might I achieve such a trick using Jackson?
I had a simpler solution using #JsonAnyGetter annotation, and it worked like a charm.
import java.util.Collections;
import java.util.Map;
public class Response {
private Status status;
private String error;
#JsonIgnore
private Object data;
[getters, setters]
#JsonAnyGetter
public Map<String, Object> any() {
//add the custom name here
//use full HashMap if you need more than one property
return Collections.singletonMap(data.getClass().getName(), data);
}
}
No wrapper needed, no custom serializer needed.
Using a custom JsonSerializer.
public class Response {
private String status;
private String error;
#JsonProperty("p")
#JsonSerialize(using = CustomSerializer.class)
private Object data;
// ...
}
public class CustomSerializer extends JsonSerializer<Object> {
public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
jgen.writeStartObject();
jgen.writeObjectField(value.getClass().getName(), value);
jgen.writeEndObject();
}
}
And then, suppose you want to serialize the following two objects:
public static void main(String... args) throws Exception {
ObjectMapper mapper = new ObjectMapper();
Response r1 = new Response("Error", "Some error", 20);
System.out.println(mapper.writeValueAsString(r1));
Response r2 = new Response("Error", "Some error", "some string");
System.out.println(mapper.writeValueAsString(r2));
}
The first one will print:
{"status":"Error","error":"Some error","p":{"java.lang.Integer":20}}
And the second one:
{"status":"Error","error":"Some error","p":{"java.lang.String":"some string"}}
I have used the name p for the wrapper object since it will merely serve as a placeholder. If you want to remove it, you'd have to write a custom serializer for the entire class, i.e., a JsonSerializer<Response>.
my own solution.
#Data
#EqualsAndHashCode
#ToString
#JsonSerialize(using = ElementsListBean.CustomSerializer.class)
public class ElementsListBean<T> {
public ElementsListBean()
{
}
public ElementsListBean(final String fieldName, final List<T> elements)
{
this.fieldName = fieldName;
this.elements = elements;
}
private String fieldName;
private List<T> elements;
public int length()
{
return (this.elements != null) ? this.elements.size() : 0;
}
private static class CustomSerializer extends JsonSerializer<Object> {
public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException,
JsonProcessingException
{
if (value instanceof ElementsListBean) {
final ElementsListBean<?> o = (ElementsListBean<?>) value;
jgen.writeStartObject();
jgen.writeArrayFieldStart(o.getFieldName());
for (Object e : o.getElements()) {
jgen.writeObject(e);
}
jgen.writeEndArray();
jgen.writeNumberField("length", o.length());
jgen.writeEndObject();
}
}
}
}
You can use the annotation JsonTypeInfo, which tell Jackson exactly that and you don't need to write a custom serializer. There's various way to include this information, but for your specific question you'd use As.WRAPPER_OBJECT and Id.CLASS. For example:
public static class Response {
private Status status;
private String error;
#JsonTypeInfo(include = As.WRAPPER_OBJECT, use = Id.CLASS)
private Object data;
}
This, however, will not work on primitive type, such as a String or Integer. You don't need that information for primitives anyways, since they are natively represented in JSON and Jackson knows how to handle them. The added bonus with using the annotation is that you get deserialization for free, if you ever need it. Here's an example:
public static void main(String[] args) throws Exception {
ObjectMapper mapper = new ObjectMapper();
Response r1 = new Response("Status", "An error", "some data");
Response r2 = new Response("Status", "An error", 10);
Response r3 = new Response("Status", "An error", new MyClass("data"));
System.out.println(mapper.writeValueAsString(r1));
System.out.println(mapper.writeValueAsString(r2));
System.out.println(mapper.writeValueAsString(r3));
}
#JsonAutoDetect(fieldVisibility=Visibility.ANY)
public static class MyClass{
private String data;
public MyClass(String data) {
this.data = data;
}
}
and the result:
{"status":"Status","error":"An error","data":"some data"}
{"status":"Status","error":"An error","data":10}
{"status":"Status","error":"An error","data":{"some.package.MyClass":{"data":"data"}}}
Based on #tlogbon response,
Here is my solution to wrap a List of Items with a specific/dynamic filed name
public class ListResource<T> {
#JsonIgnore
private List<T> items;
#JsonIgnore
private String fieldName;
public ListResource(String fieldName, List<T> items) {
this.items = items;
this.fieldName = fieldName;
}
#JsonAnyGetter
public Map<String, List<T>> getMap() {
return Collections.singletonMap(fieldName, items);
}