Merge pull request #6464 from rockoder/gson-list-advance

gson advanced list examples

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";
+}

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;
+    }
+}
+

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;
+    }
+}

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);
+    }
+}

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<Animal> {
+    private String animalTypeElementName;
+    private Gson gson;
+    private Map<String, Class<? extends Animal>> animalTypeRegistry;
+
+    public AnimalDeserializer(String animalTypeElementName) {
+        this.animalTypeElementName = animalTypeElementName;
+        this.gson = new Gson();
+        this.animalTypeRegistry = new HashMap<>();
+    }
+
+    public void registerBarnType(String animalTypeName, Class<? extends Animal> animalType) {
+        animalTypeRegistry.put(animalTypeName, animalType);
+    }
+
+    public Animal deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) {
+        JsonObject animalObject = json.getAsJsonObject();
+        JsonElement animalTypeElement = animalObject.get(animalTypeElementName);
+
+        Class<? extends Animal> animalType = animalTypeRegistry.get(animalTypeElement.getAsString());
+        return gson.fromJson(animalObject, animalType);
+    }
+}

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<MyClass> 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<MyClass> 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<MyClass> inputList = Arrays.asList(new MyClass(1, "name1"), new MyClass(2, "name2"));
+
+        Type listOfMyClassObject = new TypeToken<ArrayList<MyClass>>() {}.getType();
+
+        Gson gson = new Gson();
+        List<MyClass> 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<Animal> 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<Animal> outList = gson.fromJson(inputString, new TypeToken<List<Animal>>(){}.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<Animal> 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<ArrayList<Animal>>() {}.getType();
+
+        RuntimeTypeAdapterFactory<Animal> adapter = RuntimeTypeAdapterFactory.of(Animal.class, "type")
+          .registerSubtype(Dog.class)
+          .registerSubtype(Cow.class);
+
+        Gson gson = new GsonBuilder().registerTypeAdapterFactory(adapter).create();
+
+        List<Animal> outList = gson.fromJson(inputString, listOfAnimals);
+
+        assertEquals(2, outList.size());
+        assertTrue(outList.get(0) instanceof Dog);
+        assertTrue(outList.get(1) instanceof Cow);
+    }
+}

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:
+ * <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>
+ */
+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();
+  }
+}