In the last tutorial, we got familiar with creating a custom HTTPMessageConverter. In this tutorial, we will create another one. This HTTPMessageConverter will convert request body containing YAML content to user defined object and vice-versa. We are going to use SnakeYAML, which is a Java based processor for parsing YAML data to/from Java Objects.
Example
Creating the Controller
package com.logicbig.example;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;
import java.util.HashMap;
import java.util.Map;
@Controller
public class ExampleController {
private Map<String, Employee> employeeMap
= new HashMap<>();
@PostMapping(
value = "/newEmployee",
consumes = "text/yaml",
produces = MediaType.TEXT_PLAIN_VALUE)
@ResponseBody
@ResponseStatus(HttpStatus.OK)
public String handleRequestPost(@RequestBody Employee employee) {
employeeMap.put(employee.getId(), employee);
return String.format("Employee saved: %s", employee.getName());
}
@GetMapping(
value = "/employee",
produces = "text/yaml")
@ResponseBody
@ResponseStatus(HttpStatus.OK)
public Employee handleRequestGet(@RequestParam("id") String id) {
return employeeMap.get(id);
}
}
package com.logicbig.example;
public class Employee {
private String id;
private String name;
private String phoneNumber;
.............
}
Creating the Converter
package com.logicbig.example;
import org.springframework.http.HttpInputMessage;
import org.springframework.http.HttpOutputMessage;
import org.springframework.http.MediaType;
import org.springframework.http.converter.AbstractHttpMessageConverter;
import org.springframework.http.converter.HttpMessageNotReadableException;
import org.springframework.http.converter.HttpMessageNotWritableException;
import org.yaml.snakeyaml.DumperOptions;
import org.yaml.snakeyaml.Yaml;
import org.yaml.snakeyaml.nodes.Tag;
import org.yaml.snakeyaml.representer.Representer;
import java.io.IOException;
import java.io.OutputStreamWriter;
public class YamlHttpMessageConverter<T>
extends AbstractHttpMessageConverter<T> {
public YamlHttpMessageConverter () {
super(new MediaType("text", "yaml"));
}
@Override
protected boolean supports (Class<?> clazz) {
return true;
}
@Override
protected T readInternal (Class<? extends T> clazz, HttpInputMessage inputMessage)
throws IOException, HttpMessageNotReadableException {
Yaml yaml = new Yaml();
T t = yaml.loadAs(inputMessage.getBody(), clazz);
return t;
}
@Override
protected void writeInternal (T t, HttpOutputMessage outputMessage)
throws IOException, HttpMessageNotWritableException {
DumperOptions options = new DumperOptions();
options.setDefaultFlowStyle(DumperOptions.FlowStyle.BLOCK);
Representer representer = new Representer(options);
representer.addClassTag(Employee.class, Tag.MAP);
Yaml yaml = new Yaml(representer, options);
OutputStreamWriter writer = new OutputStreamWriter(outputMessage.getBody());
yaml.dump(t, writer);
writer.close();
}
}
Registering the Converter
package com.logicbig.example;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import org.springframework.web.servlet.config.annotation.ViewResolverRegistry;
import java.util.List;
@EnableWebMvc
@ComponentScan("com.logicbig.example")
public class AppConfig implements WebMvcConfigurer {
@Override
public void extendMessageConverters (List<HttpMessageConverter<?>> converters) {
converters.add(new YamlHttpMessageConverter<>());
}
}
Integration Test
package com.logicbig.example;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.MediaType;
import org.springframework.test.context.junit.jupiter.web.SpringJUnitWebConfig;
import org.springframework.test.web.servlet.assertj.MockMvcTester;
import org.springframework.web.context.WebApplicationContext;
import static org.assertj.core.api.Assertions.assertThat;
@SpringJUnitWebConfig(AppConfig.class)
public class ControllerTest {
@Autowired
private WebApplicationContext wac;
private MockMvcTester mockMvcTester;
@BeforeEach
public void setup() {
this.mockMvcTester = MockMvcTester.from(this.wac);
}
@Test
public void testConsumerController() {
String employeeInYml = getNewEmployeeInYaml();
assertThat(this.mockMvcTester.post().uri("/newEmployee")
.contentType("text/yaml")
.accept(MediaType.TEXT_PLAIN_VALUE)
.content(employeeInYml)
.exchange())
.hasStatusOk()
.bodyText().isEqualTo("Employee saved: Tina");
assertThat(this.mockMvcTester.get().uri("/employee")
.accept("text/yaml")
.param("id", "1")
.exchange())
.hasStatusOk()
.bodyText().isEqualTo(employeeInYml);
}
public String getNewEmployeeInYaml() {
return "id: '1'\nname: Tina\nphoneNumber: 111-111-1111\n";
}
}
mvn clean test -Dtest="ControllerTest" Output$ mvn clean test -Dtest="ControllerTest"
[INFO] Scanning for projects...
