I have seen the responses from many other posts but would like to understand if there is a better way to do the same thing.
Requirement:-
I am using restTemplate to talk to web service which returns JSON output which is dynamic. As a consumer I don't want to access all fields but is interested in few of them. I am using Spring framework with Jackson parser and found the way of accessing it
String response = restTemplate.getForObject(targetUrl, String.class);
System.out.println(response);
ObjectMapper mapper = new ObjectMapper();
JsonNode rootNode = mapper.readValue(response, JsonNode.class);
JsonNode uri = rootNode.get("uri");
System.out.println(uri.asText());
Do you know any better way to do it? Mapping to java Object is something that I dont want to do as the json output is not in my control
If your RestTemplate is configured with the default HttpMessageConverters, which is provided by Jackson2ObjectMapperBuilder, you may directly get a JsonNode from restTemplate.getForObject.
For example,
ArrayNode resources = restTemplate.getForObject("/resources", ArrayNode.class);
Or,
ObjectNode resource = restTemplate.getForObject("/resources/123", ObjectNode.class);
Note that ArrayNode and ObjectNode are sub-classes of JsonNode.
Related
I'm using Flink to process some JSON-format data coming from some Data Source.
For now, my process is quite simple: extract each element from the JSON-format data and print them into log file.
Here is my piece of code:
// create proper deserializer to deserializer the JSON-format data into ObjectNode
PravegaDeserializationSchema<ObjectNode> adapter = new PravegaDeserializationSchema<>(ObjectNode.class, new JavaSerializer<>());
// create connector to receive data from Pravega
FlinkPravegaReader<ObjectNode> source = FlinkPravegaReader.<ObjectNode>builder()
.withPravegaConfig(pravegaConfig)
.forStream(stream)
.withDeserializationSchema(adapter)
.build();
final StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
DataStream<ObjectNode> dataStream = env.addSource(source).name("Pravega Stream");
dataStream.???.print();
Saying that the data coming from Pravega is like this: {"name":"titi", "age":18}
As I said, for now I simply need to extract name and age and print them.
So how could I do this?
As my understanding, I need to make some customized codes at ???. I might need to create a custom POJO class which contains ObjectNode. But I don't know how. I've read the official doc of Flink and also tried to google about how to create a custom POJO for Flink but I can't still figure out clearly.
Could you please show me an example?
Why don't You simply use something more meaningful instead of JavaSerializer? Perhaps something from here.
You could then create a POJO with the fields you want to use and simply deserialize JSON data to Your POJO instead of ObjectNode
Also, if there is some specific reason that You need to have ObjectNode on deserialization then You can simply do something like :
//I assume You have created the class named MyPojo
dataStream.map(new MapFunction<ObjectNode, MyPojo>() {
ObjectMapper mapper = new ObjectMapper();
#Override
public MyPojo map(final ObjectNode value) throws Exception {
mapper.readValue(value.asText(), MyPojo.class)
}
})
I would like to de-serialize a JSON string and conduct object mutations including replicating nodes, adding new nodes to arrays, and changing the value of text nodes. I read that JsonNodes are for reading and ObjectNodes are for editting.
The only thing I could find to attempt was:
root = mapper.readTree(apiResponseTemplate);
ObjectNode rootTwo = mapper.valueToTree(root);
I'm using jackson 1.9.12
How can I do this? Thanks!
To parse the JSON string you could use something like this.
ObjectMapper mapper = new ObjectMapper();
JsonNode node = mapper.readTree(jsonText);
To add new nodes:
ObjectNode objNode= mapper.createObjectNode();
objNode.put("NodeName", "NodeValue");
To add new ArrayNodes:
objNode.putArray("NodeName");
JsonNode has many useful methods like has("NodeName"), path("NodeName"), etc.
I need to pass a map back to the web application.
I'm used to encapsulating the map in a JSONObject
http://json.org/java/
But since I am using Spring and Jackson Haus.
is there an easier way to maintain the pojo? May I can just annotate the MAP ?
Jackson has com.fasterxml.jackson.core.JsonNode, and specific subtypes like ObjectNode.
These form so-called Tree Model, which is one of 3 ways to handle JSON with Jackson -- some other libraries (like org.json) only offer this way.
So you should be able to just use JsonNode instead; there is little point in using org.json library; it is slow, and has outdated API.
Alternatively you can just use java.util.Map, and return that. Jackson can handle standard Lists, Maps and other JDK types just fine.
If you need to manipulate the output, ie, you don't want to provide all the fields of the object you can use JSonArray:
#RequestMapping(value = "/api/users", method = RequestMethod.GET)
public
#ResponseBody
String listUsersJson(ModelMap model) throws JSONException {
JSONArray userArray = new JSONArray();
for (User user : userRepository.findAll()) {
JSONObject userJSON = new JSONObject();
userJSON.put("id", user.getId());
userJSON.put("firstName", user.getFirstName());
userJSON.put("lastName", user.getLastName());
userJSON.put("email", user.getEmail());
userArray.put(userJSON);
}
return userArray.toString();
}
Use the example from here
Otherwise if you add jackson to your dependencies and set the controller method anotatted with #ResponseBody the response will automatically mapped to JSON. Check here for a simple example.
I'm looking for a way to directly convert some POJO to a Jackson TreeModel. I know that a translation from POJO-to-JSON-String exists, and TreeModel-to-JSON-String is supported — hovewer I am looking for a POJO-to-TreeModel translation. Is there a way?
The use-case is as follows:
Server-side templating is done with the Java implementation of Mustache. This uses Jackson's TreeModel.
After that, I need a slimmed-down version of the TreeModel on the client-side, so I want to be able to first filter the TreeModel, serialize that to JSON, then send it to the client-side for further processing.
This, ideally, involves two serialization steps. However, in my workaround, I am currently using three — which you can see here:
map = // a map of pojos with jackson annotations
//pojo >> JSON
StringWriter w = new StringWriter();
objectmapper.writeValue(new JsonFactory().createJsonGenerator(w), map);
String json = w.toString();
w.close();
//JSON >> Treemodel
JsonNode tree = GenericJcrDTO.mapper.readTree(json);
//filter tree here
//treemodel >>JSON
StringWriter w = new StringWriter();
GenericJcrDTO.mapper.writeValue(new JsonFactory().createJsonGenerator(w), tree);
json = w.toString();
w.close();
Anyone?
To answer my own question:
JsonNode node = objectMapper.valueToTree(map);
API publisher added new field to their response object that isn't in my model classes. Is there a way to loosen up the mapper to ignore unknown fields? I still want to use my old legacy model classes to parse, but now I get an exception...
Switch to Jackson JSON Processor and do this:
ObjectMapper mapper = new ObjectMapper();
// THIS IS WHAT I WAS LOOKING FOR TO HANDLE IN XSTREAM!!!!!!
mapper.configure(org.codehaus.jackson.map.DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);
User user = mapper.readValue(new File("user.json"), User.class);