使用Gson和抽象类 [英] Using Gson and Abstract Classes

问题描述

问题如下：
$ b 我试图在使用GSON的客户端和服务器之间交换消息。 $ b

我有这样的结构：

  public class Message 
 {
 private TypeOfContent type; //这是一个枚举
私人内容; 
 .... 
} 
  

然后对象内容可以是各种

我找到2个教程 here 和此处，但没有一个能解决问题。

Edit1：

类Message是这个：

---

  public class Mensagem 
 {
 private TipoMensagem类型; 
 
 private Conteudo conteudo; 
 
私人Cliente作者; 
私人客户destino; // null  - >到所有（广播）
} 
  

---

内容是这样的：

  public class Conteudo 
 {
 
 protected TipoConteudo typeConteudo; 
 
保护字符串texto; 
 
保护Posicao posicao; 
 
 public Conteudo（TipoConteudo typeConteudo，String texto，Posicao posicao）
 {
 this.texto = texto; 
 this.posicao = posicao; 
 this.typeConteudo = typeConteudo; 
} 
} 
  

contedo的扩展类的一个例子是1：

  public class ConteudoTweet extends Conteudo 
 {
 
保护字符串pathImagem; 
 
 
 public ConteudoTweet（TipoConteudo typeConteudo，String tweet，Posicao location，String picturePath）
 {
 super（typeConteudo，tweet，location）; 
 
 this.pathImagem = picturePath; 
 
} 
 
 
 
} 
  

---

最后我做的是这样的：String strObject = new Gson（）。toJson（mensage）;哪些工作，但反序列化它并不是因为它假定它始终是从内容类

解决方案

我终于解决了它！

  // GSON 
 
 GsonBuilder gsonBilder = new GsonBuilder（）; 
 gsonBilder.registerTypeAdapter（Conteudo.class，new InterfaceAdapter< Conteudo>（））; 
 gsonBilder.setPrettyPrinting（）; 
 
 Gson gson = gsonBilder.create（）; 
 
 String str2send = gson.toJson（message）; 
 
 Mensagem msg_recv = gson.fromJson（str2send，Mensagem.class）; 
  

请注意：registerTypeAdapter（ AbstractClass.class ，new InterfaceAdapter（） ）;

通过 AbstractClass.class ，我的意思是你正在实现的类是Conteúdo，可以是ConteudoTweet或ConteudoUserSystem，等等......

InterfaceAdapter 的实现是：

  import java.lang.reflect.Type; 
 
 import com.google.gson.JsonDeserializationContext; 
 import com.google.gson.JsonDeserializer; 
 import com.google.gson.JsonElement; 
 import com.google.gson.JsonObject; 
 import com.google.gson.JsonParseException; 
 import com.google.gson.JsonSerializationContext; 
 import com.google.gson.JsonSerializer; 
 
 public class InterfaceAdapter< T> 
实现了JsonSerializer< T>，JsonDeserializer< T> {
 
 @Override 
 public final JsonElement serialize（final T object，final Type interfaceType，final JsonSerializationContext context）
 {
 final JsonObject member = new JsonObject（）; 
 
 member.addProperty（type，object.getClass（）。getName（））; 
 
 member.add（data，context.serialize（object））; 
 
返回成员; 
 
 $ b @Override 
 public final T反序列化（final JsonElement elem，final Type interfaceType，final JsonDeserializationContext context）
 throws JsonParseException 
 {
 final JsonObject member =（JsonObject）elem; 
 final JsonElement typeString = get（member，type）; 
 final JsonElement data = get（member，data）; 
 final类型actualType = typeForName（typeString）; 
 
 return context.deserialize（data，actualType）; 
 
 $ b $ private类型typeForName（final JsonElement typeElem）
 {
 try 
 {
 return Class.forName（typeElem.getAsString（） ）; 
} 
 catch（ClassNotFoundException e）
 {
 throw new JsonParseException（e）; 
 
 
 
 private JsonElement get（final JsonObject wrapper，final String memberName）
 {
 final JsonElement elem = wrapper.get（memberName）; 
 
 if（elem == null）
 {
抛出新的JsonParseException（
no+ memberName +'json文件中找到的成员。 
} 
 return elem; 
} 
 
} 
  

这个InterfaceAdapter是通用的，所以它应该一般工作......

