[英]How can I get Jackson to deserialize into my own Array implementation
Given my own array implementation MyArray<T>
, how can I make it known to Jackson, so that it is able to deserialize from a JSON Array into MyArray<T>
? 给定我自己的数组实现
MyArray<T>
,我如何让Jackson知道它,以便它能够从JSON数组反序列化为MyArray<T>
? So far I am only getting this exception: 到目前为止,我只收到此异常:
com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of MyArray out of START_ARRAY token
The Array class from libgdx has a constructor which accepts an array: public Array (T[] array)
. libgdx中的Array类具有一个接受数组的构造函数:
public Array (T[] array)
。
Instead of trying to serialize libgdx array use a simple class with an array as a base for serialization/desrialization, and then create a libgdx array based on the deserialized data. 与其尝试序列化libgdx数组,不如使用带有数组的简单类作为序列化/反序列化的基础,然后基于反序列化的数据创建libgdx数组。
In general it is a good rule to serialize only POJO-type objects. 通常,仅序列化POJO类型的对象是一个好规则。
In short: 简而言之:
{
//serialize:
com.badlogic.gdx.utils.Array<MyObj> arr = ...;
MyObj[] myArr = arr.toArray();
MyCustomContainer cont = new MyCustomContainer(myArr);
String serializedData = mapper.writeValueAsString(cont);
// do sth with the data
}
{
//deserialize
MyCusomContainer cont = mapper.readValue(..., MyCustomContainer.class);
com.badlogic.gdx.utils.Array<MyObj> arr = new com.badlogic.gdx.utils.Array<MyObj>(cont.getArray());
// done!
}
As Dariusz mentioned, it's good to take advantage of the fact that Array
class has constructor accepting normal array. 正如Dariusz所提到的,利用
Array
类具有接受常规数组的构造函数这一事实是很好的。
Look, if you use default serializer - your array serialized to JSON would look like: 看,如果您使用默认的序列化程序,则序列化为JSON的数组如下所示:
{"items":["item1","item2"],"size":2,"ordered":true}
it's clearly a waste of space, unless you want size
and ordered
fields to be preserved. 除非您希望保留
size
和ordered
字段,否则这显然是在浪费空间。
I suggest you changing the way you serialize your object so that it would look more like normal array, on the other end - deserialization can build Array
object again. 我建议您更改序列化对象的方式,使其看上去更像普通数组,另一方面,反序列化可以再次构建
Array
对象。
If you add following pair of serializer and deserializer: 如果添加以下对串行器和解串器:
SimpleModule module = new SimpleModule();
module.addDeserializer(Array.class, new StdDelegatingDeserializer<>(
new StdConverter<Object[], Array>() {
@Override
public Array convert(Object[] value) {
return new Array(value);
}
}));
module.addSerializer(Array.class, new StdDelegatingSerializer(
new StdConverter<Array, Object>() {
@Override
public Object convert(Array value) {
return value.toArray();
}
}));
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(module);
you will have transparent conversion between these types 您将在这些类型之间进行透明转换
One way to do it is to write a serializer like 一种方法是编写一个类似
import java.io.IOException;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.map.SerializerProvider;
import org.codehaus.jackson.map.ser.std.SerializerBase;
public class MyArraySerializer extends SerializerBase<MyArray> {
protected MyArraySerializer() {
super(MyArray.class);
}
@Override
public void serialize(MyArray myArray, JsonGenerator gen, SerializerProvider p)
throws IOException, JsonGenerationException {
gen.writeStartArray();
Iterator<MyObject> it = myArray.iterator();
while (it.hasNext()) {
MyObject ob = it.next();
gen.writeObject(p);
if (it.hasNext()) {
gen.writeRaw(',');
}
}
gen.writeEndArray();
}
}
And a deserializer like 还有一个反序列化器
import java.io.IOException;
import org.codehaus.jackson.JsonParser;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.map.DeserializationContext;
import org.codehaus.jackson.map.JsonDeserializer;
public class MyArrayDeserializer extends JsonDeserializer<MyArray> {
@Override
public MyArray deserialize(JsonParser parser, DeserializationContext ctx)
throws IOException, JsonProcessingException {
MyObject[] obs = parser.readValueAs(MyObject[].class);
return new MyArray(obs); //presuming you have a copy-constructor
}
}
Then annotate the property that holds such an array with @JsonSerialize(using = MyArraySerializer.class) @JsonDeserialize(using = MyArrayDeserializer.class)
. 然后使用
@JsonSerialize(using = MyArraySerializer.class) @JsonDeserialize(using = MyArrayDeserializer.class)
注释保存此类数组的属性。
If you use your array implementation directly, instead of inside a container class, this page has an example of how to register serialization handlers at run-time http://wiki.fasterxml.com/JacksonHowToCustomSerializers 如果直接使用数组实现而不是在容器类内部使用,则此页面提供了一个示例,该示例如何在运行时注册序列化处理程序http://wiki.fasterxml.com/JacksonHowToCustomSerializers
I should note that in this answer I am using the Jackson 1.9 API and the 2.x may be slightly different. 我应该注意,在此答案中,我使用的是Jackson 1.9 API,而2.x可能略有不同。 According to http://wiki.fasterxml.com/JacksonUpgradeFrom19To20 the most noticeable differences are the changes in package names and where some classes are located.
根据http://wiki.fasterxml.com/JacksonUpgradeFrom19To20 ,最明显的区别是包名称的更改以及某些类的位置。 Otherwise this code should be unaffected.
否则,该代码将不受影响。
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