java - 通用树的自定义 Jackson 序列化程序

Question

假设我有一个用 Java 实现的参数化树，如下所示:

public class Tree<E> {
   private static class Node {
      E element;
      List<Node> children.
   }

   Node root;

   //... You get the idea.
}

这里的想法是，上面的实现只关心树的拓扑结构，但对实例化将存储在树中的元素一无所知。

现在，假设我希望我的树元素是地理。它们以树状组织的原因是大陆包含国家，国家包含州或省，等等。为简单起见，地理具有名称和类型:

public class GeoElement { String name; String type; }

因此，最终，地理层次结构如下所示:

public class Geography extends Tree<GeoElement> {}

现在开始 Jackson 连载。假设 Jackson 序列化程序可以看到字段，此实现的直接序列化将如下所示:

{
   "root": {
      "element": {
         "name":"Latin America",
         "type":"Continent"
      }
      "children": [
          {
             "element": {
                "name":"Brazil",
                "type":"Country"
             },
             "children": [
                 // ... A list of states in Brazil
             ]
          },
          {
             "element": {
                "name":"Argentina",
                "type":"Country"
             },
             "children": [
                 // ... A list of states in Argentina
             ]
          }
      ]
   }

这种 JSON 呈现并不好，因为它包含来自 Tree 和 Node 类的不必要的工件，即“root”和“element”。我需要的是:

{
   "name":"Latin America",
   "type":"Continent"
   "children": [
       {
          "name":"Brazil",
          "type":"Country"
          "children": [
             // ... A list of states in Brazil
          ]
       },
       {
          "name":"Argentina",
          "type":"Country"
          "children": [
             // ... A list of states in Argentina
          ]
       }
   ]
}

非常感谢任何帮助。 -伊戈尔。

Answer 1

你需要的是@JsonUnwrapped .

Annotation used to indicate that a property should be serialized "unwrapped"; that is, if it would be serialized as JSON Object, its properties are instead included as properties of its containing Object

将此注释添加到 Tree 的 root 字段和 Node 类的 element 字段，如下所示:

public class Tree<E> {
   private static class Node {

      @JsonUnwrapped
      E element;
      List<Node> children.
   }

   @JsonUnwrapped
   Node root;

   //... You get the idea.
}

它会给你你想要的输出:

{
    "name": "Latin America",
    "type": "Continent",
    "children": [{
        "name": "Brazil",
        "type": "Country",
        "children": []
    }, {
        "name": "Argentina",
        "type": "Country",
        "children": []
    }]
}