Develop Reference

Jackson JSON Array Value Deserialization

I am trying to de-serialize this JSON object using Jackson 2.8 as part of Retrofit response. Here is the JSON response I get from the server.
{
"id":"8938209912"
"version":"1.1"
"cars":{
"mercedes":[
{
"property":"color"
},
{
"property":"price"
},
{
"property":"location"
}
],
"tesla":[
{
"property":"environment"
}
]
}
}
Based on the query, the cars above may have one or more models returned. I cannot create a class each for each model as these get created/removed arbitrarily. For each model of the car (say tesla), there may be one or more property key-value pairs.
I am new to Jackson. I have been looking at several examples and looks like a custom #JsonDeserialize is the best way to go. So, I created Root class and Cars class like this:
// In file Root.java
public class Root {
#JsonProperty("id")
private String id = null;
#JsonProperty("version")
private String version = null;
#JsonProperty("cars")
private Cars cars = null;
}
// In file Cars.java
public class Cars {
public Cars(){}
#JsonDeserialize(using = CarDeserializer.class)
private Map<String, List<Property>> properties;
public Map<String, List<Property>> getProperties() {
return properties;
}
public void setProperties(Map<String, List<Property>> properties) {
this.properties = properties;
}
}
// Property.java
public class Property {
#JsonProperty("property")
private String property;
}
My de-serializer is below. However, even though the empty constructor gets called, the parse method itself is not called at all!
// CarDeserializer.class
public class RelationshipDeserializer extends StdDeserializer<Map<String, List<Action>>>{
protected RelationshipDeserializer(){
super(Class.class);
}
#Override
public Map<String, List<Action>> deserialize(JsonParser parser, DeserializationContext ctx)
throws IOException, JsonProcessingException
{
// This method never gets invoked.
}
}
My questions:
Is this the right approach in the first place?
Why do you think the execution never gets to the deserialize()? (I checked, the cars object is present in JSON.
Are there better approaches to parse this JSON using Jackson?

The "properties" deserializer is never called because that does not match anything in that JSON. The field name in the JSON is "property" and it does not match Map<String, List<Property>>. It looks like it would be closer to List<Property>
Do you control the in coming JSON? It would be better for the car name/type to be in its own field rather than the name of the object. Then you can use a generic object. What you have now is going to break. Any time they add a new name/type and you do not have a matching object for it.

Jersey MOXy not parsing snake_case

I'm passing a JSON object from a PUT request to my server. The request itself works, however the fields in the JSON which have an underscore (snake_case) seem to bi ignored. The request outputs the received data to see what comes out, and the value with the underscore converts to camelCase, and doesn't get parsed. Here's the class:
Public User{
private int id;
private String name;
private int some_value;
}
The JSON object I pass to the PUT request:
{ "id":1, "name":John, "some_value":5 }
The PUT method only returns what MOXy caught in this case
#PUT
#Path("user")
#Consumes(MediaType.APPLICATION_JSON)
#Produces(MediaType.APPLICATION_JSON)
public User addUser(User user){
return user;
}
And the output is:
{ "id":1, "name":John, "someValue":0 }
Notice how "some_value" changed to "someValue" and didn't get the actual value updated. Any idea on why this is happening?

MOXy follows Java Bean conventions by default, which suggest camel case. If you don't want to (or can't) use camel case, you can add an annotation to the field:
#XmlElement(name = "some_value")
private int some_value;
If you don't want to annotate all your fields, use an XMLNameTransformer.

Parsing JSON with a value with dynamic type (either string or object) with Jackson's ObjectMapper

I am new to Jackson and I am having some problems determining the best way to deal with processing JSON files that are dynamic in nature. I know I could solve the issue with the streaming or tree API, but this would involve a lot of code which will not be easily maintained. For example, take the following two json files:
{
something: "somethingValue"
somethingelse: "anotherValue"
url: "http://something.com"
}
and
{
something: "somethingValue"
somethingelse: "anotherValue"
url: {
service1: [
"http://something.com",
"https://something.com" ],
service2: [
"http://something2.com",
"https://something2.com" ],
}
}
the default behaviour of the first json object after being parsed, should add the URL to both service1 and service2 url lists in the subclass "URL". where the second allow specifying very specific urls to each. The data object for url class I was planning on use is as follows:
public class url {
// ideally, I would use the java.net.URL instead of String
public List<String> service1;
public List<String> service2;
// also includes getter/setters using a fluent style
...
}
There would also be some other parent class which would have a parameter for URL and other first level json parameters.
What is the best way to handle this in jackson?

