Generate Json Schema from POJO with a twist

Question

What I have:

I'm generating a JSON schema from a pojo. My code to generate the schema looks like so:

ObjectMapper mapper = new ObjectMapper();
TitleSchemaFactoryWrapper visitor = new TitleSchemaFactoryWrapper();
mapper.acceptJsonFormatVisitor(clazz, visitor);
JsonSchema schema = visitor.finalSchema();
schemas.put(clazz, mapper.writerWithDefaultPrettyPrinter().writeValueAsString(schema));

I'm generating several schemas via the above code. One of the pojos has an internal embedded enum to limit the possible values, like so:

public class MyClass {

    @JsonProperty("name")
    private String name;
    @JsonProperty("startDayOfWeek")
    private MyClass.StartDayOfWeek startDayOfWeek;
    /**
     * The ID of a timezone returned by the timezones route.
     * 
     */
    @JsonProperty("timezone")
    private String timezone;
    @JsonIgnore
    private Map<String, Object> additionalProperties = new HashMap<String, Object>();

    /**
     * 
     * @return
     *     The startDayOfWeek
     */
    @JsonProperty("startDayOfWeek")
    public MyClass.StartDayOfWeek getStartDayOfWeek() {
        return startDayOfWeek;
    }

    /**
     * 
     * @param startDayOfWeek
     *     The startDayOfWeek
     */
    @JsonProperty("startDayOfWeek")
    public void setStartDayOfWeek(MyClass.StartDayOfWeek startDayOfWeek) {
        this.startDayOfWeek = startDayOfWeek;
    }

    public static enum StartDayOfWeek {

        MONDAY("Monday"),
        TUESDAY("Tuesday"),
        WEDNESDAY("Wednesday"),
        THURSDAY("Thursday"),
        FRIDAY("Friday"),
        SATURDAY("Saturday"),
        SUNDAY("Sunday");
        private final String value;
        private static Map<String, MyClass.StartDayOfWeek> constants = new HashMap<String, MyClass.StartDayOfWeek>();

        static {
            for (MyClass.StartDayOfWeek c: values()) {
                constants.put(c.value, c);
            }
        }

        private StartDayOfWeek(String value) {
            this.value = value;
        }

        @JsonValue
        @Override
        public String toString() {
            return this.value;
        }

        @JsonCreator
        public static MyClass.StartDayOfWeek fromValue(String value) {
            MyClass.StartDayOfWeek constant = constants.get(value);
            if (constant == null) {
                throw new IllegalArgumentException(value);
            } else {
                return constant;
            }
        }

    }

}

The above code should limit the possible String values in the JSON data that's passed around to "Monday", "Tuesday", "Wednesday", etc.

When I run the schema generator on the code in question, I expect to get something like the following schema:

{
  "type" : "object",
  "javaType" : "my.package.MyClass",
  "properties": {
    "startDayOfWeek" : {
      "type" : "string",
      "enum" : [ "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday" ]
    }
  }
}

but instead I'm getting this:

{
  "type" : "object",
  "id" : "urn:jsonschema:my:package:MyClass",
  "title" : "Lmy/package/MyClass;",
  "properties" : {
    "startDayOfWeek" : {
      "type" : "string"
    }
  }
}

I've done some digging in the Jackson Schema Module source code and figured out that what's happening is Jackson's using ".toString()" as the default serialization method for enum types, but what I need it to do instead is create the line that looks like this based on StartDayOfWeek.values():

"enum" : [ "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday" ]

Does anyone know how to do that?

Given that I get a NPE when following their example of use, the fact that there hasn't been an update to the project in 6 months and the fact that it's still apparently in a beta state, I don't think that's a very good option — StormeHawke, Jan 09 '15 at 17:13
Do you alread use a custom deserializer to properly deserialize (i.e. as enum, not as String) days of week values? — user3159253, Jan 09 '15 at 19:38
Also enums are supported in the json spec: http://jsonary.com/documentation/json-schema/?section=keywords/General%20keywords#keywords/General%20keywords/01%20-%20enum — StormeHawke, Jan 09 '15 at 19:43

score 19 · Answer 1 · answered Jan 13 '15 at 01:45

It seems to not be possible using the instructions I found using databind. However I found another jackson module that seems to do the trick nicely. Oddly several of the objects are named the same.

TLDR: use objects from the org.codehaus.jackson.map package rather than the com.fasterxml.jackson.databind package. If you're following the instructions on this page then you're doing it wrong. Just use the jackson-mapper module instead.

Here's the code for future googlers:

private static String getJsonSchema(Class clazz) throws IOException {
    org.codehaus.jackson.map.ObjectMapper mapper = new ObjectMapper();
    //There are other configuration options you can set.  This is the one I needed.
    mapper.configure(SerializationConfig.Feature.WRITE_ENUMS_USING_TO_STRING, true);

    JsonSchema schema = mapper.generateJsonSchema(clazz);

    return mapper.writerWithDefaultPrettyPrinter().writeValueAsString(schema);
}

I think so. I just know this worked for me where other attempts didn't — StormeHawke, Feb 17 '16 at 15:25

score 9 · Accepted Answer · answered Mar 09 '16 at 20:39

Storme's answer references org.codehaus, which is an older version of jackson. The following is similar but uses fasterxml (newer version).

Pom:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.7.1</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.7.1</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-annotations</artifactId>
    <version>2.7.1</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.module</groupId>
    <artifactId>jackson-module-jsonSchema</artifactId>
    <version>2.1.0</version>
</dependency>

Code:

import ...TargetClass;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.jsonschema.JsonSchema;

import java.io.IOException;

public final class JsonSchemaGenerator {

    private JsonSchemaGenerator() { };

    public static void main(String[] args) throws IOException {
        System.out.println(JsonSchemaGenerator.getJsonSchema(TargetClass.class));
    }

    public static String getJsonSchema(Class clazz) throws IOException {
        ObjectMapper mapper = new ObjectMapper();
        mapper.configure(SerializationFeature.WRITE_ENUMS_USING_TO_STRING, true);
        JsonSchema schema = mapper.generateJsonSchema(clazz);
        return mapper.writerWithDefaultPrettyPrinter().writeValueAsString(schema);
    }

}

Note that both org.codehaus.jackson and com.fasterxml.jackson will generate v3 version of json schema and not v4. More details at - https://github.com/FasterXML/jackson-module-jsonSchema/issues/9 — Mohit Chugh, Apr 18 '16 at 23:16

score 1 · Answer 3 · answered May 27 '19 at 15:13

1

If someone comes here and wants to support the newest draft version in his code.

Look here for your preferred language: https://json-schema.org/implementations.html

answered May 27 '19 at 15:13

rufreakde

542
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Generate Json Schema from POJO with a twist

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