Jackson: generate schemas with references

问题:

When using Jackson's JSON schema module, instead of serializing the complete graph I'd like to stop whenever one of my model classes is encountered, and use the class name to insert a $ref for another schema. Can you guide me to the right place in the jackson-module-jsonSchema source to start tinkering?

Here's some code to illustrate the issue:

public static class Zoo {
    public String name;
    public List<Animal> animals;
}

public static class Animal {
    public String species;
}

public static void main(String[] args) throws Exception {
    SchemaFactoryWrapper visitor = new SchemaFactoryWrapper();

    ObjectMapper mapper = objectMapperFactory.getMapper();
    mapper.acceptJsonFormatVisitor(mapper.constructType(Zoo.class), visitor);
    JsonSchema jsonSchema = visitor.finalSchema();

    System.out.println(mapper.writeValueAsString(jsonSchema));
}

Output:

{
  "type" : "object",
  "properties" : {
    "animals" : {
      "type" : "array",
      "items" : {
        "type" : "object",
        "properties" : {          <---- Animal schema is inlined :-(
          "species" : {
            "type" : "string"
          }
        }
      }
    },
    "name" : {
      "type" : "string"
    }
  }
}

DESIRED Output:

{
  "type" : "object",
  "properties" : {
    "animals" : {
      "type" : "array",
      "items" : {
        "$ref" : "#Animal"       <----  Reference to another schema :-)
      }
    },
    "name" : {
      "type" : "string"
    }
  }
}

回答1:

Here's a custom SchemaFactoryWrapper that solves the problem. No guarantees, but it seems to work pretty well with Jackson 2.4.3.

UPDATE: With Jackson 2.5 onward it's a lot easier. Now you can specify a custom VisitorContext.

回答2:

You can use the HyperSchemaFactoryWrapper instead of SchemaFactoryWrapper. In this way you will get urn reference for nested entities:

HyperSchemaFactoryWrapper visitor= new HyperSchemaFactoryWrapper();
ObjectMapper mapper = objectMapperFactory.getMapper();
mapper.acceptJsonFormatVisitor(mapper.constructType(Zoo.class), visitor);
JsonSchema jsonSchema = visitor.finalSchema();

System.out.println(mapper.writeValueAsString(jsonSchema));

回答3:

You can try and use following code -

    ObjectMapper MAPPER = new ObjectMapper();
    SchemaFactoryWrapper visitor = new SchemaFactoryWrapper();

    JsonSchemaGenerator generator = new JsonSchemaGenerator(MAPPER);

    JsonSchema jsonSchema = generator.generateSchema(MyBean.class);

    System.out.println(MAPPER.writeValueAsString(jsonSchema));

But your expected output is not valid, it won't say $ref, unless it has specified the schema for "Animals" at least once.

{
    "type": "object",
    "id": "urn:jsonschema:com:tibco:tea:agent:Zoo",
    "properties": {
        "animals": {
            "type": "array",
            "items": {
                "type": "object",
                "id": "urn:jsonschema:com:tibco:tea:agent:Animal",
                "properties": {
                    "species": {
                        "type": "string"
                    }
                }
            }
        },
        "name": {
            "type": "string"
        }
    }
}