This example demonstrates how to create and register a custom HttpMessageConverter.
Backing Java Object
In this example we want to convert a custom message body to the Report object. The converter will expect that the first line of message body will be the report name and the rest will be the report content.
package com.logicbig.example;
public class Report {
private int id;
private String reportName;
private String content;
.............
}
Implementing HttpMessageConverter
In following implementation, we are extending AbstractHttpMessageConverter (instead of directly implementing HttpMessageConverter) that's because to avoid repetitive, error-prone plumbing that every HttpMessageConverter implementation would otherwise need to duplicate.
AbstractHttpMessageConverter adds support for setting supported MediaTypes, through the supportedMediaTypes bean property. It also adds support for Content-Type and Content-Length when writing to output messages.
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 java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Scanner;
public class ReportConverter
extends AbstractHttpMessageConverter<Report> {
public ReportConverter() {
super(new MediaType("text", "report"));
}
@Override
protected boolean supports(Class<?> clazz) {
return Report.class.isAssignableFrom(clazz);
}
@Override
protected Report readInternal(Class<? extends Report> clazz,
HttpInputMessage inputMessage)
throws IOException, HttpMessageNotReadableException {
String requestBody = toString(inputMessage.getBody());
int i = requestBody.indexOf("\n");
if (i == -1) {
throw new HttpMessageNotReadableException("No first line found", inputMessage);
}
String reportName = requestBody.substring(0, i).trim();
String content = requestBody.substring(i).trim();
Report report = new Report();
report.setReportName(reportName);
report.setContent(content);
return report;
}
@Override
protected void writeInternal(Report report,
HttpOutputMessage outputMessage)
throws IOException, HttpMessageNotWritableException {
try {
OutputStream outputStream = outputMessage.getBody();
String body = report.getReportName() + "\n" +
report.getContent();
outputStream.write(body.getBytes());
outputStream.close();
} catch (Exception e) {
}
}
private static String toString(InputStream inputStream) {
Scanner scanner = new Scanner(inputStream, "UTF-8");
return scanner.useDelimiter("\\A").next();
}
}
A Controller utilizing the conversion
package com.logicbig.example;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;
import java.util.ArrayList;
import java.util.List;
@Controller
public class ReportController {
private List<Report> reports = new ArrayList<>();
@RequestMapping(value = "/reports",
method = RequestMethod.POST,
consumes = "text/report")
@ResponseBody
public String handleRequest(@RequestBody Report report) {
report.setId(reports.size() + 1);
reports.add(report);
return "report saved: " + report;
}
@RequestMapping(
value = "/reports/{id}",
method = RequestMethod.GET)
@ResponseBody
public Report reportById(@PathVariable("id") int reportId) {
if (reportId > reports.size()) {
throw new RuntimeException("No found for the id :" + reportId);
}
return reports.get(reportId - 1);
}
}
Registering the Converter
package com.logicbig.example;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.converter.HttpMessageConverters;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
@EnableWebMvc
@ComponentScan
@Configuration
public class AppConfig implements WebMvcConfigurer {
@Override
public void configureMessageConverters(
HttpMessageConverters.ServerBuilder builder) {
builder.addCustomConverter(new ReportConverter());
}
}
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.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 ReportTests {
@Autowired
private WebApplicationContext wac;
private MockMvcTester mockMvcTester;
@BeforeEach
public void setup() {
this.mockMvcTester = MockMvcTester.from(this.wac);
}
@Test
public void testNewReport() {
String testReport = createTestReport();
assertThat(mockMvcTester.post().uri("/reports")
.contentType("text/report")
.content(testReport)
.exchange())
.hasStatusOk()
.bodyText().startsWith("report saved: Report{");
assertThat(mockMvcTester.get().uri("/reports/1")
.exchange())
.hasStatusOk()
.bodyText().isEqualTo(testReport);
}
private String createTestReport() {
return "dummy report name\ndummy report content.";
}
}
mvn clean test -Dtest="ReportTests" Output$ mvn clean test -Dtest="ReportTests"
[INFO] Scanning for projects...
[INFO]
[INFO] -------< com.logicbig.example:custom-message-converter-example >--------
[INFO] Building custom-message-converter-example 1.0-SNAPSHOT
[INFO] from pom.xml
[INFO] --------------------------------[ war ]---------------------------------
[INFO]
[INFO] --- clean:3.2.0:clean (default-clean) @ custom-message-converter-example ---
[INFO] Deleting D:\example-projects\spring-mvc\custom-message-converter-example\target
[INFO]
[INFO] --- resources:3.3.1:resources (default-resources) @ custom-message-converter-example ---
[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-example\src\main\resources
[INFO]
[INFO] --- compiler:3.15.0:compile (default-compile) @ custom-message-converter-example ---
[INFO] Recompiling the module because of changed source code.
[INFO] Compiling 4 source files with javac [debug target 25] to target\classes
[INFO]
[INFO] --- resources:3.3.1:testResources (default-testResources) @ custom-message-converter-example ---
[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-example\src\test\resources
[INFO]
[INFO] --- compiler:3.15.0:testCompile (default-testCompile) @ custom-message-converter-example ---
[INFO] Recompiling the module because of changed dependency.
[INFO] Compiling 2 source files with javac [debug target 25] to target\test-classes
[INFO]
[INFO] --- surefire:3.2.5:test (default-test) @ custom-message-converter-example ---
[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.ReportTests
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 4.945 s -- in com.logicbig.example.ReportTests
[INFO]
[INFO] Results:
[INFO]
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 14.139 s
[INFO] Finished at: 2026-07-25T11:38:43+08:00
[INFO] ------------------------------------------------------------------------
INFO: Completed initialization in 4 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)
- 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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