Reputation: 63134
Is there a way using Jackson JSON Processor to do custom field level serialization? For example, I'd like to have the class
public class Person {
public String name;
public int age;
public int favoriteNumber;
}
serialized to the follow JSON:
{ "name": "Joe", "age": 25, "favoriteNumber": "123" }
Note that age=25 is encoded as a number while favoriteNumber=123 is encoded as a string. Out of the box Jackson marshalls int
to a number. In this case I want favoriteNumber to be encoded as a string.
Upvotes: 126
Views: 178651
Reputation: 94499
You can implement a custom serializer as follows:
import com.fasterxml.jackson.databind.JsonSerializer
import com.fasterxml.jackson.databind.SerializerProvider
import com.fasterxml.jackson.core.JsonGenerator
public class Person {
public String name;
public int age;
@JsonSerialize(using = IntToStringSerializer.class, as=String.class)
public int favoriteNumber:
}
public class IntToStringSerializer extends JsonSerializer<Integer> {
@Override
public void serialize(Integer tmpInt,
JsonGenerator jsonGenerator,
SerializerProvider serializerProvider)
throws IOException, JsonProcessingException {
jsonGenerator.writeObject(tmpInt.toString());
}
}
Java should handle the autoboxing from int
to Integer
for you.
Upvotes: 141
Reputation: 1023
I ended up combining the two answers (and using the implementation provided by ToStringSerializer)
POJO:
public class MyPojo{
LocalDate date;
@JsonSerialize(using = CurrencySerializer.class)
double amount;
}
Serializer:
import com.fasterxml.jackson.databind.annotation.JacksonStdImpl;
import com.fasterxml.jackson.databind.ser.std.ToStringSerializerBase;
@JacksonStdImpl
public class CurrencySerializer extends ToStringSerializerBase
{
public final static CurrencySerializer instance = new CurrencySerializer();
public CurrencySerializer() { super(Object.class); }
public CurrencySerializer(Class<?> handledType) {
super(handledType);
}
@Override
public final String valueToString(Object value) {
return "$ " + value.toString();
}
}
Upvotes: 0
Reputation: 1440
You can create a custom serializer inline in the mixin. Then annotate a field with it. See example below that appends " - something else " to lang field. This is kind of hackish - if your serializer requires something like a repository or anything injected by spring, this is going to be a problem. Probably best to use a custom deserializer/serializer instead of a mixin.
package com.test;
import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import com.test.Argument;
import java.io.IOException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
//Serialize only fields explicitly mentioned by this mixin.
@JsonAutoDetect(
fieldVisibility = Visibility.NONE,
setterVisibility = Visibility.NONE,
getterVisibility = Visibility.NONE,
isGetterVisibility = Visibility.NONE,
creatorVisibility = Visibility.NONE
)
@JsonPropertyOrder({"lang", "name", "value"})
public abstract class V2ArgumentMixin {
@JsonProperty("name")
private String name;
@JsonSerialize(using = LangCustomSerializer.class, as=String.class)
@JsonProperty("lang")
private String lang;
@JsonProperty("value")
private Object value;
public static class LangCustomSerializer extends JsonSerializer<String> {
@Override
public void serialize(String value,
JsonGenerator jsonGenerator,
SerializerProvider serializerProvider)
throws IOException, JsonProcessingException {
jsonGenerator.writeObject(value.toString() + " - something else");
}
}
}
Upvotes: 1
Reputation: 7019
In case you don't want to pollute your model with annotations and want to perform some custom operations, you could use mixins.
ObjectMapper mapper = new ObjectMapper();
SimpleModule simpleModule = new SimpleModule();
simpleModule.setMixInAnnotation(Person.class, PersonMixin.class);
mapper.registerModule(simpleModule);
Override age:
public abstract class PersonMixin {
@JsonSerialize(using = PersonAgeSerializer.class)
public String age;
}
Do whatever you need with the age:
public class PersonAgeSerializer extends JsonSerializer<Integer> {
@Override
public void serialize(Integer integer, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
jsonGenerator.writeString(String.valueOf(integer * 52) + " months");
}
}
Upvotes: 21
Reputation: 8415
jackson-annotations provides @JsonFormat
which can handle a lot of customizations without the need to write the custom serializer.
