sri77 sri77 - 3 months ago 31
JSON Question

Extract certain fields and values from request JSON using Jackson

I am looking for a way to include only certain fields from the JSON request received to my service and then log them accordingly to avoid logging too much data.

The fields to include and hence log would be configured in a properties file.

Since I use Spring Boot for my service, Jackson JARs should already be available.

Since the request JSON is complex with nested arrays and objects as fields am not sure if I can achieve my requirement with Jackson.

Is there a way to extract only certain fields along with their values from a input request JSON using the Jackson API?

Basically, I am looking at 2 use cases.

1.Select one or more elements (which I intend to pass by config) from Json String and then render them

2.Select and update one or more elements inline. I want to mask the values of the elements before rendering them.

I am providing the code for selecting the element and Json which I used along with what I expect as below.

public String getValues(String key,String jsonString){
String fieldNodeStr =null;
try {
ObjectMapper mapper = new ObjectMapper();
JsonNode node = mapper.readTree(jsonString);
JsonNode fieldNode = node.at(key);
fieldNodeStr = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(fieldNode);
System.out.println(fieldNodeStr);
} catch (IOException e) {
System.out.println("IOException:",e);
}catch (Exception e) {
System.out.println("Exception:",e);
}
}


My Json is as below,

{
"employeeId" : "5353",
"salesId" : "sales005",
"manager" : {
"userId" : "managerUser",
"isSuperUser" : false,
"firstName":"manager first name",
"lastName":"manager last name"
},
"administrator" : {
"userId" : "administratorUser",
"isSuperUser" : false,
"firstName":"admin first name",
"lastName":"admin last name"
},
"requester" : [
{
"id":"1234",
"demographic" : {
"firstName" : "hello",
"lastName" : "hai"
}
},
{
"id":"1235",
"demographic" : {
"firstName" : "welcome",
"lastName" : "user"
}
}
]

}


I have 2 issues as below.

If I pass "/manager/userId" ,"/administrator/isSuperUser" (OR) "/salesId" I am able to get the expected value.

But, If want to get the /requester/id (OR) /requester/demographic (OR) /requester/demographic/lastName , I am not able to fetch.
I am getting null values.

I expect the following when I pass , "/requester/id" (OR) "/requester/demographic" respectively.

"requester" : [
{
"id":"1234"
},
{
"id":"1235"
}
]


"requester" : [
{
"demographic" : {
"firstName" : "hello",
"lastName" : "hai"
}
},
{
"demographic" : {
"firstName" : "welcome",
"lastName" : "user"
}
}
]


Along with fetch I also want to update the values inline after locating them with JsonPointer

I have my code as below for the updation,

public String findAndUpdate(String key,String jsonString,String repValue){
String fieldNodeStr =null;
try {
ObjectMapper mapper = new ObjectMapper();
JsonNode node = mapper.readTree(jsonString);
JsonNode fieldNode = node.at(key);

//Update the value of located node to a different one
((ObjectNode) fieldNode).put(key,repValue);

fieldNodeStr = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(fieldNode);
System.out.println(fieldNodeStr);
} catch (IOException e) {
System.out.println("IOException:",e);
}catch (Exception e) {
System.out.println("Exception:",e);
}
return fieldNodeStr;
}


When I pass, "/manager/userId" as value of key, I get the below error,

17:21:24.829 [main] ERROR com.demo.jsondemo.TestClass - Exception:
java.lang.ClassCastException: com.fasterxml.jackson.databind.node.TextNode cannot be cast to com.fasterxml.jackson.databind.node.ObjectNode
at com.demo.jsondemo.TestClass.findAndUpdate(TestClass.java:95) [classes/:na]
at com.demo.jsondemo.TestClass.main(TestClass.java:221) [classes/:na]

Answer

JSON Pointer

You could use JSON Pointer (a string syntax for identifying a specific value within a JSON document) defined by the RFC 6901.

For example purposes, consider the following JSON:

{
  "firstName": "John",
  "lastName": "Doe",
  "address": {
    "street": "21 2nd Street",
    "city": "New York",
    "postalCode": "10021-3100",
    "coordinates": {
      "latitude": 40.7250387,
      "longitude": -73.9932568
    }
  }
}

To query the coordinates node, you could use the following JSON Pointer expression:

/address/coordinates

JSON Pointer and Jackson

Jackson 2.3.0 introduced support to JSON Pointer and it can be used as following:

String json = "{\"firstName\":\"John\",\"lastName\":\"Doe\",\"address\":{\"street\":"
        + "\"21 2nd Street\",\"city\":\"New York\",\"postalCode\":\"10021-3100\","
        + "\"coordinates\":{\"latitude\":40.7250387,\"longitude\":-73.9932568}}}";

ObjectMapper mapper = new ObjectMapper();
JsonNode node = mapper.readTree(json);
JsonNode coordinatesNode = node.at("/address/coordinates");

The coordinates node could be parsed into a bean:

Coordinates coordinates = mapper.treeToValue(coordinatesNode, Coordinates.class);

Or can be written as String:

String coordinatesNodeAsString = mapper.writerWithDefaultPrettyPrinter()
                                       .writeValueAsString(coordinatesNode);

Jayway JsonPath

A good alternative to JSON Pointer is JSONPath. In Java, there's an implementation called Jayway JsonPath, which integrates with Jackson.

To query the coordinates node with JsonPath, you would use the following expression:

$.address.coordinates

And the code to query the node would be like:

JsonNode coordinatesNode = JsonPath.parse(json)
                                   .read("$.address.coordinates", JsonNode.class);

JsonPath requires the following dependency:

<dependency>
    <groupId>com.jayway.jsonpath</groupId>
    <artifactId>json-path</artifactId>
    <version>2.2.0</version>
</dependency>

And, to integrate with Jackson, following lines are required:

Configuration.setDefaults(new Configuration.Defaults() {

    private final JsonProvider jsonProvider = new JacksonJsonProvider();
    private final MappingProvider mappingProvider = new JacksonMappingProvider();

    @Override
    public JsonProvider jsonProvider() {
        return jsonProvider;
    }

    @Override
    public MappingProvider mappingProvider() {
        return mappingProvider;
    }

    @Override
    public Set<Option> options() {
        return EnumSet.noneOf(Option.class);
    }
});

Update based on your requirements

Based on the additional details you have provided in your question, I would say JSONPath will offer you more flexibility the JSON Pointer.

You can try the following:

  • Instead of /requester/id, use $.requester[*].id.
  • Instead of /requester/demographic, use $.requester[*].demographic.

These expressions can be tested online. Have a look at the following resources:

And read the Jayway JsonPath documentation to understand how to use it properly.

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