I am currently working on a vertx.io application and wanted to use the provide mongo api for data storage. I currently have a rather clunky abstraction on top of the stock JsonObject classes where all get and set methods are replaced with things like:
this.backingObject.get(KEY_FOR_THIS_PROPERTY);
This is all well and good for now, but it won't scale particularly well. it also seems dirty, specifically when using nested arrays or objects. For example, if I want to be able to fill fields only when actual data is known, I have to check if the array exists, and if it doesn't create it and store it in the object. Then I can add an element to the list. For example:
if (this.backingObject.getJsonArray(KEY_LIST) == null) {
this.backingObject.put(KEY_LIST, new JsonArray());
}
this.backingObject.getJsonArray(KEY_LIST).add(p.getBackingObject());
I have thought about potential solutions but don't particularly like any of them. Namely, I could use Gson or some similar library with annotation support to handle loading the object for the purposes of manipulating the data in my code, and then using the serialize and unserialize function of both Gson and Vertx to convert between the formats (vertx to load data -> json string -> gson to parse json into pojos -> make changes -> serialize to json string -> parse with vertx and save) but that's a really gross and inefficient workflow. I could also probably come up with some sort of abstract wrapper that extends/implements the vertx json library but passes all the functionality through to gson, but that also seems like a lot of work.
Is there any good way to achieve more friendly and maintainable serialization using vertx?
I just submitted a patch to Vert.x that defines two new convenience functions for converting between JsonObject and Java object instances without the inefficiency of going through an intermediate JSON string representation. This will be in version 3.4.
// Create a JsonObject from the fields of a Java object.
// Faster than calling `new JsonObject(Json.encode(obj))`.
public static JsonObject mapFrom(Object obj)
// Instantiate a Java object from a JsonObject.
// Faster than calling `Json.decodeValue(Json.encode(jsonObject), type)`.
public <T> T mapTo(Class<T> type)
Internally this uses ObjectMapper#convertValue(...), see Tim Putnam's answer for caveats of this approach. The code is here.
I believe Jackson's ObjectMapper.convertValue(..) functions don't convert via String, and Vert.x is using Jackson for managing JsonObject anyway.
JsonObject just has an underlying map representing the values, accessible via JsonObject.getMap(), and a Jackson serializer/deserializer on the public ObjectMapper instance in io.vertx.core.json.Json.
To switch between JsonObject and a data model expressed in Pojos serializable with Jackson, you can do:
JsonObject myVertxMsg = ...
MyPojo pojo = Json.mapper.convertValue ( myVertxMsg.getMap(), MyPojo.class );
I would guess this is more efficient than going via a String (but its just a guess), and I hate the idea of altering the data class just to suit the environment, so it depends on the context - form vs performance.
To convert from Pojo to JsonObject, convert to a map with Jackson and then use the constructor on JsonObject:
JsonObject myobj = new JsonObject ( Json.mapper.convertValue ( pojo, Map.class ));
If you have implied nested JsonObjects or JsonArray objects in your definition, they will get instantiated as Maps and Lists by default. JsonObject will internally re-wrap these when you access fields specifying those types (e.g. with getJsonArray(..).
Because JsonObject is freeform and you're converting to a static type, you may get some unwanted UnrecognizedPropertyException to deal with. It may be useful to create your own ObjectMapper, add the vertx JsonObjectSerializer and JsonArraySerializer, and then make configuration changes to suit (such as DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES in Jackson).
Not sure if I've understood you correctly, but it sounds like you're trying to find a simple way of converting POJOs to JsonObject?
So, we have lots of pojos that we send over the EventBus as JsonObjects
I've found the easiest way is to use the vert.x Json class which has loads of helper methods to convert to / from Json Strings
JsonObject jsonObject = new JsonObject(Json.encode(myPojo));
Sometimes you need to add some custom (de)serializers, but we always stick with Jackson - that is what Vert.x is using so they work out of the box.
What we actually do, is provide an interface like the following:
public JsonObjectSerializable {
public JsonObject toJson();
}
And all our pojos that need to be sent over the EventBus have to implement this interface.
Then our EventBus sending code looks something like (simplified):
public <T extends JsonObjectSerializable> Response<T> dispatch(T eventPayload);
Also, as we generally don't unit test Pojos, adding this interface encourages the developers to unit test their conversion.
Hope this helps,
Will
Try this:
io.vertx.core.json.Json.mapper.convertValue(json.getMap(), cls)
I think that using Gson as you described is the best possible solution at the current time.
While I agree that if a protocol layer was included in Vert.x it would indeed be first prize, using Gson keeps your server internals pretty organised and is unlikely to be the performance bottleneck.
When and only when this strategy becomes the performance bottleneck have you reached the point to engineer a better solution. Anything before that is premature optimisation.
My two cents.
You can try:
new JsonObject().mapFrom(object)
Related
I am receiving massive json objects from a service and so far i've been creating POJOs to match the json that comes in.
However, this is getting far too tedious as with every different service I hit I have to build 15-20 new model classes to represent the new service i'm hitting.