For example, requesting a STRING
shape for a field with numeric type will output the numeric value as string
public class Person {
public String name;
public int age;
@JsonFormat(shape = JsonFormat.Shape.STRING)
public int favoriteNumber;
}
will result in the desired output
{"name":"Joe","age":25,"favoriteNumber":"123"}
Upvotes: 18
Reputation: 39
with the help of @JsonView we can decide fields of model classes to serialize which satisfy the minimal criteria ( we have to define the criteria) like we can have one core class with 10 properties but only 5 properties can be serialize which are needful for client only
Define our Views by simply creating following class:
public class Views
{
static class Android{};
static class IOS{};
static class Web{};
}
Annotated model class with views:
public class Demo
{
public Demo()
{
}
@JsonView(Views.IOS.class)
private String iosField;
@JsonView(Views.Android.class)
private String androidField;
@JsonView(Views.Web.class)
private String webField;
// getters/setters
...
..
}
Now we have to write custom json converter by simply extending HttpMessageConverter class from spring as:
public class CustomJacksonConverter implements HttpMessageConverter<Object>
{
public CustomJacksonConverter()
{
super();
//this.delegate.getObjectMapper().setConfig(this.delegate.getObjectMapper().getSerializationConfig().withView(Views.ClientView.class));
this.delegate.getObjectMapper().configure(MapperFeature.DEFAULT_VIEW_INCLUSION, true);
this.delegate.getObjectMapper().setSerializationInclusion(Include.NON_NULL);
}
// a real message converter that will respond to methods and do the actual work
private MappingJackson2HttpMessageConverter delegate = new MappingJackson2HttpMessageConverter();
@Override
public boolean canRead(Class<?> clazz, MediaType mediaType) {
return delegate.canRead(clazz, mediaType);
}
@Override
public boolean canWrite(Class<?> clazz, MediaType mediaType) {
return delegate.canWrite(clazz, mediaType);
}
@Override
public List<MediaType> getSupportedMediaTypes() {
return delegate.getSupportedMediaTypes();
}
@Override
public Object read(Class<? extends Object> clazz,
HttpInputMessage inputMessage) throws IOException,
HttpMessageNotReadableException {
return delegate.read(clazz, inputMessage);
}
@Override
public void write(Object obj, MediaType contentType, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException
{
synchronized(this)
{
String userAgent = ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest().getHeader("userAgent");
if ( userAgent != null )
{
switch (userAgent)
{
case "IOS" :
this.delegate.getObjectMapper().setConfig(this.delegate.getObjectMapper().getSerializationConfig().withView(Views.IOS.class));
break;
case "Android" :
this.delegate.getObjectMapper().setConfig(this.delegate.getObjectMapper().getSerializationConfig().withView(Views.Android.class));
break;
case "Web" :
this.delegate.getObjectMapper().setConfig(this.delegate.getObjectMapper().getSerializationConfig().withView( Views.Web.class));
break;
default:
this.delegate.getObjectMapper().setConfig(this.delegate.getObjectMapper().getSerializationConfig().withView( null ));
break;
}
}
else
{
// reset to default view
this.delegate.getObjectMapper().setConfig(this.delegate.getObjectMapper().getSerializationConfig().withView( null ));
}
delegate.write(obj, contentType, outputMessage);
}
}
}
Now there is need to tell spring to use this custom json convert by simply putting this in dispatcher-servlet.xml
<mvc:annotation-driven>
<mvc:message-converters register-defaults="true">
<bean id="jsonConverter" class="com.mactores.org.CustomJacksonConverter" >
</bean>
</mvc:message-converters>
</mvc:annotation-driven>
That's how you will able to decide which fields to get serialize.
Upvotes: 2
Reputation: 796
Jackson-databind (at least 2.1.3) provides special ToStringSerializer
(com.fasterxml.jackson.databind.ser.std.ToStringSerializer
)
Example:
public class Person {
public String name;
public int age;
@JsonSerialize(using = ToStringSerializer.class)
public int favoriteNumber:
}
Upvotes: 73
Reputation: 91349
Add a @JsonProperty
annotated getter, which returns a String
, for the favoriteNumber
field:
public class Person {
public String name;
public int age;
private int favoriteNumber;
public Person(String name, int age, int favoriteNumber) {
this.name = name;
this.age = age;
this.favoriteNumber = favoriteNumber;
}
@JsonProperty
public String getFavoriteNumber() {
return String.valueOf(favoriteNumber);
}
public static void main(String... args) throws Exception {
Person p = new Person("Joe", 25, 123);
ObjectMapper mapper = new ObjectMapper();
System.out.println(mapper.writeValueAsString(p));
// {"name":"Joe","age":25,"favoriteNumber":"123"}
}
}
Upvotes: 16