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();
}
Related
I use Jackson to serialise POJOs into CSV. Now we need to change the naming for certain fields to snake_case. This is easily done by #JsonNaming(PropertyNamingStrategy.SnakeCaseStrategy.class).
For compatibility reasons we need some of the renamed fields also with their old name.
E.g.:
public class Pojo {
private int someField;
}
Default will serialise to "someField", SnakeCaseStrategy will serialise to "some_field".
How to get serialization with both?:
{
"someField" : "one",
"some_field" : "one"
}
My first try was a mixin:
public abstract class PojoFormat {
#JsonProperty("someField")
abstract String getSomeField();
}
but this effectively only undoes the naming strategy change.
So how to copy a field in serialization - preferable not by changing the Pojo (this copied fields should be removed when all clients can cope with it).
Little update:
in my real class there some nested class that use JsonUnwrapped and the doc stated that this is not working with custom serializer (didn't know that this makes a difference here).
Well, I have never seen this before, I would be very happy if someone here in this site knows how.
The easy way, in my opinion, is to use a Custom Serializer.
For example:
Using the #JsonSerialize annotation
Register a module
Dynamic Serializer with Reflection
#JsonSerialize annotation
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;
#JsonSerializer(using=PojoSerializer.class)
class Pojo {
private String myValue;
// getters and setters
}
class PojoSerializer extends StdSerializer<Pojo> {
public PojoSerializer() {
super(Pojo.class);
}
#Override
public void serialize(Pojo value, JsonGenerator gen, SerializerProvider provider) throws IOException {
gen.writeStartObject();
gen.writeStringField("myValue", value.getMyValue());
gen.writeStringField("my_value", value.getMyValue());
gen.writeEndObject();
}
}
Module
static class Pojo {
private String myValue;
public String getMyValue() {
return myValue;
}
public Pojo setMyValue(String myValue) {
this.myValue = myValue;
return this;
}
}
static class PojoSerializer extends StdSerializer<Pojo> {
public PojoSerializer() {
super(Pojo.class);
}
#Override
public void serialize(Pojo value, JsonGenerator gen, SerializerProvider provider) throws IOException {
gen.writeStartObject();
gen.writeStringField("myValue", value.getMyValue());
gen.writeStringField("my_value", value.getMyValue());
gen.writeEndObject();
}
}
public static void main(String[] args) throws JsonProcessingException {
final ObjectMapper mapper = new ObjectMapper();
final SimpleModule module = new SimpleModule("PojoModule");
module.addSerializer(Pojo.class, new PojoSerializer());
mapper.registerModule(module);
final Pojo pojo = new Pojo();
pojo.setMyValue("This is the value of my pojo");
System.out.println(mapper.writeValueAsString(pojo));
}
Reflection
I write some code for you, you might want to see to get new ideias.
This works as a generic way(just to not write several serializers).
// The serializer will be register in the ObjectMapper module.
static class Pojo {
private String myValue = "With snake and camel";
private String value = "Without snake case";
private String thirdValue = "snake & camel";
}
// using the annotation
#JsonSerialize(using = PojoSerializer.class)
static class Pojo2 {
private String pojoName = "Pojo 2";
private String pojo = "pojp";
}
static class PojoSerializer extends StdSerializer<Object> {
public PojoSerializer() {
super(Object.class);
}
#Override
public void serialize(Object value, JsonGenerator gen, SerializerProvider provider) throws IOException {
gen.writeStartObject();
final Field[] fields = value.getClass().getDeclaredFields();
for(final Field field : fields) {
final String name = field.getName();
final String fieldValue;
try {
// Do not use this!
fieldValue = (String)field.get(value);
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
}
byte firstUpperCase = -1;
for(byte index = 0; index < name.length(); index++) {
final char caractere = name.charAt(index);
// A ascii code is 66 decimal, and 90 is the Z in decimal
if(caractere > 'A' && caractere < 'Z') {
// found the first upper
firstUpperCase = index;
break;
}
}
// writes the normal field name
gen.writeStringField(name, fieldValue);
// if the name is in camel case, we will write in snake case too.
if(firstUpperCase != -1) {
final char lowerLetter = (char)((int) name.charAt(firstUpperCase) + 32);
final String left = name.substring(0, firstUpperCase);
final String right = String.format("%c%s",lowerLetter, name.substring(firstUpperCase + 1));
gen.writeStringField(String.format("%s_%s", left, right), fieldValue);
}
}
gen.writeEndObject();
}
}
You can try to use JsonAnyGetter annotation and define for every POJO extra mapping for backward compatibility.
