Null values on swagger JSON file

Question

I'm having some trouble with the JSON swagger document generated through Java annotation (REST are exposed using Jersey, serialization is handled by Jackson). Looking at the generated Swagger, it includes null values, which cause the swagger UI to crash (the generated YAML doesn't have this issue).

Here an extract of the JSON:

{
  "swagger": "2.0",
  "info": { "description": null, "version": "1.0.0", "title": "", "termsOfService": null, "contact": null, "license": null },
  "host": "localhost:8080",
  "basePath": "/api",
  "tags": [ { "name": "dataset", "description": null, "externalDocs": null } ],
  "schemes": [ "http" ],
  "consumes": null,
  "produces": null,
  "paths": {
    "/dataset": {
      "get": {
        "tags": ["dataset"],
        "summary": "A dataset",
        "description": "All the available datasets",
        "operationId": "datasetGet",
        "schemes": null,
        "consumes": null,
        "produces": ["application/json"],
        "parameters": [],
        "responses": {
          "200": {
            "description": "Available datasets",
            "schema": {
              "type": "object",
              "format": null,
              "example": null,
              "xml": null,
              "position": null,
              "description": null,
              "title": null,
              "readOnly": null,
              "additionalProperties": {
                "type": "object",
                "format": null,
                "example": null,
                "xml": null,
                "position": null,
                "description": null,
                "title": null,
                "readOnly": null,
                "additionalProperties": {
                  "type": "object",
                  "format": null,
                  "example": null,
                  "xml": null,
                  "position": null,
                  "description": null,
                  "title": null,
                  "readOnly": null,
                  "properties": null
                }
              }
            },
            "examples": null,
            "headers": null
          }
        },
        "security": null,
        "externalDocs": null,
        "deprecated": null
      },
      "head": null,
      "post": null,
      "put": null,
      "delete": null,
      "options": null,
      "patch": null,
      "parameters": null
    }
  },
  "parameters": null,
  "responses": null,
  "externalDocs": null,
  "securityRequirement": null
}

This solution suggest to set the object mapper to omit the null value to solve the issue, but the reality is that I don't know where or how to easily access the mapper, and using NON_NULL annotations on the REST service class is pointless. A similar question has been asked as well, but I don't use Spring (so I don't have a place to set a custom mapper or setting for it).

I used Swagger in the past, but with different configuration settings (combined with wink, now I'm using Jersey) and didn't have this issue.

In case there is some obvious misconfiguration, this is my web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    version="3.0">

    <display-name>MyProject</display-name>

    <!-- Rest services mapping -->
    <servlet>
        <servlet-name>jersey</servlet-name>
        <servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
        <init-param>
        <param-name>jersey.config.server.provider.classnames</param-name>
        <param-value>
            io.swagger.jersey.listing.ApiListingResourceJSON,
            org.something.DatasetApi
        </param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>jersey</servlet-name>
        <url-pattern>/service/*</url-pattern>
    </servlet-mapping>

    <!-- Swagger config class -->
    <servlet>
        <servlet-name>DefaultJaxrsConfig</servlet-name>
        <servlet-class>io.swagger.jaxrs.config.DefaultJaxrsConfig</servlet-class>
        <init-param>
            <param-name>api.version</param-name>
            <param-value>1.0.0</param-value>
        </init-param>
        <init-param>
            <param-name>swagger.api.basepath</param-name>
            <param-value>http://localhost:8080/api</param-value>
        </init-param>
        <load-on-startup>2</load-on-startup>
    </servlet>

    <!-- Just the CORS filter -->
    <filter>
        <filter-name>ApiOriginFilter</filter-name>
        <filter-class>org.something.ApiOriginFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>ApiOriginFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

</web-app>

And this is my pom.xml (I'm always confused with swagger dependencies):

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">

    <groupId>org.something</groupId>
    <artifactId>my_project</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <modelVersion>4.0.0</modelVersion>
    <packaging>war</packaging>
    <name>My Project</name>
    <url>http://maven.apache.org</url>

    <build><finalName>MyProject</finalName></build>

    <properties>
        <maven.compiler.source>1.6</maven.compiler.source>
        <maven.compiler.target>1.6</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>

        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.0.13</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.8.1</version>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.glassfish.jersey.containers</groupId>
            <!-- if your container implements Servlet API older than 3.0, use "jersey-container-servlet-core" -->
            <artifactId>jersey-container-servlet</artifactId>
            <version>2.6</version>
        </dependency>
        <!-- Required only when you are using JAX-RS Client -->
        <dependency>
            <groupId>org.glassfish.jersey.core</groupId>
            <artifactId>jersey-client</artifactId>
            <version>2.6</version>
        </dependency>

        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <!-- scope>provided</scope -->
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.jaxrs</groupId>
            <artifactId>jackson-jaxrs-json-provider</artifactId>
            <version>2.4.2</version>
        </dependency>

        <dependency>
            <groupId>io.swagger</groupId>
            <artifactId>swagger-jersey2-jaxrs</artifactId>
            <version>1.5.4</version>
        </dependency>

    </dependencies>


</project>

Finally, for completeness, this is an extract of my Java class:

package org.something;

import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;
import io.swagger.annotations.ApiResponse;
import io.swagger.annotations.ApiResponses;

import java.util.Map;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.Response;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@Path("/dataset")
@Produces({ "application/json" })
@Api(value = "/dataset", description = "the dataset API")
public class DatasetApi  {

    private static final Logger log = LoggerFactory.getLogger(DatasetApi.class);

    @GET
    @ApiOperation(value = "All the available datasets.", notes = "Available datasets", response = Map.class, responseContainer = "Map")
    @ApiResponses(value = { @ApiResponse(code = 200, message = "Map of the available datasets", response = Map.class, responseContainer = "Map") })
    public Map<String, String> datasetGet() {
        try {
            log.info("Returning list of dataset");
            return Storage.datasets().getDatasets();
        } catch(Exception e) {
            log.info("Exception!", e);
            throw new WebJsonException(e, Response.Status.INTERNAL_SERVER_ERROR);
        }
    }

}

Ideally I'd like to have a class which either is called before or wrap the swagger logic (by declaring it in the web.xml) and does a simple mapper.setSerializationInclusion(Include.NON_NULL); which solves all the troubles, but I don't know if and how this is possible.

Answer 1

I've spent a week on that and I found the solution only few hours after I posted my question, sorry for that.

It seems that in web.xml was missing the io.swagger.jaxrs.listing.SwaggerSerializers class in the ServletContainer, the full portion is:

<servlet>
    <servlet-name>jersey</servlet-name>
    <servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
    <init-param>
    <param-name>jersey.config.server.provider.classnames</param-name>
    <param-value>
        io.swagger.jersey.listing.ApiListingResourceJSON,
        io.swagger.jaxrs.listing.SwaggerSerializers,
        org.something.DatasetApi
    </param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>

With the io.swagger.jaxrs.listing.SwaggerSerializers bit everything is now working as expected.