Java GSON 和 InstanceCreator 问题
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GSON and InstanceCreator issue
提问by IAmYourFaja
I have the following POJOs:
我有以下 POJO：
public interface Shape {
public double calcArea();
public double calcPerimeter();
}
public class Rectangle implement Shape {
// Various properties of a rectangle
}
public class Circle implements Shape {
// Various properties of a circle
}
public class ShapeHolder {
private List<Shape> shapes;
// other stuff
}
I have no problem getting GSON to serialize an instance of ShapeHolderto JSON. But when I try to deserialize a String of that JSON back into a ShapeHolderinstance, I get errors:
让 GSON 将 的实例序列化为ShapeHolderJSON没有问题。但是，当我尝试将该 JSON 的字符串反序列化回ShapeHolder实例时，出现错误：
String shapeHolderAsStr = getString();
ShapeHolder holder = gson.fromJson(shapeHodlderAsStr, ShapeHolder.class);
Throws:
抛出：
Exception in thread "main" java.lang.RuntimeException: Unable to invoke no-args constructor for interface
net.myapp.Shape. Register an InstanceCreator with Gson for this type may fix this problem.
at com.google.gson.internal.ConstructorConstructor.construct(ConstructorConstructor.java:167)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:162)
... rest of stack trace ommitted for brevity
So I looked hereand started implementing my own ShapeInstanceCreator:
所以我看这里并开始实现我自己的ShapeInstanceCreator：
public class ShapeInstanceCreator implements InstanceCreator<Shape> {
@Override
public Shape createInstance(Type type) {
// TODO: ???
return null;
}
}
But now I'm stuck: I'm only given a java.lang.reflect.Type, but I really need a java.lang.Objectso I can write code like:
但现在我被困住了：我只得到了一个java.lang.reflect.Type，但我真的需要一个，java.lang.Object这样我就可以编写如下代码：
public class ShapeInstanceCreator implements InstanceCreator<Shape> {
@Override
public Shape createInstance(Type type) {
Object obj = convertTypeToObject(type);
if(obj instanceof Rectangle) {
Rectangle r = (Rectangle)obj;
return r;
} else {
Circle c = (Circle)obj;
return c;
}
return null;
}
}
What can I do?
我能做什么？
Update
更新
Per @raffian's suggestion (the link he/she posted), I implemented an InterfaceAdapterexactlylike the one in the link (I didn't change anything). Now I'm getting the following exception:
根据@raffian 的建议（他/她发布的链接），我实现了一个与链接中的InterfaceAdapter完全一样的（我没有更改任何内容）。现在我收到以下异常：
Exception in thread "main" com.google.gson.JsonParseException: no 'type' member found in what was expected to be an interface wrapper
at net.myapp.InterfaceAdapter.get(InterfaceAdapter.java:39)
at net.myapp.InterfaceAdapter.deserialize(InterfaceAdapter.java:23)
Any ideas?
有任何想法吗？
采纳答案by raffian
Did you look at this? Looks like a nice clean way to implement InstanceCreators.
你看这个了吗？看起来是实现 InstanceCreators 的一种非常干净的方式。
I was using Gson too, but switched to FlexJSONdue to serialization issues. With Flex, you don't need instance creators, just make sure your objects have getters/setters for all fields based on JavaBean spec, and you're good to go:
我也使用 Gson，但由于序列化问题切换到FlexJSON。使用 Flex，您不需要实例创建者，只需确保您的对象具有基于 JavaBean 规范的所有字段的 getter/setter，您就可以开始了：
ShapeHolder sh = new ShapeHolder();
sh.addShape(new Rectangle());
sh.addShape(new Circle());
JSONSerializer ser = new JSONSerializer();
String json = ser.deepSerialize(sh);
JSONDeserializer<ShapeHolder> der = new JSONDeserializer<ShapeHolder>();
ShapeHolder sh2 = der.deserialize(json);
回答by Kanagavelu Sugumar
NOTE that FlexJSONis adding class name as part of json like below serialize time.
请注意，FlexJSON将类名添加为 json 的一部分，如下所示序列化时间。
{
"HTTPStatus": "OK",
"class": "com.XXX.YYY.HTTPViewResponse",
"code": null,
"outputContext": {
"class": "com.XXX.YYY.ZZZ.OutputSuccessContext",
"eligible": true
}
}
So JSON will be cumber some; but you don't need write InstanceCreatorwhich is required in GSON.
所以JSON会有些麻烦；但您不需要编写InstanceCreatorGSON 中所需的内容。
