问题
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.
- Key of my map will be
79720
which isid
ofcategories
section and value should be10987
which isid
of lastparentCategory
.
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
.
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?
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
}
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.
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>();
...
}
回答1:
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.
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.
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
.
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();
}
来源:https://stackoverflow.com/questions/48433294/parse-recursive-nested-field-using-jackson