I want to parse JSON data from a RESTful service.
Unlike a SOAP-based service, where a service consumer can create stubs and skeleton from WSDL, in the case of the RESTful service, the service consumer gets a raw JSON string.
Since the service consumer does not have a Java object matching the JSON structure, we are not able to use the JSON to Java Mappers like GSON, Jackson etc.
One another way is to use parsers like JsonPath, minimal-json, etc which help traversing the JSON structure and read the data.
Is there any better way of reading JSON data?
The official docs for Jackson mention 3 different ways to parse a JSON doc from Java. The first 2 do not require "Java object matching the JSON structure". In Summary :
Streaming API (aka "Incremental parsing/generation") reads and writes JSON content as discrete events.
Tree Model provides a mutable in-memory tree representation of a JSON document. ObjectMapper can build trees that consist of JsonNode nodes.
Data Binding converts JSON to and from POJOs based either on property accessor conventions or annotations.
With simple data binding you convert to and from Java Maps, Lists, Strings, Numbers, Booleans and nulls
With full data binding you convert to and from any Java bean type (as well as "simple" types mentioned above)
Another option is to generate Java Beans from JSON documents. You mileage may vary and you may/probably will have to modify the generated files. There are at least 5 online tools for that purpose that you can try:
http://www.jsonschema2pojo.org/
http://pojo.sodhanalibrary.com/
https://timboudreau.com/blog/json/read
http://jsongen.byingtondesign.com/
http://json2java.azurewebsites.net/
There are also IDE plugins that you can use. For instance this one for Intellij https://plugins.jetbrains.com/idea/plugin/7678-jackson-generator-plugin
The GSON supports work without objects, too. Something as this:
JsonObject propertiesWrapper = new JsonParser().parse(responseContent).getAsJsonObject();
assertNotNull(propertiesWrapper);
propertiesWrapper = propertiesWrapper.getAsJsonObject("properties");
assertNotNull(propertiesWrapper);
JsonArray propertiesArray = propertiesWrapper.getAsJsonArray("property");
assertNotNull(propertiesArray);
assertTrue(propertiesArray.size()>0, "The list of properties should not be empty. ");
The problem is that the work this way is so inconvenient that it is really better to create objects instead.
Jackson has absolutely the same problems, and to greater extent - extremal inconvenient for direct json reading/creation. All its tutorials advice to use POJOs instead, too.
The only really convenient way is use Groovy. Groovy works as an envelope on Java, you can simply write Java code and use Groovy operators at need. And in JSON or XML reading and creation Groovy is incomparably more powerful that Java with all its libraries multiplied on each other! It is even much more convenient than already prepared by somebody else tree structure of ready POJOs.
Related
I have a following use case :
parse the json from stream (kafka topic)
extract some fields (likely 35 out of 100 fields)
Build a json out of those fields
Publish it to pub/sub for further processing
My implementation is very much java language bound. Can anyone suggest optimal solution for this ? and why is it optimal ?
For json parsing, I am thinking of https://bolerio.github.io/mjson/
Kafka includes Jackson JSON library and includes its own JSON Deserializer that returns a JsonNode class
Alternatively,as listed in the comments, you can use higher level frameworks such as Spring, Vertx, Quarkus, etc to build Kafka consumers
For the listed use case, I would opt for Spark, Flink, or NiFi for integration with PubSub. Each also offering JSON proessing, with NiFi being more advanced in that it can do JSONPath
I need to parse the jax-ws rest response and I tried the following two ways of parsing the response.Both works good.But I am in need to know the best efficient way of implementation.Please provide me your view.
First Approach:
Use getEntity Object and get the response as Input Stream.
Using Jackson ObjectMapper readValue() -covert the inputstream to java
object.
Using getters and setters of nested java class get the response objects member values.
Second Approach:
Use getEntity Object and get the response as Input Stream and and
convert the Input Stream to String.
Using Google Json API,convert the string to json object.
Using Json parser and get the nested objects member values.
I would say the first approach is better for two reasons:
You don't go through the intermediate process of reading the response payload into String
The setter methods that are called during Jackson deserialization may perform validation on input and throw appropriate exceptions, so you do validation during deserialization.
Maybe not a general answer to this question but another variant of what you're describing under "First approach". I would start with a generic data structure and would only introduce an extra bean if necessary. I wouldn't use String to pass structured data around.
Use jackson to convert the JSON response to a
Map<String,Object> or JsonNode.
Advantage:
You don't need to implement a specialized bean class. Even a very simple bean can become unhandy over time (if format changes or new nested structures are added to the json response, etc.). It also introduces some kind of metaphor to your code which sometimes helps but also can be misleading.
Map<String,Object> is in the JDK and offers a good interface to access data. You don't have to change any interfaces even if the JSON format changes.
You can always pass your data in form of a Map<String,Object>
Disadvantage
Data Encapsulation. The map is a very close representation of the input data and therefore offers not same level of abstraction like a bean.
Does smooks support json output or thirdparty plugin for json?
For example, to do XML-to-JSON or EDI-to-JSON
I see it has json reader/parser, but can't seem to find an output/writer.
TIA!
Not directly, but it would support populating of a Java Object model from e.g. XML or EDI and then you could use something like Jackson to serialize the Java to JSON. So should be easy enough to do once you get the data into a Java Object model.
Also note that you do not need to create an actual Java Object model. You can create what Smooks calls a "virtual object model", which is basically collection types (Maps, Lists etc).
So there is a nice library for VB6 JSON parsing. HERE
but i actually used one that built on the original and optimized. HERE
Essentially I'm using the parser to deserialize the json i get from a web service. I need to update some values, and resend to the server. Using the Collection/Dictionary objects made it very easy. But now, How do i take those objects and serialize them to a JSON string? is there a library for that?
thanks you for your help.
There are quite a few JSON parser/serializer/DOM classes written in VB6. Perhaps you might want to consider one of those instead. E.g.:
JsonBag, Another JSON Parser/Generator
In my GWT project I need to process json data retrieved from a database via PHP. I have seen the Google examples using JavaScriptObject overlay classes. What I don't understand is why this seems to be the prefered method of processing the json data. Why shouldn't I use all native Java code to pull in the data?
Think about it the other way around: what does it mean to use POJOs? (or native Java classes as you name them)
You have to:
parse the JSON into some Java-accessible structure (e.g. com.google.gwt.json.client.JSONObject, or elemental.json.JsonObject)
create POJOs
fill the POJOs with the data from the parsed JSON structure
now you can forget the parsed JSON structure from step 1
On the other hand, with JavaScriptObject, you use JsonUtil.safeEval and TA-DA! you get your JSON parsed right into a typed Java object!
Now, to deal with JSON, there's also AutoBeans.
Choose your poison.