I have a generic interface with several implementation classes, which I need to serialise and deserialise via Json. I'm trying to get started with Jackson, using full data-binding, without much luck.
The sample code illustrates the problem:
import org.codehaus.jackson.map.*;
import org.codehaus.jackson.map.type.TypeFactory;
import org.codehaus.jackson.type.JavaType;
public class Test {
interface Result<T> {}
static class Success<T> implements Result<T> {
T value;
T getValue() {return value;}
Success(T value) {this.value = value;}
}
public static void main(String[] args) {
Result<String> result = new Success<String>("test");
JavaType type = TypeFactory.defaultInstance().constructParametricType(Result.class, String.class);
ObjectMapper mapper = new ObjectMapper().enableDefaultTyping();
ObjectWriter writer = mapper.writerWithType(type);
ObjectReader reader = mapper.reader(type);
try {
String json = writer.writeValueAsString(result);
Result<String> result2 = reader.readValue(json);
Success<String> success = (Success<String>)result2;
} catch (Throwable ex) {
System.out.print(ex);
}
}
}
The call to writeValueAsString to causes the following exception:
org.codehaus.jackson.map.JsonMappingException: No serializer found for class Test$Success and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS) )
Why is Jackson expecting me to register a serializer - I though the point of full data-binding was that I wouldn't need to do this?
Is the above approach correct?
First of all, you need to register the specialized type to use it with Jackson using the factory method TypeFactory.constructSpecializedType. Then, the specialized type should be a bean (it should have a default constructor, getters and setters) to deserialize it.
Take a look at these tests clarifiers.
#Test
public void canSerializeParametricInterface() throws IOException {
final ObjectMapper mapper = new ObjectMapper().enableDefaultTyping();
final JavaType baseInterface = TypeFactory.defaultInstance().constructParametricType(Result.class, String.class);
final JavaType subType = TypeFactory.defaultInstance().constructSpecializedType(baseInterface, Success.class);
final ObjectWriter writer = mapper.writerWithType(subType);
final String json = writer.writeValueAsString(Success.create("test"));
Assert.assertEquals("{\"value\":\"test\"}", json);
}
#Test
public void canDeserializeParametricInterface() throws IOException {
final ObjectMapper mapper = new ObjectMapper().enableDefaultTyping();
final JavaType baseInterface = TypeFactory.defaultInstance().constructParametricType(Result.class, String.class);
final JavaType subType = TypeFactory.defaultInstance().constructSpecializedType(baseInterface, Success.class);
final ObjectReader reader = mapper.reader(subType);
final Success<String> success = reader.readValue("{\"value\":\"test\"}");
Assert.assertEquals("test", success.getValue());
}
public static interface Result<T> {
}
public static class Success<T> implements Result<T> {
private T value;
public static <T> Success<T> create(T value) {
final Success<T> success = new Success<T>();
success.value = value;
return success;
}
public T getValue() {
return value;
}
public void setValue(T value) {
this.value = value;
}
}
Related
How can I deserialize JSON string that contains enum values that are case insensitive? (using Jackson Databind)
The JSON string:
[{"url": "foo", "type": "json"}]
and my Java POJO:
public static class Endpoint {
public enum DataType {
JSON, HTML
}
public String url;
public DataType type;
public Endpoint() {
}
}
in this case,deserializing the JSON with "type":"json" would fail where as "type":"JSON" would work.
But I want "json" to work as well for naming convention reasons.
Serializing the POJO also results in upper case "type":"JSON"
I thought of using #JsonCreator and #JsonGetter:
#JsonCreator
private Endpoint(#JsonProperty("name") String url, #JsonProperty("type") String type) {
this.url = url;
this.type = DataType.valueOf(type.toUpperCase());
}
//....
#JsonGetter
private String getType() {
return type.name().toLowerCase();
}
And it worked. But I was wondering whether there's a better solutuon because this looks like a hack to me.
I can also write a custom deserializer but I got many different POJOs that use enums and it would be hard to maintain.
Can anyone suggest a better way to serialize and deserialize enums with proper naming convention?
I don't want my enums in java to be lowercase!
