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OpenAPI generated classes and applying JsonView for the generated classes

I'm using OpenAPI to define my api and resources and the classes are auto-generated. I've been looking for a way to have a single model and multiple representations so am looking at JsonViews or Filters.
Is there any way to add JsonViews to the properties of the generated model classes ? I haven't been able to figure it out.

I've found a way to arrive to the intended behaviour without modifying the generated classes.
The steps are :
create a subclass of the generated class
add the additional properties that are to be internal fields into the subclass
configure the ObjectMapper to MapperFeature.DEFAULT_VIEW_INCLUSION = true, which means that any properties without the JsonView model will be included in Serialization (the defualt is false)
add JsonView to the subclass properties
#JsonView(Views.Private.class)
and different JsonView at the controller endpoints
#JsonView(Views.Public.class)
With the above in place the controller endpoints will Serialise only the fields of the generated model, since they do not have the JsonView, and the fields with the JsonView on the subclass will remin internal to the application.
Code snippet of the ObjectMapper config :
#Bean
public ObjectMapper objectMapper() {
ObjectMapper mapper = new ObjectMapper();
mapper.configure(MapperFeature.DEFAULT_VIEW_INCLUSION, true);
return mapper;
}

Java Jackson Always Serialize One Type As Another

Is there a way to tell Jackson to always serialize one type to another. In my case I would like to always serialize Long to String. Right now whenever there is an object with a Long property we have to annotate it with #JsonSerialize(using=ToStringSerializer.class). This is tedious and easy to forget.
I would like to be able to configure the Jackson object mapper to always convert Long to String in the spring boot bean creation.

IMHO, multiple options are there.
I
com.fasterxml.jackson.databind.ser.std.StdSerializer implementation that can be set to your ObjectMapper in the spring context.
#Bean
public Jackson2ObjectMapperBuilder objectMapperBuilder() {
Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();
....
builder.serializerByType(<type>, <your custom serializer>);
return builder;
}
As for the custom serializer, you can extend the above-mentioned class StdSerializer.
II
spring.jackson.generator.write-numbers-as-strings=true
Note
Be aware of that Feature.WRITE_NUMBERS_AS_STRINGS has deprecated Since 2.10 of jackson version.
I hope it helps.

This can be done using this serialization feature.
jsonGenerator.configure(Feature.WRITE_NUMBERS_AS_STRINGS,true);
http://fasterxml.github.io/jackson-core/javadoc/2.10/com/fasterxml/jackson/core/json/JsonWriteFeature.html#WRITE_NUMBERS_AS_STRINGS

How can I read yaml (Configuration) file as JSON in dropwizard?

I want to parse configuration yaml file as a JSON Object in Dropwizard.
As in Python and Ruby we can directly read yaml file as JSON:
require 'yaml'
conf = YAML.load_file('some.yml')
puts conf.<some key>
I want to follow the same protocol and do not want to make a separate class to map the yaml structure, but not sure how to achieve it in Java.

If I understand correctly, instead of defining a class to represent the structure of you JSON or YAML, you want to retrieve an object that gives you access to the JSON object in a generic manner.
Even though this is a bit contrary to the way dropwizard wants to do things (i.e., having typed class to access configuration data), it is relatively easy:
You need an instance of Jackson ObjectMapper: the one provided by dropwizard or you own, YAML-aware (see example below).
You can call the readTree method to transform an input into a JsonNode which gives you access to the JSON/YAML object in memory.
See ObjectMapper#readTree and similar methods.
ObjectMapper mapper = new ObjectMapper(new YAMLFactory());
JsonNode json = mapper.readTree(new File("some.yml"));
System.out.println(json.get("test"));

