问gson -在序列化任何类型的对象时如何包含类名属性

EN

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
 *   shapeAdapter.registerSubtype(Rectangle.class, "Rectangle");
 *   shapeAdapter.registerSubtype(Circle.class, "Circle");
 *   shapeAdapter.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 RuntimeClassNameTypeAdapterFactory<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 RuntimeClassNameTypeAdapterFactory(Class<?> baseType, String typeFieldName) {
    if (typeFieldName == null || baseType == null) {
      throw new NullPointerException();
    }
    this.baseType = baseType;
    this.typeFieldName = typeFieldName;
  }

  /**
   * 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> RuntimeClassNameTypeAdapterFactory<T> of(Class<T> baseType, String typeFieldName) {
    return new RuntimeClassNameTypeAdapterFactory<T>(baseType, typeFieldName);
  }

  /**
   * Creates a new runtime type adapter for {@code baseType} using {@code "type"} as
   * the type field name.
   */
  public static <T> RuntimeClassNameTypeAdapterFactory<T> of(Class<T> baseType) {
    return new RuntimeClassNameTypeAdapterFactory<T>(baseType, "class");
  }

  /**
   * 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 RuntimeClassNameTypeAdapterFactory<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 RuntimeClassNameTypeAdapterFactory<T> registerSubtype(Class<? extends T> type) {
    return registerSubtype(type, type.getSimpleName());
  }

  public <R> TypeAdapter<R> create(Gson gson, TypeToken<R> type) {

    final Map<String, TypeAdapter<?>> labelToDelegate
        = new LinkedHashMap<String, TypeAdapter<?>>();
    final Map<Class<?>, TypeAdapter<?>> subtypeToDelegate
        = new LinkedHashMap<Class<?>, TypeAdapter<?>>();

//    && !String.class.isAssignableFrom(type.getRawType())

    if(Object.class.isAssignableFrom(type.getRawType()) ) {
        TypeAdapter<?> delegate = gson.getDelegateAdapter(this, type);
        labelToDelegate.put("class", delegate);
        subtypeToDelegate.put(type.getRawType(), delegate);
    }

//    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 = 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 = srcType.getName();
        @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?");
        }
        JsonElement jsonTree = delegate.toJsonTree(value);
        if(jsonTree.isJsonPrimitive()) {
            Streams.write(jsonTree, out);
        } else {
            JsonObject jsonObject = jsonTree.getAsJsonObject();
            if (jsonObject.has(typeFieldName)) {
              throw new JsonParseException("cannot serialize " + srcType.getName()
                  + " because it already defines a field named " + typeFieldName);
            }
            JsonObject clone = new JsonObject();
            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();
  }
}

if(jsonTree.isJsonPrimitive()) {
            Streams.write(jsonTree, out);

JsonObject clone = new JsonObject();
            clone.add(typeFieldName, new JsonPrimitive(label));
            for (Map.Entry<String, JsonElement> e : jsonObject.entrySet()) {
              clone.add(e.getKey(), e.getValue());
            }
            Streams.write(clone, out);

public class GsonClassNameTest {
    static Gson create = new GsonBuilder().registerTypeAdapterFactory(RuntimeClassNameTypeAdapterFactory.of(Object.class)).create();
    public static void main(String[] args) {
        String json = create.toJson(new X());
        System.out.println(json);
    }
    public static class X {
        public String test = "asd";
        public int xyz = 23;
        public Y y_class = new Y();
    }
    public static class Y {
        String yTest = "asd2";

        Z zTest = new Z();
    }
    public static class Z {
        long longVal = 25;
        double doubleTest = 2.4;
    }
}

{  
   "class":"google.GsonClassNameTest$X",
   "test":"asd",
   "xyz":23,
   "y_class":{  
      "class":"google.GsonClassNameTest$Y",
      "yTest":"asd2",
      "zTest":{  
         "class":"google.GsonClassNameTest$Z",
         "longVal":25,
         "doubleTest":2.4
      }
   }
}

package com.mycompany.javatest;

import com.google.gson.*;
import java.lang.reflect.*;
import org.junit.*;

public class JavaTest {

    public static class GenericSerializer implements JsonSerializer<Object>, JsonDeserializer<Object> {

        private static final String CLASS_PROPERTY_NAME = "class";
        private final Gson gson;

        public GenericSerializer() {
            gson = new Gson();
        }

        public GenericSerializer(Gson gson) {
            this.gson = gson;
        }

        @Override
        public Object deserialize(JsonElement json, Type typeOfT,
                                  JsonDeserializationContext context) throws JsonParseException {

            Class actualClass;
            if (json.isJsonObject()) {
                JsonObject jsonObject = json.getAsJsonObject();
                String className = jsonObject.get(CLASS_PROPERTY_NAME).getAsString();
                try {
                    actualClass = Class.forName(className);
                }
                catch (ClassNotFoundException e) {
                    e.printStackTrace();
                    throw new JsonParseException(e.getMessage());
                }
            }
            else {
                actualClass = typeOfT.getClass();
            }

            return gson.fromJson(json, actualClass);
        }

        @Override
        public JsonElement serialize(Object src, Type typeOfSrc,
                                     JsonSerializationContext context) {
            JsonElement retValue = gson.toJsonTree(src);
            if (retValue.isJsonObject()) {
                retValue.getAsJsonObject().addProperty(CLASS_PROPERTY_NAME, src.getClass().getName());
            }
            return retValue;
        }

    }

    public static void main(String[] args) {

        GsonBuilder builder = new GsonBuilder();
        builder.registerTypeHierarchyAdapter(Object.class, new GenericSerializer());
        Gson gson = builder.create();

        SomeSuperClass x = new SomeSubClass();
        String json = gson.toJson(x);
        
        SomeSuperClass y = gson.fromJson(json, SomeSuperClass.class); // Usually, y would now be of type SomeSuperClass
        Assert.assertEquals(x.getClass(), y.getClass()); // y is actually of type SomeSubClass (!)
        
        System.out.println("y.getClass()= " + y.getClass());
    }

    public static class SomeSuperClass {
    }

    public static class SomeSubClass extends SomeSuperClass {

        private final String someMember = "12345";
    }
}

public class GsonClassNameTest {


    public static void main(String[] args) {

        Gson create = new GsonBuilder().registerTypeHierarchyAdapter(Object.class, new ODeserialiser()).create();
        String json = create.toJson(new X());
        System.out.println(json);

    }

    public static class ODeserialiser implements JsonSerializer<Object> {

        @Override
        public JsonElement serialize(Object src, Type typeOfSrc, JsonSerializationContext context) {
            Gson gson = new Gson();
            JsonElement serialize = gson.toJsonTree(src);
            JsonObject o = (JsonObject) serialize;
            o.addProperty("class", src.getClass().getName());
            return serialize;
        }
    }

    public static class X {
        public String test = "asd";
    }
}

{"test":"asd","class":"google.GsonClassNameTest$X"}