I have a use case where I receive some attributes in the request like this,
"filters": [
{
"field": "fName",
"value": "Tom"
},
{
"field": "LName",
"value": "Hanks"
}
]
I don't have a model defined for this. I just receive these attributes in the request and fire a query on elastic search using these attributes. My records in elastic search have the same attribute names.
Now, I have to support a legacy application where attribute's names are completely different.
E.g.: fName becomes firstName and lName becomes lastName.
Problem: Need to accept old attribute names in the request, convert them to new ones so that it matches my elastic search records. Fetch the data with new attribute names and convert back to old ones before sending out the response from the application.
NOTE: I don't have POJO's defined for these records.
How can this be achieved effectively? I was thinking of using Orika mapper but not sure how that will work without defining classes first.
What prevents you from writing a transformer from request JSON to your normalized JSON?
The normal flow I can think of is:
Request JSON -> POJO -> POJO with normalized value -> Normalized JSON
So your POJO looks like:
public class Filter {
List<FieldFilter> filters;
public static class FieldFilter {
private String field;
private String value;
}
}
Now you will have a transformation map like:
Map<String, String> fieldNameMapping = new HashMap<>();
fieldNameMapping.put("fName", "firstName");
fieldNameMapping.put("firstName", "firstName");
// The process of populating this map can be done either by a static initializer, or config/properties reader
Then you transform your POJO:
Filter filterRequest;
List<FieldFilters> normlizedFilters =
filterReq.getFilters().stream()
.map(f -> new FieldFilter(fieldNameMapping.get(f.getField()), f.getValue())
.collect(toList());
Then convert the Filter class to your normalized JSON.
We have a similar scenario and we are using apache JOLT.If you want to try some samples, you can refer jolt-demo-online-utility
Use a JSON to JSON-transformer instead. Good answers regarding this can be found here: JSON to JSON transformer and here : XSLT equivalent for JSON
In the end you do not require an intermediate object type here. You even said, that you do not have such a type yet and inventing it, just to transform it, doesn't really make sense.
Related
I have a spring boot app that among others, has an endpoint that when hit, returns a list of strings. I also have another spring boot app that hits the first app's endpoint to get the data. The fetch code:
return webClient.get().uri("/sensors/get-cities").headers(httpHeaders -> {
httpHeaders.set("Authorization", auth);
}).retrieve()
.bodyToFlux(String.class).collectList().block();
The above yields a list but with this format when I inspect it in the debbuger, "["city"]". The outer double quotes, I get them because it's a string but the brackets and the inside double quotes, I do not. I tried replacing these characters but I had no luck with the brackets (tried regex). It is like they are not there, but at the same time they are. I am confused at this point. But I think that the behavior of the fetch code is not normal, it should yield a valid array of strings.
What you are probably getting (im guessing here) is a response body that looks something like this:
[
"New York",
"Madrid",
"London"
]
You then tell webflux that you want to convert the body to a Flux of String by calling bodyToFlux(String.class).
So the framework takes the entire response and makes a string out of it
// A string of the entire array (im escaping the quotation marks)
"[\"New York\",\"Madrid\",\"London\"]"
And then the framework will throw the entire thing into a Flux which means it takes the first position in the Flux. You then emit all the values into a List by calling collectList The equivalent code is sort of:
List<String> oneString = Flux.just("[\"New York\",\"Madrid\",\"London\"]")
.collectList()
.block();
So you get a list, with one string in it, which is the entire body.
What you probably want to do is to get a list out if it. And this is one way to do it:
List<String> strings = webClient.get()
.uri("/sensors/get-cities")
.headers(httpHeaders -> {
httpHeaders.set("Authorization", auth);
})
.retrieve()
.bodyToMono(new ParameterizedTypeReference<List<String>>() {})
.block();
Spring explains ParameterizedTypeReference:
The purpose of this class is to enable capturing and passing a generic Type. In order to capture the generic type and retain it at runtime
So its sort of a class that makes sure we can use generic types like List<T> and helps us with type information.
So what we do is that we now take the response and tell the framework that the body is a list of strings directly. We dont need to do collectList anymore as the framework will stick it in a list for us. We then call block to wait in the response.
Your Springboot API returns result as parsed to JSON (this is default behavior). So it first builds a list of Strings (in your case just a single String "city" and than serializes it to Json. In this case since it is a list it serializes it to JSON array as opposed to JSON Object. Read about JSON here. So in your second Springboot app that hits the API from the first one should assume that you are getting JSON which you need to parse to get your list. To parse it you can use readValue() method of ObjectMapper class of Json Jackson library which is a default JSON library in Springboot. your code would be
List<String> myList;
ObjectMapper = new ObjectMapper();
//Add setters for ObjectMapper configuration here if you want a specific config
try {
myList = objectMapper.readValue(myJsonString, List.class);
} catch(IOException ioe) {
...