You can just use the Configuration object from DropWizard, either the default or a custom one that has been created to hold additional parameters. This object is available on the Application class, under the "run" method in particular. Using the DW configuration example:
public class ExampleConfiguration extends Configuration {
#Valid
#NotNull
private MessageQueueFactory messageQueue = new MessageQueueFactory();
#JsonProperty("messageQueue")
public MessageQueueFactory getMessageQueueFactory() {
return messageQueue;
}
#JsonProperty("messageQueue")
public void setMessageQueueFactory(MessageQueueFactory factory) {
this.messageQueue = factory;
}
}
You can get/set all the attributes from YAML file as below:
public class MyApplication extends Application<ExampleConfiguration> {
...
public void run(ExampleConfiguration configuration, Environment environment) {
configuration.getMessageQueueFactory();
configuration.getServerFactory();
}
}

Jackson can both parse yaml and format to JSON.
See an example here.

Jackson changes order of private variables when changing to json? [duplicate]

I'm implementing a RESTful web service where user has to send a signed verification token along with the request so that I could ensure that the request has not been tampered by a middle man. My current implementation is as follows.
Verification token is a VerifData object serialized into a String and then hashed and encrypted.
class VerifData {
int prop1;
int prop2;
}
In my service, I put data to be serialized into an instance of VerifData and then serialize it using Jackson ObjectMapper and passed along to the verification engine along with the verification token.
VerfiData verifData = new VerifData(12345, 67890);
ObjectMapper mapper = new ObjectMapper();
String verifCodeGenerated = mapper.writeValueAsString(verifData);
But it seems that each time the application container is started, the order of properties being mapped into a string by ObjectMapper changes.
Ex: one time it would be
{"prop1":12345,"prop2":67890}
and another time it would be
{"prop2":67890,"prop1":12345}
So if client has serialized the VerifData instance as into the first String, there is 50% chance of it being failed even though it is correct.
Is there a way to get around this? Can I specify the order of properties to map by ObjectMapper (like in ascending order)? Or is there any other way to best implement this verification step. Both client and server implementations are developed by me. I use Java Security API for signing and verifying.

The annotations are useful, but can be a pain to apply everywhere. You can configure your whole ObjectMapper to work this way with
Current Jackson versions:
objectMapper.configure(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY, true)
Older Jackson versions:
objectMapper.configure(SerializationConfig.Feature.SORT_PROPERTIES_ALPHABETICALLY, true);

From the Jackson Annotations documentation:
// ensure that "id" and "name" are output before other properties
#JsonPropertyOrder({ "id", "name" })
// order any properties that don't have explicit setting using alphabetic order
#JsonPropertyOrder(alphabetic=true)

The following 2 ObjectMapper configuration are required:
ObjectMapper.configure(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY, true)
or
ObjectMapper.enable(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY)
defines the property serialization order used for POJO fields
Note: does not apply to java.util.Map serialization!
and
ObjectMapper.configure(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS, true)
or
ObjectMapper.enable(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS)
Feature that determines whether java.util.Map entries are first sorted by key before serialization
Spring Boot config example (yaml):
spring:
jackson:
mapper:
SORT_PROPERTIES_ALPHABETICALLY: true
serialization:
ORDER_MAP_ENTRIES_BY_KEYS: true

In Spring Boot you can add this behaviour globally by adding the following to your Application entry point class:
#Bean
public Jackson2ObjectMapperBuilder objectMapperBuilder() {
Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();
builder.featuresToEnable(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY);
return builder;
}

In Jackson 2.x, which you are probably using today, use:
ObjectMapper mapper = new ObjectMapper();
mapper.configure(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS, true);
If you care about looks, you may also consider SerializationFeature.INDENT_OUTPUT as well.
Note that you must serialize Maps or Objects for this to sort correctly. If you serialize a JsonNode for example (from readTree), that won't be properly indented.
Example
import com.fasterxml.jackson.databind.*;
ObjectMapper mapper = new ObjectMapper();
mapper.configure(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS, true);
mapper.configure(SerializationFeature.INDENT_OUTPUT, true);
String input = "{\"hello\": {\"cruel\" : \"world\"} }";
Object pojo = mapper.readValue(input, Object.class);
System.out.println(mapper.writeValueAsString(pojo));
results in:
{
"hello" : {
"cruel" : "world"
}
}

There is an easier way in Spring Boot by specifying a property (in application.properties for example:
spring.jackson.mapper.sort_properties_alphabetically=true

From Duncan McGregor's answer:
Its better to use it like this:
objectMapper.configure(SerializationConfig.Feature.SORT_PROPERTIES_ALPHABETICALLY, true);
as MapperFeature is for XMLs and comes with jackson-databind which is not required...

