Remove JSON node from json object (a json file) in Java

Question

I'm trying to remove few nodes from JSON file. But I'm getting class cast exception when I try to remove node. java.lang.ClassCastException: class com.fasterxml.jackson.databind.node.TextNode cannot be cast to class com.fasterxml.jackson.databind.node.ObjectNode (com.fasterxml.jackson.databind.node.TextNode and com.fasterxml.jackson.databind.node.ObjectNode are in unnamed module of loader 'app')

I tried other stackoverflow useful links, but not working for me. Here is the code that I have written.

public static void removeNodes(String filePath, String... nodeNames) throws IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        JsonNode jsonNodes = objectMapper.readTree(new File(filePath));
        for (JsonNode node : jsonNodes) {
            ((ObjectNode) node).remove(Arrays.asList(nodeNames));
        }
        objectMapper
                .writerWithDefaultPrettyPrinter()
                .writeValue(new File(filePath.split("\\.")[0] + "_modified.json"), jsonNodes);
    }

This is the json file I'm reading.

{
  "boolean_key": "--- true\n",
  "empty_string_translation": "",
  "key_with_description": "Check it out! This key has a description! (At least in some formats)",
  "key_with_line-break": "This translations contains\na line-break.",
  "nested": {
    "deeply": {
      "key": "Wow, this key is nested even deeper."
    },
    "key": "This key is nested inside a namespace."
  },
  "null_translation": null,
  "pluralized_key": {
    "one": "Only one pluralization found.",
    "other": "Wow, you have %s pluralizations!",
    "zero": "You have no pluralization."
  },
  "Dog_key": {
    "nest": "Only one pluralization found.",
    "sample_collection": [
    "first item",
    "second item",
    "third item"
  ],
  "Pest": "Only two pluralization found."
  },
  "simple_key": "Just a simple key with a simple message.",
  "unverified_key": "This translation is not yet verified and waits for it. (In some formats we also export this status)"
}

Caller:

import org.junit.jupiter.api.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.io.IOException;

// import static org.junit.jupiter.api.Assertions.*;

@RunWith(SpringRunner.class)
@SpringBootTest
class JSONUtilTest {

    @Test
    void removeNodes() throws IOException {
        JSONUtil.removeNodes("D:\\data\\JSON_A.json", "pluralized_key", "Dog_key", "simple_key");
    }
}

Can you help me to figure out what is causing the problem?

There are no nodes in JSON files. JSON is just string that needs to be parsed to a real object before you can work with it, at which point it's not JSON anymore. So that's also the hint at the "how to": parse the JSON first, then operate on the resulting data object, instead of trying to manipulate the JSON string itself. — Mike 'Pomax' Kamermans
– Mike 'Pomax' Kamermans, Commented Aug 10, 2021 at 5:00

this.srivastava · Accepted Answer · 2021-08-10 10:35:15Z

As mentioned in the comment, you need to first parse the JSON then do operations on it.

Read file.
Parse and convert it to JSONObject using JSONParser's parse() method.
Remove the nodes you want.

Using ObjectMapper's writerWithDefaultPrettyPrinter() method you get proper indentation and write that to output file.

Here is the code:

public static void removeNodes(String filePath, String... nodeNames) {
   try (FileReader fileReader = new FileReader(filePath)) {
       JSONParser jsonParser = new JSONParser();
       JSONObject jsonObject = (JSONObject) jsonParser.parse(fileReader);

       Stream<String> nodeStream = Stream.of(nodeNames);
       nodeStream.forEach(jsonObject::remove);

       ObjectMapper objectMapper = new ObjectMapper();
       String jsonObjectPrettified = objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonObject);

       FileWriter fileWriter = new FileWriter(filePath.split("\\.")[0] + "_modified.json");
       fileWriter.write(jsonObjectPrettified);
       fileWriter.close();

   } catch (IOException | ParseException e) {
       e.printStackTrace();
   }
}

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