Written by Jamie Tanna
on 
CC-BY-NC-SA-4.0 Apache-2.0
2 mins

Adding both an ObjectMapper and a YAMLMapper to Spring Boot

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There are times where you may want to interact with both JSON and YAML in your Spring Boot services, for instance if your HTTP layer is JSON, and you want to read YAML files from some data source.

The below is based on a Spring Boot 2.6.2 service, with Jackson v2.13.1.

If we assume that we have the following configuration class:

import org.springframework.context.annotation.Configuration;

@Configuration
public class SpringConfiguration {
}

And when we send an API request, we get the following response:

HTTP/1.1 200
X-Content-Type-Options: nosniff
X-XSS-Protection: 1; mode=block
Cache-Control: no-cache, no-store, max-age=0, must-revalidate
Pragma: no-cache
Expires: 0
X-Frame-Options: DENY
Content-Type: application/vnd.spring-boot.actuator.v3+json
Transfer-Encoding: chunked
Date: Mon, 10 Jan 2022 17:28:05 GMT

{
  "java": {
    "jvm": {
      "name": "OpenJDK 64-Bit Server VM",
      "vendor": "Oracle Corporation",
      "version": "17.0.1+12-39"
    },
    "runtime": {
      "name": "OpenJDK Runtime Environment",
      "version": "17.0.1+12-39"
    },
    "vendor": "Oracle Corporation",
    "version": "17.0.1"
  },
  "test": "hello"
}

Now, if we add a YAMLMapper:

import com.fasterxml.jackson.dataformat.yaml.YAMLMapper;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class SpringConfiguration {
  @Bean
  public YAMLMapper yamlMapper() {
    return new YAMLMapper();
  }
}

We get the following back from the API:

HTTP/1.1 200
X-Content-Type-Options: nosniff
X-XSS-Protection: 1; mode=block
Cache-Control: no-cache, no-store, max-age=0, must-revalidate
Pragma: no-cache
Expires: 0
X-Frame-Options: DENY
Content-Type: application/vnd.spring-boot.actuator.v3+json
Transfer-Encoding: chunked
Date: Mon, 10 Jan 2022 17:30:16 GMT

---
test: "hello"
java:
  vendor: "Oracle Corporation"
  version: "17.0.1"
  runtime:
    name: "OpenJDK Runtime Environment"
    version: "17.0.1+12-39"
  jvm:
    name: "OpenJDK 64-Bit Server VM"
    vendor: "Oracle Corporation"
    version: "17.0.1+12-39"

Which hopefully you can see does not look right, as it's rendering as YAML, although the content-type describes itself as JSON.

This is because the YAMLMapper extends ObjectMapper, and Spring Boot doesn't autoconfigure an ObjectMapper for us, as there's already an ObjectMapper (the YAMLMapper) available as a bean.

To solve this, we can make sure that we explicitly opt-in to the Jackson autoconfiguration which enables the creation of the ObjectMapper, as well as the existing YAMLMapper:

import com.fasterxml.jackson.dataformat.yaml.YAMLMapper;

import org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

@Configuration
@Import(JacksonAutoConfiguration.class})
public class SpringConfiguration {
  @Bean
  public YAMLMapper yamlMapper() {
    return new YAMLMapper();
  }
}

This now returns us a valid JSON response, again, and the two beans can coexist safely.

Written by Jamie Tanna's profile image Jamie Tanna on , and last updated on .

Content for this article is shared under the terms of the Creative Commons Attribution Non Commercial Share Alike 4.0 International, and code is shared under the Apache License 2.0.

#blogumentation #java #jackson #spring-boot.

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