play framework2学习之旅<2.5>Body parsers

Body parsers（body解析器）

What is a body parser?（还是那句话，认真读第一段内容介绍！）

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.（这是最关键的一句话！！！！）

Note: You can’t write BodyParser implementation directly using Java. Because a Play BodyParser must handle the body content incrementaly using anIteratee[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.RequestBodyvalue. This value computed by the body parser can then be retrieved viarequest().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 [e-mail] 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 aplay.mvc.Http.RequestBody value. From this body object you can retrieve the request body content in the most appropriate Java type.

这点要十分注意！！！这个是可以背过的O(∩_∩)O

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 [e-mail](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)pulic static Result index() {  BodyLength body = request().body().as(BodyLength.class);  ok("Request body length: " + body.getLength());}

Default body parser: AnyContent（这个遇到了去查吧，留个印象，浏览带过）

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 viaasFormUrlEncoded()
• multipart/form-data: Http.MultipartFormData, accessible viaasMultipartFormData()
• Any other content type: Http.RawBuffer, accessible via asRaw()

Example:

pulic 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（知道有这个东西，知道在哪去改即可）

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 [e-mail](value = BodyParser.Text.class, maxLength = 10 * 1024)pulic static Result index() {  if(request().body().isMaxSizeExceeded()) {    return badRequest("Too much data!");  } else {    ok("Got body: " + request().body().asText());   }}