from://http://www.studytrails.com/java/json/java-jackson-Serialization-polymorphism.jsp
Jackson provides a way to maintain sub type information while serializing java objects. It is possible to recreate the exact sub type. The type information can be embedded into the json as a property. In the example below we create a zoo, that has a list of animals. The animal may be an elephant or a lion, and they both extend the Animal abstract class. While deserializing we want to create the exact animal type. We also demonstrate the use of @JsonTypeInfo and @JsonSubTypes annotations.
Data Serialization and Polymorphism Example
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package
com.studytrails.json.jackson;
import
java.io.File;
import
java.io.FileWriter;
import
java.io.IOException;
import
java.util.ArrayList;
import
java.util.List;
import
com.fasterxml.jackson.core.JsonGenerationException;
import
com.fasterxml.jackson.databind.JsonMappingException;
import
com.fasterxml.jackson.databind.ObjectMapper;
public
class
SerializeExample1 {
private
static
String outputFile =
"zoo.json"
;
public
static
void
main(String[] args)
throws
JsonGenerationException, JsonMappingException, IOException {
// let start creating the zoo
Zoo zoo =
new
Zoo(
"Samba Wild Park"
,
"Paz"
);
Lion lion =
new
Lion(
"Simba"
);
Elephant elephant =
new
Elephant(
"Manny"
);
List<Animal> animals =
new
ArrayList<>();
animals.add(lion);
animals.add(elephant);
zoo.setAnimals(animals);
ObjectMapper mapper =
new
ObjectMapper();
mapper.writerWithDefaultPrettyPrinter().writeValue(
new
FileWriter(
new
File(outputFile)), zoo);
}
}
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Before we look at the various classes, lets also see how to deserialize this
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package
com.studytrails.json.jackson;
import
java.io.File;
import
java.io.IOException;
import
org.apache.commons.io.FileUtils;
import
com.fasterxml.jackson.core.JsonParseException;
import
com.fasterxml.jackson.databind.JsonMappingException;
import
com.fasterxml.jackson.databind.ObjectMapper;
public
class
DeSerializeExample1 {
public
static
void
main(String[] args)
throws
JsonParseException, JsonMappingException, IOException {
ObjectMapper mapper =
new
ObjectMapper();
Zoo zoo = mapper.readValue(FileUtils.readFileToByteArray(
new
File(
"zoo.json"
)), Zoo.
class
);
System.out.println(zoo);
}
}
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Zoo class
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package
com.studytrails.json.jackson;
import
java.util.List;
import
com.fasterxml.jackson.annotation.JsonCreator;
import
com.fasterxml.jackson.annotation.JsonProperty;
import
com.fasterxml.jackson.annotation.JsonTypeInfo;
import
com.fasterxml.jackson.annotation.JsonTypeInfo.As;
@JsonTypeInfo
(use = JsonTypeInfo.Id.MINIMAL_CLASS, include = As.PROPERTY, property =
"@class"
)
public
class
Zoo {
public
String name;
public
String city;
public
List<Animal> animals;
@JsonCreator
public
Zoo(
@JsonProperty
(
"name"
) String name,
@JsonProperty
(
"city"
) String city) {
this
.name = name;
this
.city = city;
}
public
void
setAnimals(List<animal> animals) {
this
.animals = animals;
}
@Override
public
String toString() {
return
"Zoo [name="
+ name +
", city="
+ city +
", animals="
+ animals +
"]"
;
}
}
</animal>
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Animal Abstract class
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package
com.studytrails.json.jackson;
import
com.fasterxml.jackson.annotation.JsonProperty;
import
com.fasterxml.jackson.annotation.JsonSubTypes;
import
com.fasterxml.jackson.annotation.JsonSubTypes.Type;
import
com.fasterxml.jackson.annotation.JsonTypeInfo;
import
com.fasterxml.jackson.annotation.JsonTypeInfo.As;
@JsonTypeInfo
(use = JsonTypeInfo.Id.CLASS, include = As.PROPERTY, property =
"@class"
)
@JsonSubTypes
({
@Type
(value = Lion.
class
, name =
"lion"
),
@Type
(value = Elephant.
class
, name =
"elephant"
) })
public
abstract
class
Animal {
@JsonProperty
(
"name"
)
String name;
@JsonProperty
(
"sound"
)
String sound;
@JsonProperty
(
"type"
)
String type;
@JsonProperty
(
"endangered"
)
boolean
endangered;
}
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Lion class
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package
com.studytrails.json.jackson;
import
com.fasterxml.jackson.annotation.JsonCreator;
import
com.fasterxml.jackson.annotation.JsonProperty;
public
class
Lion
extends
Animal {
private
String name;
@JsonCreator
public
Lion(
@JsonProperty
(
"name"
) String name) {
this
.name = name;
}
public
String getName() {
return
name;
}
public
String getSound() {
return
"Roar"
;
}
public
String getType() {
return
"carnivorous"
;
}
public
boolean
isEndangered() {
return
true
;
}
@Override
public
String toString() {
return
"Lion [name="
+ name +
", getName()="
+ getName() +
", getSound()="
+ getSound() +
", getType()="
+ getType() +
", isEndangered()="
+ isEndangered() +
"]"
;
}
}
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Elephant class
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package
com.studytrails.json.jackson;
import
com.fasterxml.jackson.annotation.JsonCreator;
import
com.fasterxml.jackson.annotation.JsonProperty;
public
class
Elephant
extends
Animal {
@JsonProperty
private
String name;
@JsonCreator
public
Elephant(
@JsonProperty
(
"name"
) String name) {
this
.name = name;
}
public
String getName() {
return
name;
}
public
String getSound() {
return
"trumpet"
;
}
public
String getType() {
return
"herbivorous"
;
}
public
boolean
isEndangered() {
return
false
;
}
@Override
public
String toString() {
return
"Elephant [name="
+ name +
", getName()="
+ getName() +
", getSound()="
+ getSound() +
", getType()="
+ getType()
+
", isEndangered()="
+ isEndangered() +
"]"
;
}
}
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