将 JSON 反序列化为现有对象 (Java)

Question

I'd like to know how one might get the Jackson JSON library to deserialize JSON into an existing object? I've tried to find how to to this; but it seems to only be able to take a Class and instantiate it itself.

Or if not possible, I'd like to know if any Java JSON deserialization libraries can do it.

This seems to be a corresponding question for C#: Overlay data from JSON string to existing object instance . It seems JSON.NET has a PopulateObject(string,object).

Answer 1

You can do this using Jackson:

mapper.readerForUpdating(object).readValue(json);

See also Merging Two JSON Documents Using Jackson

Answer 2

If you can use another library instead of Jackson you can try Genson http://owlike.github.io/genson/ . In addition of some other nice features (such as deserialize using a non empty constructor without any annotation, deserialize to polymorphic types, etc) it supports deserialization of JavaBean into an existing instance. Here is an example:

BeanDescriptorProvider provider = new Genson().getBeanDescriptorFactory();
BeanDescriptor<MyClass> descriptor = provider.provide(MyClass.class, genson);
ObjectReader reader = new JsonReader(jsonString);
MyClass existingObject = descriptor.deserialize(existingObject, reader, new Context(genson));

If you have any question don't hesitate to use its mailing list http://groups.google.com/group/genson .

Answer 3

If you are using spring framework you can use BeanUtils library for this task. First deserialize your json String normally and then use BeanUtils to set this object inside a parent object. It also expects the variable name of the object to be set inside the parent object. Here is the code snippet:

childObject = gson.fromJson("your json string",class.forName(argType))
BeanUtils.setProperty(mainObject, "childObjectName", childObject);

Answer 4

One solution is to parse a new object graph/tree and then unify-copy into the existing object graph/tree. But that's of course less efficient, and more work, especially if concrete types differ because of less availability of type information. (So not really an answer. I hope there's a better answer, just want to avoid others answering in this way.)

Answer 5

flexJson can also help you do the same.

Here is an example copied from FlexJson Doc

The deserializeInto function takes your string and reference to existing object.

 Person charlie = new Person("Charlie", "Hubbard", cal.getTime(), home, work );
 Person charlieClone = new Person( "Chauncy", "Beauregard", null, null, null );
 Phone fakePhone = new Phone( PhoneNumberType.MOBILE, "303 555 1234");
 charlieClone.getPhones().add( fakePhone ); 
 String json = new JSONSerializer().include("hobbies").exclude("firstname", "lastname").serialize( charlie ); 
 Person p = new JSONDeserializer<Person>().deserializeInto(json, charlieClone);

Note that the reference returned in p is same as charlieClone just with updated values.

Answer 6

I used Jackson + Spring's DataBinder to accomplish something like this. This code handles arrays but not nested objects.

private void bindJSONToObject(Object obj, String json) throws IOException, JsonProcessingException {
    MutablePropertyValues mpv = new MutablePropertyValues();
    JsonNode rootNode = new ObjectMapper().readTree(json);
    for (Iterator<Entry<String, JsonNode>> iter = rootNode.getFields(); iter.hasNext(); ) {
        Entry<String, JsonNode> entry = iter.next();
        String name = entry.getKey();
        JsonNode node = entry.getValue();
        if (node.isArray()) {
            List<String> values = new ArrayList<String>();
            for (JsonNode elem : node) {
                values.add(elem.getTextValue());
            }
            mpv.addPropertyValue(name, values);
            if (logger.isDebugEnabled()) {
                logger.debug(name + "=" + ArrayUtils.toString(values));
            }
        }
        else {
            mpv.addPropertyValue(name, node.getTextValue());
            if (logger.isDebugEnabled()) {
                logger.debug(name + "=" + node.getTextValue());
            }
        } 
    }
    DataBinder dataBinder = new DataBinder(obj);
    dataBinder.bind(mpv);
}

Answer 7

could always load into a dummy object and use reflection to transfer the data. if your heart is set on just using gson

example. assuming this code is in the object you want to copy data into

    public void loadObject(){
Gson gson = new Gson();
//make temp object
YourObject tempStorage = (YourObject) gson.fromJson(new FileReader(theJsonFile), YourObject.class);
//get the fields for that class
ArrayList<Field> tempFields = new ArrayList<Field>();
ArrayList<Field> ourFields = new ArrayList<Field>();
getAllFields(tempFields, tempStorage.getClass());
getAllFields(thisObjectsFields, this.getClass());
for(Field f1 : tempFields){
    for(Field f2 : thisObjectsFields){
        //find matching fields
        if(f1.getName().equals(f2.getName()) && f1.getType().equals(f2.getType())){
            //transient and statics dont get serialized and deserialized.
            if(!Modifier.isTransient(f1.getModifiers())&&!Modifier.isStatic(f1.getModifiers())){
                //make sure its a loadable thing
                f2.set(this, f1.get(tempStorage));
            }
        }
    }
}

}

public static List<Field> getAllFields(List<Field> fields, Class<?> type) {
    for (Field field : type.getDeclaredFields()) {
        fields.add(field);
    }
    if (type.getSuperclass() != null) {
        fields = getAllFields(fields, type.getSuperclass());
    }
    return fields;
}

Answer 8

You can use my repositories :).

Object yo = //yourObject
String js = //json source

Map remote = Object$.remoteMap(yo, false); //or you can use Bean.forInstance(yo);
Reader reader = new StringReader(js);//you can replace this with any reader :)
AtomicReference buffer = new AtomicReference(remote);

try {
    JSON.global.parse(buffer, reader, null, null);
} catch (IOException ignored) {
    //If any exception got thrown by the reader
}

this way, JSON will parse values to the map it finds in the buffer. And if the map contains a list and the JSON value also has a list. The list on the map will not be replaced. instead, it will be used to contain the values.

If you used Bean.forInstance(yo) the returned remote map will have some additional features.

repositories:

util repo (required): github.com/cufyorg/util

base repo (required): github.com/cufyorg/base

JSON repo (required): github.com/cufyorg/json

beans repo (optional): github.com/cufyorg/beans