}
In addition I wrote my own Open-source library called MgntUtils, that includes JsonUtils class which is a thin wrapper over Json Jackson library. It provides just Json parser and serializer, but in many cases that is all you need. With my library you would only need one dependency as oppose to Jackson, and JsonUtils class just have 4 methods, so by far easier to understand. But in your case if you use my library the code would be very similar to the above code. It would be something like this:
List<String> myList;
try {
myList = JsonUtils.readObjectFromJsonString(myJsonString, List.class);
} catch(IOException ioe) {
...
}
Note that in this case you won't have to instantiate and configure ObjectMapper instance as readObjectFromJsonString is a static method. Anyway if you are interested in using my library you can find maven artifacts here and The library itself with source code and javadoc is on Github here. Javadoc for JsonUtils class is here
My application is receiving JSON messages from a WebSocket connection.
There are different types of answers, which are formatted like that:
{
"type": "snapshot",
"product_id": "BTC-EUR",
"bids": [["1", "2"]],
"asks": [["2", "3"]]
}
or
{
"type": "l2update",
"product_id": "BTC-EUR",
"changes": [
["buy", "1", "3"],
["sell", "3", "1"],
["sell", "2", "2"],
["sell", "4", "0"]
]
}
... for example (see full API here).
Depending on the "type", I would like GSON to map a different class (e.g. Snapshot.class and l2update.class).
I have message handlers that subscribe to the WebSocket connection and I want the message to be processed by the relevant handler. For instance:
ErrorMessageHandler would manage the errors
SnapshotMessageHandler would create the initial order book
L2UpdateMessageHandler would update the order book
and so on
My problem is to dispatch the messages depending on their type.
I was thinking to convert them to the appropriate class and then call the relevant handler using a factory. I'm currently stuck at the first step, converting the JSON in Error.class or Snapshot.class depending on the "type".
How can I do that?
For Gson you could use com.google.gson.typeadapters.RuntimeTypeAdapterFactory.
Assuming you have - for example - following classes:
public class BaseResponse {
private String type, product_id;
// rest of the common fields
}
public class Snapshot extends BaseResponse {
// rest of the fields
}
public class L2Update extends BaseResponse {
// rest of the fields
}
then you would build following RuntimeTypeAdapterFactory:
RuntimeTypeAdapterFactory<BaseResponse> runtimeTypeAdapterFactory =
RuntimeTypeAdapterFactory
.of(BaseResponse.class, "type") // set the field where to look for value
.registerSubtype(L2Update.class, "l2update") // values map to 'type'
.registerSubtype(Snapshot.class, "snapshot");// value in json
Registering this with Gson will then enable automativcal instantiation of each type of responses:
Gson gson = new GsonBuilder()
.registerTypeAdapterFactory(runtimeTypeAdapterFactory).create();
and provide BaseResponse for fromJson(..) if using it , like:
gson.fromJson( json , BaseResponse.class);
NOTE: that Gson omits de- & serializing the type field. However it needs to be set in Json. Just as it is now in responses you get.
You may want to consider using a library that requires a bit less of a solid object model, at least at first. I use JsonPath for this type of thing. You could use it to at least find out the type you're dealing with:
String type = JsonPath.read(yourIncomingJson, "$.type");
and then, based on the string, do a switch statement as #ShafinMahmud suggests.
However, you could use JsonPath for the whole thing too. You could read all of the values using the path notation and know how to parse based on the type.
Adding another library to read a single value may or may not work for you but if you use it to read other values it might end up being worthwhile.
In my test I need to compare the expected and actual JSON response. But the JSON response is limited depending upon the role. So I need to exclude certain fields while comparing.
Below is the JSON and I want to filter out 2 things from it.
1. CompanyId
2. status.
{
userId=dg4d6g4dg45-rgdre-543-dfg,
userName=test123,
effectives=[
{
companyId=345634-54-547-74,
companyName=xyz,
roleId=685-345863490-634,
roleName=This is the test Role
},
{
companyId=345634-54-547-74,
companyName=xyz,
roleId=685-345863490-634,
roleName=This is the test Role
}
],
status=Active
}
Can you someone please let me know how to achieve this.
I explored the filterOutAllExcep method of SimpleBeanPropertyFilter but then I will have to figure out the logic to remember all the fields that should be included as well.
I think i have found a resolution for this.
I am using Object Mapper and converting the data model into a Map.
Then iterating over the map and removing the fields.
Flat filtering is straight forward but had to right up some logic for nested fields.
// Convert the DataModel into a Map object
ObjectMapper mapper = new ObjectMapper();
Map mainObjectMap = mapper.convertValue(object, Map.class);
This is the json response returned by MediaWiki API. I want to create a class to be able to deserialize it to it use Jackson library. The problem is that this json contains a key which is different from each request (here is 290).