The second one is not valid JSON, this is :
{
"something": "somethingValue",
"somethingelse": "anotherValue",
"url": {
"service1" : [
"http://something.com",
"https://something.com" ],
"service2" : [
"http://something2.com",
"https://something2.com" ]
}
}
You can create it/consume it with class A which looks like following
class A{
String something;
String somethingElse;
B url;
}
class B{
Str service1;
List<String> service2;
}
To achieve anything dynamically no matter what, you have to put it in Lists, therefore instead of solution above, you can do this
class A{
String something;
String somethingElse;
B url;
}
class B{
List<C> services;
}
class C{
List<String> service;
}

I ended up mixing JsonNode to get this working.
public class Foo {
#JsonProperty("something")
private String something;
#JsonProperty("somethingelse")
private String somethingelse;
#JsonProperty("url")
JsonNode url;
// getters setters
public static Foo parse(String jsonString) {
ObjectMapper mapper = new ObjectMapper();
Foo foo = mapper.readValue(jsonString, Foo.class);
return foo;
}
public static boolean validate(Foo foo) {
JsonNode url = foo.path("url");
if (url.isTextual()) {
// this is the first case {"url": "http://something.com"}
System.out.println(url.getTextValue());
} else {
// This is the second case
}
}
}

Answer:
After struggling with Jackson to do what I want in a simple and elegant way, I ended up switching to Gson library for JSON parsing. it allowed me to create a custom deserializer for my class that was extremely easy.
An example of something similar that I did can be found here:
http://www.baeldung.com/gson-deserialization-guide
I appreciate the help and guidance with Jackson, however it just made me realize that Jackson was just not going to meet my needs.
-Stewart

Jersey - JSON marshall only specific fields

My REST service returns following JSON
{
"name": "John",
"id" : 10
}
Can I use Jersey to marshall it into following Bean:
public class User{
private String name;
//getter & setter
}
I wanted to do this with following code but it doesn't work
WebResource webResource = client.resource(url);
webResource.accept(MediaType.APPLICATION_JSON_TYPE);
User user = webResource.get(User.class);
Is this even possible or I have to implement full JSON structure in Java Beans to get it work?
I know that I can parse this JSON with Jackson and any other methods.

With Jackson, easiest way is to configure ObjectMapper like so:
objectMapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES,
false);
Check this sample provider
package com.company.rest.jersey;
#Provider
#Component
#Produces({MediaType.APPLICATION_JSON})
public class JacksonMapperProvider implements ContextResolver<ObjectMapper> {
ObjectMapper mapper;
public JacksonMapperProvider(){
mapper = new ObjectMapper();
mapper.configure(Feature.INDENT_OUTPUT, true);
// Serialize dates using ISO8601 format
// Jackson uses timestamps by default, so use StdDateFormat to get ISO8601
mapper.getSerializationConfig().setDateFormat(new StdDateFormat());
// Deserialize dates using ISO8601 format
// MilliDateFormat simply adds milliseconds to string if missing so it will parse
mapper.getDeserializationConfig().setDateFormat(new MilliDateFormat());
// Prevent exceptions from being thrown for unknown properties
mapper.configure(
DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES,false);
}
#Override
public ObjectMapper getContext(Class<?> aClass) {
return mapper;
}
}

With Jackson :
You have two options:
Jackson works on setters-getters of fields. So, you can just remove getter of field which you want to omit in JSON. ( If you don't need getter at other place.)
Or, you can use the #JsonIgnore annotation of Jackson on getter method of that field and you see there in no such key-value pair in resulted JSON.
#JsonIgnore
public int getSecurityCode(){
return securityCode;
}

