부모 객체를 상속받아 여러 자식객체들로 이루어진 jsonString을 java backend에서
VO로 mapping하고 싶은 경우가 있다. (deserialize)
다음과 같은 구조의 class들이 있다.
public abstract class Animal{
private String type;
private String name;
}
public class Dog extends Animal{
private int age;
//getter , setter
}
public class Cat extends Animal{
private boolean isHome;
//getters, setters
}
Animal이 부모이고 Dog과 Cat이 자식이다. Dog과 Cat 모두 Animal을 상속 받고 있다.
다음과 같은 json String이 있으면 이 code를 사용해서 vo객체에 mapping 해줄 수 있다.
public List<Animal> deserializeJsonStringToObj(String str){
// example : str = "[{\"name\":\"Milo\",\"age\":\"9\",\"type\":\"Dog\"},{\"name\":\"miyao\",\"isHome\":\"true\",\"type\":\"Cat\"}]";
Type listOfAnimals = new TypeToken<ArrayList<Animal>>(){}.getType();
RuntimeTypeAdapterFactory<Animal> adapter = RuntimeTypeAdapterFactory.of(Animal.class, "type")
.registerSubtype(Dog.class)
.registerSubtype(Cat.class);
Gson gson = new GsonBuilder().registerTypeAdapterFactory(adapter).create();
return gson.fromJson(str, listOfFilterJson);
}
RuntimeTypeAdapterFactory을 사용하는게 쉬운데,
gson에 RuntimeTypeAdapterFactory가 종종 없다고도 한다.
그러면 다음 파일을 불러와서 쓰면된다.
package com.sds.lowcode.data.functions;/*
* Copyright (C) 2011 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import com.google.gson.Gson;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.internal.Streams;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;
import java.io.IOException;
import java.util.LinkedHashMap;
import java.util.Map;
/**
* Adapts values whose runtime type may differ from their declaration type. This
* is necessary when a field's type is not the same type that GSON should create
* when deserializing that field. For example, consider these types:
* <pre> {@code
* abstract class Shape {
* int x;
* int y;
* }
* class Circle extends Shape {
* int radius;
* }
* class Rectangle extends Shape {
* int width;
* int height;
* }
* class Diamond extends Shape {
* int width;
* int height;
* }
* class Drawing {
* Shape bottomShape;
* Shape topShape;
* }
* }</pre>
* <p>Without additional type information, the serialized JSON is ambiguous. Is
* the bottom shape in this drawing a rectangle or a diamond? <pre> {@code
* {
* "bottomShape": {
* "width": 10,
* "height": 5,
* "x": 0,
* "y": 0
* },
* "topShape": {
* "radius": 2,
* "x": 4,
* "y": 1
* }
* }}</pre>
* This class addresses this problem by adding type information to the
* serialized JSON and honoring that type information when the JSON is
* deserialized: <pre> {@code
* {
* "bottomShape": {
* "type": "Diamond",
* "width": 10,
* "height": 5,
* "x": 0,
* "y": 0
* },
* "topShape": {
* "type": "Circle",
* "radius": 2,
* "x": 4,
* "y": 1
* }
* }}</pre>
* Both the type field name ({@code "type"}) and the type labels ({@code
* "Rectangle"}) are configurable.
*
* <h3>Registering Types</h3>
* Create a {@code RuntimeTypeAdapterFactory} by passing the base type and type field
* name to the {@link #of} factory method. If you don't supply an explicit type
* field name, {@code "type"} will be used. <pre> {@code
* RuntimeTypeAdapterFactory<Shape> shapeAdapterFactory
* = RuntimeTypeAdapterFactory.of(Shape.class, "type");
* }</pre>
* Next register all of your subtypes. Every subtype must be explicitly
* registered. This protects your application from injection attacks. If you
* don't supply an explicit type label, the type's simple name will be used.
* <pre> {@code
* shapeAdapterFactory.registerSubtype(Rectangle.class, "Rectangle");
* shapeAdapterFactory.registerSubtype(Circle.class, "Circle");
* shapeAdapterFactory.registerSubtype(Diamond.class, "Diamond");
* }</pre>
* Finally, register the type adapter factory in your application's GSON builder:
* <pre> {@code
* Gson gson = new GsonBuilder()
* .registerTypeAdapterFactory(shapeAdapterFactory)
* .create();
* }</pre>
* Like {@code GsonBuilder}, this API supports chaining: <pre> {@code
* RuntimeTypeAdapterFactory<Shape> shapeAdapterFactory = RuntimeTypeAdapterFactory.of(Shape.class)
* .registerSubtype(Rectangle.class)
* .registerSubtype(Circle.class)
* .registerSubtype(Diamond.class);
* }</pre>
*
* <h3>Serialization and deserialization</h3>
* In order to serialize and deserialize a polymorphic object,
* you must specify the base type explicitly.