Let's create a simple interface:
interface CompatibleToVer1 {
#JsonAnyGetter
Map<String, Object> getCompatibilityView();
}
and two classes which implement it:
#Data
#NoArgsConstructor
#AllArgsConstructor
#JsonNaming(PropertyNamingStrategy.SnakeCaseStrategy.class)
class RootPojo implements CompatibleToVer1 {
private int rootId;
#JsonUnwrapped
private SomePojo pojo;
#Override
public Map<String, Object> getCompatibilityView() {
return Collections.singletonMap("rootId", rootId);
}
}
#Data
#NoArgsConstructor
#AllArgsConstructor
#JsonNaming(PropertyNamingStrategy.SnakeCaseStrategy.class)
class SomePojo implements CompatibleToVer1 {
private int someField;
private String someName;
#Override
public Map<String, Object> getCompatibilityView() {
Map<String, Object> extra = new LinkedHashMap<>();
extra.put("someField", someField);
return extra;
}
}
As you can see, I defined extra columns for each POJO with custom names. Serialising to JSON is straightforward:
ObjectMapper mapper = new ObjectMapper();
mapper.enable(SerializationFeature.INDENT_OUTPUT);
SomePojo pojo = new SomePojo(123, "Tom");
mapper.writeValue(System.out, new RootPojo(1, pojo));
Above code prints:
{
"root_id" : 1,
"some_field" : 123,
"some_name" : "Tom",
"someField" : 123,
"rootId" : 1
}
But for CSV we need to create extra configuration:
CsvMapper csvMapper = CsvMapper.builder().build();
CsvSchema pojoExtraScheme = CsvSchema.builder()
.addColumn("someField")
.build();
CsvSchema rootExtraScheme = CsvSchema.builder()
.addColumn("rootId")
.build();
CsvSchema compatibleSchema = CsvSchema.emptySchema()
.withHeader()
.withColumnsFrom(csvMapper.schemaFor(RootPojo.class))
.withColumnsFrom(rootExtraScheme)
.withColumnsFrom(csvMapper.schemaFor(SomePojo.class))
.withColumnsFrom(pojoExtraScheme);
SomePojo tom = new SomePojo(123, "Tom");
SomePojo jerry = new SomePojo(124, "Jerry");
List<RootPojo> pojos = Arrays.asList(new RootPojo(1, tom), new RootPojo(2, jerry));
ObjectWriter writer = csvMapper.writer(compatibleSchema);
System.out.println(writer.writeValueAsString(pojos));
Above code prints:
some_field,some_name,root_id,rootId,someField
123,Tom,1,1,123
124,Jerry,2,2,124
If you do not want to specify extra columns two times you can implement builder method based on our interface:
CsvSchema createSchemaFor(CompatibleToVer1 entity) {
CsvSchema.Builder builder = CsvSchema.builder();
entity.getCompatibilityView().keySet().forEach(builder::addColumn);
return builder.build();
}
and use as below:
CsvSchema compatibleSchema = CsvSchema.emptySchema()
.withHeader()
.withColumnsFrom(csvMapper.schemaFor(RootPojo.class))
.withColumnsFrom(createSchemaFor(new RootPojo()))
.withColumnsFrom(csvMapper.schemaFor(SomePojo.class))
.withColumnsFrom(createSchemaFor(new SomePojo()));
Using JsonAnyGetter with CSV is really tricky and could be problematic mixing it with other annotations, take a look at: Could please add JsonAnyGetter and JsonAnySetter annotations support?
I am trying to include raw JSON inside a Java object when the object is (de)serialized using Jackson. In order to test this functionality, I wrote the following test:
public static class Pojo {
public String foo;
#JsonRawValue
public String bar;
}
#Test
public void test() throws JsonGenerationException, JsonMappingException, IOException {
String foo = "one";
String bar = "{\"A\":false}";
Pojo pojo = new Pojo();
pojo.foo = foo;
pojo.bar = bar;
String json = "{\"foo\":\"" + foo + "\",\"bar\":" + bar + "}";
ObjectMapper objectMapper = new ObjectMapper();
String output = objectMapper.writeValueAsString(pojo);
System.out.println(output);
assertEquals(json, output);
Pojo deserialized = objectMapper.readValue(output, Pojo.class);
assertEquals(foo, deserialized.foo);
assertEquals(bar, deserialized.bar);
}
The code outputs the following line:
{"foo":"one","bar":{"A":false}}
The JSON is exactly how I want things to look. Unfortunately, the code fails with an exception when attempting to read the JSON back in to the object. Here is the exception:
org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of java.lang.String out of START_OBJECT token
at [Source: java.io.StringReader#d70d7a; line: 1, column: 13] (through reference chain: com.tnal.prism.cobalt.gather.testing.Pojo["bar"])
Why does Jackson function just fine in one direction but fail when going the other direction? It seems like it should be able to take its own output as input again. I know what I'm trying to do is unorthodox (the general advice is to create an inner object for bar that has a property named A), but I don't want to interact with this JSON at all. My code is acting as a pass-through for this code -- I want to take in this JSON and send it back out again without touching a thing, because when the JSON changes I don't want my code to need modifications.
