问题描述
之前一定要问过这个问题,但我找不到。
This question must have been asked before, but I couldn't find it.
我正在使用第三方库来检索JSON格式的数据。该库以 org.json.JSONObject
的形式向我提供数据。我想将此 JSONObject
映射到用于更简单的访问/代码。
I'm using a 3rd party library to retrieve data in JSON format. The library offers the data to me as a org.json.JSONObject
. I want to map this JSONObject
to a POJO (Plain Old Java Object) for simpler access/code.
对于映射,我目前使用 ObjectMapper
来自这样的Jackson库:
For mapping, I currently use the ObjectMapper
from the Jackson library in this way:
JSONObject jsonObject = //...
ObjectMapper mapper = new ObjectMapper();
MyPojoClass myPojo = mapper.readValue(jsonObject.toString(), MyPojoClass.class);
根据我的理解,上面的代码可以显着优化,因为目前<$ c中的数据已经解析的$ c> JSONObject 再次被送入带有 JSONObject.toString()
方法的序列化 - 反序列化链,然后到 ObjectMapper
。
To my understanding, the above code can be optimized significantly, because currently the data in the JSONObject
, which is already parsed, is again fed into a serialization-deserialization chain with the JSONObject.toString()
method and then to the ObjectMapper
.
我想避免这两次转换( toString()
和解析)。有没有办法使用 JSONObject
将其数据直接映射到POJO?
I want to avoid these two conversions (toString()
and parsing). Is there a way to use the JSONObject
to map its data directly to a POJO?
推荐答案
由于您有一些JSON数据的抽象表示( object)你计划使用杰克逊库 - 它有自己的JSON数据抽象表示() - 然后从一个表示转换到另一个表示将使您免于parse-serialize-parse过程。因此,不使用接受 String
的 readValue
方法,而是使用接受 JsonParser
:
Since you have an abstract representation of some JSON data (an org.json.JSONObject
object) and you're planning to use the Jackson library - that has its own abstract representation of JSON data (com.fasterxml.jackson.databind.JsonNode
) - then a conversion from one representation to the other would save you from the parse-serialize-parse process. So, instead of using the readValue
method that accepts a String
, you'd use this version that accepts a JsonParser
:
JSONObject jsonObject = //...
JsonNode jsonNode = convertJsonFormat(jsonObject);
ObjectMapper mapper = new ObjectMapper();
MyPojoClass myPojo = mapper.readValue(new TreeTraversingParser(jsonNode), MyPojoClass.class);
JSON是一种非常简单的格式,因此创建 convertJsonFormat 手动。这是我的尝试:
JSON is a very simple format, so it should not be hard to create the convertJsonFormat
by hand. Here's my attempt:
static JsonNode convertJsonFormat(JSONObject json) {
ObjectNode ret = JsonNodeFactory.instance.objectNode();
@SuppressWarnings("unchecked")
Iterator<String> iterator = json.keys();
for (; iterator.hasNext();) {
String key = iterator.next();
Object value;
try {
value = json.get(key);
} catch (JSONException e) {
throw new RuntimeException(e);
}
if (json.isNull(key))
ret.putNull(key);
else if (value instanceof String)
ret.put(key, (String) value);
else if (value instanceof Integer)
ret.put(key, (Integer) value);
else if (value instanceof Long)
ret.put(key, (Long) value);
else if (value instanceof Double)
ret.put(key, (Double) value);
else if (value instanceof Boolean)
ret.put(key, (Boolean) value);
else if (value instanceof JSONObject)
ret.put(key, convertJsonFormat((JSONObject) value));
else if (value instanceof JSONArray)
ret.put(key, convertJsonFormat((JSONArray) value));
else
throw new RuntimeException("not prepared for converting instance of class " + value.getClass());
}
return ret;
}
static JsonNode convertJsonFormat(JSONArray json) {
ArrayNode ret = JsonNodeFactory.instance.arrayNode();
for (int i = 0; i < json.length(); i++) {
Object value;
try {
value = json.get(i);
} catch (JSONException e) {
throw new RuntimeException(e);
}
if (json.isNull(i))
ret.addNull();
else if (value instanceof String)
ret.add((String) value);
else if (value instanceof Integer)
ret.add((Integer) value);
else if (value instanceof Long)
ret.add((Long) value);
else if (value instanceof Double)
ret.add((Double) value);
else if (value instanceof Boolean)
ret.add((Boolean) value);
else if (value instanceof JSONObject)
ret.add(convertJsonFormat((JSONObject) value));
else if (value instanceof JSONArray)
ret.add(convertJsonFormat((JSONArray) value));
else
throw new RuntimeException("not prepared for converting instance of class " + value.getClass());
}
return ret;
}
注意,杰克逊的 JsonNode
可以代表一些额外的类型(例如 BigInteger
, Decimal
等),因为它们不是必需的上面的代码涵盖 JSONObject
可以表示的所有内容。
Note that, while the Jackson's JsonNode
can represent some extra types (such as BigInteger
, Decimal
, etc) they are not necessary since the code above covers everything that JSONObject
can represent.
这篇关于如何有效地将org.json.JSONObject映射到POJO?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!