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Module for generating JSON Schema (v3) definitions from POJOs
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README.md

Jackson JSON Schema Module

This module supports the creation of a JSON Schema (v3) This module is intended to be an upgrade path from the hardcoded JSON Schema generation currently in jackson databind (pre 2.1), in order to allow for the generation of arbitrary formats specifying the expected output from a particular jackson enabled application.

Thus, it might feasibly be extended or mirrored to produce xml or even google closure interfaces or classes in addition to the current json schema format.

Note that since JSON Schema draft version 3 and 4 are incompatible, this module CAN NOT, as-is, support v4. There is another module mbknor-jackson-jsonSchema that does support v4, however.

It is possible that in future this repo could have 2 different modules; one for v3, another v4. And if necessary, more if future revisions also prove incompatible.

Status

Build Status Maven Central Javadoc

Version 2.4 was considered the first stable version of the module.

Example Usage

(from TestGenerateJsonSchema)

simply add a dependency (this is from my gradle config) "com.fasterxml.jackson.module:jackson-module-jsonSchema:2.9.0" and for gradle, at least, you can simply add mavenLocal() to your repositories. Maven should resolve the dependency from its local repo transparently.

ObjectMapper mapper = new ObjectMapper();
// configure mapper, if necessary, then create schema generator
JsonSchemaGenerator schemaGen = new JsonSchemaGenerator(mapper);
JsonSchema schema = schemaGen.generateSchema(SimpleBean.class);

This will yield a java pojo representing a JSON Schema, which can itself easily be serialized with jackson, or configured with java. Customizing the generation should be simply a matter of locating the particular stage of generation you want to override, and replacing or extending that particular object in the dependency injection cycle in schemafactory wrapper.

Adding Property Processing

See com.fasterxml.jackson.module.jsonSchema.customProperties.TitleSchemaFactoryWrapper for an example of writing custom schema properties.

Required Fields

JSON Schema has the ability to mark fields as required. This module supports this via the @JsonProperty(required = true) field annotation.

JsonSchema Hypermedia support

Generic support

Current implementation is partial for IETF published draft v4 (http://json-schema.org/latest/json-schema-hypermedia.html).

Currently 2 aspects of IETF supported:

  • pathStart - URI that defines what the instance's URI MUST start with in order to validate.
  • links - associated Link Description Objects with instances.

You can enable HypermediaSupport using com.fasterxml.jackson.module.jsonSchema.customProperties.HyperSchemaFactoryWrapper. Example:

HyperSchemaFactoryWrapper personVisitor = new HyperSchemaFactoryWrapper();
ObjectMapper mapper = new ObjectMapper();
mapper.acceptJsonFormatVisitor(Person.class, personVisitor);
JsonSchema personSchema = personVisitor.finalSchema();

By default all default values for Link Description Object are ignored in the output (method = GET, enctype = application/json, mediaType = application/json), to enable default setIgnoreDefaults(true)

Describing JSON hyper-schema

You can describe hyperlinks, using annotations @JsonHyperSchema & @Link

 public class Pet {
     public String genus;
 }

 @JsonHyperSchema(
     pathStart = "http://localhost:8080/persons/",
     links = {
         @Link(href = "{name}", rel = "self"),
         @Link(href = "{name}/pet", rel = "pet", targetSchema = Pet.class)
 })
 public class Person {
     public String name;
     public String hat;
 }

Would generate following values:

{
  "type" : "object",
  "pathStart" : "http://localhost:8080/persons/",
  "links" : [ {
    "href" : "http://localhost:8080/persons/{name}",
    "rel" : "self"
  }, {
    "href" : "http://localhost:8080/persons/{name}/pet",
    "rel" : "pet",
    "targetSchema" : {
      "type" : "object",
      "properties" : {
        "genus" : {
          "type" : "string"
        }
      }
    }
  } ],
  "properties" : {
    "name" : {
      "type" : "string"
    },
    "hat" : {
      "type" : "string"
    }
  }
}

More

Check out Project Wiki for more information (javadocs, downloads).

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