6.13.1 Using the @Body Annotation

To parse the request body, you first indicate to Micronaut which parameter receives the data with the Body annotation.

The following example implements a simple echo server that echoes the body sent in the request:

Using the @Body annotation

import io.micronaut.http.HttpResponse;
import io.micronaut.http.MediaType;
import io.micronaut.http.annotation.Body;
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Post;
import javax.validation.constraints.Size;
@Controller("/receive")
public class MessageController {
    @Post(value = "/echo", consumes = MediaType.TEXT_PLAIN) (1)
    String echo(@Size(max = 1024) @Body String text) { (2)
        return text; (3)
    }
}

Using the @Body annotation

import io.micronaut.http.HttpResponse
import io.micronaut.http.MediaType
import io.micronaut.http.annotation.Body
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Post
import javax.validation.constraints.Size
@Controller("/receive")
class MessageController {
    @Post(value = "/echo", consumes = MediaType.TEXT_PLAIN) (1)
    String echo(@Size(max = 1024) @Body String text) { (2)
        text (3)
    }
}

Using the @Body annotation

import io.micronaut.http.HttpResponse
import io.micronaut.http.MediaType
import io.micronaut.http.annotation.Body
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Post
import javax.validation.constraints.Size
@Controller("/receive")
open class MessageController {
    @Post(value = "/echo", consumes = [MediaType.TEXT_PLAIN]) (1)
    open fun echo(@Size(max = 1024) @Body text: String): String { (2)
        return text (3)
    }
}

Note that reading the request body is done in a non-blocking manner in that the request contents are read as the data becomes available and accumulated into the String passed to the method.

Regardless of the limit, for a large amount of data accumulating the data into a String in-memory may lead to memory strain on the server. A better approach is to include a Reactive library in your project (such as Reactor, RxJava,or Akka) that supports the Reactive streams implementation and stream the data it becomes available:

Using Reactive Streams to Read the request body

import io.micronaut.http.HttpResponse;
import io.micronaut.http.MediaType;
import io.micronaut.http.annotation.Body;
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Post;
import javax.validation.constraints.Size;
@Controller("/receive")
public class MessageController {
    @Post(value = "/echo-publisher", consumes = MediaType.TEXT_PLAIN) (1)
    @SingleResult
    Publisher<HttpResponse<String>> echoFlow(@Body Publisher<String> text) { (2)
        return Flux.from(text)
                .collect(StringBuffer::new, StringBuffer::append) (3)
                .map(buffer -> HttpResponse.ok(buffer.toString()));
    }
}

Using Reactive Streams to Read the request body

import io.micronaut.http.HttpResponse
import io.micronaut.http.MediaType
import io.micronaut.http.annotation.Body
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Post
import javax.validation.constraints.Size
@Controller("/receive")
class MessageController {
    @Post(value = "/echo-publisher", consumes = MediaType.TEXT_PLAIN) (1)
    @SingleResult
    Publisher<HttpResponse<String>> echoFlow(@Body Publisher<String> text) { (2)
        return Flux.from(text)
                .collect({ x -> new StringBuffer() }, { StringBuffer sb, String s -> sb.append(s) }) (3)
                .map({ buffer -> HttpResponse.ok(buffer.toString()) });
    }
}

Using Reactive Streams to Read the request body

import io.micronaut.http.HttpResponse
import io.micronaut.http.MediaType
import io.micronaut.http.annotation.Body
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Post
import javax.validation.constraints.Size
@Controller("/receive")
open class MessageController {
    @Post(value = "/echo-publisher", consumes = [MediaType.TEXT_PLAIN]) (1)
    @SingleResult
    open fun echoFlow(@Body text: Publisher<String>): Publisher<HttpResponse<String>> { (2)
        return Flux.from(text)
            .collect({ StringBuffer() }, { obj, str -> obj.append(str) }) (3)
            .map { buffer -> HttpResponse.ok(buffer.toString()) }
    }
}