Conversione da JSon a più tipi di oggetti java sconosciuti utilizzando GSon

Question

Ho un decodificatore piccolo che utilizza GSon per convertire JSon proveniente da client Web in oggetti java appropriati. Il requisito è: Il client potrebbe inviare classi non correlate, Classe A, Classe B, Classe C ecc ma vorrei utilizzare la stessa stessa istanza del decodificatore singleton nella pipeline per eseguire la conversione (poiché utilizzo spring per la sua configurazione) . Il problema che sto affrontando è che ho bisogno di conoscere l'oggetto class in anticipo.

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

Questo non può decodificare B o C. Gli utenti della mia biblioteca, ora bisogno di scrivere decoder separati per ogni classe al posto di un cast in seguito su tutta la linea. L'unico modo che posso vedere per farlo è passare il nome String della classe "org.example.C" nella stringa JSon dal client web, analizzarlo nel decodificatore e quindi usare Class.forName per ottenere la classe. C'è un modo migliore per farlo?

Answer 1

GSon DEVE conoscere la classe corrispondente alla stringa JSON. Se non vuoi fornirlo con json(), puoi specificarlo in the Json. Un modo è definire un'interfaccia e associarvi un adattatore.

come:

class A implements MyInterface { 
    // ... 
    } 

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

adattatore può essere come:

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; 
    } 
} 

Answer 2

Supponiamo di avere questi 2 possibili risposte JSON:

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

è possibile creare una struttura di classe come questo:

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... 
} 

Quindi è in grado di analizzare una delle possibili risposte JSON con:

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

Gson ignorerà tutti i campi JSON che non corrispondono a nessuno degli attributi in la struttura di classe, in modo da poter adattare una sola classe per analizzare risposte diverse ...

Quindi è possibile controllare quali degli attributi classA, classB, ... non è null e saprete che risposta avete ricevuto .

Answer 3

Crea classe del modello,

public class MyModel { 

    private String errorId; 

    public String getErrorId() { 
     return errorId; 
    } 

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

Creare sottoclasse

public class SubClass extends MyModel { 
     private String subString; 

     public String getSubString() { 
      return subString; 
     } 

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

chiamata Metodo parseGson

parseGson(subClass); 

metodo GSON parse con classe di oggetti

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

È possibile impostare le variabili globali che gettano a MyModel

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

Answer 4

Incerto se questo è quello che stavi chiedendo , ma modificando la classe RuntimeTypeAdapterFactory, ho creato un sistema per la sottoclasse in base alle condizioni nell'origine Json. 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); 

} 

esempio (tratto da un progetto che sto attualmente lavorando su):

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"; 
    } 
} 

Uso:

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(); 

La classe di base della gerarchia è Elemento. Valuta, equipaggiamento, gemma e mappa lo estendono.