就是这样！

I'm trying to exchange messages between a client and a server using GSON.

The problem is the following:

I have this structure:

public class Message 
{
    private TypeOfContent type; //  It's a enum 
    private Content       content;
    ....
}

Then the object content can be a various set of Classes.

I found 2 tutorials here and here, but none of them solves the problem.

Edit1:

The class Message is this one:

---

public class Mensagem
{
private TipoMensagem    type;

    private Conteudo        conteudo;

    private Cliente         autor;
    private Cliente         destino;    // null -> to all(broadcast)
}

---

And Content is this one:

public class Conteudo
{

protected   TipoConteudo typeConteudo; 

protected   String      texto;

protected   Posicao     posicao;

public Conteudo(TipoConteudo typeConteudo, String texto, Posicao posicao)
{
    this.texto   = texto;
    this.posicao = posicao;  
    this.typeConteudo = typeConteudo;
}    
} 

And an example of a extend class from contedo is this one:

public class ConteudoTweet extends Conteudo 
{

protected   String      pathImagem;


public ConteudoTweet(TipoConteudo typeConteudo, String tweet, Posicao location, String picturePath) 
{
    super(typeConteudo,tweet, location);

    this.pathImagem = picturePath;

}



}

---

Finaly what i do is like : "String strObject = new Gson().toJson(mensage);" which works but on deserialization it doesnt because it assumes always that it is from Content class

解决方案

I finally solved it!

    // GSON

    GsonBuilder gsonBilder = new GsonBuilder();
    gsonBilder.registerTypeAdapter(Conteudo.class, new InterfaceAdapter<Conteudo>());
    gsonBilder.setPrettyPrinting();

    Gson gson =gsonBilder.create();

    String str2send = gson.toJson(message);

    Mensagem msg_recv = gson.fromJson(str2send,Mensagem.class);

Note that: "registerTypeAdapter(AbstractClass.class, new InterfaceAdapter());"

by AbstractClass.class i mean the class that you are implementing in my case it was Conteúdo that could be ConteudoTweet or ConteudoUserSystem and so on...

The implementation of InterfaceAdapter is :

import java.lang.reflect.Type;

import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParseException;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;

public class InterfaceAdapter<T>
    implements JsonSerializer<T>, JsonDeserializer<T> {

    @Override
    public final JsonElement serialize(final T object, final Type interfaceType, final JsonSerializationContext context) 
    {
        final JsonObject member = new JsonObject();

        member.addProperty("type", object.getClass().getName());

        member.add("data", context.serialize(object));

        return member;
    }

    @Override
    public final T deserialize(final JsonElement elem, final Type interfaceType, final JsonDeserializationContext context) 
            throws JsonParseException 
    {
        final JsonObject member = (JsonObject) elem;
        final JsonElement typeString = get(member, "type");
        final JsonElement data = get(member, "data");
        final Type actualType = typeForName(typeString);

        return context.deserialize(data, actualType);
    }

    private Type typeForName(final JsonElement typeElem) 
    {
        try 
        {
            return Class.forName(typeElem.getAsString());
        } 
        catch (ClassNotFoundException e) 
        {
            throw new JsonParseException(e);
        }
    }

    private JsonElement get(final JsonObject wrapper, final String memberName) 
    {
        final JsonElement elem = wrapper.get(memberName);

        if (elem == null) 
        {
            throw new JsonParseException(
                "no '" + memberName + "' member found in json file.");
        }
        return elem;
    }

}

And this InterfaceAdapter is generic so it should work in general...

That's it!

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