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如何将serialize DefaultMutableTreeNode(Java)转换成JSON?

jtree gson serialization json java

ikevin8me · 技术社区 · 6 年前

如何序列化树(用Java实现) DefaultMutableTreeNode 类)到JSON(用于通过RESTful方法传输到IOS客户机)?

我试过:

String jsonString = (new Gson()).toJson(topNode);
// topNode is DefaultMutableTreeNode at the root

它坠毁了。 StackOverflowError .

1 回复 | 直到 6 年前

Thomas Fritsch 6 年前

秋千 DefaultMutableTreeNode 类是类似树的数据结构其中包含此类型的实例 children 作为 parent . 这就是为什么gson的默认序列化程序遇到无限递归的原因。然后扔了一个 StackOverflowError .

要解决此问题,您需要自定义 Gson 聪明的人 JsonSerializer 专门为 默认可变TreeNode S.

为了这个创造你的 格森 实例不只是由 new Gson() 但通过

Gson gson = new GsonBuilder()
        .registerTypeAdapter(DefaultMutableTreeNode.class, new DefaultMutableTreeNodeSerializer())
        .setPrettyPrinting()
        .create();

这个 DefaultMutableTreeNodeSerializer 以下是责任用于转换 默认可变TreeNode 给JSON。它转换其属性 allowsChildren , leaf , userObject 和 儿童 给JSON。请注意,它不会转换 起源 JSON的属性, 因为这样做会再次产生一个极小的递归。

public class DefaultMutableTreeNodeSerializer implements JsonSerializer<DefaultMutableTreeNode> {

    @Override
    public JsonElement serialize(DefaultMutableTreeNode src, Type typeOfSrc, JsonSerializationContext context) {
        JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty("allowsChildren", src.getAllowsChildren());
        jsonObject.addProperty("leaf", src.isLeaf());
        jsonObject.add("userObject", context.serialize(src.getUserObject()));
        JsonArray jsonArray = new JsonArray();
        for (int i= 0; i < src.getChildCount(); i++) {
           jsonArray.add(context.serialize(src.getChildAt(i)));
        }
        jsonObject.add("children", jsonArray);
        return jsonObject;
    }
}

对于测试,让我们序列化示例的根节点 JTree .

JTree tree = new JTree();  // create a sample tree
Object topNode = tree.getModel().getRoot();
String jsonString = gson.toJson(topNode);
System.out.println(jsonString);

它生成以下JSON输出:

{
  "allowsChildren": true,
  "leaf": false,
  "userObject": "JTree",
  "children": [
    {
      "allowsChildren": true,
      "leaf": false,
      "userObject": "colors",
      "children": [
        {
          "allowsChildren": true,
          "leaf": true,
          "userObject": "blue",
          "children": []
        },
        {
          "allowsChildren": true,
          "leaf": true,
          "userObject": "violet",
          "children": []
        },
        {
          "allowsChildren": true,
          "leaf": true,
          "userObject": "red",
          "children": []
        },
        {
          "allowsChildren": true,
          "leaf": true,
          "userObject": "yellow",
          "children": []
        }
      ]
    },
    {
      "allowsChildren": true,
      "leaf": false,
      "userObject": "sports",
      "children": [
        {
          "allowsChildren": true,
          "leaf": true,
          "userObject": "basketball",
          "children": []
        },
        {
          "allowsChildren": true,
          "leaf": true,
          "userObject": "soccer",
          "children": []
        },
        {
          "allowsChildren": true,
          "leaf": true,
          "userObject": "football",
          "children": []
        },
        {
          "allowsChildren": true,
          "leaf": true,
          "userObject": "hockey",
          "children": []
        }
      ]
    },
    {
      "allowsChildren": true,
      "leaf": false,
      "userObject": "food",
      "children": [
        {
          "allowsChildren": true,
          "leaf": true,
          "userObject": "hot dogs",
          "children": []
        },
        {
          "allowsChildren": true,
          "leaf": true,
          "userObject": "pizza",
          "children": []
        },
        {
          "allowsChildren": true,
          "leaf": true,
          "userObject": "ravioli",
          "children": []
        },
        {
          "allowsChildren": true,
          "leaf": true,
          "userObject": "bananas",
          "children": []
        }
      ]
    }
  ]
}