java - Gson 序列化多态对象列表

Question

我正在尝试使用 Gson 将涉及多态性的对象序列化/反序列化为 JSON。

这是我的序列化代码:

ObixBaseObj lobbyObj = new ObixBaseObj();
lobbyObj.setIs("obix:Lobby");

ObixOp batchOp = new ObixOp();
batchOp.setName("batch");
batchOp.setIn("obix:BatchIn");
batchOp.setOut("obix:BatchOut");

lobbyObj.addChild(batchOp);

Gson gson = new Gson();
System.out.println(gson.toJson(lobbyObj));

结果如下:

 {"obix":"obj","is":"obix:Lobby","children":[{"obix":"op","name":"batch"}]}

序列化主要工作，除了它缺少继承成员的内容(特别是 obix:BatchIn 和 obixBatchout 字符串丢失)。这是我的基类:

public class ObixBaseObj  {
    protected String obix;
    private String display;
    private String displayName;
    private ArrayList<ObixBaseObj> children;

    public ObixBaseObj()
    {
        obix = "obj";
    }

    public void setName(String name) {
        this.name = name;
    }
        ...
}

这是我继承的类 (ObixOp) 的样子:

public class ObixOp extends ObixBaseObj {
    private String in;
    private String out;

    public ObixOp() {
        obix = "op";
    }
    public ObixOp(String in, String out) {
        obix = "op";
        this.in = in;
        this.out = out;
    }
    public String getIn() {
        return in;
    }
    public void setIn(String in) {
        this.in = in;
    }
    public String getOut() {
        return out;
    }
    public void setOut(String out) {
        this.out = out;
    }
}

我意识到我可以为此使用适配器，但问题是我正在序列化基类类型 ObixBaseObj 的集合。大约有 25 个类继承自此。我怎样才能优雅地完成这项工作？

Answer 1

有一个简单的解决方案:Gson's RuntimeTypeAdapterFactory (来自 com.google.code.gson:gson-extras:$gsonVersion)。您不必编写任何序列化程序，这个类为您工作。用你的代码试试这个:

    ObixBaseObj lobbyObj = new ObixBaseObj();
    lobbyObj.setIs("obix:Lobby");

    ObixOp batchOp = new ObixOp();
    batchOp.setName("batch");
    batchOp.setIn("obix:BatchIn");
    batchOp.setOut("obix:BatchOut");

    lobbyObj.addChild(batchOp);

    RuntimeTypeAdapterFactory<ObixBaseObj> adapter = 
                    RuntimeTypeAdapterFactory
                   .of(ObixBaseObj.class)
                   .registerSubtype(ObixBaseObj.class)
                   .registerSubtype(ObixOp.class);


    Gson gson2=new GsonBuilder().setPrettyPrinting().registerTypeAdapterFactory(adapter).create();
    Gson gson = new Gson();
    System.out.println(gson.toJson(lobbyObj));
    System.out.println("---------------------");
    System.out.println(gson2.toJson(lobbyObj));

}

输出:

{"obix":"obj","is":"obix:Lobby","children":[{"obix":"op","name":"batch","children":[]}]}
---------------------
{
  "type": "ObixBaseObj",
  "obix": "obj",
  "is": "obix:Lobby",
  "children": [
    {
      "type": "ObixOp",
      "in": "obix:BatchIn",
      "out": "obix:BatchOut",
      "obix": "op",
      "name": "batch",
      "children": []
    }
  ]
}

编辑:更好的工作示例。

您说大约有 25 个类继承自 ObixBaseObj。

我们开始编写一个新类，GsonUtils

public class GsonUtils {

    private static final GsonBuilder gsonBuilder = new GsonBuilder()
            .setPrettyPrinting();

    public static void registerType(
            RuntimeTypeAdapterFactory<?> adapter) {
        gsonBuilder.registerTypeAdapterFactory(adapter);
    }

    public static Gson getGson() {
        return gsonBuilder.create();
    }

每次我们需要一个Gson对象时，我们都会调用

，而不是调用 new Gson()

GsonUtils.getGson()

我们将此代码添加到 ObixBaseObj:

public class ObixBaseObj {
    protected String obix;
    private String display;
    private String displayName;
    private String name;
    private String is;
    private ArrayList<ObixBaseObj> children = new ArrayList<ObixBaseObj>();
    // new code
    private static final RuntimeTypeAdapterFactory<ObixBaseObj> adapter = 
            RuntimeTypeAdapterFactory.of(ObixBaseObj.class);

    private static final HashSet<Class<?>> registeredClasses= new HashSet<Class<?>>();

    static {
        GsonUtils.registerType(adapter);
    }

    private synchronized void registerClass() {
        if (!registeredClasses.contains(this.getClass())) {
            registeredClasses.add(this.getClass());
            adapter.registerSubtype(this.getClass());
        }
    }
    public ObixBaseObj() {
        registerClass();
        obix = "obj";
    }

为什么？因为每次实例化这个类或 ObixBaseObj 的子类时，它将在 RuntimeTypeAdapter

中注册的类

在子类中，只需要进行最小的更改:

public class ObixOp extends ObixBaseObj {
    private String in;
    private String out;

    public ObixOp() {
        super();
        obix = "op";
    }

    public ObixOp(String in, String out) {
        super();
        obix = "op";
        this.in = in;
        this.out = out;
    }

工作示例:

public static void main(String[] args) {

        ObixBaseObj lobbyObj = new ObixBaseObj();
        lobbyObj.setIs("obix:Lobby");

        ObixOp batchOp = new ObixOp();
        batchOp.setName("batch");
        batchOp.setIn("obix:BatchIn");
        batchOp.setOut("obix:BatchOut");

        lobbyObj.addChild(batchOp);



        Gson gson = GsonUtils.getGson();
        System.out.println(gson.toJson(lobbyObj));

    }

输出:

{
  "type": "ObixBaseObj",
  "obix": "obj",
  "is": "obix:Lobby",
  "children": [
    {
      "type": "ObixOp",
      "in": "obix:BatchIn",
      "out": "obix:BatchOut",
      "obix": "op",
      "name": "batch",
      "children": []
    }
  ]
}

希望对你有帮助。