JavaBodyParsers

Body parsers

What is a body parser?

An HTTP request (at least for those using the POST and PUT operations) contains a body. This body can be formatted with any format specified in the Content-Type header. A body parser transforms this request body into a Java value.

Note: You can't write BodyParser implementation directly using Java. Because a Play BodyParser must handle the body content incrementaly using an Iteratee[Array[Byte], A] it must be implemented in Scala.

However Play provides default BodyParsers that should fit most use cases (parsing Json, Xml, Text, uploading files). And you can reuse these default parsers to create your own directly in Java; for example you can provide an RDF parsers based on the Text one.

The BodyParser Java API

In the Java API, all body parsers must generate a play.mvc.Http.RequestBody value. This value computed by the body parser can then be retrieved via request().body():

public static Result index() {
  RequestBody body = request().body();
  return ok("Got body: " + body);
}

You can specify the BodyParser to use for a particular action using the @BodyParser.Of annotation:

@BodyParser.Of(BodyParser.Json.class)
public static Result index() {
  RequestBody body = request().body();
  return ok("Got json: " + body.asJson());
}

The Http.RequestBody API

As we just said all body parsers in the Java API will give you a play.mvc.Http.RequestBody value. From this body object you can retrieve the request body content in the most appropriate Java type.

Note: The RequestBody methods like asText() or asJson() will return null if the parser used to compute this request body doesn't support this content type. For example in an action method annotated with @BodyParser.Of(BodyParser.Json.class), calling asXml() on the generated body will retun null.

Some parsers can provide a most specific type than Http.RequestBody (ie. a subclass of Http.RequestBody). You can automatically cast the request body into another type using the as(...) helper method:

@BodyParser.Of(BodyLengthParser.class)
public static Result index() {
  BodyLength body = request().body().as(BodyLength.class);
  ok("Request body length: " + body.getLength());
}

Default body parser: AnyContent

If you don't specify your own body parser, Play will use the default one guessing the most appropriate content type from the Content-Type header:

• text/plain: String, accessible via asText()
• application/json: JsonNode, accessible via asJson()
• text/xml: org.w3c.Document, accessible via asXml()
• application/form-url-encoded: Map<String, String[]>, accessible via asFormUrlEncoded()
• multipart/form-data: Http.MultipartFormData, accessible via asMultipartFormData()
• Any other content type: Http.RawBuffer, accessible via asRaw()

Example:

public static Result save() {
  RequestBody body = request().body();
  String textBody = body.asText();
  
  if(textBody != null) {
    ok("Got: " + text);
  } else {
    badRequest("Expecting text/plain request body");
  }
}

Max content length

Text based body parsers (such as text, json, xml or formUrlEncoded) use a max content length because they have to load all the content into memory.

There is a default content length (the default is 100KB).

Tip: The default content size can be defined in application.conf:

parsers.text.maxLength=128K

You can also specify a maximum content length via the @BodyParser.Of annotation:

// Accept only 10KB of data.
@BodyParser.Of(value = BodyParser.Text.class, maxLength = 10 * 1024)
public static Result index() {
  if(request().body().isMaxSizeExceeded()) {
    return badRequest("Too much data!");
  } else {
    ok("Got body: " + request().body().asText()); 
  }
}

Next: Actions composition