Here is some test code that I used:
String data = "[{\"url\":\"foo\", \"type\":\"json\"}]";
Endpoint[] arr = new ObjectMapper().readValue(data, Endpoint[].class);
System.out.println("POJO[]->" + Arrays.toString(arr));
System.out.println("JSON ->" + new ObjectMapper().writeValueAsString(arr));
Jackson 2.9
This is now very simple, using jackson-databind 2.9.0 and above
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.enable(MapperFeature.ACCEPT_CASE_INSENSITIVE_ENUMS);
// objectMapper now deserializes enums in a case-insensitive manner
Full example with tests
import com.fasterxml.jackson.databind.MapperFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
public class Main {
private enum TestEnum { ONE }
private static class TestObject { public TestEnum testEnum; }
public static void main (String[] args) {
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.enable(MapperFeature.ACCEPT_CASE_INSENSITIVE_ENUMS);
try {
TestObject uppercase =
objectMapper.readValue("{ \"testEnum\": \"ONE\" }", TestObject.class);
TestObject lowercase =
objectMapper.readValue("{ \"testEnum\": \"one\" }", TestObject.class);
TestObject mixedcase =
objectMapper.readValue("{ \"testEnum\": \"oNe\" }", TestObject.class);
if (uppercase.testEnum != TestEnum.ONE) throw new Exception("cannot deserialize uppercase value");
if (lowercase.testEnum != TestEnum.ONE) throw new Exception("cannot deserialize lowercase value");
if (mixedcase.testEnum != TestEnum.ONE) throw new Exception("cannot deserialize mixedcase value");
System.out.println("Success: all deserializations worked");
} catch (Exception e) {
e.printStackTrace();
}
}
}
I ran into this same issue in my project, we decided to build our enums with a string key and use #JsonValue and a static constructor for serialization and deserialization respectively.
public enum DataType {
JSON("json"),
HTML("html");
private String key;
DataType(String key) {
this.key = key;
}
#JsonCreator
public static DataType fromString(String key) {
return key == null
? null
: DataType.valueOf(key.toUpperCase());
}
#JsonValue
public String getKey() {
return key;
}
}
Since Jackson 2.6, you can simply do this:
public enum DataType {
#JsonProperty("json")
JSON,
#JsonProperty("html")
HTML
}
For a full example, see this gist.
In version 2.4.0 you can register a custom serializer for all the Enum types (link to the github issue). Also you can replace the standard Enum deserializer on your own that will be aware about the Enum type. Here is an example:
public class JacksonEnum {
public static enum DataType {
JSON, HTML
}
public static void main(String[] args) throws IOException {
List<DataType> types = Arrays.asList(JSON, HTML);
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.setDeserializerModifier(new BeanDeserializerModifier() {
#Override
public JsonDeserializer<Enum> modifyEnumDeserializer(DeserializationConfig config,
final JavaType type,
BeanDescription beanDesc,
final JsonDeserializer<?> deserializer) {
return new JsonDeserializer<Enum>() {
#Override
public Enum deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException {
Class<? extends Enum> rawClass = (Class<Enum<?>>) type.getRawClass();
return Enum.valueOf(rawClass, jp.getValueAsString().toUpperCase());
}
};
}
});
module.addSerializer(Enum.class, new StdSerializer<Enum>(Enum.class) {
#Override
public void serialize(Enum value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
jgen.writeString(value.name().toLowerCase());
}
});
mapper.registerModule(module);
String json = mapper.writeValueAsString(types);
System.out.println(json);
List<DataType> types2 = mapper.readValue(json, new TypeReference<List<DataType>>() {});
System.out.println(types2);
}
}
Output:
["json","html"]
[JSON, HTML]
If you're using Spring Boot 2.1.x with Jackson 2.9 you can simply use this application property:
spring.jackson.mapper.accept-case-insensitive-enums=true
I went for the solution of Sam B. but a simpler variant.