{
"query-continue": {
"revisions": {
"rvcontinue": 633308090
}
},
"query": {
"pages": {
"290": {
"pageid": 290,
"ns": 0,
"title": "A",
"revisions": [
{
"user": "Mr. Guye",
"timestamp": "2014-12-07T17:45:55Z",
"comment": "comment",
"contentformat": "text/x-wiki",
"contentmodel": "wikitext",
"*": "content"
}
]
}
}
}
}
How could create a class (or configure the mapper) to be able to deserialize this json?
You can deserialize JSON to multiple formats using Jackson. One way that you mentioned is to convert the JSON to a POJO which may be difficult when the keys are dynamic. Another approach is to deserialize the JSON to the Jackson Tree Model which is called JsonNode. The following illustrates how you can parse the provided JSON to a JsonNode and then retrieve the various attributes.
final ObjectMapper mapper = new ObjectMapper();
// Parse the JSON, deserialize to the Tree Model
final JsonNode jsonNode = mapper.readTree(jsonString);
// Get hold of the "query -> pages" node.
final JsonNode pages = jsonNode.path("query").path("pages");
// Iterate the pages
for (final JsonNode page : pages) {
// Work with the page object here...
System.out.println(page.get("pageid")); // -> 290
}
The JsonNode object is very flexible and contains various convenience functions for accessing the data. As shown in the example above the path() and get() methods are two ways of accessing the data. If you use get() the property MUST exist, if you use path the property MAY exist. Furthermore, there are multiple ways of iterating the sub-elements and the loop shown above is one way.
Take a look at the Jackson docs for more info.
The short answer is you can't, at least not in the current format with that abominable asterisk being present. Therefore, we will have to employ a bit of hackery here to get the job done, and I warn you upfront, it's not going to be pretty.
Firstly, copy that response, then go to http://www.jsonschema2pojo.org/ and paste it into the JSON textbox. After pasting it, change the asterisk to something more civilized, like "content". Select JSON (default is JSON Schema) for the Source Type, input your package and root class name respectively, and click JAR to generate the package with all the POJO's that map to this JSON. You could also click "Preview" and copy paste the code into your source files -- it's really up to you.
Now that we have a valid version of this JSON structure, we use Jackson to read it in. If your JSON String is called jsonResponse and the corresponding POJO class is MediaWiki, then you convert it with Jackson like this:
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
MediaWiki mw = objectMapper.readValue(profileJson, MediaWiki.class);
The key here is the FAIL_ON_UNKNOWN_PROPERTIES being set to false, which means it will ignore that asterisk, and create everything else for you.
Now, to actually grab whatever value was present for that asterisk and store it into our "content" attribute (or whatever else you wanted replace the asterisk with), you are going to have to parse this sucker out client-side and pass it as a separate input parameter, and to do that, you will have to yank it out by calling something like this:
var content = query.pages.290.revisions["*"];
This content parameter is passed and stored it into your POJO's content attribute.
I know it's a lot of work, and if anyone else has a more elegant solution, please share. As I said, mine was not going to be pretty. :-)
This looks like key value pair.
You can use map in order to deserialize key value pairs:
public class Query {
private Map<Integer, Page> pages;
public Map<Integer, Page> getPages() {
return pages;
}
public void setPages(Map<Integer, Page> pages) {
this.pages = pages;
}
}
Jackson handles such deserialization by default.
I have the following type of JSON I want to send to Java (I'm using Jersey and the default JSON Parser it comes with)
{ "something" : "1", "someOtherThing" : "2" , ... }
But instead of creating an Object with all these properties in Java, I would like to have a Single HashMap (or whatever) that will allow me to still have access to the Key and the Value
Is such a thing possible?
I don't really have any code that does the transformation, I use Jersey like this
#POST
#Path("/purchase")
#Produces(MediaType.APPLICATION_JSON)
#Consumes(MediaType.APPLICATION_JSON)
public StatusResult purchase(UserPurchaseRequest upr) {
}
If i put properties something and someOtherThing as Strings in my UserPurchaseRequest object, everything will come in fine, but I want to have everything in one structure (because I don't know how many values I will get, and I need their names as well)
Yes, it is possible. But still, it depends on what JSON java API you are using. For example using Jackson JSON you can create HashMap json string like this
ObjectMapper obj = new ObjectMapper();
String json = pbj.writeValue(<HashMap object>);
or vice-versa
HashMap obj = obj.readValue(json, HashMap.class);
Note - org.codehaus.jackson.map.ObjectMapper
You just need to add a Property to your Object like this
private HashMap<String,String> purchaseValues;
Jersey takes care of the rest, for some reason while you are debugging, most of the entries appear as null in the HashMap