Thanks for the advice.
EDIT: Made Pojo a static class, which was causing a different error.
#JsonRawValue is intended for serialization-side only, since the reverse direction is a bit trickier to handle. In effect it was added to allow injecting pre-encoded content.
I guess it would be possible to add support for reverse, although that would be quite awkward: content will have to be parsed, and then re-written back to "raw" form, which may or may not be the same (since character quoting may differ).
This for general case. But perhaps it would make sense for some subset of problems.
But I think a work-around for your specific case would be to specify type as 'java.lang.Object', since this should work ok: for serialization, String will be output as is, and for deserialization, it will be deserialized as a Map. Actually you might want to have separate getter/setter if so; getter would return String for serialization (and needs #JsonRawValue); and setter would take either Map or Object. You could re-encode it to a String if that makes sense.
Following #StaxMan answer, I've made the following works like a charm:
public class Pojo {
Object json;
#JsonRawValue
public String getJson() {
// default raw value: null or "[]"
return json == null ? null : json.toString();
}
public void setJson(JsonNode node) {
this.json = node;
}
}
And, to be faithful to the initial question, here is the working test:
public class PojoTest {
ObjectMapper mapper = new ObjectMapper();
#Test
public void test() throws IOException {
Pojo pojo = new Pojo("{\"foo\":18}");
String output = mapper.writeValueAsString(pojo);
assertThat(output).isEqualTo("{\"json\":{\"foo\":18}}");
Pojo deserialized = mapper.readValue(output, Pojo.class);
assertThat(deserialized.json.toString()).isEqualTo("{\"foo\":18}");
// deserialized.json == {"foo":18}
}
}
I was able to do this with a custom deserializer (cut and pasted from here)
package etc;
import java.io.IOException;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.TreeNode;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
/**
* Keeps json value as json, does not try to deserialize it
* #author roytruelove
*
*/
public class KeepAsJsonDeserializer extends JsonDeserializer<String> {
#Override
public String deserialize(JsonParser jp, DeserializationContext ctxt)
throws IOException {
TreeNode tree = jp.getCodec().readTree(jp);
return tree.toString();
}
}
Use it by annotating the desired member like this:
#JsonDeserialize(using = KeepAsJsonDeserializer.class)
private String value;
#JsonSetter may help. See my sample ('data' is supposed to contain unparsed JSON):
class Purchase
{
String data;
#JsonProperty("signature")
String signature;
#JsonSetter("data")
void setData(JsonNode data)
{
this.data = data.toString();
}
}
This is a problem with your inner classes. The Pojo class is a non-static inner class of your test class, and Jackson cannot instantiate that class. So it can serialize, but not deserialize.
Redefine your class like this:
public static class Pojo {
public String foo;
#JsonRawValue
public String bar;
}
Note the addition of static
Adding to Roy Truelove's great answer, this is how to inject the custom deserialiser in response to appearance of #JsonRawValue:
import com.fasterxml.jackson.databind.Module;
#Component
public class ModuleImpl extends Module {
#Override
public void setupModule(SetupContext context) {
context.addBeanDeserializerModifier(new BeanDeserializerModifierImpl());
}
}
import java.util.Iterator;
import com.fasterxml.jackson.annotation.JsonRawValue;
import com.fasterxml.jackson.databind.BeanDescription;
import com.fasterxml.jackson.databind.DeserializationConfig;
import com.fasterxml.jackson.databind.deser.BeanDeserializerBuilder;
import com.fasterxml.jackson.databind.deser.BeanDeserializerModifier;
import com.fasterxml.jackson.databind.deser.SettableBeanProperty;
public class BeanDeserializerModifierImpl extends BeanDeserializerModifier {
#Override
public BeanDeserializerBuilder updateBuilder(DeserializationConfig config, BeanDescription beanDesc, BeanDeserializerBuilder builder) {
Iterator<SettableBeanProperty> it = builder.getProperties();
while (it.hasNext()) {
SettableBeanProperty p = it.next();
if (p.getAnnotation(JsonRawValue.class) != null) {
builder.addOrReplaceProperty(p.withValueDeserializer(KeepAsJsonDeserialzier.INSTANCE), true);
}
}
return builder;
}
}
This easy solution worked for me:
public class MyObject {
private Object rawJsonValue;
public Object getRawJsonValue() {
return rawJsonValue;
}
public void setRawJsonValue(Object rawJsonValue) {
this.rawJsonValue = rawJsonValue;
}
}
So I was able to store raw value of JSON in rawJsonValue variable and then it was no problem to deserialize it (as object) with other fields back to JSON and send via my REST. Using #JsonRawValue didnt helped me because stored JSON was deserialized as String, not as object, and that was not what I wanted.