In short, what i'm looking for is a way to get a value I need from a neested object in the json as below (sorry for format):
random1 {
random2 {
arrayOfRandoms
}
random3 {
random4 {
random5 {
someValueIWant
}
}
}
}
so in this case I want random5s someValueIWant object. I want to get it without creating the models for random1/3/4/5 as i've been doing this whole time.
I should mention that I use Jacksons ObjectMapper to turn the json into java objects.
Hope this makes sense.
You could experiment with this online pojo generator:
http://www.jsonschema2pojo.org/
It will generate java classes from plain json (or json schema) and even add jackson annotations.
Make sure you check "Allow additional properties".
It requires valid json as input, so don't forget double quotes around fields names and values
If you find yourself doing that often, there's even scriptable versions and maven plugins.
I want to parse json from a server and place it into a class. I use json4s for this. The issue is that a json object contains too many fields, it's about 40-50 of them, some of them have the long names.
I wonder, what will be a sensible way to store all of them, will I have to create 40-50 fields in a class? Remember, some of them will have the long names, as I said earlier.
I use Scala, but a Java's approach might be similar to it, so I added a tag of Java also.
I don't know json4s but in Jersey with Jackson, for example, you can use a Map to hold the Json data or you can use a POJO with all those names.
Sometimes its better to have the names. It makes the code much easier to understand.
Sometimes its better to use a Map. For example, if the field names change from time to time.
If I recall it correctly, using pure Jackson you do something like this:
String jsonString = ....; // This is the string of JSON stuff
JsonFactory factory = new JsonFactory();
ObjectMapper mapper = new ObjectMapper(factory); // A Jackson class
Map<String,Object> data = mapper.readValue(jsonString, HashMap.class);
You can use a TypeReference to make it a little cleaner as regards the generics. Jackson docs tell more about it. There is also more here: StackOverflow: JSON to Map
There are generally two ways of parsing json to object
1) Parse json to object representation.
the other which might suit you as you mention that your object has too many fields is amap/hashtable, or you could just keep it as JObject, an get fields ehrn you need them
It's a kind of odd question for an odd situation. I have a large JSON structure which I would like to represent in running groovy code. I need groovy objects that mirror the same structure as the JSON objects.
As to be expected a web search mostly returns results with groovy/json runtime conversion stuff, but nothing about things that output groovy code.
You might think this lazy but really it is a massive JSON structure! A converter would save days!
You can use Groovy's own JsonSlurper to parse JSON objects:
import groovy.json.*
def json = '{"name":"john", "surname":"doe", "languages": ["groovy", "python"]}'
def obj = new JsonSlurper().parseText(json)
assert obj.name == "john"
assert obj.surname == "doe"
assert obj.languages.containsAll("python", "groovy")
Of course the class is untyped: it's only known at runtime. If you want it to be typed, you can write a code which writes the code based on an example (since a json schema may be rare).
EDIT: if you want to generate the model classes code, you can try JSONGen, which "parses JSON to create client side source files to model the JSON data structure". I'm not aware of a solution for Groovy, but since java-groovy integrations is seamless, it shall work fine.
If you want a Groovy representation of your JSON, you can get that via the built-in JsonSlurper. This will give you Java Maps and Lists of data you can work with.
You can populate more specific, custom objects you've written to represent your JSON entities using the (3rd party) Jackson's data binding functionality (see this question as well).
Try using a JSON parser like this one. According to its documentation you just need to do
JSON.parse
to deserialize the data
I have a rest service returning some data. I use Restlet client api as shown below to access this service. As you can see, it returns org.json.JSONObject. Is there a easy way to map this to the domain object (may be through annotations?) or should I have to write code to create the domain object?
Representation entity = new ClientResource(uri).get();
JSONObject json = new JsonRepresentation(entity).getJsonObject();
May be you can leverage from Gson library which has a function you need:
// Convert JSON into Java object
SomeObj obj = gson.fromJson(jsonObjStr, SomeObj.class)
You can read more here...
While there are decent APIs for easily mapping between Java data structures, e.g., from the JSONObject to your preferred data structure, since the incoming data format is JSON, I'd much prefer to just use a good JSON-to/from-Java API like Jackson. Depending on the preferred transformation details, the solution might be just one simple line of code with such an API.
I'm using json.org JSONObject. I've tried to serialize it to memcache and got the not so cool java.io.NotSerializableException: org.json.JSONObject. Looking at the JSONObject code it seems that it's nothing more then a Map wrapped by JSON logic. Why not make it serializble then?
I would like to be able to store the object into memcache in an easy interface. Is there a similar API implementation of JSONObject that is also serializble. Alternatively, what memcache friendly serialization / deserialization technique do you use ?
Thank you,
Maxim.
JSONObjects are meant be sent as simple strings. So instead of storing the Java serialized form of your JSONObjects you should store the stringified forms.
if you use org.json.JSONObject, it doesn't implement the Serializable interface. For that reason it can't be serialized. Instead, you can put the String version of JSONObject into MemCache.
I have found http://code.google.com/p/json-simple/ to be API compatible implementation of org.json.JSONObject. It does not have all the getDouble, getLong, getJSONArray methods but other then that the concepts are pretty much the same.
It excels over org.json implementation by the fact that it simply extends HashMap for JSONObject and ArrayList for JSONArray making these objects by definition serializble and thus cacheable.