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); }} |
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); }} |
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> |
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;} |
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() + "]"; }} |
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() + "]"; }} |