This even works in a JPA entity:
private String json;
#JsonRawValue
public String getJson() {
return json;
}
public void setJson(final String json) {
this.json = json;
}
#JsonProperty(value = "json")
public void setJsonRaw(JsonNode jsonNode) {
// this leads to non-standard json, see discussion:
// setJson(jsonNode.toString());
StringWriter stringWriter = new StringWriter();
ObjectMapper objectMapper = new ObjectMapper();
JsonGenerator generator =
new JsonFactory(objectMapper).createGenerator(stringWriter);
generator.writeTree(n);
setJson(stringWriter.toString());
}
Ideally the ObjectMapper and even JsonFactory are from the context and are configured so as to handle your JSON correctly (standard or with non-standard values like 'Infinity' floats for example).
Here is a full working example of how to use Jackson modules to make #JsonRawValue work both ways (serialization and deserialization):
public class JsonRawValueDeserializerModule extends SimpleModule {
public JsonRawValueDeserializerModule() {
setDeserializerModifier(new JsonRawValueDeserializerModifier());
}
private static class JsonRawValueDeserializerModifier extends BeanDeserializerModifier {
#Override
public BeanDeserializerBuilder updateBuilder(DeserializationConfig config, BeanDescription beanDesc, BeanDeserializerBuilder builder) {
builder.getProperties().forEachRemaining(property -> {
if (property.getAnnotation(JsonRawValue.class) != null) {
builder.addOrReplaceProperty(property.withValueDeserializer(JsonRawValueDeserializer.INSTANCE), true);
}
});
return builder;
}
}
private static class JsonRawValueDeserializer extends JsonDeserializer<String> {
private static final JsonDeserializer<String> INSTANCE = new JsonRawValueDeserializer();
#Override
public String deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
return p.readValueAsTree().toString();
}
}
}
Then you can register the module after creating the ObjectMapper:
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.registerModule(new JsonRawValueDeserializerModule());
String json = "{\"foo\":\"one\",\"bar\":{\"A\":false}}";
Pojo deserialized = objectMapper.readValue(json, Pojo.class);
I had the exact same issue.
I found the solution in this post :
Parse JSON tree to plain class using Jackson or its alternatives
Check out the last answer.
By defining a custom setter for the property that takes a JsonNode as parameter and calls the toString method on the jsonNode to set the String property, it all works out.
Using an object works fine both ways... This method has a bit of overhead deserializing the raw value in two times.
ObjectMapper mapper = new ObjectMapper();
RawJsonValue value = new RawJsonValue();
value.setRawValue(new RawHello(){{this.data = "universe...";}});
String json = mapper.writeValueAsString(value);
System.out.println(json);
RawJsonValue result = mapper.readValue(json, RawJsonValue.class);
json = mapper.writeValueAsString(result.getRawValue());
System.out.println(json);
RawHello hello = mapper.readValue(json, RawHello.class);
System.out.println(hello.data);
RawHello.java
public class RawHello {
public String data;
}
RawJsonValue.java
public class RawJsonValue {
private Object rawValue;
public Object getRawValue() {
return rawValue;
}
public void setRawValue(Object value) {
this.rawValue = value;
}
}
I had a similar problem, but using a list with a lot of JSON itens (List<String>).
public class Errors {
private Integer status;
private List<String> jsons;
}
I managed the serialization using the #JsonRawValue annotation. But for deserialization I had to create a custom deserializer based on Roy's suggestion.
public class Errors {
private Integer status;
#JsonRawValue
#JsonDeserialize(using = JsonListPassThroughDeserialzier.class)
private List<String> jsons;
}
Below you can see my "List" deserializer.
public class JsonListPassThroughDeserializer extends JsonDeserializer<List<String>> {
#Override
public List<String> deserialize(JsonParser jp, DeserializationContext cxt) throws IOException, JsonProcessingException {
if (jp.getCurrentToken() == JsonToken.START_ARRAY) {
final List<String> list = new ArrayList<>();
while (jp.nextToken() != JsonToken.END_ARRAY) {
list.add(jp.getCodec().readTree(jp).toString());
}
return list;
}
throw cxt.instantiationException(List.class, "Expected Json list");
}
}
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 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;
}
}