[WARNING]
[WARNING] Some problems were encountered while building the effective model for com.logicbig.example:custom-message-converter-yaml:war:1.0-SNAPSHOT
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-war-plugin is missing. @ line 51, column 21
[WARNING]
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING]
[INFO]
[INFO] ---------< com.logicbig.example:custom-message-converter-yaml >---------
[INFO] Building custom-message-converter-yaml 1.0-SNAPSHOT
[INFO] from pom.xml
[INFO] --------------------------------[ war ]---------------------------------
[INFO]
[INFO] --- clean:3.2.0:clean (default-clean) @ custom-message-converter-yaml ---
[INFO] Deleting D:\example-projects\spring-mvc\custom-message-converter-yaml\target
[INFO]
[INFO] --- resources:3.3.1:resources (default-resources) @ custom-message-converter-yaml ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory D:\example-projects\spring-mvc\custom-message-converter-yaml\src\main\resources
[INFO]
[INFO] --- compiler:3.3:compile (default-compile) @ custom-message-converter-yaml ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 4 source files to D:\example-projects\spring-mvc\custom-message-converter-yaml\target\classes
[INFO]
[INFO] --- resources:3.3.1:testResources (default-testResources) @ custom-message-converter-yaml ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory D:\example-projects\spring-mvc\custom-message-converter-yaml\src\test\resources
[INFO]
[INFO] --- compiler:3.3:testCompile (default-testCompile) @ custom-message-converter-yaml ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 2 source files to D:\example-projects\spring-mvc\custom-message-converter-yaml\target\test-classes
[INFO]
[INFO] --- surefire:3.2.5:test (default-test) @ custom-message-converter-yaml ---
[INFO] Using auto detected provider org.apache.maven.surefire.junitplatform.JUnitPlatformProvider
[WARNING] file.encoding cannot be set as system property, use <argLine>-Dfile.encoding=...</argLine> instead
[INFO]
[INFO] -------------------------------------------------------
[INFO] T E S T S
[INFO] -------------------------------------------------------
[INFO] Running com.logicbig.example.ControllerTest
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 2.249 s -- in com.logicbig.example.ControllerTest
[INFO]
[INFO] Results:
[INFO]
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 7.944 s
[INFO] Finished at: 2026-07-25T15:50:07+08:00
[INFO] ------------------------------------------------------------------------
INFO: Completed initialization in 3 ms
Example ProjectDependencies and Technologies Used: - spring-webmvc 7.0.6 (Spring Web MVC)
Version Compatibility: 4.1.3.RELEASE - 7.0.6 Version compatibilities of spring-webmvc with this example: Versions in green have been tested.
- spring-test 7.0.6 (Spring TestContext Framework)
- jakarta.servlet-api 6.1.0 (Jakarta Servlet API documentation)
- junit-jupiter-engine 6.0.3 (Module "junit-jupiter-engine" of JUnit)
- snakeyaml 2.6 (YAML 1.1 parser and emitter for Java)
- hamcrest 3.0 (Core API and libraries of hamcrest matcher framework)
- assertj-core 3.26.3 (Rich and fluent assertions for testing in Java)
- JDK 25
- Maven 3.9.11
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