public enum Type {
PIZZA, APPLE, PEAR, SOUP;
#JsonCreator
public static Type fromString(String key) {
for(Type type : Type.values()) {
if(type.name().equalsIgnoreCase(key)) {
return type;
}
}
return null;
}
}
For those who tries to deserialize Enum ignoring case in GET parameters, enabling ACCEPT_CASE_INSENSITIVE_ENUMS will not do any good. It won't help because this option only works for body deserialization. Instead try this:
public class StringToEnumConverter implements Converter<String, Modes> {
#Override
public Modes convert(String from) {
return Modes.valueOf(from.toUpperCase());
}
}
and then
#Configuration
public class WebConfig implements WebMvcConfigurer {
#Override
public void addFormatters(FormatterRegistry registry) {
registry.addConverter(new StringToEnumConverter());
}
}
The answer and code samples are from here
To allow case insensitive deserialization of enums in jackson, simply add the below property to the application.properties file of your spring boot project.
spring.jackson.mapper.accept-case-insensitive-enums=true
If you have the yaml version of properties file, add below property to your application.yml file.
spring:
jackson:
mapper:
accept-case-insensitive-enums: true
With apologies to #Konstantin Zyubin, his answer was close to what I needed - but I didn't understand it, so here's how I think it should go:
If you want to deserialize one enum type as case insensitive - i.e. you don't want to, or can't, modify the behavior of the entire application, you can create a custom deserializer just for one type - by sub-classing StdConverter and force Jackson to use it only on the relevant fields using the JsonDeserialize annotation.
Example:
public class ColorHolder {
public enum Color {
RED, GREEN, BLUE
}
public static final class ColorParser extends StdConverter<String, Color> {
#Override
public Color convert(String value) {
return Arrays.stream(Color.values())
.filter(e -> e.getName().equalsIgnoreCase(value.trim()))
.findFirst()
.orElseThrow(() -> new IllegalArgumentException("Invalid value '" + value + "'"));
}
}
#JsonDeserialize(converter = ColorParser.class)
Color color;
}
Problem is releated to com.fasterxml.jackson.databind.util.EnumResolver. it uses HashMap to hold enum values and HashMap doesn't support case insensitive keys.
in answers above, all chars should be uppercase or lowercase. but I fixed all (in)sensitive problems for enums with that:
https://gist.github.com/bhdrk/02307ba8066d26fa1537
CustomDeserializers.java
import com.fasterxml.jackson.databind.BeanDescription;
import com.fasterxml.jackson.databind.DeserializationConfig;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.deser.std.EnumDeserializer;
import com.fasterxml.jackson.databind.module.SimpleDeserializers;
import com.fasterxml.jackson.databind.util.EnumResolver;
import java.util.HashMap;
import java.util.Map;
public class CustomDeserializers extends SimpleDeserializers {
#Override
#SuppressWarnings("unchecked")
public JsonDeserializer<?> findEnumDeserializer(Class<?> type, DeserializationConfig config, BeanDescription beanDesc) throws JsonMappingException {
return createDeserializer((Class<Enum>) type);
}
private <T extends Enum<T>> JsonDeserializer<?> createDeserializer(Class<T> enumCls) {
T[] enumValues = enumCls.getEnumConstants();
HashMap<String, T> map = createEnumValuesMap(enumValues);
return new EnumDeserializer(new EnumCaseInsensitiveResolver<T>(enumCls, enumValues, map));
}
private <T extends Enum<T>> HashMap<String, T> createEnumValuesMap(T[] enumValues) {
HashMap<String, T> map = new HashMap<String, T>();
// from last to first, so that in case of duplicate values, first wins
for (int i = enumValues.length; --i >= 0; ) {
T e = enumValues[i];
map.put(e.toString(), e);
}
return map;
}
public static class EnumCaseInsensitiveResolver<T extends Enum<T>> extends EnumResolver<T> {
protected EnumCaseInsensitiveResolver(Class<T> enumClass, T[] enums, HashMap<String, T> map) {
super(enumClass, enums, map);
}
#Override
public T findEnum(String key) {
for (Map.Entry<String, T> entry : _enumsById.entrySet()) {
if (entry.getKey().equalsIgnoreCase(key)) { // magic line <--
return entry.getValue();
}
}
return null;
}
}
}
Usage:
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.module.SimpleModule;
public class JSON {
public static void main(String[] args) {
SimpleModule enumModule = new SimpleModule();
enumModule.setDeserializers(new CustomDeserializers());
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(enumModule);
}
}
I used a modification of Iago Fernández and Paul solution .