In your bean, add the annotation #JsonIgnoreProperties(ignoreUnknown = true) at the class level and it should skip the id property in the JSON since it's not present in the bean.
#JsonIgnoreProperties(ignoreUnknown = true)
public class User{
private String name;
//getter & setter
}
(See http://wiki.fasterxml.com/JacksonAnnotations for details)

Parsing JSON object using jQuery and GSON returned by Spring controller

I was looking for some solution around here and I didnt find any correct answer to my question so I would like to ask you.
I have POJO with some simple attribs. and one List of another POJOs.
public class Standard implements Serializable {
private String id;
private String title;
private String description;
private Set<Interpretation> interpretations = new LinkedHashSet<Interpretation>();
}
public class Interpretation implements Serializable {
private String id;
private String title;
private String description;
}
In my controller class, I am returning Standard POJO with GSON.
#RequestMapping(value="/fillStandard", method= RequestMethod.GET)
public #ResponseBody String getStandard(#RequestParam String id) {
Standard s = DAOFactory.getInstance().getStandardDAO().findById(id);
return new Gson().toJson(s);
}
The question is, am I able to get the list of interpretations in my Standard POJO using jQuery ? Something like :
function newStandard() {
$.get("standard/fillStandard.htm", {id:"fe86742b2024"}, function(data) {
alert(data.interpretations[0].title);
});
}
Thanks a lot !
EDIT:
Well, thanks to #Atticus, there is solution of my problem. Hope that it will help somebody.
#RequestMapping(value="/fillStandard", method= RequestMethod.GET, produces="application/json")
public #ResponseBody Standard getStandard(#RequestParam String id) {
Standard s = DAOFactory.getInstance().getStandardDAO().findById(id);
return s;
}
Using #ResponseBody allows you to return the whole POJO, but you need to add produces="application/json" to your #RequestMapping annotation. Then you will be able to catch a returning object as JSON in jQuery like as I supposed.
function newStandard() {
$.get("standard/fillStandard.htm", {id:"idOfStandard"}, function(data) {
alert(data.id); //Standard id
alert(data.interpretations[0].title); //id of Interpretation on first place in array
});

Well you have to create and register your custom serializer.
It goes like this:
//You create your builder that registers your custom serializer with the class you want to serialize
GsonBuilder builder = new GsonBuilder();
builder.registerTypeAdapter(Standard.class, new StandardSerializer());
//Then you create your Gson object
Gson gson = builder.create();
//Then you pass your object to the gson like
Standard s = DAOFactory.getInstance().getStandardDAO().findById(id);
gson.toJson(s);
Your serializer looks like this:
public class StandardSerializer implements JsonSerializer<Standard>{
#Override
public JsonElement serialize(Standard src, Type typeOfSrc,
JsonSerializationContext context) {
JsonObject obj = new JsonObject();
//You put your simple objects in like this
obj.add("id",new JsonPrimitive(src.getId()));
//You put your complex objects in like this
JsonObject interpretations = new JsonObject();
//Here you need to parse your LinkedHashSet object and set up the values.
//For the sake of simplicity I just access the properties (even though I know this would not compile)
interpretations.add("title", src.getInterpretation().getTitle());
obj.add("interpretations", interpretations);
return obj;
}
}
In this case your Json would look something like:
{"id":"idValue", "title":"titleValue", "description":"descriptionValue", "interpretations":["id":"interpretationIdValue"]}
Now, you can access your data with jQuery like this:
function newStandard() {
$.get("standard/fillStandard.htm", {id:"fe86742b2024"}, function(data) {
alert(data.interpretations.title);
});
}
I hope this helps.
EDIT:
I see that your response gets converted to the declared method argument type which is String (as stated here: 16.3.3.2 Supported method return types). But what you really want is your Standrad POJO converted to JSON. I am not very familiar with Spring but as I have read here (16.3.2.6 Producible Media Types) there is another, maybe easier solution. If you want to return a JSON object, then change the return type of the
getStandard method to Standard instead of String and add produces="application/json" to your #RequestMapping annotation. As far as I have read this should tell Spring that the return type should be converted to JSON. In this case you do not need to use Gson.