it-swarm.com.de

Konvertierung von JSon in mehrere unbekannte Java-Objekttypen mit GSon

Ich habe einen netty-Decoder, der mithilfe von GSon JSon vom Web-Client in entsprechende Java-Objekte konvertiert. Die Anforderung lautet: Der Client könnte nicht zusammenhängende Klassen, Klasse A, Klasse B, Klasse C usw. senden Ich möchte jedoch die same singleton-Decoder-Instanz in der Pipeline verwenden, um die Konvertierung durchzuführen (da ich Spring für die Konfiguration benutze). Das Problem, vor dem ich stehe, ist, dass ich das class-Objekt vorab kennen muss.

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

Dies kann weder B noch C decodieren. Die Benutzer meiner Bibliothek müssen jetzt für jede Klasse separate Decoder schreiben, anstatt später einen Cast in der Zeile zu erstellen. Die einzige Möglichkeit, dies zu tun, besteht darin, den String-Namen der Klasse mit dem Namen "org.example.C" in der JSon-Zeichenfolge vom Web-Client aus zu übergeben, im Decoder auszulesen und dann mit Class.forName die Klasse abzurufen. Gibt es einen besseren Weg, dies zu tun?

13
Abe

GSon MUSS die Klasse kennen, die der Json-Saite entspricht. Wenn Sie es nicht mit fromJson () zur Verfügung stellen möchten, können Sie es tatsächlich im Json angeben. Eine Möglichkeit besteht darin, eine Schnittstelle zu definieren und einen Adapter daran zu binden.

Mögen :

  class A implements MyInterface {
    // ...
  }

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

Adapter kann sein wie:

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;
  }
}
10
PomPom

Angenommen, Sie haben diese 2 möglichen JSON-Antworten:

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

Sie können eine Klassenstruktur folgendermaßen erstellen:

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...
}

Dann können Sie alle möglichen JSON-Antworten analysieren mit:

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

Gson ignoriert alle JSON-Felder, die mit keinem der Attribute in Ihrer Klassenstruktur übereinstimmen. Sie können also eine einzelne Klasse anpassen, um verschiedene Antworten zu analysieren.

Dann können Sie prüfen, welches der Attribute classA, classB, ... nicht null ist, und Sie wissen, welche Antwort Sie erhalten haben.

5
MikO

Ich bin nicht sicher, ob Sie danach gefragt haben, aber durch das Ändern der Klasse RuntimeTypeAdapterFactory habe ich ein System für die Unterklassen erstellt, das auf den Bedingungen in der Json-Quelle basiert. 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);

}

Beispiel (aus einem Projekt, an dem ich gerade arbeite):

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";
    }
}

Verwendungszweck:

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();

Die Hierarchie-Basisklasse ist Item. Währung, Ausrüstung, Edelstein und Karte erweitern dies.

3
Johan Ljungberg

Modellklasse erstellen,

public class MyModel {

    private String errorId;

    public String getErrorId() {
        return errorId;
    }

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

Erstellen Sie eine Unterklasse

   public class SubClass extends MyModel {
        private String subString;

       public String getSubString() {
            return subString;
        }

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

rufen Sie die parseGson-Methode auf

parseGson(subClass);

gson-parse-methode mit objektklasse

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

Sie können globale Variablen festlegen, die in myModel umgewandelt werden

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