您可以使用JsonParser将Json转换为一个中间结构，该结构允许您检查json内容。

String yourJson = "{your json here}";
JsonElement element = JsonParser.parseString(yourJson);
JsonObject obj = element.getAsJsonObject(); //since you know it's a JsonObject
Set<Map.Entry<String, JsonElement>> entries = obj.entrySet();//will return members of your object
for (Map.Entry<String, JsonElement> entry: entries) {
    System.out.println(entry.getKey());
}

从Java 8开始，您可以使用Streams作为外观更好的替代方案：

String str = "{\"key1\":\"val1\", \"key2\":\"val2\"}";

JsonParser parser = new JsonParser();
JsonObject jObj = (JsonObject) parser.parse(str);

List<String> keys = jObj.entrySet()
    .stream()
    .map(i -> i.getKey())
    .collect(Collectors.toCollection(ArrayList::new));

keys.forEach(System.out::println);

从Gson 2.8.1开始，您可以使用keySet()：

String json = "{\"key1\":\"val\", \"key2\":\"val\"}";

JsonParser parser = new JsonParser();
JsonObject jsonObject = parser.parse(json).getAsJsonObject();

Set<String> keys = jsonObject.keySet();

String str = "{\"key1\":\"val1\", \"key2\":\"val2\"}";

        JsonParser parser = new JsonParser();
        JsonObject jObj = (JsonObject)parser.parse(str);

        List<String> keys = new ArrayList<String>();
        for (Entry<String, JsonElement> e : jObj.entrySet()) {
            keys.add(e.getKey());
        }

        // keys contains jsonObject's keys