How can nested JSON files in Java be combined?

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To combine nested JSON files in Java, you can follow these steps:

1. Parse the JSON files into Java objects using a JSON parser library like Jackson or Gson.
2. Merge the Java objects by updating values from one object with values from another object.
3. Convert the merged Java object back to JSON using the same library.

Here's an example code snippet that shows how you can merge two nested JSON files in Java using Jackson:

// Parse the JSON files into Java objects
ObjectMapper mapper = new ObjectMapper();
JsonNode json1 = mapper.readTree(new File("file1.json"));
JsonNode json2 = mapper.readTree(new File("file2.json"));

// Merge the Java objects
JsonNode mergedJson = mergeJson(json1, json2);

// Print the merged JSON
System.out.println(mergedJson.toString());

// Convert the merged Java object back to JSON
String mergedJsonString = mapper.writeValueAsString(mergedJson);

// Write the merged JSON to a file
Files.write(Paths.get("merged.json"), mergedJsonString.getBytes());

// Recursive function to merge two JSON trees
private static JsonNode mergeJson(JsonNode json1, JsonNode json2) {
    // Create a new object node to hold the merged values
    ObjectNode mergedNode = JsonNodeFactory.instance.objectNode();

    // Merge the values from each JSON tree into the merged node
    for (Iterator<String> fieldNames = json1.fieldNames(); fieldNames.hasNext();) {
        String fieldName = fieldNames.next();
        JsonNode value1 = json1.get(fieldName);
        JsonNode value2 = json2.get(fieldName);

        // If both values are objects, recursively merge them
        if (value1.isObject() && value2.isObject()) {
            mergedNode.set(fieldName, mergeJson(value1, value2));
        }
        // If both values are arrays, merge them
        else if (value1.isArray() && value2.isArray()) {
            mergedNode.set(fieldName, mergeArrays(value1, value2));
        }
        // If only one value is null, use the other value
        else if (value1.isNull()) {
            mergedNode.set(fieldName, value2);
        }
        else if (value2.isNull()) {
            mergedNode.set(fieldName, value1);
        }
        // Otherwise, use the value from the second JSON tree
        else {
            mergedNode.set(fieldName, value2);
        }
    }

    return mergedNode;
}

// Helper function to merge two JSON arrays
private static ArrayNode mergeArrays(JsonNode array1, JsonNode array2) {
    ArrayNode mergedArray = JsonNodeFactory.instance.arrayNode();

    for (JsonNode element : array1) {
        mergedArray.add(element);
    }

    for (JsonNode element : array2) {
        if (!mergedArray.contains(element)) {
            mergedArray.add(element);
        }
    }

    return mergedArray;
}

Note that this code snippet assumes that the JSON files contain objects as the top-level elements. If your JSON files contain arrays or primitive types at the top level, you may need to modify the code to handle those cases. Additionally, this code snippet merges arrays by combining elements from both arrays and removing duplicates. If you want to preserve the order of the elements or merge arrays differently, you may need to modify the mergeArrays() function.