* <pre> {@code
* Diamond diamond = new Diamond();
* String json = gson.toJson(diamond, Shape.class);
* }</pre>
* And then:
* <pre> {@code
* Shape shape = gson.fromJson(json, Shape.class);
* }</pre>
*/
public final class RuntimeTypeAdapterFactory<T> implements TypeAdapterFactory {
private final Class<?> baseType;
private final String typeFieldName;
private final Map<String, Class<?>> labelToSubtype = new LinkedHashMap<String, Class<?>>();
private final Map<Class<?>, String> subtypeToLabel = new LinkedHashMap<Class<?>, String>();
private final boolean maintainType;
private RuntimeTypeAdapterFactory(Class<?> baseType, String typeFieldName, boolean maintainType) {
if (typeFieldName == null || baseType == null) {
throw new NullPointerException();
}
this.baseType = baseType;
this.typeFieldName = typeFieldName;
this.maintainType = maintainType;
}
/**
* Creates a new runtime type adapter using for {@code baseType} using {@code
* typeFieldName} as the type field name. Type field names are case sensitive.
* {@code maintainType} flag decide if the type will be stored in pojo or not.
*/
public static <T> RuntimeTypeAdapterFactory<T> of(Class<T> baseType, String typeFieldName, boolean maintainType) {
return new RuntimeTypeAdapterFactory<T>(baseType, typeFieldName, maintainType);
}
/**
* Creates a new runtime type adapter using for {@code baseType} using {@code
* typeFieldName} as the type field name. Type field names are case sensitive.
*/
public static <T> RuntimeTypeAdapterFactory<T> of(Class<T> baseType, String typeFieldName) {
return new RuntimeTypeAdapterFactory<T>(baseType, typeFieldName, false);
}
/**
* Creates a new runtime type adapter for {@code baseType} using {@code "type"} as
* the type field name.
*/
public static <T> RuntimeTypeAdapterFactory<T> of(Class<T> baseType) {
return new RuntimeTypeAdapterFactory<T>(baseType, "type", false);
}
/**
* Registers {@code type} identified by {@code label}. Labels are case
* sensitive.
*
* @throws IllegalArgumentException if either {@code type} or {@code label}
* have already been registered on this type adapter.
*/
public RuntimeTypeAdapterFactory<T> registerSubtype(Class<? extends T> type, String label) {
if (type == null || label == null) {
throw new NullPointerException();
}
if (subtypeToLabel.containsKey(type) || labelToSubtype.containsKey(label)) {
throw new IllegalArgumentException("types and labels must be unique");
}
labelToSubtype.put(label, type);
subtypeToLabel.put(type, label);
return this;
}
/**
* Registers {@code type} identified by its {@link Class#getSimpleName simple
* name}. Labels are case sensitive.
*
* @throws IllegalArgumentException if either {@code type} or its simple name
* have already been registered on this type adapter.
*/
public RuntimeTypeAdapterFactory<T> registerSubtype(Class<? extends T> type) {
return registerSubtype(type, type.getSimpleName());
}
public <R> TypeAdapter<R> create(Gson gson, TypeToken<R> type) {
if (type.getRawType() != baseType) {
return null;
}
final Map<String, TypeAdapter<?>> labelToDelegate
= new LinkedHashMap<String, TypeAdapter<?>>();
final Map<Class<?>, TypeAdapter<?>> subtypeToDelegate
= new LinkedHashMap<Class<?>, TypeAdapter<?>>();
for (Map.Entry<String, Class<?>> entry : labelToSubtype.entrySet()) {
TypeAdapter<?> delegate = gson.getDelegateAdapter(this, TypeToken.get(entry.getValue()));
labelToDelegate.put(entry.getKey(), delegate);
subtypeToDelegate.put(entry.getValue(), delegate);
}
return new TypeAdapter<R>() {
@Override public R read(JsonReader in) throws IOException {
JsonElement jsonElement = Streams.parse(in);
JsonElement labelJsonElement;
if (maintainType) {
labelJsonElement = jsonElement.getAsJsonObject().get(typeFieldName);
} else {
labelJsonElement = jsonElement.getAsJsonObject().remove(typeFieldName);
}
if (labelJsonElement == null) {
throw new JsonParseException("cannot deserialize " + baseType
+ " because it does not define a field named " + typeFieldName);
}
String label = labelJsonElement.getAsString();
@SuppressWarnings("unchecked") // registration requires that subtype extends T
TypeAdapter<R> delegate = (TypeAdapter<R>) labelToDelegate.get(label);
if (delegate == null) {
throw new JsonParseException("cannot deserialize " + baseType + " subtype named "
+ label + "; did you forget to register a subtype?");
}
return delegate.fromJsonTree(jsonElement);
}
@Override public void write(JsonWriter out, R value) throws IOException {
Class<?> srcType = value.getClass();
String label = subtypeToLabel.get(srcType);
@SuppressWarnings("unchecked") // registration requires that subtype extends T
TypeAdapter<R> delegate = (TypeAdapter<R>) subtypeToDelegate.get(srcType);
if (delegate == null) {
throw new JsonParseException("cannot serialize " + srcType.getName()
+ "; did you forget to register a subtype?");
}
JsonObject jsonObject = delegate.toJsonTree(value).getAsJsonObject();
if (maintainType) {
Streams.write(jsonObject, out);
return;
}
JsonObject clone = new JsonObject();
if (jsonObject.has(typeFieldName)) {
throw new JsonParseException("cannot serialize " + srcType.getName()
+ " because it already defines a field named " + typeFieldName);
}
clone.add(typeFieldName, new JsonPrimitive(label));
for (Map.Entry<String, JsonElement> e : jsonObject.entrySet()) {
clone.add(e.getKey(), e.getValue());
}
Streams.write(clone, out);
}
}.nullSafe();
}
}
참고
https://www.baeldung.com/gson-list