test 文件内容:

{
    "user": {
        "code": "U-0000000001",
        "methods": [
            {},
            {}
        ],
        "methods2": {
            "marr": [],
            "marr2": [1,2,3]
        }
    },
    "testNull": null,
    "department": [
        [
            [
                {
                    "name": "layer-map-3"
                }
            ],
            [
                "layer-array-3"
            ],
            [
                33333,
                3.333
            ]
        ]
    ]
}

====

java 代码实现方式1:

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonArray;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;

import java.io.BufferedReader;
import java.io.FileReader;
import java.util.HashSet;

public class Main {
    public static void main(String[] args) throws Exception {
        String jsonStr = getJsonStrFromFile();

        Gson gson = new GsonBuilder().create();
        JsonElement jsonElement = gson.fromJson(jsonStr, JsonElement.class);

        removeEmptyElements(jsonElement);

        String resultJson = gson.toJson(jsonElement);
        System.out.println(jsonStr);
        System.out.println(resultJson);
    }

    private static boolean removeEmptyElements(JsonElement element) {
        if (element.isJsonObject()) {
            JsonObject obj = element.getAsJsonObject();
            for (String key : new HashSet<>(obj.keySet())) {
                JsonElement value = obj.get(key);
                // delete null
                if (value == null || value.isJsonNull()) {
                    obj.remove(key);
                } else if (value.isJsonArray()) {
                    if (!removeEmptyElements(value)) {
                        // delete it when its children.size() == 0
                        obj.remove(key);
                    }
                } else if (value.isJsonObject()) {
                    if (!removeEmptyElements(value)) {
                        obj.remove(key);
                    }
                }
            }
            // return parent loop to judge
            return obj.size() > 0;
        } else if (element.isJsonArray()) {
            JsonArray array = element.getAsJsonArray();
            for (int i = 0; i < array.size(); i++) {
                JsonElement value = array.get(i);
                if (value == null || value.isJsonNull()) {
                    array.remove(i);
                    // Adjust index after removal
                    i--;
                } else if (value.isJsonArray()) {
                    if (!removeEmptyElements(value)) {
                        array.remove(i);
                        // Adjust index after removal
                        i--;
                    }
                } else if (value.isJsonObject()) {
                    if (!removeEmptyElements(value)) {
                        array.remove(i);
                        // Adjust index after removal
                        i--;
                    }
                }
            }
            // return parent loop to judge
            return array.size() > 0;
        }
        return true;
    }

    public static String getJsonStrFromFile() throws Exception {
        String filePath = "c:\\test";

        BufferedReader br = new BufferedReader(new FileReader(filePath));
        StringBuffer sb = new StringBuffer();
        String line;
        while ((line = br.readLine()) != null) {
            sb.append(line).append("\n");
        }

        br.close();

        return sb.toString();
    }
}