diff --git a/gson/src/main/java/org/baeldung/gson/entities/Animal.java b/gson/src/main/java/org/baeldung/gson/entities/Animal.java new file mode 100644 index 0000000000..2eec5f8704 --- /dev/null +++ b/gson/src/main/java/org/baeldung/gson/entities/Animal.java @@ -0,0 +1,5 @@ +package org.baeldung.gson.entities; + +public abstract class Animal { + public String type = "Animal"; +} diff --git a/gson/src/main/java/org/baeldung/gson/entities/Cow.java b/gson/src/main/java/org/baeldung/gson/entities/Cow.java new file mode 100644 index 0000000000..020bcd5860 --- /dev/null +++ b/gson/src/main/java/org/baeldung/gson/entities/Cow.java @@ -0,0 +1,19 @@ +package org.baeldung.gson.entities; + +public class Cow extends Animal { + private String breed; + + public Cow() { + breed = "Jersey"; + type = "Cow"; + } + + public String getBreed() { + return breed; + } + + public void setBreed(String breed) { + this.breed = breed; + } +} + diff --git a/gson/src/main/java/org/baeldung/gson/entities/Dog.java b/gson/src/main/java/org/baeldung/gson/entities/Dog.java new file mode 100644 index 0000000000..042d73adcf --- /dev/null +++ b/gson/src/main/java/org/baeldung/gson/entities/Dog.java @@ -0,0 +1,18 @@ +package org.baeldung.gson.entities; + +public class Dog extends Animal { + private String petName; + + public Dog() { + petName = "Milo"; + type = "Dog"; + } + + public String getPetName() { + return petName; + } + + public void setPetName(String petName) { + this.petName = petName; + } +} diff --git a/gson/src/main/java/org/baeldung/gson/entities/MyClass.java b/gson/src/main/java/org/baeldung/gson/entities/MyClass.java new file mode 100644 index 0000000000..4e717e72c3 --- /dev/null +++ b/gson/src/main/java/org/baeldung/gson/entities/MyClass.java @@ -0,0 +1,49 @@ +package org.baeldung.gson.entities; + +import java.util.Objects; + +public class MyClass { + private int id; + private String name; + + public MyClass(int id, String name) { + this.id = id; + this.name = name; + } + + public MyClass() { } + + public int getId() { + return id; + } + + public void setId(int id) { + this.id = id; + } + + public String getName() { + return name; + } + + public void setName(String name) { + this.name = name; + } + + @Override + public boolean equals(Object o) { + if (this == o) { + return true; + } + if (o == null || getClass() != o.getClass()) { + return false; + } + MyClass myClass = (MyClass) o; + return id == myClass.id && Objects.equals(name, myClass.name); + } + + @Override + public int hashCode() { + + return Objects.hash(id, name); + } +} diff --git a/gson/src/main/java/org/baeldung/gson/serialization/AnimalDeserializer.java b/gson/src/main/java/org/baeldung/gson/serialization/AnimalDeserializer.java new file mode 100644 index 0000000000..9dcef0e10b --- /dev/null +++ b/gson/src/main/java/org/baeldung/gson/serialization/AnimalDeserializer.java @@ -0,0 +1,35 @@ +package org.baeldung.gson.serialization; + +import com.google.gson.Gson; +import com.google.gson.JsonDeserializationContext; +import com.google.gson.JsonDeserializer; +import com.google.gson.JsonElement; +import com.google.gson.JsonObject; +import java.lang.reflect.Type; +import java.util.HashMap; +import java.util.Map; +import org.baeldung.gson.entities.Animal; + +public class AnimalDeserializer implements JsonDeserializer { + private String animalTypeElementName; + private Gson gson; + private Map> animalTypeRegistry; + + public AnimalDeserializer(String animalTypeElementName) { + this.animalTypeElementName = animalTypeElementName; + this.gson = new Gson(); + this.animalTypeRegistry = new HashMap<>(); + } + + public void registerBarnType(String animalTypeName, Class animalType) { + animalTypeRegistry.put(animalTypeName, animalType); + } + + public Animal deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) { + JsonObject animalObject = json.getAsJsonObject(); + JsonElement animalTypeElement = animalObject.get(animalTypeElementName); + + Class animalType = animalTypeRegistry.get(animalTypeElement.getAsString()); + return gson.fromJson(animalObject, animalType); + } +} \ No newline at end of file diff --git a/gson/src/test/java/org/baeldung/gson/advance/GsonAdvanceUnitTest.java b/gson/src/test/java/org/baeldung/gson/advance/GsonAdvanceUnitTest.java new file mode 100644 index 0000000000..5b787f1956 --- /dev/null +++ b/gson/src/test/java/org/baeldung/gson/advance/GsonAdvanceUnitTest.java @@ -0,0 +1,117 @@ +package org.baeldung.gson.advance; + +import static org.junit.Assert.assertEquals; +import static org.junit.Assert.assertTrue; + +import com.google.gson.Gson; +import com.google.gson.GsonBuilder; +import