I had an enum in my requestobject which needed to be case insensitive
#POST
public Response doSomePostAction(RequestObject object){
//resource implementation
}
class RequestObject{
//other params
MyEnumType myType;
#JsonSetter
public void setMyType(String type){
myType = MyEnumType.valueOf(type.toUpperCase());
}
#JsonGetter
public String getType(){
return myType.toString();//this can change
}
}
Here's how I sometimes handle enums when I want to deserialize in a case-insensitive manner (building on the code posted in the question):
#JsonIgnore
public void setDataType(DataType dataType)
{
type = dataType;
}
#JsonProperty
public void setDataType(String dataType)
{
// Clean up/validate String however you want. I like
// org.apache.commons.lang3.StringUtils.trimToEmpty
String d = StringUtils.trimToEmpty(dataType).toUpperCase();
setDataType(DataType.valueOf(d));
}
If the enum is non-trivial and thus in its own class I usually add a static parse method to handle lowercase Strings.
Deserialize enum with jackson is simple. When you want deserialize enum based in String need a constructor, a getter and a setter to your enum.Also class that use that enum must have a setter which receive DataType as param, not String:
public class Endpoint {
public enum DataType {
JSON("json"), HTML("html");
private String type;
#JsonValue
public String getDataType(){
return type;
}
#JsonSetter
public void setDataType(String t){
type = t.toLowerCase();
}
}
public String url;
public DataType type;
public Endpoint() {
}
public void setType(DataType dataType){
type = dataType;
}
}
When you have your json, you can deserialize to Endpoint class using ObjectMapper of Jackson:
ObjectMapper mapper = new ObjectMapper();
mapper.enable(SerializationFeature.INDENT_OUTPUT);
try {
Endpoint endpoint = mapper.readValue("{\"url\":\"foo\",\"type\":\"json\"}", Endpoint.class);
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
I have the following class
private static class ClassWithGenericType<T> {
Set<T> values;
}
If I initialize now the class with a Set of Enum-values, serialize and deserialize the object by using gson, the Set of the deserialized object does not contain the Enum-values, but the values as String.
I think this is because the generic type is thrown away through the serialization. I saw, that I could use new TypeToken<...>(){}.getType();, but the problem is, that the class above is part of a bigger object, so I cannot call gson.fromJson(classWithGenericType, typeToken) directly.
Is there a smart way of solving this problem? I thought of a TypeAdapter, which does not serialize only the values of the Set, but also it's type.
I found now a solution and created a TypeAdapter.
public class SetTypeAdapterFactory implements TypeAdapterFactory {
#Override
public <T> TypeAdapter<T> create(Gson gson, #NonNull TypeToken<T> type) {
if (!Set.class.isAssignableFrom(type.getRawType())) {
return null;
}
return (TypeAdapter<T>) new SetTypeAdapter(gson);
}
}
public class SetTypeAdapter extends TypeAdapter<Set<?>> {
public static final String TYPE = "#type";
public static final String DATA = "#data";
private final Gson gson;
public SetTypeAdapter(#NonNull Gson gson) {
this.gson = gson;
}
#Override
public void write(final JsonWriter out, final Set<?> set
) throws IOException {
out.beginArray();
for (Object item : set) {
out.beginObject();
out.name(TYPE).value(item.getClass().getName());
out.name(DATA).jsonValue(gson.toJson(item));
out.endObject();
}
out.endArray();
}
#Override
public Set<?> read(final JsonReader in) throws IOException {
final Set<Object> set = Sets.newHashSet();
in.beginArray();
while (in.hasNext()) {
in.beginObject();
set.add(readNextObject(in));
in.endObject();
}
in.endArray();
return set;
}
private Object readNextObject(JsonReader in) throws IOException {
try {
checkNextName(in, TYPE);
Class<?> cls = Class.forName(in.nextString());
checkNextName(in, DATA);
return gson.fromJson(in, cls);
} catch (ClassNotFoundException exception) {
throw new IOException(exception);
}
}
private void checkNextName(JsonReader in, String name) throws IOException {
if (!in.nextName().equals(name)) {
throw new IOException("Name was not: " + name);
}
}
}
We can add the factory to the GsonBuilder and afterwards we are capable of serializing a Set with generic types.
var gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapterFactory(new SetTypeAdapterFactory());
var gson = gsonBuilder.create();
The serialized Set has then the following structure:
[
{
"#type":<class_name_first_element>,
"#data":<first_element_as_json>
},
...
