web-dev-qa-db-ja.com

GSonを使用してJSonから複数の不明なJavaオブジェクトタイプに変換する

GSonを使用してWebクライアントからのJSonを適切なJavaオブジェクトに変換するnettyデコーダーがあります。要件は次のとおりです。クライアントは無関係のクラス、クラスA、クラスB、クラスCなどを送信できますがパイプラインで同じシングルトンデコーダーインスタンスを使用して変換を実行したいと思います（構成にSpringを使用しているため）。直面している問題は、classを知る必要があることです。手前のオブジェクト。

public Object decode()
{
    gson.fromJson(jsonString, A.class);
}

これはBまたはCをデコードできません。私のライブラリのユーザーは、後でキャストするのではなく、クラスごとに個別のデコーダーを作成する必要があります。これを行うために私が見ることができる唯一の方法は、WebクライアントからJSon文字列で「org.example.C」と言うクラスの文字列名を渡し、デコーダーでそれを解析してから、Class.forNameを使用して取得することです。クラス。これを行うためのより良い方法はありますか？

javajsongsonnetty
13
Abe

GSonは、json文字列に一致するクラスを認識している必要があります。 fromJson（）を提供したくない場合は、実際にJsonで指定できます。方法は、インターフェースを定義し、それにアダプターをバインドすることです。

お気に入り ：

  class A implements MyInterface {
    // ...
  }

  public Object decode()
  {
    Gson  gson = builder.registerTypeAdapter(MyInterface.class, new MyInterfaceAdapter());
    MyInterface a =  gson.fromJson(jsonString, MyInterface.class);
  }

アダプターは次のようになります。

public final class MYInterfaceAdapter implements JsonDeserializer<MyInterface>, JsonSerializer<MyInterface> {
  private static final String PROP_NAME = "myClass";

  @Override
  public MyInterface deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
    try {
      String classPath = json.getAsJsonObject().getAsJsonPrimitive(PROP_NAME).getAsString();
      Class<MyInterface> cls = (Class<MyInterface>) Class.forName(classPath);

      return (MyInterface) context.deserialize(json, cls);
    } catch (ClassNotFoundException e) {
      e.printStackTrace();
    }

    return null;
  }

  @Override
  public JsonElement serialize(MyInterface src, Type typeOfSrc, JsonSerializationContext context) {
    // note : won't work, you must delegate this
    JsonObject jo = context.serialize(src).getAsJsonObject();

    String classPath = src.getClass().getName();
    jo.add(PROP_NAME, new JsonPrimitive(classPath));

    return jo;
  }
}
9
PomPom

次の2つの可能なJSON応答があるとします。

{
  "classA": {"foo": "fooValue"}
}
  or
{
  "classB": {"bar": "barValue"}
}

次のようなクラス構造を作成できます。

public class Response {
  private A classA;
  private B classB;
  //more possible responses...
  //getters and setters...
}

public class A {
  private String foo;
  //getters and setters...
}

public class B {
  private String bar;
  //getters and setters...
}

次に、次の方法で可能なJSON応答を解析できます。

Response response = gson.fromJson(jsonString, Response.class);

Gsonは、クラス構造内のどの属性にも対応しないすべてのJSONフィールドを無視するため、単一のクラスを適応させてさまざまな応答を解析できます...

次に、属性classA、classB、...のどれがnullでないかを確認でき、どの応答を受信したかがわかります。

5
MikO

これがあなたが求めていたものであるかどうかはわかりませんが、RuntimeTypeAdapterFactoryクラスを変更することで、Jsonソースの条件に基づいてサブクラス化するためのシステムを作成しました。 RuntimeTypeAdapterFactory.class：

/*
 * 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.
 */

package com.google.gson.typeadapters;

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 RuntimeTypeAdapter} 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
 *   RuntimeTypeAdapter<Shape> shapeAdapter
 *       = RuntimeTypeAdapter.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 in your application's GSON builder:
 * <pre>   {@code
 *   Gson gson = new GsonBuilder()
 *       .registerTypeAdapter(Shape.class, shapeAdapter)
 *       .create();
 * }</pre>
 * Like {@code GsonBuilder}, this API supports chaining: <pre>   {@code
 *   RuntimeTypeAdapter<Shape> shapeAdapter = 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 RuntimeTypeAdapterPredicate predicate;
    private final Map<String, Class<?>> labelToSubtype = new LinkedHashMap<String, Class<?>>();
    private final Map<Class<?>, String> subtypeToLabel = new LinkedHashMap<Class<?>, String>();

    private RuntimeTypeAdapterFactory(Class<?> baseType, RuntimeTypeAdapterPredicate predicate) {
        if (predicate == null || baseType == null) {
            throw new NullPointerException();
        }
        this.baseType = baseType;
        this.predicate = predicate;
    }

    /**
     * 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, RuntimeTypeAdapterPredicate predicate) {
        return new RuntimeTypeAdapterFactory<T>(baseType, predicate);
    }

    /**
     * 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, null);
    }

    /**
     * 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);
                String label = predicate.process(jsonElement);
                @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 { // Unimplemented as we don't use write.
                /*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 (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(null, out);
            }
        };
    }
}

RuntimeTypeAdapterPredicate.class：

package com.google.gson.typeadapters;

import com.google.gson.JsonElement;

/**
 * Created by Johan on 2014-02-13.
 */
public abstract class RuntimeTypeAdapterPredicate {

    public abstract String process(JsonElement element);

}

例（私が現在取り組んでいるプロジェクトから取得）：

ItemTypePredicate.class：

package org.libpoe.serial;

import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.typeadapters.RuntimeTypeAdapterPredicate;

/**
 * Created by Johan on 2014-02-13.
 */
public class ItemTypePredicate extends RuntimeTypeAdapterPredicate {

    @Override
    public String process(JsonElement element) {
        JsonObject obj = element.getAsJsonObject();
        int frameType = obj.get("frameType").getAsInt();

        switch(frameType) {
            case 4: return "Gem";
            case 5: return "Currency";
        }
        if (obj.get("typeLine").getAsString().contains("Map")
                && obj.get("descrText").getAsString() != null
                && obj.get("descrText").getAsString().contains("Travel to this Map")) {
            return "Map";
        }

        return "Equipment";
    }
}

使用法：

RuntimeTypeAdapterFactory<Item> itemAdapter = RuntimeTypeAdapterFactory.of(Item.class, new ItemTypePredicate())
        .registerSubtype(Currency.class)
        .registerSubtype(Equipment.class)
        .registerSubtype(Gem.class)
        .registerSubtype(Map.class);

Gson gson = new GsonBuilder()
        .enableComplexMapKeySerialization()
        .registerTypeAdapterFactory(itemAdapter).create();

階層的な基本クラスはItemです。通貨、装備、宝石、地図はすべてこれを拡張します。

3
Johan Ljungberg

モデルクラスを作成し、

public class MyModel {

    private String errorId;

    public String getErrorId() {
        return errorId;
    }

    public void setErrorId(String errorId) {
        this.errorId = errorId;
    }
}

サブクラスを作成する

   public class SubClass extends MyModel {
        private String subString;

       public String getSubString() {
            return subString;
        }

        public void setSubString(String subString) {
            this.subString = subString;
        }
 }

parseGsonメソッドを呼び出す

parseGson(subClass);

オブジェクトクラスを使用したgson解析メソッド

   public void parseGson(Object object){
     object = gson.fromJson(response.toString(), object.getClass());
     SubClass subclass = (SubClass)object;
   }

MyModelにキャストするグローバル変数を設定できます

((MyModel)object).setErrorId(response.getString("errorid"));
1
SUcpinar