com.google.gson.reflect.TypeToken; +import java.lang.reflect.Type; +import java.util.ArrayList; +import java.util.Arrays; +import java.util.List; +import org.baeldung.gson.entities.Animal; +import org.baeldung.gson.entities.Cow; +import org.baeldung.gson.entities.Dog; +import org.baeldung.gson.entities.MyClass; +import org.baeldung.gson.serialization.AnimalDeserializer; +import org.junit.Test; + +public class GsonAdvanceUnitTest { + + @Test + public void givenListOfMyClass_whenSerializing_thenCorrect() { + List list = Arrays.asList(new MyClass(1, "name1"), new MyClass(2, "name2")); + + Gson gson = new Gson(); + String jsonString = gson.toJson(list); + String expectedString = "[{\"id\":1,\"name\":\"name1\"},{\"id\":2,\"name\":\"name2\"}]"; + + assertEquals(expectedString, jsonString); + } + + @Test(expected = ClassCastException.class) + public void givenJsonString_whenIncorrectDeserializing_thenThrowClassCastException() { + String inputString = "[{\"id\":1,\"name\":\"name1\"},{\"id\":2,\"name\":\"name2\"}]"; + + Gson gson = new Gson(); + List outputList = gson.fromJson(inputString, ArrayList.class); + + assertEquals(1, outputList.get(0).getId()); + } + + @Test + public void givenJsonString_whenDeserializing_thenReturnListOfMyClass() { + String inputString = "[{\"id\":1,\"name\":\"name1\"},{\"id\":2,\"name\":\"name2\"}]"; + List inputList = Arrays.asList(new MyClass(1, "name1"), new MyClass(2, "name2")); + + Type listOfMyClassObject = new TypeToken>() {}.getType(); + + Gson gson = new Gson(); + List outputList = gson.fromJson(inputString, listOfMyClassObject); + + assertEquals(inputList, outputList); + } + + @Test + public void givenPolymorphicList_whenSerializeWithTypeAdapter_thenCorrect() { + String expectedString = "[{\"petName\":\"Milo\",\"type\":\"Dog\"},{\"breed\":\"Jersey\",\"type\":\"Cow\"}]"; + + List inList = new ArrayList<>(); + inList.add(new Dog()); + inList.add(new Cow()); + + String jsonString = new Gson().toJson(inList); + + assertEquals(expectedString, jsonString); + } + + @Test + public void givenPolymorphicList_whenDeserializeWithTypeAdapter_thenCorrect() { + String inputString = "[{\"petName\":\"Milo\",\"type\":\"Dog\"},{\"breed\":\"Jersey\",\"type\":\"Cow\"}]"; + + AnimalDeserializer deserializer = new AnimalDeserializer("type"); + deserializer.registerBarnType("Dog", Dog.class); + deserializer.registerBarnType("Cow", Cow.class); + Gson gson = new GsonBuilder() + .registerTypeAdapter(Animal.class, deserializer) + .create(); + + List outList = gson.fromJson(inputString, new TypeToken>(){}.getType()); + + assertEquals(2, outList.size()); + assertTrue(outList.get(0) instanceof Dog); + assertTrue(outList.get(1) instanceof Cow); + } + + @Test + public void givenPolymorphicList_whenSerializeWithRuntimeTypeAdapter_thenCorrect() { + String expectedString = "[{\"petName\":\"Milo\",\"type\":\"Dog\"},{\"breed\":\"Jersey\",\"type\":\"Cow\"}]"; + + List inList = new ArrayList<>(); + inList.add(new Dog()); + inList.add(new Cow()); + String jsonString = new Gson().toJson(inList); + + assertEquals(expectedString, jsonString); + } + + @Test + public void givenPolymorphicList_whenDeserializeWithRuntimeTypeAdapter_thenCorrect() { + String inputString = "[{\"petName\":\"Milo\",\"type\":\"Dog\"},{\"breed\":\"Jersey\",\"type\":\"Cow\"}]"; + + Type listOfAnimals = new TypeToken>() {}.getType(); + + RuntimeTypeAdapterFactory adapter = RuntimeTypeAdapterFactory.of(Animal.class, "type") + .registerSubtype(Dog.class) + .registerSubtype(Cow.class); + + Gson gson = new GsonBuilder().registerTypeAdapterFactory(adapter).create(); + + List outList = gson.fromJson(inputString, listOfAnimals); + + assertEquals(2, outList.size()); + assertTrue(outList.get(0) instanceof Dog); + assertTrue(outList.get(1) instanceof Cow); + } +} \ No newline at end of file diff --git a/gson/src/test/java/org/baeldung/gson/advance/RuntimeTypeAdapterFactory.java b/gson/src/test/java/org/baeldung/gson/advance/RuntimeTypeAdapterFactory.java new file mode 100644 index 0000000000..739dd889c7 --- /dev/null +++ b/gson/src/test/java/org/baeldung/gson/advance/RuntimeTypeAdapterFactory.java @@ -0,0 +1,265 @@ +package org.baeldung.gson.advance; + +/* + * 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 java.io.IOException; +import java.util.LinkedHashMap; +import java.util.Map; + +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; + +/** + * 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: + * 
   {@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;
+ *   }
+ * }
+ *

Without additional type information, the serialized JSON is ambiguous. Is + * the bottom shape in this drawing a rectangle or a diamond? 