]
I am trying a combination of #JsonValue and #JsonSerialize. Let's start with my current container class:
public class Container {
private final Map<SomeKey, Object> data;
#JsonValue
#JsonSerialize(keyUsing = SomeKeySerializer.class)
public Map<SomeKey, Object> data() {
return data;
}
}
In this case, the custom serializer SomeKeySerializer is not used.
If I change the container as following, the serializer is called:
public class Container {
#JsonSerialize(keyUsing = SomeKeySerializer.class)
private final Map<SomeKey, Object> data;
}
However, this is not what I want, as this introduces another 'data' level in the output JSON.
Is it possible to combine #JsonValue and #JsonSerialize in some way?
I could always write another custom serializer for Container, which more or less does the same as the functionality behind #JsonValue. This would be more or less a hack, in my opinion.
Jackson version: 2.6.2
This combination seems to do what you want: make a Converter to extract the Map from the Container, and add #JsonValue to SomeKey itself to serialize it:
#JsonSerialize(converter = ContainerToMap.class)
public class ContainerWithFieldData {
private final Map<SomeKey, Object> data;
public ContainerWithFieldData(Map<SomeKey, Object> data) {
this.data = data;
}
}
public static final class SomeKey {
public final String key;
public SomeKey(String key) {
this.key = key;
}
#JsonValue
public String toJsonValue() {
return "key:" + key;
}
#Override
public String toString() {
return "SomeKey:" + key;
}
}
public static final class ContainerToMap extends StdConverter<ContainerWithFieldData, Map<SomeKey, Object>> {
#Override
public Map<SomeKey, Object> convert(ContainerWithFieldData value) {
return value.data;
}
}
#Test
public void serialize_container_with_custom_keys_in_field_map() throws Exception {
ObjectMapper mapper = new ObjectMapper();
assertThat(
mapper.writeValueAsString(new ContainerWithFieldData(ImmutableMap.of(new SomeKey("key1"), "value1"))),
equivalentTo("{ 'key:key1' : 'value1' }"));
}
I simply can't get annotating an accessor method of Container to DTRT at all easily, not in combination with #JsonValue. Given that #JsonValue on the container is basically designating a converter anyway (that is implemented by calling the annotated method), this is effectively what you're after, although not as pleasant as it seems it should be. (tried with Jackson 2.6.2)
(Something I learned from this: key serializers aren't like normal serializers, even though they implement JsonSerializer just the same. They need to call writeFieldName on the JsonGenerator, not writeString, for example. On the deserialization side, the distinction between JsonDeserializer and KeyDeserializer is spelled out, but not on the serialization side. You can make a key serializer from SomeKey with #JsonValue, but not by annotating SomeKey with #JsonSerialize(using=...), which surprised me).
Have you tried using #JsonSerialize(using = SomeKeySerializer.class) instead of keyUsing?
Doc for using() says:
Serializer class to use for serializing associated value.
...while for keyUsing you get:
Serializer class to use for serializing Map keys of annotated property
Tested it out myself and it works...
public class Demo {
public static class Container {
private final Map<String, String> data = new HashMap<>();
#JsonValue
#JsonSerialize(using = SomeKeySerializer.class)
public Map<String, String> data() {
return data;
}
}
public static class SomeKeySerializer extends JsonSerializer<Map> {
#Override
public void serialize(Map value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
jgen.writeStartObject();
jgen.writeObjectField("aKeyInTheMap", "theValueForThatKey");
jgen.writeEndObject();
}
}
public static void main(String[] args) throws JsonProcessingException {
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.enable(SerializationFeature.INDENT_OUTPUT);
String s = objectMapper.writeValueAsString(new Container());
System.out.println(s);
}
}
This is the output when I'm NOT using com.fasterxml.jackson.annotation.JsonValue
{
"data" : {
"aKeyInTheMap" : "theValueForThatKey"
}
}
And this is the output when I'm using com.fasterxml.jackson.annotation.JsonValue
{
"aKeyInTheMap" : "theValueForThatKey"
}
I am using Jackson fasterxml for unmarshalling JSON. In my object there are two kinds of properties:Input properties and Calculated properties. In the input JSON, I get only input values.
