Mapping the request body with the @RequestBody annotation

The @RequestBody method parameter annotation indicates that a method parameter should be bound to the value of the HTTP request body. For example:

@PutMapping("/something")
public void handle(@RequestBody String body, Writer writer) throws IOException { 
     writer.write(body);
}

You convert the request body to the method argument by using an HttpMessageConverter. HttpMessageConverter is responsible for converting from the HTTP request message to an object and converting from an object to the HTTP response body. The RequestMappingHandlerAdapter
supports the @RequestBody annotation with the following default HttpMessageConverters :
ByteArrayHttpMessageConverter converts byte arrays.
StringHttpMessageConverter converts strings.
FormHttpMessageConverter converts form data to/from a MultiValueMap<String, String>.
SourceHttpMessageConverter converts to/from a javax.xml.transform.Source.

For more information on these converters, see Message Converters. Also note that if using the MVC namespace or the MVC Java config, a wider range of message converters are registered by default. See Section 22.16.1, “Enabling the MVC Java Config or the MVC XML Namespace” for more information.

If you intend to read and write XML, you will need to configure the MarshallingHttpMessageConverter with a specific Marshaller and an Unmarshaller
implementation from the org.springframework.oxm package. The example below shows how to do that directly in your configuration but if your application is configured through the MVC namespace or the MVC Java config see Section 22.16.1, “Enabling the MVC Java Config or the MVC XML Namespace” instead.

<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter"> 
  <property name="messageConverters">
    <util:list id="beanList"> 
      <ref bean="stringHttpMessageConverter"/> 
      <ref bean="marshallingHttpMessageConverter"/>
    </util:list> 
  </property
</bean>

<bean id="stringHttpMessageConverter" 
                class="org.springframework.http.converter.StringHttpMessageConverter"/>
<bean id="marshallingHttpMessageConverter" 
             class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter"> 
    <property name="marshaller" ref="castorMarshaller"/> 
    <property name="unmarshaller" ref="castorMarshaller"/>
</bean>

<bean id="castorMarshaller" class="org.springframework.oxm.castor.CastorMarshaller"/>

An @RequestBody method parameter can be annotated with @Valid, in which case it will be validated using the configured Validator instance. When using the MVC namespace or the MVC Java config, a JSR-303 validator is configured automatically assuming a JSR-303 implementation is available on the classpath.

Just like with @ModelAttribute parameters, an Errors argument can be used to examine the errors. If such an argument is not declared, a MethodArgumentNotValidException
will be raised. The exception is handled in the DefaultHandlerExceptionResolver
, which sends a 400 error back to the client.

Also see Section 22.16.1, “Enabling the MVC Java Config or the MVC XML Namespace” for information on configuring message converters and a validator through the MVC namespace or the MVC Java config.