Gson多态序列化 [英] Gson Polymorphic Serialization

问题描述

使用Gson 2.2.2我试图序列化POJO（行为）的数组列表。

我有一个适配器，它几乎是我的副本'在线看到：

  public class BehaviorAdapter实现了JsonSerializer< Behavior> {
 
 private static final String CLASSNAME =CLASSNAME; 
 private static final String INSTANCE =INSTANCE; 
 
 @Override 
 public JsonElement serialize（Behavior src，Type typeOfSrc，
 JsonSerializationContext context）{
 
 JsonObject retValue = new JsonObject（）; 
 String className = src.getClass（）。getCanonicalName（）; 
 retValue.addProperty（CLASSNAME，className）; 
 JsonElement elem = context.serialize（src）; 
 retValue.add（INSTANCE，elem）; 
返回retValue; 
 
 
 $ / code $ / pre 
 $ b $ p我注册它像这样：
  GsonBuilder builder = new GsonBuilder（）; 
 builder.registerTypeHierarchyAdapter（Behavior.class，new BehaviorAdapter（））; 
 gson = builder.create（）; 
  
然后当我尝试序列化我的ArrayList时：
 字符串json2 = gson.toJson（行为）; 
  
我得到一个堆栈溢出。
 
 
看起来在线上：
  JsonElement elem = context.serialize（src）; 
  
它启动一个递归循环，一次又一次地通过我的序列化程序。那么，我如何注册它，以避免这种情况发生？我需要序列化列表并维护多态。
解决方案
看起来像是发现了无限循环
 
 
然而，你不应该在src对象上调用它本身，因为这将导致无限循环（Gson将再次调用您的回调方法）。
 
我能想到的最简单的方法是是创建一个新的Gson实例，它不会 安装处理程序，并通过它运行实例。
 
 
 
作为最终运行，您可以序列化 List< Behavior> 来代替： 
 
 
  public class BehaviorListAdapter实现JsonSerializer< List< Behavior>> {
 
 private static final String CLASSNAME =CLASSNAME; 
 private static final String INSTANCE =INSTANCE; 
 $ b $ @Override 
 public JsonElement serialize（List< Behavior> src，Type typeOfSrc，
 JsonSerializationContext context）{
 JsonArray array = new JsonArray（）; 
 for（Behavior behavior：src）{
 JsonObject behaviorJson = new JsonObject（）; 
 String className = behavior.getClass（）。getCanonicalName（）; 
 behaviorJson.addProperty（CLASSNAME，className）; 
 JsonElement elem = context.serialize（behavior）; 
 behaviorJson.add（INSTANCE，elem）; 
 array.add（behaviorJson）; 
} 
返回数组; 
} 
} 
 
 GsonBuilder builder = new GsonBuilder（）; 
 //使用TypeToken为参数化类型创建一个Type实例
 builder.registerTypeAdapter（
（new TypeToken< List< Behavior>>（）{}）.getType（）， 
 new BehaviorListAdapter（））; 
 gson = builder.create（）; 
  
 
using Gson 2.2.2 I'm trying to serialize an array list of POJOs (Behaviors).


i have an adapter that's pretty much a copy of what i've seen online:
public class BehaviorAdapter implements JsonSerializer<Behavior> {

    private static final String CLASSNAME = "CLASSNAME";
    private static final String INSTANCE = "INSTANCE";

    @Override
    public JsonElement serialize(Behavior src, Type typeOfSrc,
            JsonSerializationContext context) {

        JsonObject retValue = new JsonObject();
        String className = src.getClass().getCanonicalName();
        retValue.addProperty(CLASSNAME, className);
        JsonElement elem = context.serialize(src);
        retValue.add(INSTANCE, elem);
        return retValue;
    }
}
The i register it like this:
GsonBuilder builder = new GsonBuilder();        
builder.registerTypeHierarchyAdapter(Behavior.class, new BehaviorAdapter());
gson = builder.create();
Then when i try to serialize my ArrayList:
String json2 = gson.toJson(behaviors);
I get a stack overflow.

It appears that on line:
JsonElement elem = context.serialize(src);
It starts a recursive loop, going again and again through my serializer. So How do i register it so that this won't happen? I need to serialize the list and maintain polymorphism.
解决方案
Looks like you found the infinite loop the JsonSerializer docs warn about:

  
However, you should never invoke it on the src object itself since that will cause an infinite loop (Gson will call your call-back method again).
The easiest way I can think of is to create a new Gson instance that does not have the handler installed, and run your instances through that.

As an end run, you could just serialize the List<Behavior> instead:
public class BehaviorListAdapter implements JsonSerializer<List<Behavior>> {

    private static final String CLASSNAME = "CLASSNAME";
    private static final String INSTANCE = "INSTANCE";

    @Override
    public JsonElement serialize(List<Behavior> src, Type typeOfSrc,
            JsonSerializationContext context) {
        JsonArray array = new JsonArray();
        for (Behavior behavior : src) {
            JsonObject behaviorJson = new JsonObject();
            String className = behavior.getClass().getCanonicalName();
            behaviorJson.addProperty(CLASSNAME, className);
            JsonElement elem = context.serialize(behavior);
            behaviorJson.add(INSTANCE, elem);
            array.add(behaviorJson);
        }
        return array;
    }
}

GsonBuilder builder = new GsonBuilder();
// use a TypeToken to make a Type instance for a parameterized type
builder.registerTypeAdapter(
    (new TypeToken<List<Behavior>>() {}).getType(),
    new BehaviorListAdapter());
gson = builder.create();


                        
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