The calculated values are actually dependent on input values. I have to populate these values before the object gets referred. So I am just checking if there are any hooks provided by Jackson so that I can do my calculations there. For example JAXB provides afterUnmarshal method to customize the unmarshaling behavior:
void afterUnmarshal(Unmarshaller u, Object parent)
But I could not find similar information about customizing Jackson. Are any such framework hooks provided by Jackson to customize the unmarshaling behavior?
I'd rather recommend to keep your model objects immutable by using constructor creators. That is, all the JSON values are passed to a constructor which would initialize the other calculated properties.
Anyway, if you want to customize an object after deserialization (without writing a deserializer for every type) you can modify the deserializer in a way that at the end it calls a special method(s) of a newly constructed instance. Here is an example which would work for all the classes that implements a special interface (one can consider using an annotation to mark the post construct methods).
public class JacksonPostConstruct {
public static interface PostConstructor {
void postConstruct();
}
public static class Bean implements PostConstructor {
private final String field;
#JsonCreator
public Bean(#JsonProperty("field") String field) {
this.field = field;
}
public void postConstruct() {
System.out.println("Post construct: " + toString());
}
#Override
public String toString() {
return "Bean{" +
"field='" + field + '\'' +
'}';
}
}
private static class PostConstructDeserializer extends DelegatingDeserializer {
private final JsonDeserializer<?> deserializer;
public PostConstructDeserializer(JsonDeserializer<?> deserializer) {
super(deserializer);
this.deserializer = deserializer;
}
#Override
protected JsonDeserializer<?> newDelegatingInstance(JsonDeserializer<?> newDelegatee) {
return deserializer;
}
#Override
public Object deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException {
Object result = _delegatee.deserialize(jp, ctxt);
if (result instanceof PostConstructor) {
((PostConstructor) result).postConstruct();
}
return result;
}
}
public static void main(String[] args) throws IOException {
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.setDeserializerModifier(new BeanDeserializerModifier() {
#Override
public JsonDeserializer<?> modifyDeserializer(DeserializationConfig config,
BeanDescription beanDesc,
final JsonDeserializer<?> deserializer) {
return new PostConstructDeserializer(deserializer);
}
});
mapper.registerModule(module);
String json = "{\"field\":\"value\"}";
System.out.println(mapper.readValue(json, Bean.class));
}
}
Output:
Post construct: Bean{field='value'}
Bean{field='value'}
Let's assume that your JSON looks like this:
{
"input1" : "Input value",
"input2" : 3
}
And your POJO class looks like this:
class Entity {
private String input1;
private int input2;
private String calculated1;
private long calculated2;
...
}
In this case you can write a custom deserializer for your Entity class:
class EntityJsonDeserializer extends JsonDeserializer<Entity> {
#Override
public Entity deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException,
JsonProcessingException {
InnerEntity innerEntity = jp.readValueAs(InnerEntity.class);
Entity entity = new Entity();
entity.setInput1(innerEntity.input1);
entity.setInput2(innerEntity.input2);
entity.recalculate();
return entity;
}
public static class InnerEntity {
public String input1;
public int input2;
}
}
In above class you can see that Entity has a recalculate method. It could look like this:
public void recalculate() {
calculated1 = input1 + input2;
calculated2 = input1.length() + input2;
}
You can also move this logic to your deserializer class.
Now, you have to inform Jackson that you want to use your custom deserializer:
#JsonDeserialize(using = EntityJsonDeserializer.class)
class Entity {
...
}
The example below shows how to use these classes:
ObjectMapper mapper = new ObjectMapper();
System.out.println(mapper.readValue(json, Entity.class));
This program prints:
Entity [input1=Input value, input2=3, calculated1=Input value3, calculated2=14]
I have a Map<A,B> fieldOfC as a field of a class C. When I try to deserialize C with Jackson, an Exception is thrown because it can't find a Deserializer for Map's key A. So, I guess the solution is to extend StdJsonDeserializer and do it manually.
My problem is that I can't find an example on how to use the parser and the context of the method "deserialize" that I have to implement.
