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() + "]" ; } } |
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