I discovered yet another way today in case alphabetic is not your desired sorting order. It turns out adding a #JsonProperty annotation on a field places it last when writing if the rest of the fields are not annotated. I discovered that when I wanted to specify a property name which did not conform to java naming conventions.
By Adding an index attribute you can define the order. Lowest index is placed first.
#JsonProperty(index=20)
String prop1;
#JsonProperty(index=10)
String prop2;
Would render:
{"prop2": "valueProp2", "prop1": "valueProp1"}

You can use mix-in and specify the order of properties as you like:
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;
#Component
public final class ObjectMapperUtils {
private static final ObjectMapper MAPPER = new ObjectMapper();
static {
MAPPER.addMixIn(Object.class, IdFirst.class);
}
#Bean
public ObjectMapper objectMapper() {
return MAPPER;
}
#JsonPropertyOrder({"id", "...", "..."})
private abstract static class IdFirst {}
}

I realize this is an old thread, but since I was looking or an answer and landed here, some additional info could be handy for other people.
The #JsonProperty annotation I am using currently (jackson-annotations-2.11.2) accepts, besides the "value" argument, an "index" (numeric) argument that specifies the order of the fields during serialization.

Instead of using flag argument:
objectMapper.enable(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY);

As #Gary Rowe mentioned, we can use Jackson2ObjectMapperBuilder to sort the properties globally.
However for this to work, you must have Jackson2ObjectMapperBuilder in your classpath. It is not part of the Jackson library.
As per this documentation, spring-web dependency has Jackson2ObjectMapperBuilder file and should be in your classpath.
#Bean
public Jackson2ObjectMapperBuilder objectMapperBuilder() {
Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();
builder.featuresToEnable(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY);
return builder;
}
You can refer to this for other possible solutions

Specifying the field naming policy for Jackson

I have question related to bean to json serialziation/deserialization using Jackson. Previously I have used GSON to do that, but now I am faced with a project that already depends on Jackson and I would prefer not to introduce new dependency if I can do with what I already have at hand.
So imagine I have a bean like:
class ExampleBean {
private String firstField;
private String secondField;
// respective getters and setters
}
And then Jackson serializes it to:
{
"firstField": "<first_field_value>",
"secondField": "<second_field_value>"
}
I am using the following code to produce the above result:
ExampleBean bean;
...
ObjectMapper mapper = new ObjectMapper();
mapper.writeValue(outStream, bean);
However I would like (am expected) to get the following serialization:
{
"first_field": "<first_field_value>",
"second_field": "<second_field_value>"
}
I have deliberately simplified my example, but I have big hierarchy of beans that I want to serialize and I want to specify that the serialized attributes should always be in snake_style (that is with underscores) and the corresponding bean fields should always be camelCased. Is there any way I can enforce such field /attribute naming policies and use them without annotating the corresponding attribute for every field?

And yes I found it (it turned out that after 2 hours of searching I had been only 30 minutes away from finding it):
ObjectMapper mapper = new ObjectMapper();
mapper.setPropertyNamingStrategy(
PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES);
mapper.writeValue(outStream, bean);
Hopefully this will turn out to be helpful to somebody else too.

Now CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES is the deprecated strategy use SNAKE_CASE instead
ObjectMapper mapper = new ObjectMapper();
mapper.setPropertyNamingStrategy(
PropertyNamingStrategy.SNAKE_CASE);
mapper.writeValue(outStream, bean);