Java Jackson JsonNode 到类型集合
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Hymanson JsonNode to typed Collection
提问by kag0
What is the proper way to convert a Hymanson JsonNodeto a java collection?
将 Hymanson 转换JsonNode为 Java 集合的正确方法是什么？
If it were a json string I could use ObjectMapper.readValue(String, TypeReference)but for a JsonNodethe only options are ObjectMapper.treeToValue(TreeNode, Class)which wouldn't give a typed collection, or ObjectMapper.convertValue(Object, JavaType)which feels wrong on account of its accepting any POJO for conversion.
如果它是一个 json 字符串，我可以使用，ObjectMapper.readValue(String, TypeReference)但JsonNode唯一的选项是ObjectMapper.treeToValue(TreeNode, Class)不提供类型化集合，或者ObjectMapper.convertValue(Object, JavaType)由于接受任何 POJO 进行转换而感觉错误。
Is there another "correct" way or is it one of these?
还有另一种“正确”的方式还是其中一种？
采纳答案by Sotirios Delimanolis
Acquire an ObjectReaderwith ObjectMapper#readerFor(TypeReference)using a TypeReferencedescribing the typed collection you want. Then use ObjectReader#readValue(JsonNode)to parse the JsonNode(presumably an ArrayNode).
获取ObjectReader与ObjectMapper#readerFor(TypeReference)使用TypeReference描述你想要的类型集合。然后用于ObjectReader#readValue(JsonNode)解析JsonNode（大概是一个ArrayNode）。
For example, to get a List<String>out of a JSON array containing only JSON strings
例如，List<String>从仅包含 JSON 字符串的 JSON 数组中获取
ObjectMapper mapper = new ObjectMapper();
// example JsonNode
JsonNode arrayNode = mapper.createArrayNode().add("one").add("two");
// acquire reader for the right type
ObjectReader reader = mapper.readerFor(new TypeReference<List<String>>() {
});
// use it
List<String> list = reader.readValue(arrayNode);
回答by DanJ
The ObjectMapper.convertValue()function is convenient and type-aware. It can perform a wide array of conversions between tree nodes and Java types/collections, and vice-versa.
该ObjectMapper.convertValue（）函数是方便和感知类型。它可以在树节点和 Java 类型/集合之间执行广泛的转换，反之亦然。
An example of how you might use it:
您可能如何使用它的示例：
List<String> list = new ArrayList<>();
list.add("one");
list.add("two");
Map<String,List<String>> hashMap = new HashMap<>();
hashMap.put("myList", list);
ObjectMapper mapper = new ObjectMapper();
ObjectNode objectNode = mapper.convertValue(hashMap, ObjectNode.class);
Map<String,List<String>> hashMap2 = mapper.convertValue(objectNode, HashMap.class);