Can anyone write the code for this simple example so I can use it as a start to build my real deserializer?
public class A{
private String a1;
private Integer a2;
}
public class B{
private String b1;
}
public class C{
#JsonDeserialize(keyUsing=ADeserializer.class)
//also tried this: #JsonDeserialize(keyAs=A.class) without success
private Map<A,B> fieldOfC;
private String c1;
}
public class ADeserializer extends StdKeyDeserializer {
protected ADeserializer(Class<A> cls) {
super(cls);
}
protected Object _parse(String key, DeserializationContext ctxt) throws Exception {
ObjectMapper mapper = new ObjectMapper();
return mapper.readValue(key, A.class);
}
}
Thanks in advance
EDIT: googling, I found a test of the same problem I have. This is exactly my problem
EDIT: changed extended class from StdDeserializer to StdKeyDeserializer as I read here in method findKeyDeserializer(org.codehaus.jackson.map.DeserializationConfig, org.codehaus.jackson.type.JavaType, org.codehaus.jackson.map.BeanProperty)
EDIT: After solving this issue I got this one that is related.
I am a complete newbie with Jackson, but the following works for me.
First I add a JsonCreator method to A:
public class A {
private String a1;
private Integer a2;
public String getA1() { return a1; }
public Integer getA2() { return a2; }
public void setA1(String a1) { this.a1 = a1; }
public void setA2(Integer a2) { this.a2 = a2; }
#JsonCreator
public static A fromJSON(String val) throws JsonParseException, JsonMappingException, IOException {
ObjectMapper mapper = new ObjectMapper();
A a = mapper.readValue(val,A.class);
return a;
}
}
That alone solves the deserialization problem. The harder part for me was the correct serialization of the keys. What I did there was to define a key serializer that serializes named classes as there JSON serialization, like this:
public class KeySerializer extends SerializerBase<Object> {
private static final SerializerBase<Object> DEFAULT = new StdKeySerializer();
private Set<Class<?>> objectKeys_ = Collections.synchronizedSet(new HashSet<Class<?>>());
protected KeySerializer(Class<?>... objectKeys) {
super(Object.class);
for(Class<?> cl:objectKeys) {
objectKeys_.add(cl);
}
}
#Override
public JsonNode getSchema(SerializerProvider provider, Type typeHint) throws JsonMappingException {
return DEFAULT.getSchema(provider, typeHint);
}
#Override
public void serialize(Object value, JsonGenerator jgen,
SerializerProvider provider) throws IOException,
JsonGenerationException {
if (objectKeys_.contains(value.getClass())) {
ObjectMapper mapper = new ObjectMapper();
StringWriter writer = new StringWriter();
mapper.writeValue(writer, value);
jgen.writeFieldName(writer.toString());
} else {
DEFAULT.serialize(value, jgen, provider);
}
}
}
Then to prove it works, serializing and deserializing an instance of class C:
ObjectMapper mapper = new ObjectMapper();
StdSerializerProvider provider = new StdSerializerProvider();
provider.setKeySerializer(new KeySerializer(A.class));
mapper.setSerializerProvider(provider);
StringWriter out = new StringWriter();
mapper.writeValue(out, c);
String json = out.toString();
System.out.println("JSON= "+json);
C c2 = mapper.readValue(json, C.class);
System.out.print("C2= ");
StringWriter outC2 = new StringWriter();
mapper.writeValue(outC2, c2);
System.out.println(outC2.toString());
For me this produced the output:
JSON= {"c1":"goo","map":{"{\"a1\":\"1ccf\",\"a2\":7376}":{"b1":"5ox"},"{\"a1\":\"1cd2\",\"a2\":7379}":{"b1":"5p0"},"{\"a1\":\"1cd5\",\"a2\":7382}":{"b1":"5p3"},"{\"a1\":\"1cd8\",\"a2\":7385}":{"b1":"5p6"}}}
C2= {"c1":"goo","map":{"{\"a1\":\"1ccf\",\"a2\":7376}":{"b1":"5ox"},"{\"a1\":\"1cd2\",\"a2\":7379}":{"b1":"5p0"},"{\"a1\":\"1cd5\",\"a2\":7382}":{"b1":"5p3"},"{\"a1\":\"1cd8\",\"a2\":7385}":{"b1":"5p6"}}}
I feel there ought to have been a better way of doing saying how to serialize the key by using annotations, but I could not work it out.