使用 jackson 解析递归嵌套字段 [英] parse recursive nested field using jackson
问题描述
我有一个下面的 JSON，我需要从中制作一个 Map.在下面的 JSON 中，我只有三个级别的 parentCategory 但通常它可以更多，有时也可以更少.
I have a below JSON and from which I need to make a Map<String, String>. In the below JSON, I have only three levels of parentCategory but in general it can be more or sometimes it can be less.
- 我的地图的键是
79720这是categories部分的id和值应该是10987是最后一个parentCategory的id.
- Key of my map will be
79720which isidofcategoriessection and value should be10987which isidof lastparentCategory.
现在我可以在它们内部嵌套 parentCategory 所以我在为此制作 POJO 时遇到了问题.我可以有一个级别 parentCategory 或者我可以在每个 parentCategory 中嵌套 parentCategory 并且我总是需要获取最后一个 parentCategory 的 id.
Now I can have nested parentCategory inside them so I am having issues making a POJO for this. I can have one level parentCategory or I can have nested parentCategory inside each parentCategory and I always need to get id for the last parentCategory.
所以我通过转到 jsonschema2pojo 来为此创建一个 POJO，并在它生成我的地方提供了我的 JSON我需要的所有文件.使用下面的 JSON，它为 parentCategory 字段创建了三个类，例如 ParentCategory、ParentCategory_ 和 ParentCategory__.现在因为我不知道我有多少 parentCategory 级别，所以我不确定为它们生成 POJO 并提取 id 字段的最佳方法是什么 id代码>父类别.有没有办法使用 Jackson 来做到这一点?
So I am creating a POJO for this by going to jsonschema2pojo and provided my JSON where it generated me all the files that I need. With the below JSON, it has created three classes like this ParentCategory, ParentCategory_ and ParentCategory__ for parentCategory field. Now since I don't know how many parentCategory levels I have so I am not sure what is the best way to generate a POJO for them and extract id field for last parentCategory. Is there any way to do this using Jackson?
我必须在 POJO 中读取所有这些数据，因为我还要读取所有其他字段.
I have to read all this data in POJO as I am also reading all other fields as well.
{
"paginationResponse": {
"pageNumber": 1,
"entriesPerPage": 200,
"totalPages": 3
},
"listings": [
{
"categories": [
{
"id": "79720",
"name": "Sunglasses",
"localizedName": "Sunglasses",
"level": 4,
"leafCategory": true,
"parentCategory": {
"id": "394",
"name": "Sunglasses & Fashion Eyewear",
"localizedName": "Sunglasses & Fashion Eyewear",
"level": 3,
"leafCategory": false,
"parentCategory": {
"id": "2340",
"name": "Men's Accessories",
"localizedName": "Men's Accessories",
"level": 2,
"leafCategory": false,
"parentCategory": {
"id": "10987",
"name": "Clothing, Shoes & Accessories",
"localizedName": "Clothing, Shoes & Accessories",
"level": 1,
"leafCategory": false
}
}
}
}
],
"processlisting": {
....
},
"processlistingmetainfo": {
...
},
"processlistingproperties": [
{
"propertyName": "item_url",
"propertyValues": [
{
"stringValue": "url"
}
]
},
{
"propertyName": "listing_site_id",
"propertyValues": [
{
"stringValue": "0"
}
]
}
]
}
],
"total": 100
}
注意:我无法控制此 JSON 结构，因为它不归我们所有，因此根本无法更改 JSON 结构.
Note: I don't have control over this JSON structure as it's not owned by us so can't change JSON structure at all.
以下是基于上述 JSON 生成的 ParentCategory 的三个类，但通常我可以有多个级别的 ParentCategory 而我事先不知道.
Below are the three classes for ParentCategory which was generated basis on above JSON but in general I can have multiple levels of ParentCategory and I don't know beforehand.
public class ParentCategory {
@JsonProperty("id")
private String id;
@JsonProperty("name")
private String name;
@JsonProperty("localizedName")
private String localizedName;
@JsonProperty("level")
private long level;
@JsonProperty("leafCategory")
private boolean leafCategory;
@JsonProperty("parentCategory")
private ParentCategory_ parentCategory;
@JsonIgnore
private Map<String, Object> additionalProperties = new HashMap<String, Object>();
....
}
public class ParentCategory_ {
@JsonProperty("id")
private String id;
@JsonProperty("name")
private String name;
@JsonProperty("localizedName")
private String localizedName;
@JsonProperty("level")
private long level;
@JsonProperty("leafCategory")
private boolean leafCategory;
@JsonProperty("parentCategory")
private ParentCategory__ parentCategory;
@JsonIgnore
private Map<String, Object> additionalProperties = new HashMap<String, Object>();
...
}
public class ParentCategory__ {
@JsonProperty("id")
private String id;
@JsonProperty("name")
private String name;
@JsonProperty("localizedName")
private String localizedName;
@JsonProperty("level")
private long level;
@JsonProperty("leafCategory")
private boolean leafCategory;
@JsonIgnore
private Map<String, Object> additionalProperties = new HashMap<String, Object>();
...
}
推荐答案
一般来说 - 检索特定 JSON 属性任务的最佳工具是 Json-Path 提供了丰富的查询语言来搜索 JSON 树.
Generally speaking - The best tool for the task of retrieving particular JSON properties is Json-Path which provides a rich query language to search a JSON tree.
关于这个问题，需要检索两个不相关的属性，所以需要对JSON树进行两次扫描.问题没有具体说明如何读取输入，所以也许可以将整个输入流读入一个字符串.
Regarding the question, it is requried to retrieve two unrelated properties, so two scans of the JSON tree are required. The question does not specify how the input is read, so perhaps it is possible to read the whole input stream into one String.
以下是检索这两个属性所需的查询代码.无论 parentCategory 级别的数量如何，这都将起作用.诀窍是最后一个对象是唯一一个没有子 parentCategory 的对象.
Below is the code with the queries needed to retrieve both properties. This will work regardless of the number of parentCategory levels. The trick is that the last object is the only one that does not have a child parentCategory.
我在解释查询文本的代码中添加了注释
I have added comments to the code that explain the query text
String categoryIdJsonPath =
"$" + // start from tree root
".listings[0]" + // get listings array's first (only) object
".categories[0]" + // get categories array's first (only) object
".id"; // get id property
String lastParentIdJsonPath =
"$" + // start from tree root
".listings[0]" + // get listings array's first (only) object
".categories[0]" + // get categories array's first (only) object
"..parentCategory" + // do deep scan for all nested parentCategory objects
"[?(!(@.parentCategory))]" + // filter by the object that does NOT have parentCategory property
".id"; // get id property
try {
// read the whole input so it can be scanned twice
String jsonInput = new String(Files.readAllBytes(Paths.get("C://temp/test.json")), Charset.forName("UTF-8"));
String categoryId = JsonPath.read(jsonInput, categoryIdJsonPath);
System.out.println(categoryId);
// return type is always List when deep scan is requested
List<String> lastParent = JsonPath.read(jsonInput, lastParentIdJsonPath);
System.out.println(lastParent.get(0));
} catch (Exception e) {
e.printStackTrace();
}
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