   {@code
+ *   {
+ *     "bottomShape": {
+ *       "width": 10,
+ *       "height": 5,
+ *       "x": 0,
+ *       "y": 0
+ *     },
+ *     "topShape": {
+ *       "radius": 2,
+ *       "x": 4,
+ *       "y": 1
+ *     }
+ *   }}
+ * This class addresses this problem by adding type information to the + * serialized JSON and honoring that type information when the JSON is + * deserialized: 
   {@code
+ *   {
+ *     "bottomShape": {
+ *       "type": "Diamond",
+ *       "width": 10,
+ *       "height": 5,
+ *       "x": 0,
+ *       "y": 0
+ *     },
+ *     "topShape": {
+ *       "type": "Circle",
+ *       "radius": 2,
+ *       "x": 4,
+ *       "y": 1
+ *     }
+ *   }}
+ * Both the type field name ({@code "type"}) and the type labels ({@code + * "Rectangle"}) are configurable. + * + *

Registering Types

+ * 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. 
   {@code
+ *   RuntimeTypeAdapterFactory shapeAdapterFactory
+ *       = RuntimeTypeAdapterFactory.of(Shape.class, "type");
+ * }
+ * 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. + * 
   {@code
+ *   shapeAdapterFactory.registerSubtype(Rectangle.class, "Rectangle");
+ *   shapeAdapterFactory.registerSubtype(Circle.class, "Circle");
+ *   shapeAdapterFactory.registerSubtype(Diamond.class, "Diamond");
+ * }
+ * Finally, register the type adapter factory in your application's GSON builder: + * 
   {@code
+ *   Gson gson = new GsonBuilder()
+ *       .registerTypeAdapterFactory(shapeAdapterFactory)
+ *       .create();
+ * }
+ * Like {@code GsonBuilder}, this API supports chaining: 
   {@code
+ *   RuntimeTypeAdapterFactory shapeAdapterFactory = RuntimeTypeAdapterFactory.of(Shape.class)
+ *       .registerSubtype(Rectangle.class)
+ *       .registerSubtype(Circle.class)
+ *       .registerSubtype(Diamond.class);
+ * }
+ */ +public final class RuntimeTypeAdapterFactory implements TypeAdapterFactory { + private final Class baseType; + private final String typeFieldName; + private final Map> labelToSubtype = new LinkedHashMap>(); + private final Map, String> subtypeToLabel = new LinkedHashMap, 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 RuntimeTypeAdapterFactory of(Class baseType, String typeFieldName, boolean maintainType) { + return new RuntimeTypeAdapterFactory(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 RuntimeTypeAdapterFactory of(Class baseType, String typeFieldName) { + return new RuntimeTypeAdapterFactory(baseType, typeFieldName, false); + } + + /** + * Creates a new runtime type adapter for {@code baseType} using {@code "type"} as + * the type field name. + */ + public static RuntimeTypeAdapterFactory of(Class baseType) { + return new RuntimeTypeAdapterFactory(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 registerSubtype(Class 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 registerSubtype(Class type) { + return registerSubtype(type, type.getSimpleName()); + } + + public TypeAdapter create(Gson gson, TypeToken type) { + if (type.getRawType() != baseType) { + return null; + } + + final Map> labelToDelegate + = new LinkedHashMap>(); + final Map, TypeAdapter> subtypeToDelegate + = new LinkedHashMap, TypeAdapter>(); + for (Map.Entry> 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() { + @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 delegate = (TypeAdapter) 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 delegate = (TypeAdapter) 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 e : jsonObject.entrySet()) { + clone.add(e.getKey(), e.getValue()); + } + Streams.write(clone, out); + } + }.nullSafe(); + } +}