使用snakeYaml解析根有地图的YAML文档

Parsing a YAML document with a map at the root using snakeYaml(使用snakeYaml解析根有地图的YAML文档)

问题描述

我想将 YAML 文档读取到自定义对象的映射(而不是映射，snakeYaml 默认会这样做).所以这个:

I want to read a YAML document to a map of custom objects (instead of maps, which snakeYaml does by default). So this:

19:
  typeID: 2
  limit: 300
20:
  typeID: 8
  limit: 100

将加载到如下所示的地图:

Would be loaded to a map which looks like this:

Map<Integer, Item>

项目在哪里:

class Item {
    private Integer typeId;
    private Integer limit;
}

我找不到使用snakeYaml 的方法，也找不到更好的库来完成这项任务.

I could not find a way to do this with snakeYaml, and I couldn't find a better library for the task either.

文档仅包含嵌套在其他对象中的地图/集合的示例，因此您可以执行以下操作:

The documentation only has examples with maps/collections nested inside other objects, so that you can do the following:

    TypeDescription typeDescription = new TypeDescription(ClassContainingAMap.class);
    typeDescription.putMapPropertyType("propertyNameOfNestedMap", Integer.class, Item.class);
    Constructor constructor = new Constructor(typeDescription);
    Yaml yaml = new Yaml(constructor);
    /* creating an input stream (is) */
    ClassContainingAMap obj = (ClassContainingAMap) yaml.load(is);

但是当 Map 格式位于文档的根目录时，我该如何定义它呢?

But how do I go about defining the Map format when it is at the root of the document?

推荐答案

你需要添加一个自定义构造函数.但是，在您的情况下，您不想注册项目"或项目列表"标签.

You need to add a custom Constructor. However, in your case you don't want register an "item" or "item-list" tag.

实际上，您希望将 Duck Typing 应用于您的 Yaml.这不是超级高效，但有一种相对简单的方法可以做到这一点.

In effect, you want to apply Duck Typing to your Yaml. It's not super efficient, but there is a relatively easy way to do this.

class YamlConstructor extends Constructor {
  @Override
  protected Object constructObject(Node node) {

    if (node.getTag() == Tag.MAP) {
        LinkedHashMap<String, Object> map = (LinkedHashMap<String, Object>) super
                .constructObject(node);
        // If the map has the typeId and limit attributes
        // return a new Item object using the values from the map
        ...
    }
     // In all other cases, use the default constructObject.
    return super.constructObject(node);

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