Java Jackson - Json Polymorphism

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() + "]";

    }

}
时间： 2024-10-11 05:39:58

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